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Content and Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus × giganteus Depending on Nitrogen Fertilization

Content and Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus ×... agriculture Article Content and Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus  giganteus Depending on Nitrogen Fertilization 1 2 2 2 2 , Izabela Gołab-Bogacz ˛ , Waldemar Helios , Andrzej Kotecki , Marcin Kozak and Anna Jama-Rodzenska ´ * Bugaj Sp. z o.o, Bugaj Zakrzewski 5, 97-512 Kodrab, ˛ Poland; iza.golab@o2.pl Institute of Agroecology and Plant Production, Wroclaw University of Environmental and Life Sciences, Pl. Grunwaldzki 24A, 50-363 Wrocław, Poland; waldemar.helios@upwr.edu.pl (W.H.); andrzej.kotecki@upwr.edu.pl (A.K.); marcin.kozak@upwr.edu.pl (M.K.) * Correspondence: anna.jama@upwr.edu.pl; Tel.: +48-320-1627 Abstract: Fertilisation has a significant impact not only on the yielding, but also on the quality of the harvested biomass. Among energy crops, Miscanthus  giganteus are some of the most important plants used for combustion process. The chemical composition of biomass has significant impact on the quality of combustion biomass. The effect of nitrogen fertilisation (with dose of 60 kg N ha ) in different terms of biomass sampling on the content and uptake of crude ash, potassium, calcium and sulphur by rhizomes, stems, leaves and the aboveground part of miscanthus was evaluated in the paper. Nitrogen fertilisation contributed to the increase of ash content in the rhizomes and the aboveground part of plants. Independently of nitrogen fertilisation potassium content decreased in the whole vegetation period; in the case of stems this decrease amounted 60%. Calcium content in various parts of plants was highly differentiated compared to potassium content. Average calcium content in the aboveground parts was 2.68 higher compared to rhizomes. Nitrogen fertilisation Citation: Gołab-Bogacz, ˛ I.; Helios, affected significantly on potassium, calcium and sulphur uptake in all examined parts of plants W.; Kotecki, A.; Kozak, M.; (except stems in the case of calcium uptake). Uptake of crude ash under nitrogen fertilisation was Jama-Rodzenska, ´ A. Content and significantly higher in all examined parts of plants during the whole vegetation period. Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus Keywords: aboveground; belowground part of Miscanthus  giganteus; ash; potassium; calcium; giganteus Depending on Nitrogen sulphur content; uptake Fertilization. Agriculture 2021, 11, 76. https://doi.org/10.3390/agriculture Received: 20 December 2020 1. Introduction Accepted: 14 January 2021 The need to counteract and prevent increasingly rapid climate change is leading to the Published: 18 January 2021 implementation of processes that will reduce greenhouse gas emissions by replacing fossil fuels with renewable energy sources. Besides the continued use of non-renewable fossil Publisher’s Note: MDPI stays neutral fuels, which include hard coal, lignite, natural gas and oil, energy from renewable sources with regard to jurisdictional claims in is increasingly used. The acquisition of renewable energy sources is currently directed published maps and institutional affil- towards agriculture [1–8]. iations. Energy from plant biomass is mainly obtained by pyrolysis, gasification or direct combustion of appropriately ground or granulated mass [9,10]. Miscanthus (Miscanthus giganteus Greef et Deuter) can play a significant role as a source of renewable energy for Europe [11–13]. Obtaining high quality biomass for the combustion process depends Copyright: © 2021 by the authors. on the quality of the raw material (biomass) [14,15], while the quality of the raw material Licensee MDPI, Basel, Switzerland. depends on the content of various elements (for example, high lignin content is desirable This article is an open access article for thermochemical and undesirable for biochemical processes) [16,17]. distributed under the terms and The content of elements in the biomass is significantly influenced by genetic proper- conditions of the Creative Commons ties [14,18] which can be modified by environmental conditions, such as soil properties, pH, Attribution (CC BY) license (https:// weather conditions (precipitation, temperature), as well as agrotechnical treatments—mainly creativecommons.org/licenses/by/ fertilisation [19–23]. Date of harvest (late winter or spring) can also contribute to the 4.0/). Agriculture 2021, 11, 76. https://doi.org/10.3390/agriculture11010076 https://www.mdpi.com/journal/agriculture Agriculture 2021, 11, 76 2 of 16 reduced content of nutrients that results from their translocation from aboveground part of plant to rhizomes or natural leaching of components from leaves and stems [23–25]. Appropriate chemical composition, especially low content of contaminants in biomass, is desirable during harvest, especially for biomass for thermal combustion, as it contributes to the minimisation of their emissions [23]. Most of the available studies on the content and nutrient uptake of miscanthus concern nitrogen, phosphorus, potassium and magnesium [25–28], while only a few works concern calcium and sulphur content [29,30]. An innovative part of the study was to examine the dynamics of sulphur uptake during the whole vegetation period, taking into account nitrogen fertilisation in various parts of plants. Crude ash content and examined macroelements have a significant impact on the quality of biomass combustion; therefore, the relevance of these elements is discussed. High ash concentration decreases the heating value [31,32]. Potassium, alongside silicon, is the main component of ash [12]. The potassium content of biomass is very important because its high content can increase the corrosion effect in heating systems and lower the melting point of ash [31], and is regarded as a critical element in ash-related problems [32]. Therefore, the potassium content should be as low as possible [32]. For optimal plant growth, the potassium content should be 10–50 g of DM [31]. Sulphur also plays an important role during the combustion process. Sulphur compounds that are formed during this process lead to corrosion and are emitted into the atmosphere [30]. In turn, calcium can inhibit the occurrence of silicate melt-induced slagging and bed agglomeration, as a result of forming melting calcium potassium phosphates and silicates at high temperatures [30–32]. The work hypothesis assumes that fertilisation in a of dose 60 kg ha will contribute to changes in content an uptake of selected macronutrients and ash. It has been estimated that particular parts of the plant (rhizomes, stems, leaves) will be characterised by different ash, Ca, K, and S accumulation. Additionally, fertilisation at a dose 60 kg ha N causes the increase in uptake of ash and selected macroelement. The aim of the study was to determine the effect of nitrogen fertilisation on the content and uptake of ash and selected macroelements in Miscanthus  giganteus. 2. Materials and Methods 2.1. Study Site and Materials The experiment with miscanthus and nitrogen fertilisation started by separating plots on the plantation carried out in 2004. Detailed information is contained in the article by Bogacz et al. 2020 [33]. The study with miscanthus was conducted in the years 2014–2016 at Experimental Station belonging to Wroclaw University of Environmental and Life Sciences, 0  0 Pawlowice (geographical location 17 7 E and 51 08 N in the Lower Silesian Voivodship (Figure 1)). The tested factor was nitrogen fertilisation (0, 60 kg ha N). Miscanthus sampling started from the 30th day of the vegetation period and was done every 30 days until the end of the vegetation period (June, July, August, September, October, November and December). At each date of sampling, a plant sample of the aboveground part of the plant and rhizomes was sampled from an area of 0.25 m . Samples for chemical analysis were reduced according to the standard requirements of PN-EN 96 ISO 14780:2017- 07 [34] (which defines methods for reducing combined samples to laboratory samples and laboratory samples to sub-samples and general analysis samples, and is applicable to solid biofuels). Plant samples were sampled from the area of 0.25 m by gentle extraction of rhizomes from the soil with the whole stems. Dry mass for laboratory samples was determined by air-drying the dry mass at 105 C for three hours according to Polish standard (PN-R-04013:1988). Agriculture 2021, 11, x FOR PEER REVIEW 3 of 16 Agriculture 2021, 11, 76 3 of 16 The weather and soil condition, experiment design and agrotechnical treatments are described in research by Bogacz et al. [33]. Figure 1. Location of experiment. Figure 1. Location of experiment. The weather and soil condition, experiment design and agrotechnical treatments are 2.2. Chemical Analysis of Plant Material described in research by Bogacz et al. [33]. The content of ash and macroelements in plant material was determined in the labor- atory belonging to the Institute of Agroecology and Plant Production. The content of crude 2.2. Chemical Analysis of Plant Material ash and macroelements in the aboveground part was calculated on the basis of the content The content of ash and macroelements in plant material was determined in the lab- of these elements in the leaves and stems, taking into account the structure of the dry oratory belonging to the Institute of Agroecology and Plant Production. The content of matter yield. crude ash and macroelements in the aboveground part was calculated on the basis of the Chemical analyses comprised: content of these elements in the leaves and stems, taking into account the structure of the - crude ash by burning dry plant material at 600 °C in an electric furnace: incineration dry matter yield. of plant material and combustion 1/2 g weighing the analytical sample of plant ma- Chemical analyses comprised: terial in the muffle furnace at 600 ± 15 °C and baking the remaining ash; - crude ash by burning dry plant material at 600 C in an electric furnace: incineration of - potassium and calcium on the flame photometer (BWB Technologies UK LTD), using plant material and combustion 1/2 g weighing the analytical sample of plant material flame photometry; mineralization  of plant material through the use of sulphuric acid in the muffle furnace at 600  15 C and baking the remaining ash; and perhydrol and subsequent determination on a flame photometer; - potassium and calcium on the flame photometer (BWB Technologies UK LTD), using - total sulphur by nephelometric method, after wet mineralisation with concentrated flame photometry; mineralization of plant material through the use of sulphuric acid sulphuric acid with 30% perhydrol, by the Bradley–Lancaster nephelometric method. and perhydrol and subsequent determination on a flame photometer; - total Uptak sulphur e of crude by ash nephelometric and selected method, elementafter s vas wet calculated mineralisation based onwith yield concentrated biomass and sulphuric acid with 30% perhydrol, by the Bradley–Lancaster nephelometric method. chemical content of the examined parts of plants. Uptake of crude ash and selected elements vas calculated based on yield biomass and 2.3. Statistical Analysis chemical content of the examined parts of plants. The experiment was conducted in four replications in order to test the effects of N 2.3. Statistical Analysis fertilisation on the content and uptake of ash and macroelements in Mischanthus giganteus. The experiment was conducted in four replications in order to test the effects of N The analysis of variance (ANOVA) and the mixed model with repeated measurements fertilisation on the content and uptake of ash and macroelements in Mischanthus giganteus. were used. Doses of nitrogen fertilisers were assumed to be a fixed factor, while years was The analysis of variance (ANOVA) and the mixed model with repeated measurements assumed to be random. The results of chemical analysis of the Mischanthus were analysed were used. Doses of nitrogen fertilisers were assumed to be a fixed factor, while years was by ANOVA in the Statistica program (13.1 StatSoft, Kraków, Poland). One-way ANOVA assumed to be random. The results of chemical analysis of the Mischanthus were analysed (nitrogen fertilisation, then year of experiment) was performed including post-hoc analy- by ANOVA in the Statistica program (13.1 StatSoft, Kraków, Poland). One-way ANOVA sis. The level of significance was determined as p < 0.05. (nitrogen fertilisation, then year of experiment) was performed including post-hoc analysis. Homogeneous groups were determined on the basis of the Tukey test. The groups The level of significance was determined as p < 0.05. were determined from the lowest to the highest value. The correlation of repeated meas- Homogeneous groups were determined on the basis of the Tukey test. The groups were urements was performed as the average value over the three-year growing season of each determined from the lowest to the highest value. The correlation of repeated measurements month. The p-value concerns the subsequent months. was performed as the average value over the three-year growing season of each month. The p-value concerns the subsequent months. Agriculture 2021, 11, 76 4 of 16 Agriculture 2021, 11, x FOR PEER REVIEW 4 of 16 3. Results 3.1. Crude Ash Content and Uptake 3. Results The effect of nitrogen fertilisation on ash content in the rhizomes (p = 0.0035), stems 3.1. Crude Ash Content and Uptake (p = 0.0002) and aboveground part of Miscanthus  giganteus (p < 0.001) except for the The effect of nitrogen fertilisation on ash content in the rhizomes (p = 0.0035), stems leaves was found. Even though rhizomes are not involved in the combustion process, (p = 0.0002) and aboveground part of Miscanthus × giganteus (p < 0.001) except for the leaves knowledge of the ash content of rhizomes allowed the ash content to significantly increase was found. Even though rhizomes are not involved in the combustion process, knowledge from 2014 to 2016 in rhizomes (p = 0.0156), whereas the highest content was found in the of the ash content of rhizomes allowed the ash content to significantly increase from 2014 leaves (p = 0.0312) in 2015 (the lowest annual sum of precipitation—392 mm). The highest to 2016 in rhizomes (p = 0.0156), whereas the highest content was found in the leaves (p = content of ash was observed in the aboveground part of plants in the first year (p = 0.0047). 0.0312) in 2015 (the lowest annual sum of precipitation—392 mm). The highest content of The highest content of this component was found in leaves, which is particularly bene- ash was observed in the aboveground part of plants in the first year (p = 0.0047). The high- ficial as the stem has the greatest share in the process of biomass combustion (Table 1). est content of this component was found in leaves, which is particularly beneficial as the The highest content of crude ash was found at the beginning of the vegetation period, stem has the greatest share in the process of biomass combustion (Table 1). The highest and as the plants developed (and also as a result of the ageing processes), its content content of crude ash was found at the beginning of the vegetation period, and as the plants decreased. The decrease in ash content in stems was greater than in leaves at the beginning developed (and also as a result of the ageing processes), its content decreased. The de- of the vegetation period (Figure 2). The figures show the significance values of differences crease in ash content in stems was greater than in leaves at the beginning of the vegetation (p-values) of ash content in subsequent months of observation for control and dose 60 period (Figure 2). The figures show the significance values of differences (p-values) of ash (Figure 2). content in subsequent months of observation for control and dose 60 (Figure 2). Table 1. Crude ash content in dry matter of miscanthus in g kg (average for the years 2014–2016). −1 Table 1. Crude ash content in dry matter of miscanthus in g kg (average for the years 2014–2016). Dose kg ha N Rhizomes Stems Leaves Aboveground Part −1 Dose kg ha N Rhizomes Stems Leaves Aboveground Part 0 43.6 a 37.6 a 56.7 a 53.6 a 0 43.6 a 37.6 a 56.7 a 53.6 a 60 46.5 a 42.2 a 58.3 a 57.6 a 60 46.5 a 42.2 a 58.3 a 57.6 a p-value 0.0035 0.0002 0.2418 <0.001 p-value 0.0035 0.0002 0.2418 <0.001 2014 43.3 a 39.7 a 58.6 a 57.3 a 2014 43.3 a 39.7 a 58.6 a 57.3 a 2015 45.2 a 39.0 a 59.3 a 54.5 a 2015 45.2 a 39.0 a 59.3 a 54.5 a 2016 46.7 a 41.0 a 54.7 a 55.1 a 2016 46.7 a 41.0 a 54.7 a 55.1 a p-value 0.0156 0.1980 0.0312 0.0047 p-value 0.0156 0.1980 0.0312 0.0047 Figure 2. Crude ash content in examined part of miscanthus (g kg ) (three-year average content −1 Figure 2. Crude ash content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). from measurements during the growing season every 30 days). Agriculture 2021, 11, x FOR PEER REVIEW 5 of 16 Agriculture 2021, 11, 76 5 of 16 The crude ash uptake through individual elements of the plant was significantly de- The crude ash uptake through individual elements of the plant was significantly pendent on the nitrogen fertilisation (p ≤ 0.001). The highest uptake in the rhizomes (p < dependent on the nitrogen fertilisation (p 0.001). The highest uptake in the rhizomes (p < 0.001) was found in the third year, whereas the highest uptake in the stems (p ≤ 0.001) and 0.001) was found in the third year, whereas the highest uptake in the stems (p  0.001) and aboveground part of plants (p = 0.0467) was found in the second year of the experiment aboveground part of plants (p = 0.0467) was found in the second year of the experiment (Table 2). Crude ash accumulation by Miscanthus × giganteus per2 1 m in rhizomes in- (Table 2). Crude ash accumulation by Miscanthus giganteus per 1 m in rhizomes increased creased throughout the entire vegetation period, while in stems and aboveground parts throughout the entire vegetation period, while in stems and aboveground parts of the of the plant, it decreased at the end of the vegetation period. Nitrogen fertilization caused plant, it decreased at the end of the vegetation period. Nitrogen fertilization caused greater uptake of crude ash in all examined parts of plants during the whole vegetation greater uptake of crude ash in all examined parts of plants during the whole vegetation period (Figure 3). The p-values presented on the figure concern the date of plant material period (Figure 3). The p-values presented on the figure concern the date of plant material sampling. The figures show the significance values of differences (p-values) of ash uptake sampling. The figures show the significance values of differences (p-values) of ash uptake in subsequent months of observation for control and dose 60 (Figure 3). in subsequent months of observation for control and dose 60 (Figure 3). −2 Table 2. Crude ash uptake by g∙m (average for 2014–2016). Table 2. Crude ash uptake by gm (average for 2014–2016). Aboveground Part Rhizomes and Rhizomes and Aboveground Part Dose kg ha N Rhizomes −1 Dose kg ha N Rhizomes Aboveground Aboveground Stems Leaves All Together Stems Leaves All Together Part Part 0 44.8 a 46.0 a 33.9 a 74.4 a 119.2 a 0 44.8 a 46.0 a 33.9 a 74.4 a 119.2 a 60 54.3 b 60.1 b 46.3 b 99.0 b 153.3 b 60 54.3 b 60.1 b 46.3 b 99.0 b 153.3 b p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 2014 48.5 a 49.8 a 40.8 a 85.5 a 134.0 a 2014 48.5 a 49.8 a 40.8 a 85.5 a 134.0 a 2015 47.7 b 57.9 a 39.1 a 89.1 a 136.8 a 2015 47.7 b 57.9 a 39.1 a 89.1 a 136.8 a 2016 52.6 b 51.4 a 40.3 a 85.5 a 138.1 a 2016 52.6 b 51.4 a 40.3 a 85.5 a 138.1 a p-value <0.001 <0.001 0.3064 0.0467 0.1679 p-value <0.001 <0.001 0.3064 0.0467 0.1679 Figure 3. Crude ash uptake in examined part of miscanthus (g m ) (three-year average content from measurements during −2 Figure 3. Crude ash uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). the growing season every 30 days). Agriculture 2021, 11, x FOR PEER REVIEW 6 of 16 Agriculture 2021, 11, 76 6 of 16 3.2. Potassium Content and Uptake The potassium content in leaves (p = 0.0085) was significantly dependent on the ni- trogen fertilisation. In the stem of Miscanthus × giganteus, the highest content of potassium 3.2. Potassium Content and Uptake was found in the third year of the study (p = 0.0032), and in the second year in rhizomes The potassium content in leaves (p = 0.0085) was significantly dependent on the nitro- (p = 0.0219) and leaves (p < 0.001) (Table 3). gen fertilisation. In the stem of Miscanthus  giganteus, the highest content of potassium was found in the third year of the study (p = 0.0032), and in the second year in rhizomes (p −1 Table 3. Potassium content in dry matter of miscanthus g kg (average for the years 2014– = 0.0219) and leaves (p < 0.001) (Table 3). 2016). Table 3. Potassium content in dry matter of miscanthus g kg (average for the years 2014–2016). Aboveground −1 Dose kg ha N Rhizomes Stems Leaves Part Dose kg ha N Rhizomes Stems Leaves Aboveground Part 0 12.7 a 11.6 a 12.3 a 12.0 a 0 12.7 a 11.6 a 12.3 a 12.0 a 60 11.9 a 11.6 a 13.9 a 12.6 a 60 11.9 a 11.6 a 13.9 a 12.6 a p value 0.1455 0.9491 0.0085 0.1643 p value 0.1455 0.9491 0.0085 0.1643 2014 12.7 a 11.0 a 13.6 a 12.1 a 2014 12.7 a 11.0 a 13.6 a 12.1 a 2015 13.0 a 10.3 a 15.1 ab 12.1 a 2015 13.0 a 10.3 a 15.1 ab 12.1 a 2016 11.1 a 13.5 a 10.6 a 12.7 a 2016 11.1 a 13.5 a 10.6 a 12.7 a p value 0.0219 0.0032 <0.001 0.4601 p value 0.0219 0.0032 <0.001 0.4601 A decrease was observed in potassium content in the leaves, stems and aboveground A decrease was observed in potassium content in the leaves, stems and aboveground part of Miscanthus × giganteus since August to the December. The lowest level of this ele- part of Miscanthus  giganteus since August to the December. The lowest level of this ment was found in December, when the potassium content in the aerial part of plants was element was found in December, when the potassium content in the aerial part of plants on average about twice as low as in June. In turn, a decrease in potassium content in the was on average about twice as low as in June. In turn, a decrease in potassium content in the rhizomes was found from the beginning of vegetation period until November. The in- rhizomes was found from the beginning of vegetation period until November. The increase crease in potassium content in the rhizomes from November to the end of the vegetation in potassium content in the rhizomes from November to the end of the vegetation period period (Figure 4) might be the result of translocation of this element from the above- (Figure 4) might be the result of translocation of this element from the aboveground part of ground part of plants to the rhizomes. The figures show the significance values of differ- plants to the rhizomes. The figures show the significance values of differences (p-values) of ences (p-values) of potassium content in subsequent months of observation for control and potassium content in subsequent months of observation for control and dose 60 (Figure 4). dose 60 (Figure 4). Figure 4. Potassium content in examined part of miscanthus (g kg ). −1 Figure 4. Potassium content in examined part of miscanthus (g kg ). Potassium uptake (g m ) by Miscanthus  giganteus was dependent on nitrogen fertilisation and the years of the experiment. Nitrogen fertilisation caused an increase in potassium accumulation (g m ) in all examined parts of plants. The highest potassium Agriculture 2021, 11, x FOR PEER REVIEW 7 of 16 Agriculture 2021, 11, 76 −2 7 of 16 Potassium uptake (g m ) by Miscanthus × giganteus was dependent on nitrogen ferti- lisation and the years of the experiment. Nitrogen fertilisation caused an increase in po- −2 tassium accumulation (g m ) in all examined parts of plants. The highest potassium up- take was found in the rhizomes (p < 0.001) and the aboveground part of plants (p < 0.001) uptake was found in the rhizomes (p < 0.001) and the aboveground part of plants (p < 0.001) in the first year of research (Table 4). in the first year of research (Table 4). −2 Table 4. Potassium uptake of the giant miscanthus in g m (average for 2014–2016). Table 4. Potassium uptake of the giant miscanthus in g m (average for 2014–2016). Aboveground Parts Rhizomes and Rhizomes and Aboveground Parts −11 Dose kg ha N Dose kg ha N Rhizom Rhizomes es Aboveground Aboveground Stem Leaves Together Stem Leaves Together Part Part 0 13.3 a 17.9 a 7.6 a 22.5 a 35.8 a 0 13.3 a 17.9 a 7.6 a 22.5 a 35.8 a 60 13.9 a 19.1 a 11.4 b 27.1 b 41.0 a 60 13.9 a 19.1 a 11.4 b 27.1 b 41.0 a p-value 0.0064 0.0021 <0.001 <0.001 <0.001 p-value 0.0064 0.0021 <0.001 <0.001 <0.001 2014 15.1 b 19.7 a 10.2 b 26.5 a 41.6 a 2014 15.1 b 19.7 a 10.2 b 26.5 a 41.6 a 2015 14.3 b 16.9 a 10.4 b 24.1 a 38.4 a 2015 14.3 b 16.9 a 10.4 b 24.1 a 38.4 a 2016 11.4 a 18.9 a 7.8 a 23.8 a 35.1 a 2016 11.4 a 18.9 a 7.8 a 23.8 a 35.1 a p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 Rhizomes accumulated potassium until the end of vegetation (increasing trend). Rhizomes accumulated potassium until the end of vegetation (increasing trend). Without Without nitro nitr gen ogen fertili fertilization zation in the inaboveground the aboveground part of part plant ofs, plants, the peak the po peak tassiu potassium m up- take uptake was ob was served observed in Nov in emb November er, where , wher as th eas e high the es highest t accuaccumulation mulation was was seen seen earlier earlier on on the plots with nitrogen fertilization (Figure 5). The figures show the significance values of the plots with nitrogen fertilization (Figure 5). The figures show the significance values of differences (p-values) of potassium uptake in subsequent months of observation for control differences (p-values) of potassium uptake in subsequent months of observation for con- and dose 60 (Figure 5). trol and dose 60 (Figure 5). Figure 5. Potassium uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). −2 Figure 5. Potassium uptake in examined part of miscanthus (g m ) (three-year average content 3.3. Calcium Content and Uptake from measurements during the growing season every 30 days). Nitrogen fertilisation had no significant effect on the calcium content in the examined parts of plants (Table 5). The year of the experiment had a significant effect on calcium content in rhizomes (p < 0.001), stems (p = 0.0036) and leaves (p < 0.001) (Table 5). Agriculture 2021, 11, x FOR PEER REVIEW 8 of 16 3.3. Calcium Content and Uptake Nitrogen fertilisation had no significant effect on the calcium content in the examined Agriculture 2021, 11, 76 8 of 16 parts of plants (Table 5). The year of the experiment had a significant effect on calcium content in rhizomes (p < 0.001), stems (p = 0.0036) and leaves (p < 0.001) (Table 5). −1 Table 5. Calcium content in dry matter of the giant miscanthus in g∙kg (average for the years Table 5. Calcium content in dry matter of the giant miscanthus in gkg (average for the years 2014–2016). 2014–2016). Aboveground −1 Dose kg h 1 a N Rhizomes Stems Leaves Dose kg ha N Rhizomes Stems Leaves Aboveground Part Part 0 0.58 a 1.34 a 1.78 a 1.52 a 0 0.58 a 1.34 a 1.78 a 1.52 a 60 0.55 a 1.24 a 1.93 a 1.51 a 60 0.55 a 1.24 a 1.93 a 1.51a p-value 0.5401 0.2250 0.1717 0.8787 p-value 0.5401 0.2250 0.1717 0.8787 2014 0.64 b 1.24 a 1.80 a 1.51 a 2014 0.64b 1.24 a 1.80 a 1.51 a 2015 0.79 b 1.11 a 2.31 a 1.50 a 2015 0.79b 1.11 a 2.31 a 1.50 a 2016 0.27 a 1.52 a 1.45 b 1.54 a 2016 0.27a 1.52 a 1.45 b 1.54 a p-value 0.0000 0.0036 <0.001 0.8886 p-value 0.0000 0.0036 <0.001 0.8886 An An incr increase ease in in the the content content of of this thiselement elementin in rhizomes rhizomes was wafound s found until until August August and and in in the th stems e stem to s the to th end e end of the of th vegetation e vegetation period period (Figur (Figu e 6). re The 6). Th figur e figures es show show the significance the signifi- cance values va of lu dif es fer of ences differenc (p-values) es (p-vof alues calcium ) of cal content cium con in subsequent tent in subs months equent of mo observation nths of obse for r- vation controlfor co and dose ntrol 60 an(Figur d dose 60 (Fi e 6). gure 6). Figure 6. Calcium content in examined part of miscanthus (g kg ) (three-year average content from measurements during −1 the growing season every 30 days). Figure 6. Calcium content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). Calcium uptake depended on nitrogen fertilisation in all parts of plants (p < 0.001) except stems. Significant changes in calcium uptake were found during the years of research in the rhizomes (p  0.001), stems (p  0.001), leaves (p  0.001) and the whole plants (p  0.001) (Table 6). Agriculture 2021, 11, x FOR PEER REVIEW 9 of 16 Calcium uptake depended on nitrogen fertilisation in all parts of plants (p < 0.001) except stems. Significant changes in calcium uptake were found during the years of re- Agriculture 2021, 11, 76 9 of 16 search in the rhizomes (p ≤ 0.001), stems (p ≤ 0.001), leaves (p ≤ 0.001) and the whole plants (p ≤ 0.001) (Table 6). −2 Table 6. Calcium uptake by the giant miscanthus in g∙m (average for the years 2014–2016). Table 6. Calcium uptake by the giant miscanthus in gm (average for the years 2014–2016). Aboveground Parts Rhizomes and Rhizomes and Aboveground Parts −1 Dose kg ha N Dose kg ha N Rhizomes Rhizomes Aboveground Aboveground Stems Leaves All Together Stems Leaves All Together Parts Parts 0 0.56 a 2.80 a 1.20 a 3.51 a 4.07 a 0 0.56 a 2.80 a 1.20 a 3.51 a 4.07 a 60 0.61 a 2.80 a 1.71 b 3.98 a 4.59 a 60 0.61 a 2.80 a 1.71 b 3.98 a 4.59 a p-value <0.001 0.9045 <0.001 <0.001 <0.001 p-value <0.001 0.9045 <0.001 <0.001 <0.001 2014 0.64 b 2.81 a 1.44 ab 3.76 a 4.40 a 2014 0.64 b 2.81 a 1.44 ab 3.76 a 4.40 a 2015 0.83 c 2.41 a 1.73 a 3.64 a 4.47 a 2015 0.83 c 2.41 a 1.73 a 3.64 a 4.47 a 2016 0.28 a 3.18 a 1.19 b 3.84 a 4.12 a 2016 0.28 a 3.18 a 1.19 b 3.84 a 4.12 a p-value <0.001 <0.001 <0.001 0.0573 <0.001 p-value <0.001 <0.001 <0.001 0.0573 <0.001 An increase in calcium uptake was seen in the stems and aboveground part of plants An increase in calcium uptake was seen in the stems and aboveground part of plants through the entire vegetation period. Changes in calcium uptake in the rhizomes were through the entire vegetation period. Changes in calcium uptake in the rhizomes were lower in this period compared to aerial parts of Miscanthus  giganteus (Figure 7). The fig- lower in this period compared to aerial parts of Miscanthus × giganteus (Figure 7). The ures show the significance values of differences (p-values) of calcium uptake in subsequent figures show the significance values of differences (p-values) of calcium uptake in subse- months of observation for control and dose 60 (Figure 7). quent months of observation for control and dose 60 (Figure 7). 2 −2 Figure 7. Calcium Figure uptake 7. Calciu in m examined uptake ipart n exam of miscanthus ined part of (g mis mcanthu ) (thr s ee-year (g m ) average (three-yea content r averag from e co measur ntent from ements during measurements during the growing season every 30 days). the growing season every 30 days). 3.4. Sulphur Content and Uptake Nitrogen fertilisation had a significant impact on sulphur content in the stems (p = 0.0485) and aboveground parts (p = 0.0067). Significant changes in sulphur content were found in the different years of the experiment for rhizomes (p = 0.0345), stems (p < 0.001), leaves (p < 0.001) and aboveground parts of plants (p = 0.0219). The highest sulphur content in the rhizomes and stems was seen in the first year of field experiments and in the leaves and aboveground part of plants in the third year (Table 7). Agriculture 2021, 11, x FOR PEER REVIEW 10 of 16 3.4. Sulphur Content and Uptake Nitrogen fertilisation had a significant impact on sulphur content in the stems (p = 0.0485) and aboveground parts (p = 0.0067). Significant changes in sulphur content were found in the different years of the experiment for rhizomes (p = 0.0345), stems (p < 0.001), leaves (p < 0.001) and aboveground parts of plants (p = 0.0219). The highest sulphur con- tent in the rhizomes and stems was seen in the first year of field experiments and in the leaves and aboveground part of plants in the third year (Table 7). Agriculture 2021, 11, 76 10 of 16 −1 Table 7. Sulphur content in dry matter of miscanthus in g kg (average for years 2014–2016). Table 7. Sulphur content in dry matter of miscanthus in g kg (average for years 2014–2016). −1 Dose kg ha N Rhizomes Stems Leaves Aboveground Parts Dose kg ha N Rhizomes Stems Leaves Aboveground Parts 0 0.78 a 0.62 a 0.63 a 0.69 a 0 0.78 a 0.62 a 0.63 a 0.69 a 60 0.81 a 0.67 a 0.64 a 0.75 a 60 0.81 a 0.67 a 0.64 a 0.75 a p-pv -value alue 0.492 0.4928 8 0.048 0.0485 5 0.535 0.5357 7 0.006 0.0067 7 2014 0.90 b 0.71 b 0.56 a 0.71 a 2014 0.90 b 0.71 b 0.56 a 0.71 a 2015 0.77 ab 0.55 a 0.66 ab 0.69 a 2015 0.77 ab 0.55 a 0.66 ab 0.69 a 2016 0.72 a 0.67 b 0.69 b 0.76 a 2016 0.72 a 0.67 b 0.69 b 0.76 a p-value 0.0345 <0.001 <0.001 0.0219 p-value 0.0345 <0.001 <0.001 0.0219 The sulphur content in the aboveground parts, stems and leaves decreased with the The sulphur content in the aboveground parts, stems and leaves decreased with the development of plants. The dynamic changing of sulphur content in the aerial part of Mis- development of plants. The dynamic changing of sulphur content in the aerial part of canthus × giganteus was the highest at the beginning of the vegetation period. The lowest Miscanthus giganteus was the highest at the beginning of the vegetation period. The lowest sulphur content in the rhizomes was found in October (Figure 8). The figures show the sulphur content in the rhizomes was found in October (Figure 8). The figures show the significance values of differences (p-values) of sulphur content in subsequent months of significance values of differences (p-values) of sulphur content in subsequent months of observation for control and dose 60 (Figure 8). observation for control and dose 60 (Figure 8). Figure 8. Sulphur content in examined part of miscanthus (g kg ) (three-year average content from measurements during −1 Figure 8. Sulphur content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). the growing season every 30 days). Sulphur uptake (g m ) by Miscanthus  giganteus was significantly dependent on nitrogen fertilisation and year of the experiment (Table 8). The highest sulphur uptake was found on plots with nitrogen fertilisation in all examined parts of plants (p < 0.001). The highest sulphur accumulation per m in the rhizomes and aboveground part of plants was observed in the first year of the field experiment (Table 8). Agriculture 2021, 11, x FOR PEER REVIEW 11 of 16 −2 Sulphur uptake (g m ) by Miscanthus × giganteus was significantly dependent on ni- trogen fertilisation and year of the experiment (Table 8). The highest sulphur uptake was Agriculture 2021, 11, 76 found on plots with nitrogen fertilisation in all examined parts of plants (p < 0.001). 11 Th ofe 16 highest sulphur accumulation per m in the rhizomes and aboveground part of plants was observed in the first year of the field experiment (Table 8). Table 8. Sulphur uptake by the giant miscanthus in gm (average for the years 2014–2016). −2 Table 8. Sulphur uptake by the giant miscanthus in g∙m (average for the years 2014–2016). Number of Days Aboveground Part Number of Days after Aboveground Part Rhizomes and Rhizomes and Dose kg ha N after the Start of Rhizomes −1 Aboveground Parts Dose kg ha N the Start of the Vegeta- Rhizomes the Vegetation Stems Stems Leaves Leaves All All Tog Together ether Aboveground Parts tion 0 0.87 a 1.03 a 0.39 a 1.27 a 2.14 a 0 0.87 a 1.03 a 0.39 a 1.27 a 2.14 a 60 0.99 b 1.28 b 0.53 b 1.63 b 2.62 b 60 0.99 b 1.28 b 0.53 b 1.63 b 2.62 b p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 2014 1.06 c 1.36 b 0.40 a 1.57 a 2.63 a 2014 1.06 c 1.36 b 0.40 a 1.57 a 2.63 a 2015 0.89 ab 0.99 a 0.45 a 1.30 a 2.19 a 2015 0.89 ab 0.99 a 0.45 a 1.30 a 2.19 a 2016 0.83 a 1.12 ab 0.52 b 1.48 a 2.31 a 2016 0.83 a 1.12 ab 0.52 b 1.48 a 2.31 a p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 The highest sulphur uptake by rhizomes and stems was found in December. It should The highest sulphur uptake by rhizomes and stems was found in December. It should be noted that stems accumulated over 2–3 times more sulphur than leaves. Sulphur uptake be noted that stems accumulated over 2–3 times more sulphur than leaves. Sulphur up- in Miscanthus  giganteus increased with the progressing vegetation period in all parts of take in Miscanthus × giganteus increased with the progressing vegetation period in all parts the field experiment (Figure 9). The figures show the significance values of differences of the field experiment (Figure 9). The figures show the significance values of differences (p-values) of Sulphur uptake in subsequent months of observation for control and dose 60 (p-values) of Sulphur uptake in subsequent months of observation for control and dose 60 (Figure 9). (Figure 9). Figure 9. Sulphur uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). −2 Figure 9. Sulphur uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). 4. Discussion Mineral concentration plays an essential role in biomass combustion quality [14,35]. To improve biomass quality of Miscanthus giganteus, cultivation practice should be based on keeping the nitrogen fertilisation rate as low as possible and delaying harvest until the Agriculture 2021, 11, 76 12 of 16 spring following growth, as this will allow nutrient remobilisation and leaching of soluble minerals like K and Cl through rainfall [35,36]. Nutrient remobilisation seems to be a good strategy for perennial rhizomatous grasses [37,38] and represents an environmentally friendly strategy to reduce fertiliser ap- plications [36]. When calculating the nutrient balance and fertiliser recommendations, the remobilisation of nutrients within the plant must be taken into account [25]. Septem- ber and March are irrelevant for nutrient remobilisation [28]. The increase in nutrient content found in rhizomes in autumn and winter may be caused by remobilisation from the aboveground parts to the underground part [25]. In our research, generally, nutrient concentrations were highest at the beginning of the growing period and decreased clearly during the growing season. There were no significant differences caused by N fertilisation (except for potassium in leaves and sulphur in stems). The large loss of K from shoots between September and harvest can be attributed to leaching from the senescent plant material as K is not organically metabolised [39]. Some leaves fell after the end of the growing period, contributing to improved properties of soil by increasing the contents of elements and organic matter, thereby leading simultaneously to a decrease in ash uptake by plants [24]. The mineral concentration of aerial biomass is at its highest during spring and early summer and then declines, probably as a result of remobilization [24]. These results are also confirmed by own research in the aboveground parts of plants. It is docu- mented that mineral concentration in the aboveground biomass of Miscanthus  giganteus decreases gradually from autumn to winter [24,28]. Our results highlight a decline in the concentration of crude ash and macronutrients in aboveground parts of plants from spring to autumn. The average ash content in Giant Mischanthus according to Borkowska (2007) [31] is about 27.6 g kg . In the study Baxter et al. (2014) [15], the average ash content in leaves was between 40 and 60 g kg DM, and in stems the mean value was lower, between 10 and 30 g kg dm. In our research the highest average ash content was found in leaves 1 1 1 (57.5 g kg ), less in rhizomes (45.1 g kg ) and the lowest in stems (39.9 g kg ). In the research by Lewandowski and Heinz (2002) [36], the content of ash in the aboveground part of plants decreased from December to February. Ash content decreased also from autumn to spring in the study of Lewandowski et al. (2003) [40]. Similarly, delayed harvesting in the research of Lewandowski and Heinz (2003) [36] contributed to a reduction in ash content by 28% on average in Portugal and Great Britain, by 42% in Germany, by 50% in Sweden and by 54% in Denmark. Kotecki et al. (2010) [41] found that nutrient and crude ash yields were higher during the autumn harvest compared to the winter harvest, rising from 31 to 69%, while nitrogen fertilisation contributed to an increase in ash content. In our research, the ash content depended on nitrogen fertilisation and years of experiment in the rhizomes and aboveground part of miscanthus. Ash content decreased during the whole vegetation period. Studies by Lewandowski and Kircherer (1997) [42] showed that miscanthus leaves have a higher ash content than stems, which is also confirmed by own research. The content of potassium in the aboveground part of plants ranges from 4.3 to 10.5 g kg DM [22]. According to Borzecka-W ˛ alker ’s (2010) [31] study, the potassium content in the aerieal parts of miscanthus plants ranged from 2.7 to 9.9 g kg DM on heavy black soil and from 1.6 to 9.4 g kg DM on medium heavy black soil, depending on the genotype and year of cultivation. In the research of Kalembasa et al. (2019) [22] the mean potassium content in mischanthus grass biomass was 15.66 g kg D.M. Further- more, Lewandowski et al. 2000 [43] presented a review of potassium content obtained in field studies by several authors for some locations in Europe. Potassium concentration was significantly influenced during harvest time. According to Jensen et al. (2017) [38], potassium content decreased over the three harvests from June (2009) to February (2010) with the highest concentration during the summer. As expected, delaying the harvest by three to four months improved the combustion quality by reducing potassium content from 9 to 4 g kg DM. Agriculture 2021, 11, 76 13 of 16 Their experiment indicated that many genotypes of Mischanthus are characterised by higher concentrations of potassium in autumn. According to Beale and Long (1997) [24], potassium concentrations in the aboveground dry matter decreased from 32 to 12.0 g kg during whole vegetation period. In our study, the potassium content also decreased from summer till the end of vegetation in aboveground part of plants. Kalembasa et al. (2019) [22] proved that potassium was transferred from the aboveground parts of plants to rhizomes at the end of the growing season. According to Christian et al. (2008) [44] transfer of potassium from leaves and stem to rhizomes is 14–30%. The uptake of macronutrients is strongly dependent on the yield. The higher obtained yield, the higher the uptake of the following element [44]. In the Christian et al. (2008) [44] experiment between 1993 and 1995, the mineral uptake increased when the yield increased rapidly. The translocation of the elements during harvest depends on many external factors, especially weather conditions. While Mischanthus is characterised by higher dry yields (about 30 Mg ha ) from a three-year old crop, Beale and Long (1997) [24] found high potassium uptake gaining 38.0 g m . Nassi o Di Nasso et al. (2011) [45] obtained potassium 2 2 uptake of around 27.0 g m . In our research potassium uptake was around 24.8 gm . Greater uptake of potassium in the Roncucci et al. (2015) [28] study was found in autumn (16.0 gm ), and uptake was lower during wintertime. In this research, potassium uptake by the aboveground part of miscanthus at wintertime had values corresponding to around 33% of those recorded at autumn harvest. The time of harvest was the most relevant factor influencing miscanthus nutrient uptake in own experiments and those by Roncucci et al. (2015) [28]. Aerial parts of grasses accumulated mostly calcium, potassium and magnesium. The issue of calcium content in the rhizomes was undertaken by Stypczynska ´ et al. (2017) [21]. The concentration of this element in their study in the rhizomes was 1.5 g kg DM. In turn, Nassi di Nasso et al. 2010 [45] studied calcium content in the rhizomes and obtained values of 0.5–1.4 g kg DM which are confirmed in our research. The content of calcium was affected by the following factors: genotypes, geographical location of plantation and weather conditions, according to Helios (2018) [46]. In the lack of calcium fertilisation the content of this element relies on age of the plantation. In a 12-year study by Helios (2018) [46], the calcium content ranged from 3.1 g kg DM while calcium uptake 2 1 amounted to 0.45 g m in the first year of experiment to 0.5 g kg DM, while the calcium uptake was 1.2 g m in the tenth year of cultivation. In studies by Baxter et al. (2014) [15] and Stypczynska ´ et al. (2017) [21], leaves of miscanthus were characterised by higher calcium content compared to the stems, which is confirmed by our research. In conducted experiments by Lewandowski and Kicherer [42], the calcium concentrations in the leaves ranged from 2.3 to 3.7 g kg DM while that in the stems ranged from 0.5 to 1.1 g kg DM. In our research, the trends of changes in calcium content during vegetation were similar to those of Kotecki et al. (2010) [41] who showed that the content of this element in the aboveground part of the plant was decreasing until summer and then it increased. Sulphur plays an important role during the combustion process. Sulphur compounds that are formed during this process lead to corrosion and are emitted into the atmo- sphere [30]. In Lewandowski and Kicherer ’s [42] research no definite effect of nitrogen fertilisation on sulphur concentration in the leaves and stems was found. In our experiment, the content of this element in the stems was dependent on examined factor (p = 0.0485) while the nitrogen fertilisation had no significant impact on sulphur content in the leaves. For the entire vegetation period of miscanthus, Spiak et al. (2012) [29] showed that almost half the sulphur content is present in the stems compared to that in the leaves. In the study by Baxter et al. (2014) [15], on the other hand, the opposite results were obtained. In our study, the highest sulphur content was found in the rhizomes and there was less in the leaves and stems. The sulphur content in the leaves (0.64 g kg DM) and stems (0.65 g kg DM) was similar. Concentration of this element in aboveground parts of mis- canthus amounted to 0.72 g kg DM. In research by Kotecki (2010) [41], sulphur content in aerial parts of plants was 0.5–0.8 g kg DM. Agriculture 2021, 11, 76 14 of 16 In our field experiment, the highest content of this component was found in young plants. As the vegetation progressed, the sulphur content decreased in the aboveground part of plants by around 50%. In contrast to the content, the sulphur uptake was signifi- cantly higher in stems than in leaves. The uptake of sulphur in the aboveground part and whole plants with an increased trend was observed until the end of the vegetation season. A similar tendency was observed in rhizomes from July to December. 5. Conclusions Because of the need to reduce emissions, and to avoid worsening the air quality by producing the compounds during combustion of, e.g., hard coal for heating purposes in many Polish cities and other Central and Eastern European countries, the low content of mineral components in Miscanthus giganteus biomass is very desirable and may constitute an alternative source of biomass for energy purposes. While the research hypothesis was verified, it should be stated that only ash content in rhizomes and aboveground part of plants depended significantly on nitrogen fertilisation, while potassium (except in leaves), calcium and sulphur content (except in stems and aboveground parts) were not significantly influenced by this factor. The uptake of the studied elements was significantly dependent on nitrogen fertilisation in the case of ash, potassium, sulphur and calcium (except for stems). K and S concentrations were highest at the beginning of the growing period and decreased clearly during the growing season. The ash content was significantly higher under the influence of nitrogen fertilisation 2 2 in leaves at 58.3 g m and the lowest in stems at 42.2 g m , and the highest intake by 2 2 stems at 60.1 g m and the lowest in leaves at 46.3 g m . Significantly higher sulphur uptake was found in stems under the influence of nitrogen fertilisation at the amount of 1.28 g m . Author Contributions: Conceptualization: A.J.-R., I.G.-B., W.H.; Methodology: A.K., M.K., W.H.; Software: I.G.-B., W.H., A.J.-R.; Validation: A.K., M.K.; Investigation: I.G.-B., W.H., A.K.; Formal Analysis: I.G.-B., W.H., A.J.-R.; Writing: I.G.-B., W.H., A.J.-R.; Review: M.K., A.K., A.J.-R. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. 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[CrossRef] 41. Uprawa Miskanta Olbrzymiego. Energetyczne i Pozaenergetyczne Mozliwosci ´ Wykorzystania Słomy; Kotecki, A., Ed.; Wydawnictwo Uniwersytetu Przyrodniczego we Wrocławiu: Wrocław, Poland, 2010. 42. Lewandowski, I.; Kicherer, A. Combustion quality of biomass: Practical relevance and experiments to modify the biomass quality of Miscanthus  giganteus. Eur. J. Agron. 1997, 6, 163–177. [CrossRef] 43. Lewandowski, I.; Clifton-Brown, J.C.; Scurlock, J.M.O.; Huisman, W. Miscanthus: European experience with a novel energy crop. Biomass Bioenergy 2000, 19, 209–227. [CrossRef] 44. Christian, D.G.; Riche, A.B.; Yates, N.E. Growth, yield and mineral content of Miscanthus  giganteus grown as a biofuel for 14 successive harvests. Ind. Crops Prod. 2008, 28, 320–327. [CrossRef] 45. Di Nassi O Nasso, N.; Roncucci, N.; Triana, F.; Tozzini, C.; Bonari, E. Seasonal nutrient dynamics and biomass quality of giant reed (Arundo donax L.) and miscanthus (Miscanthus  giganteus Greef et Deuter) as energy crops. Ital. J. Agron. 2011, 6, 24. [CrossRef] 46. Helios, W. Growth and Yielding of the Giant Miscanthus Miscanthusgiganteus Greef et Deu; Monogr. CCXIV.; Wydaw. Uniw. Przyr. we Wrocławiu: Wrocław, Poland, 2018; ISBN 978-83-7717-302-2. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Agriculture Multidisciplinary Digital Publishing Institute

Content and Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus × giganteus Depending on Nitrogen Fertilization

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agriculture Article Content and Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus  giganteus Depending on Nitrogen Fertilization 1 2 2 2 2 , Izabela Gołab-Bogacz ˛ , Waldemar Helios , Andrzej Kotecki , Marcin Kozak and Anna Jama-Rodzenska ´ * Bugaj Sp. z o.o, Bugaj Zakrzewski 5, 97-512 Kodrab, ˛ Poland; iza.golab@o2.pl Institute of Agroecology and Plant Production, Wroclaw University of Environmental and Life Sciences, Pl. Grunwaldzki 24A, 50-363 Wrocław, Poland; waldemar.helios@upwr.edu.pl (W.H.); andrzej.kotecki@upwr.edu.pl (A.K.); marcin.kozak@upwr.edu.pl (M.K.) * Correspondence: anna.jama@upwr.edu.pl; Tel.: +48-320-1627 Abstract: Fertilisation has a significant impact not only on the yielding, but also on the quality of the harvested biomass. Among energy crops, Miscanthus  giganteus are some of the most important plants used for combustion process. The chemical composition of biomass has significant impact on the quality of combustion biomass. The effect of nitrogen fertilisation (with dose of 60 kg N ha ) in different terms of biomass sampling on the content and uptake of crude ash, potassium, calcium and sulphur by rhizomes, stems, leaves and the aboveground part of miscanthus was evaluated in the paper. Nitrogen fertilisation contributed to the increase of ash content in the rhizomes and the aboveground part of plants. Independently of nitrogen fertilisation potassium content decreased in the whole vegetation period; in the case of stems this decrease amounted 60%. Calcium content in various parts of plants was highly differentiated compared to potassium content. Average calcium content in the aboveground parts was 2.68 higher compared to rhizomes. Nitrogen fertilisation Citation: Gołab-Bogacz, ˛ I.; Helios, affected significantly on potassium, calcium and sulphur uptake in all examined parts of plants W.; Kotecki, A.; Kozak, M.; (except stems in the case of calcium uptake). Uptake of crude ash under nitrogen fertilisation was Jama-Rodzenska, ´ A. Content and significantly higher in all examined parts of plants during the whole vegetation period. Uptake of Ash and Selected Nutrients (K, Ca, S) with Biomass of Miscanthus Keywords: aboveground; belowground part of Miscanthus  giganteus; ash; potassium; calcium; giganteus Depending on Nitrogen sulphur content; uptake Fertilization. Agriculture 2021, 11, 76. https://doi.org/10.3390/agriculture Received: 20 December 2020 1. Introduction Accepted: 14 January 2021 The need to counteract and prevent increasingly rapid climate change is leading to the Published: 18 January 2021 implementation of processes that will reduce greenhouse gas emissions by replacing fossil fuels with renewable energy sources. Besides the continued use of non-renewable fossil Publisher’s Note: MDPI stays neutral fuels, which include hard coal, lignite, natural gas and oil, energy from renewable sources with regard to jurisdictional claims in is increasingly used. The acquisition of renewable energy sources is currently directed published maps and institutional affil- towards agriculture [1–8]. iations. Energy from plant biomass is mainly obtained by pyrolysis, gasification or direct combustion of appropriately ground or granulated mass [9,10]. Miscanthus (Miscanthus giganteus Greef et Deuter) can play a significant role as a source of renewable energy for Europe [11–13]. Obtaining high quality biomass for the combustion process depends Copyright: © 2021 by the authors. on the quality of the raw material (biomass) [14,15], while the quality of the raw material Licensee MDPI, Basel, Switzerland. depends on the content of various elements (for example, high lignin content is desirable This article is an open access article for thermochemical and undesirable for biochemical processes) [16,17]. distributed under the terms and The content of elements in the biomass is significantly influenced by genetic proper- conditions of the Creative Commons ties [14,18] which can be modified by environmental conditions, such as soil properties, pH, Attribution (CC BY) license (https:// weather conditions (precipitation, temperature), as well as agrotechnical treatments—mainly creativecommons.org/licenses/by/ fertilisation [19–23]. Date of harvest (late winter or spring) can also contribute to the 4.0/). Agriculture 2021, 11, 76. https://doi.org/10.3390/agriculture11010076 https://www.mdpi.com/journal/agriculture Agriculture 2021, 11, 76 2 of 16 reduced content of nutrients that results from their translocation from aboveground part of plant to rhizomes or natural leaching of components from leaves and stems [23–25]. Appropriate chemical composition, especially low content of contaminants in biomass, is desirable during harvest, especially for biomass for thermal combustion, as it contributes to the minimisation of their emissions [23]. Most of the available studies on the content and nutrient uptake of miscanthus concern nitrogen, phosphorus, potassium and magnesium [25–28], while only a few works concern calcium and sulphur content [29,30]. An innovative part of the study was to examine the dynamics of sulphur uptake during the whole vegetation period, taking into account nitrogen fertilisation in various parts of plants. Crude ash content and examined macroelements have a significant impact on the quality of biomass combustion; therefore, the relevance of these elements is discussed. High ash concentration decreases the heating value [31,32]. Potassium, alongside silicon, is the main component of ash [12]. The potassium content of biomass is very important because its high content can increase the corrosion effect in heating systems and lower the melting point of ash [31], and is regarded as a critical element in ash-related problems [32]. Therefore, the potassium content should be as low as possible [32]. For optimal plant growth, the potassium content should be 10–50 g of DM [31]. Sulphur also plays an important role during the combustion process. Sulphur compounds that are formed during this process lead to corrosion and are emitted into the atmosphere [30]. In turn, calcium can inhibit the occurrence of silicate melt-induced slagging and bed agglomeration, as a result of forming melting calcium potassium phosphates and silicates at high temperatures [30–32]. The work hypothesis assumes that fertilisation in a of dose 60 kg ha will contribute to changes in content an uptake of selected macronutrients and ash. It has been estimated that particular parts of the plant (rhizomes, stems, leaves) will be characterised by different ash, Ca, K, and S accumulation. Additionally, fertilisation at a dose 60 kg ha N causes the increase in uptake of ash and selected macroelement. The aim of the study was to determine the effect of nitrogen fertilisation on the content and uptake of ash and selected macroelements in Miscanthus  giganteus. 2. Materials and Methods 2.1. Study Site and Materials The experiment with miscanthus and nitrogen fertilisation started by separating plots on the plantation carried out in 2004. Detailed information is contained in the article by Bogacz et al. 2020 [33]. The study with miscanthus was conducted in the years 2014–2016 at Experimental Station belonging to Wroclaw University of Environmental and Life Sciences, 0  0 Pawlowice (geographical location 17 7 E and 51 08 N in the Lower Silesian Voivodship (Figure 1)). The tested factor was nitrogen fertilisation (0, 60 kg ha N). Miscanthus sampling started from the 30th day of the vegetation period and was done every 30 days until the end of the vegetation period (June, July, August, September, October, November and December). At each date of sampling, a plant sample of the aboveground part of the plant and rhizomes was sampled from an area of 0.25 m . Samples for chemical analysis were reduced according to the standard requirements of PN-EN 96 ISO 14780:2017- 07 [34] (which defines methods for reducing combined samples to laboratory samples and laboratory samples to sub-samples and general analysis samples, and is applicable to solid biofuels). Plant samples were sampled from the area of 0.25 m by gentle extraction of rhizomes from the soil with the whole stems. Dry mass for laboratory samples was determined by air-drying the dry mass at 105 C for three hours according to Polish standard (PN-R-04013:1988). Agriculture 2021, 11, x FOR PEER REVIEW 3 of 16 Agriculture 2021, 11, 76 3 of 16 The weather and soil condition, experiment design and agrotechnical treatments are described in research by Bogacz et al. [33]. Figure 1. Location of experiment. Figure 1. Location of experiment. The weather and soil condition, experiment design and agrotechnical treatments are 2.2. Chemical Analysis of Plant Material described in research by Bogacz et al. [33]. The content of ash and macroelements in plant material was determined in the labor- atory belonging to the Institute of Agroecology and Plant Production. The content of crude 2.2. Chemical Analysis of Plant Material ash and macroelements in the aboveground part was calculated on the basis of the content The content of ash and macroelements in plant material was determined in the lab- of these elements in the leaves and stems, taking into account the structure of the dry oratory belonging to the Institute of Agroecology and Plant Production. The content of matter yield. crude ash and macroelements in the aboveground part was calculated on the basis of the Chemical analyses comprised: content of these elements in the leaves and stems, taking into account the structure of the - crude ash by burning dry plant material at 600 °C in an electric furnace: incineration dry matter yield. of plant material and combustion 1/2 g weighing the analytical sample of plant ma- Chemical analyses comprised: terial in the muffle furnace at 600 ± 15 °C and baking the remaining ash; - crude ash by burning dry plant material at 600 C in an electric furnace: incineration of - potassium and calcium on the flame photometer (BWB Technologies UK LTD), using plant material and combustion 1/2 g weighing the analytical sample of plant material flame photometry; mineralization  of plant material through the use of sulphuric acid in the muffle furnace at 600  15 C and baking the remaining ash; and perhydrol and subsequent determination on a flame photometer; - potassium and calcium on the flame photometer (BWB Technologies UK LTD), using - total sulphur by nephelometric method, after wet mineralisation with concentrated flame photometry; mineralization of plant material through the use of sulphuric acid sulphuric acid with 30% perhydrol, by the Bradley–Lancaster nephelometric method. and perhydrol and subsequent determination on a flame photometer; - total Uptak sulphur e of crude by ash nephelometric and selected method, elementafter s vas wet calculated mineralisation based onwith yield concentrated biomass and sulphuric acid with 30% perhydrol, by the Bradley–Lancaster nephelometric method. chemical content of the examined parts of plants. Uptake of crude ash and selected elements vas calculated based on yield biomass and 2.3. Statistical Analysis chemical content of the examined parts of plants. The experiment was conducted in four replications in order to test the effects of N 2.3. Statistical Analysis fertilisation on the content and uptake of ash and macroelements in Mischanthus giganteus. The experiment was conducted in four replications in order to test the effects of N The analysis of variance (ANOVA) and the mixed model with repeated measurements fertilisation on the content and uptake of ash and macroelements in Mischanthus giganteus. were used. Doses of nitrogen fertilisers were assumed to be a fixed factor, while years was The analysis of variance (ANOVA) and the mixed model with repeated measurements assumed to be random. The results of chemical analysis of the Mischanthus were analysed were used. Doses of nitrogen fertilisers were assumed to be a fixed factor, while years was by ANOVA in the Statistica program (13.1 StatSoft, Kraków, Poland). One-way ANOVA assumed to be random. The results of chemical analysis of the Mischanthus were analysed (nitrogen fertilisation, then year of experiment) was performed including post-hoc analy- by ANOVA in the Statistica program (13.1 StatSoft, Kraków, Poland). One-way ANOVA sis. The level of significance was determined as p < 0.05. (nitrogen fertilisation, then year of experiment) was performed including post-hoc analysis. Homogeneous groups were determined on the basis of the Tukey test. The groups The level of significance was determined as p < 0.05. were determined from the lowest to the highest value. The correlation of repeated meas- Homogeneous groups were determined on the basis of the Tukey test. The groups were urements was performed as the average value over the three-year growing season of each determined from the lowest to the highest value. The correlation of repeated measurements month. The p-value concerns the subsequent months. was performed as the average value over the three-year growing season of each month. The p-value concerns the subsequent months. Agriculture 2021, 11, 76 4 of 16 Agriculture 2021, 11, x FOR PEER REVIEW 4 of 16 3. Results 3.1. Crude Ash Content and Uptake 3. Results The effect of nitrogen fertilisation on ash content in the rhizomes (p = 0.0035), stems 3.1. Crude Ash Content and Uptake (p = 0.0002) and aboveground part of Miscanthus  giganteus (p < 0.001) except for the The effect of nitrogen fertilisation on ash content in the rhizomes (p = 0.0035), stems leaves was found. Even though rhizomes are not involved in the combustion process, (p = 0.0002) and aboveground part of Miscanthus × giganteus (p < 0.001) except for the leaves knowledge of the ash content of rhizomes allowed the ash content to significantly increase was found. Even though rhizomes are not involved in the combustion process, knowledge from 2014 to 2016 in rhizomes (p = 0.0156), whereas the highest content was found in the of the ash content of rhizomes allowed the ash content to significantly increase from 2014 leaves (p = 0.0312) in 2015 (the lowest annual sum of precipitation—392 mm). The highest to 2016 in rhizomes (p = 0.0156), whereas the highest content was found in the leaves (p = content of ash was observed in the aboveground part of plants in the first year (p = 0.0047). 0.0312) in 2015 (the lowest annual sum of precipitation—392 mm). The highest content of The highest content of this component was found in leaves, which is particularly bene- ash was observed in the aboveground part of plants in the first year (p = 0.0047). The high- ficial as the stem has the greatest share in the process of biomass combustion (Table 1). est content of this component was found in leaves, which is particularly beneficial as the The highest content of crude ash was found at the beginning of the vegetation period, stem has the greatest share in the process of biomass combustion (Table 1). The highest and as the plants developed (and also as a result of the ageing processes), its content content of crude ash was found at the beginning of the vegetation period, and as the plants decreased. The decrease in ash content in stems was greater than in leaves at the beginning developed (and also as a result of the ageing processes), its content decreased. The de- of the vegetation period (Figure 2). The figures show the significance values of differences crease in ash content in stems was greater than in leaves at the beginning of the vegetation (p-values) of ash content in subsequent months of observation for control and dose 60 period (Figure 2). The figures show the significance values of differences (p-values) of ash (Figure 2). content in subsequent months of observation for control and dose 60 (Figure 2). Table 1. Crude ash content in dry matter of miscanthus in g kg (average for the years 2014–2016). −1 Table 1. Crude ash content in dry matter of miscanthus in g kg (average for the years 2014–2016). Dose kg ha N Rhizomes Stems Leaves Aboveground Part −1 Dose kg ha N Rhizomes Stems Leaves Aboveground Part 0 43.6 a 37.6 a 56.7 a 53.6 a 0 43.6 a 37.6 a 56.7 a 53.6 a 60 46.5 a 42.2 a 58.3 a 57.6 a 60 46.5 a 42.2 a 58.3 a 57.6 a p-value 0.0035 0.0002 0.2418 <0.001 p-value 0.0035 0.0002 0.2418 <0.001 2014 43.3 a 39.7 a 58.6 a 57.3 a 2014 43.3 a 39.7 a 58.6 a 57.3 a 2015 45.2 a 39.0 a 59.3 a 54.5 a 2015 45.2 a 39.0 a 59.3 a 54.5 a 2016 46.7 a 41.0 a 54.7 a 55.1 a 2016 46.7 a 41.0 a 54.7 a 55.1 a p-value 0.0156 0.1980 0.0312 0.0047 p-value 0.0156 0.1980 0.0312 0.0047 Figure 2. Crude ash content in examined part of miscanthus (g kg ) (three-year average content −1 Figure 2. Crude ash content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). from measurements during the growing season every 30 days). Agriculture 2021, 11, x FOR PEER REVIEW 5 of 16 Agriculture 2021, 11, 76 5 of 16 The crude ash uptake through individual elements of the plant was significantly de- The crude ash uptake through individual elements of the plant was significantly pendent on the nitrogen fertilisation (p ≤ 0.001). The highest uptake in the rhizomes (p < dependent on the nitrogen fertilisation (p 0.001). The highest uptake in the rhizomes (p < 0.001) was found in the third year, whereas the highest uptake in the stems (p ≤ 0.001) and 0.001) was found in the third year, whereas the highest uptake in the stems (p  0.001) and aboveground part of plants (p = 0.0467) was found in the second year of the experiment aboveground part of plants (p = 0.0467) was found in the second year of the experiment (Table 2). Crude ash accumulation by Miscanthus × giganteus per2 1 m in rhizomes in- (Table 2). Crude ash accumulation by Miscanthus giganteus per 1 m in rhizomes increased creased throughout the entire vegetation period, while in stems and aboveground parts throughout the entire vegetation period, while in stems and aboveground parts of the of the plant, it decreased at the end of the vegetation period. Nitrogen fertilization caused plant, it decreased at the end of the vegetation period. Nitrogen fertilization caused greater uptake of crude ash in all examined parts of plants during the whole vegetation greater uptake of crude ash in all examined parts of plants during the whole vegetation period (Figure 3). The p-values presented on the figure concern the date of plant material period (Figure 3). The p-values presented on the figure concern the date of plant material sampling. The figures show the significance values of differences (p-values) of ash uptake sampling. The figures show the significance values of differences (p-values) of ash uptake in subsequent months of observation for control and dose 60 (Figure 3). in subsequent months of observation for control and dose 60 (Figure 3). −2 Table 2. Crude ash uptake by g∙m (average for 2014–2016). Table 2. Crude ash uptake by gm (average for 2014–2016). Aboveground Part Rhizomes and Rhizomes and Aboveground Part Dose kg ha N Rhizomes −1 Dose kg ha N Rhizomes Aboveground Aboveground Stems Leaves All Together Stems Leaves All Together Part Part 0 44.8 a 46.0 a 33.9 a 74.4 a 119.2 a 0 44.8 a 46.0 a 33.9 a 74.4 a 119.2 a 60 54.3 b 60.1 b 46.3 b 99.0 b 153.3 b 60 54.3 b 60.1 b 46.3 b 99.0 b 153.3 b p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 2014 48.5 a 49.8 a 40.8 a 85.5 a 134.0 a 2014 48.5 a 49.8 a 40.8 a 85.5 a 134.0 a 2015 47.7 b 57.9 a 39.1 a 89.1 a 136.8 a 2015 47.7 b 57.9 a 39.1 a 89.1 a 136.8 a 2016 52.6 b 51.4 a 40.3 a 85.5 a 138.1 a 2016 52.6 b 51.4 a 40.3 a 85.5 a 138.1 a p-value <0.001 <0.001 0.3064 0.0467 0.1679 p-value <0.001 <0.001 0.3064 0.0467 0.1679 Figure 3. Crude ash uptake in examined part of miscanthus (g m ) (three-year average content from measurements during −2 Figure 3. Crude ash uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). the growing season every 30 days). Agriculture 2021, 11, x FOR PEER REVIEW 6 of 16 Agriculture 2021, 11, 76 6 of 16 3.2. Potassium Content and Uptake The potassium content in leaves (p = 0.0085) was significantly dependent on the ni- trogen fertilisation. In the stem of Miscanthus × giganteus, the highest content of potassium 3.2. Potassium Content and Uptake was found in the third year of the study (p = 0.0032), and in the second year in rhizomes The potassium content in leaves (p = 0.0085) was significantly dependent on the nitro- (p = 0.0219) and leaves (p < 0.001) (Table 3). gen fertilisation. In the stem of Miscanthus  giganteus, the highest content of potassium was found in the third year of the study (p = 0.0032), and in the second year in rhizomes (p −1 Table 3. Potassium content in dry matter of miscanthus g kg (average for the years 2014– = 0.0219) and leaves (p < 0.001) (Table 3). 2016). Table 3. Potassium content in dry matter of miscanthus g kg (average for the years 2014–2016). Aboveground −1 Dose kg ha N Rhizomes Stems Leaves Part Dose kg ha N Rhizomes Stems Leaves Aboveground Part 0 12.7 a 11.6 a 12.3 a 12.0 a 0 12.7 a 11.6 a 12.3 a 12.0 a 60 11.9 a 11.6 a 13.9 a 12.6 a 60 11.9 a 11.6 a 13.9 a 12.6 a p value 0.1455 0.9491 0.0085 0.1643 p value 0.1455 0.9491 0.0085 0.1643 2014 12.7 a 11.0 a 13.6 a 12.1 a 2014 12.7 a 11.0 a 13.6 a 12.1 a 2015 13.0 a 10.3 a 15.1 ab 12.1 a 2015 13.0 a 10.3 a 15.1 ab 12.1 a 2016 11.1 a 13.5 a 10.6 a 12.7 a 2016 11.1 a 13.5 a 10.6 a 12.7 a p value 0.0219 0.0032 <0.001 0.4601 p value 0.0219 0.0032 <0.001 0.4601 A decrease was observed in potassium content in the leaves, stems and aboveground A decrease was observed in potassium content in the leaves, stems and aboveground part of Miscanthus × giganteus since August to the December. The lowest level of this ele- part of Miscanthus  giganteus since August to the December. The lowest level of this ment was found in December, when the potassium content in the aerial part of plants was element was found in December, when the potassium content in the aerial part of plants on average about twice as low as in June. In turn, a decrease in potassium content in the was on average about twice as low as in June. In turn, a decrease in potassium content in the rhizomes was found from the beginning of vegetation period until November. The in- rhizomes was found from the beginning of vegetation period until November. The increase crease in potassium content in the rhizomes from November to the end of the vegetation in potassium content in the rhizomes from November to the end of the vegetation period period (Figure 4) might be the result of translocation of this element from the above- (Figure 4) might be the result of translocation of this element from the aboveground part of ground part of plants to the rhizomes. The figures show the significance values of differ- plants to the rhizomes. The figures show the significance values of differences (p-values) of ences (p-values) of potassium content in subsequent months of observation for control and potassium content in subsequent months of observation for control and dose 60 (Figure 4). dose 60 (Figure 4). Figure 4. Potassium content in examined part of miscanthus (g kg ). −1 Figure 4. Potassium content in examined part of miscanthus (g kg ). Potassium uptake (g m ) by Miscanthus  giganteus was dependent on nitrogen fertilisation and the years of the experiment. Nitrogen fertilisation caused an increase in potassium accumulation (g m ) in all examined parts of plants. The highest potassium Agriculture 2021, 11, x FOR PEER REVIEW 7 of 16 Agriculture 2021, 11, 76 −2 7 of 16 Potassium uptake (g m ) by Miscanthus × giganteus was dependent on nitrogen ferti- lisation and the years of the experiment. Nitrogen fertilisation caused an increase in po- −2 tassium accumulation (g m ) in all examined parts of plants. The highest potassium up- take was found in the rhizomes (p < 0.001) and the aboveground part of plants (p < 0.001) uptake was found in the rhizomes (p < 0.001) and the aboveground part of plants (p < 0.001) in the first year of research (Table 4). in the first year of research (Table 4). −2 Table 4. Potassium uptake of the giant miscanthus in g m (average for 2014–2016). Table 4. Potassium uptake of the giant miscanthus in g m (average for 2014–2016). Aboveground Parts Rhizomes and Rhizomes and Aboveground Parts −11 Dose kg ha N Dose kg ha N Rhizom Rhizomes es Aboveground Aboveground Stem Leaves Together Stem Leaves Together Part Part 0 13.3 a 17.9 a 7.6 a 22.5 a 35.8 a 0 13.3 a 17.9 a 7.6 a 22.5 a 35.8 a 60 13.9 a 19.1 a 11.4 b 27.1 b 41.0 a 60 13.9 a 19.1 a 11.4 b 27.1 b 41.0 a p-value 0.0064 0.0021 <0.001 <0.001 <0.001 p-value 0.0064 0.0021 <0.001 <0.001 <0.001 2014 15.1 b 19.7 a 10.2 b 26.5 a 41.6 a 2014 15.1 b 19.7 a 10.2 b 26.5 a 41.6 a 2015 14.3 b 16.9 a 10.4 b 24.1 a 38.4 a 2015 14.3 b 16.9 a 10.4 b 24.1 a 38.4 a 2016 11.4 a 18.9 a 7.8 a 23.8 a 35.1 a 2016 11.4 a 18.9 a 7.8 a 23.8 a 35.1 a p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 Rhizomes accumulated potassium until the end of vegetation (increasing trend). Rhizomes accumulated potassium until the end of vegetation (increasing trend). Without Without nitro nitr gen ogen fertili fertilization zation in the inaboveground the aboveground part of part plant ofs, plants, the peak the po peak tassiu potassium m up- take uptake was ob was served observed in Nov in emb November er, where , wher as th eas e high the es highest t accuaccumulation mulation was was seen seen earlier earlier on on the plots with nitrogen fertilization (Figure 5). The figures show the significance values of the plots with nitrogen fertilization (Figure 5). The figures show the significance values of differences (p-values) of potassium uptake in subsequent months of observation for control differences (p-values) of potassium uptake in subsequent months of observation for con- and dose 60 (Figure 5). trol and dose 60 (Figure 5). Figure 5. Potassium uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). −2 Figure 5. Potassium uptake in examined part of miscanthus (g m ) (three-year average content 3.3. Calcium Content and Uptake from measurements during the growing season every 30 days). Nitrogen fertilisation had no significant effect on the calcium content in the examined parts of plants (Table 5). The year of the experiment had a significant effect on calcium content in rhizomes (p < 0.001), stems (p = 0.0036) and leaves (p < 0.001) (Table 5). Agriculture 2021, 11, x FOR PEER REVIEW 8 of 16 3.3. Calcium Content and Uptake Nitrogen fertilisation had no significant effect on the calcium content in the examined Agriculture 2021, 11, 76 8 of 16 parts of plants (Table 5). The year of the experiment had a significant effect on calcium content in rhizomes (p < 0.001), stems (p = 0.0036) and leaves (p < 0.001) (Table 5). −1 Table 5. Calcium content in dry matter of the giant miscanthus in g∙kg (average for the years Table 5. Calcium content in dry matter of the giant miscanthus in gkg (average for the years 2014–2016). 2014–2016). Aboveground −1 Dose kg h 1 a N Rhizomes Stems Leaves Dose kg ha N Rhizomes Stems Leaves Aboveground Part Part 0 0.58 a 1.34 a 1.78 a 1.52 a 0 0.58 a 1.34 a 1.78 a 1.52 a 60 0.55 a 1.24 a 1.93 a 1.51 a 60 0.55 a 1.24 a 1.93 a 1.51a p-value 0.5401 0.2250 0.1717 0.8787 p-value 0.5401 0.2250 0.1717 0.8787 2014 0.64 b 1.24 a 1.80 a 1.51 a 2014 0.64b 1.24 a 1.80 a 1.51 a 2015 0.79 b 1.11 a 2.31 a 1.50 a 2015 0.79b 1.11 a 2.31 a 1.50 a 2016 0.27 a 1.52 a 1.45 b 1.54 a 2016 0.27a 1.52 a 1.45 b 1.54 a p-value 0.0000 0.0036 <0.001 0.8886 p-value 0.0000 0.0036 <0.001 0.8886 An An incr increase ease in in the the content content of of this thiselement elementin in rhizomes rhizomes was wafound s found until until August August and and in in the th stems e stem to s the to th end e end of the of th vegetation e vegetation period period (Figur (Figu e 6). re The 6). Th figur e figures es show show the significance the signifi- cance values va of lu dif es fer of ences differenc (p-values) es (p-vof alues calcium ) of cal content cium con in subsequent tent in subs months equent of mo observation nths of obse for r- vation controlfor co and dose ntrol 60 an(Figur d dose 60 (Fi e 6). gure 6). Figure 6. Calcium content in examined part of miscanthus (g kg ) (three-year average content from measurements during −1 the growing season every 30 days). Figure 6. Calcium content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). Calcium uptake depended on nitrogen fertilisation in all parts of plants (p < 0.001) except stems. Significant changes in calcium uptake were found during the years of research in the rhizomes (p  0.001), stems (p  0.001), leaves (p  0.001) and the whole plants (p  0.001) (Table 6). Agriculture 2021, 11, x FOR PEER REVIEW 9 of 16 Calcium uptake depended on nitrogen fertilisation in all parts of plants (p < 0.001) except stems. Significant changes in calcium uptake were found during the years of re- Agriculture 2021, 11, 76 9 of 16 search in the rhizomes (p ≤ 0.001), stems (p ≤ 0.001), leaves (p ≤ 0.001) and the whole plants (p ≤ 0.001) (Table 6). −2 Table 6. Calcium uptake by the giant miscanthus in g∙m (average for the years 2014–2016). Table 6. Calcium uptake by the giant miscanthus in gm (average for the years 2014–2016). Aboveground Parts Rhizomes and Rhizomes and Aboveground Parts −1 Dose kg ha N Dose kg ha N Rhizomes Rhizomes Aboveground Aboveground Stems Leaves All Together Stems Leaves All Together Parts Parts 0 0.56 a 2.80 a 1.20 a 3.51 a 4.07 a 0 0.56 a 2.80 a 1.20 a 3.51 a 4.07 a 60 0.61 a 2.80 a 1.71 b 3.98 a 4.59 a 60 0.61 a 2.80 a 1.71 b 3.98 a 4.59 a p-value <0.001 0.9045 <0.001 <0.001 <0.001 p-value <0.001 0.9045 <0.001 <0.001 <0.001 2014 0.64 b 2.81 a 1.44 ab 3.76 a 4.40 a 2014 0.64 b 2.81 a 1.44 ab 3.76 a 4.40 a 2015 0.83 c 2.41 a 1.73 a 3.64 a 4.47 a 2015 0.83 c 2.41 a 1.73 a 3.64 a 4.47 a 2016 0.28 a 3.18 a 1.19 b 3.84 a 4.12 a 2016 0.28 a 3.18 a 1.19 b 3.84 a 4.12 a p-value <0.001 <0.001 <0.001 0.0573 <0.001 p-value <0.001 <0.001 <0.001 0.0573 <0.001 An increase in calcium uptake was seen in the stems and aboveground part of plants An increase in calcium uptake was seen in the stems and aboveground part of plants through the entire vegetation period. Changes in calcium uptake in the rhizomes were through the entire vegetation period. Changes in calcium uptake in the rhizomes were lower in this period compared to aerial parts of Miscanthus  giganteus (Figure 7). The fig- lower in this period compared to aerial parts of Miscanthus × giganteus (Figure 7). The ures show the significance values of differences (p-values) of calcium uptake in subsequent figures show the significance values of differences (p-values) of calcium uptake in subse- months of observation for control and dose 60 (Figure 7). quent months of observation for control and dose 60 (Figure 7). 2 −2 Figure 7. Calcium Figure uptake 7. Calciu in m examined uptake ipart n exam of miscanthus ined part of (g mis mcanthu ) (thr s ee-year (g m ) average (three-yea content r averag from e co measur ntent from ements during measurements during the growing season every 30 days). the growing season every 30 days). 3.4. Sulphur Content and Uptake Nitrogen fertilisation had a significant impact on sulphur content in the stems (p = 0.0485) and aboveground parts (p = 0.0067). Significant changes in sulphur content were found in the different years of the experiment for rhizomes (p = 0.0345), stems (p < 0.001), leaves (p < 0.001) and aboveground parts of plants (p = 0.0219). The highest sulphur content in the rhizomes and stems was seen in the first year of field experiments and in the leaves and aboveground part of plants in the third year (Table 7). Agriculture 2021, 11, x FOR PEER REVIEW 10 of 16 3.4. Sulphur Content and Uptake Nitrogen fertilisation had a significant impact on sulphur content in the stems (p = 0.0485) and aboveground parts (p = 0.0067). Significant changes in sulphur content were found in the different years of the experiment for rhizomes (p = 0.0345), stems (p < 0.001), leaves (p < 0.001) and aboveground parts of plants (p = 0.0219). The highest sulphur con- tent in the rhizomes and stems was seen in the first year of field experiments and in the leaves and aboveground part of plants in the third year (Table 7). Agriculture 2021, 11, 76 10 of 16 −1 Table 7. Sulphur content in dry matter of miscanthus in g kg (average for years 2014–2016). Table 7. Sulphur content in dry matter of miscanthus in g kg (average for years 2014–2016). −1 Dose kg ha N Rhizomes Stems Leaves Aboveground Parts Dose kg ha N Rhizomes Stems Leaves Aboveground Parts 0 0.78 a 0.62 a 0.63 a 0.69 a 0 0.78 a 0.62 a 0.63 a 0.69 a 60 0.81 a 0.67 a 0.64 a 0.75 a 60 0.81 a 0.67 a 0.64 a 0.75 a p-pv -value alue 0.492 0.4928 8 0.048 0.0485 5 0.535 0.5357 7 0.006 0.0067 7 2014 0.90 b 0.71 b 0.56 a 0.71 a 2014 0.90 b 0.71 b 0.56 a 0.71 a 2015 0.77 ab 0.55 a 0.66 ab 0.69 a 2015 0.77 ab 0.55 a 0.66 ab 0.69 a 2016 0.72 a 0.67 b 0.69 b 0.76 a 2016 0.72 a 0.67 b 0.69 b 0.76 a p-value 0.0345 <0.001 <0.001 0.0219 p-value 0.0345 <0.001 <0.001 0.0219 The sulphur content in the aboveground parts, stems and leaves decreased with the The sulphur content in the aboveground parts, stems and leaves decreased with the development of plants. The dynamic changing of sulphur content in the aerial part of Mis- development of plants. The dynamic changing of sulphur content in the aerial part of canthus × giganteus was the highest at the beginning of the vegetation period. The lowest Miscanthus giganteus was the highest at the beginning of the vegetation period. The lowest sulphur content in the rhizomes was found in October (Figure 8). The figures show the sulphur content in the rhizomes was found in October (Figure 8). The figures show the significance values of differences (p-values) of sulphur content in subsequent months of significance values of differences (p-values) of sulphur content in subsequent months of observation for control and dose 60 (Figure 8). observation for control and dose 60 (Figure 8). Figure 8. Sulphur content in examined part of miscanthus (g kg ) (three-year average content from measurements during −1 Figure 8. Sulphur content in examined part of miscanthus (g kg ) (three-year average content from measurements during the growing season every 30 days). the growing season every 30 days). Sulphur uptake (g m ) by Miscanthus  giganteus was significantly dependent on nitrogen fertilisation and year of the experiment (Table 8). The highest sulphur uptake was found on plots with nitrogen fertilisation in all examined parts of plants (p < 0.001). The highest sulphur accumulation per m in the rhizomes and aboveground part of plants was observed in the first year of the field experiment (Table 8). Agriculture 2021, 11, x FOR PEER REVIEW 11 of 16 −2 Sulphur uptake (g m ) by Miscanthus × giganteus was significantly dependent on ni- trogen fertilisation and year of the experiment (Table 8). The highest sulphur uptake was Agriculture 2021, 11, 76 found on plots with nitrogen fertilisation in all examined parts of plants (p < 0.001). 11 Th ofe 16 highest sulphur accumulation per m in the rhizomes and aboveground part of plants was observed in the first year of the field experiment (Table 8). Table 8. Sulphur uptake by the giant miscanthus in gm (average for the years 2014–2016). −2 Table 8. Sulphur uptake by the giant miscanthus in g∙m (average for the years 2014–2016). Number of Days Aboveground Part Number of Days after Aboveground Part Rhizomes and Rhizomes and Dose kg ha N after the Start of Rhizomes −1 Aboveground Parts Dose kg ha N the Start of the Vegeta- Rhizomes the Vegetation Stems Stems Leaves Leaves All All Tog Together ether Aboveground Parts tion 0 0.87 a 1.03 a 0.39 a 1.27 a 2.14 a 0 0.87 a 1.03 a 0.39 a 1.27 a 2.14 a 60 0.99 b 1.28 b 0.53 b 1.63 b 2.62 b 60 0.99 b 1.28 b 0.53 b 1.63 b 2.62 b p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 2014 1.06 c 1.36 b 0.40 a 1.57 a 2.63 a 2014 1.06 c 1.36 b 0.40 a 1.57 a 2.63 a 2015 0.89 ab 0.99 a 0.45 a 1.30 a 2.19 a 2015 0.89 ab 0.99 a 0.45 a 1.30 a 2.19 a 2016 0.83 a 1.12 ab 0.52 b 1.48 a 2.31 a 2016 0.83 a 1.12 ab 0.52 b 1.48 a 2.31 a p-value <0.001 <0.001 <0.001 <0.001 <0.001 p-value <0.001 <0.001 <0.001 <0.001 <0.001 The highest sulphur uptake by rhizomes and stems was found in December. It should The highest sulphur uptake by rhizomes and stems was found in December. It should be noted that stems accumulated over 2–3 times more sulphur than leaves. Sulphur uptake be noted that stems accumulated over 2–3 times more sulphur than leaves. Sulphur up- in Miscanthus  giganteus increased with the progressing vegetation period in all parts of take in Miscanthus × giganteus increased with the progressing vegetation period in all parts the field experiment (Figure 9). The figures show the significance values of differences of the field experiment (Figure 9). The figures show the significance values of differences (p-values) of Sulphur uptake in subsequent months of observation for control and dose 60 (p-values) of Sulphur uptake in subsequent months of observation for control and dose 60 (Figure 9). (Figure 9). Figure 9. Sulphur uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). −2 Figure 9. Sulphur uptake in examined part of miscanthus (g m ) (three-year average content from measurements during the growing season every 30 days). 4. Discussion Mineral concentration plays an essential role in biomass combustion quality [14,35]. To improve biomass quality of Miscanthus giganteus, cultivation practice should be based on keeping the nitrogen fertilisation rate as low as possible and delaying harvest until the Agriculture 2021, 11, 76 12 of 16 spring following growth, as this will allow nutrient remobilisation and leaching of soluble minerals like K and Cl through rainfall [35,36]. Nutrient remobilisation seems to be a good strategy for perennial rhizomatous grasses [37,38] and represents an environmentally friendly strategy to reduce fertiliser ap- plications [36]. When calculating the nutrient balance and fertiliser recommendations, the remobilisation of nutrients within the plant must be taken into account [25]. Septem- ber and March are irrelevant for nutrient remobilisation [28]. The increase in nutrient content found in rhizomes in autumn and winter may be caused by remobilisation from the aboveground parts to the underground part [25]. In our research, generally, nutrient concentrations were highest at the beginning of the growing period and decreased clearly during the growing season. There were no significant differences caused by N fertilisation (except for potassium in leaves and sulphur in stems). The large loss of K from shoots between September and harvest can be attributed to leaching from the senescent plant material as K is not organically metabolised [39]. Some leaves fell after the end of the growing period, contributing to improved properties of soil by increasing the contents of elements and organic matter, thereby leading simultaneously to a decrease in ash uptake by plants [24]. The mineral concentration of aerial biomass is at its highest during spring and early summer and then declines, probably as a result of remobilization [24]. These results are also confirmed by own research in the aboveground parts of plants. It is docu- mented that mineral concentration in the aboveground biomass of Miscanthus  giganteus decreases gradually from autumn to winter [24,28]. Our results highlight a decline in the concentration of crude ash and macronutrients in aboveground parts of plants from spring to autumn. The average ash content in Giant Mischanthus according to Borkowska (2007) [31] is about 27.6 g kg . In the study Baxter et al. (2014) [15], the average ash content in leaves was between 40 and 60 g kg DM, and in stems the mean value was lower, between 10 and 30 g kg dm. In our research the highest average ash content was found in leaves 1 1 1 (57.5 g kg ), less in rhizomes (45.1 g kg ) and the lowest in stems (39.9 g kg ). In the research by Lewandowski and Heinz (2002) [36], the content of ash in the aboveground part of plants decreased from December to February. Ash content decreased also from autumn to spring in the study of Lewandowski et al. (2003) [40]. Similarly, delayed harvesting in the research of Lewandowski and Heinz (2003) [36] contributed to a reduction in ash content by 28% on average in Portugal and Great Britain, by 42% in Germany, by 50% in Sweden and by 54% in Denmark. Kotecki et al. (2010) [41] found that nutrient and crude ash yields were higher during the autumn harvest compared to the winter harvest, rising from 31 to 69%, while nitrogen fertilisation contributed to an increase in ash content. In our research, the ash content depended on nitrogen fertilisation and years of experiment in the rhizomes and aboveground part of miscanthus. Ash content decreased during the whole vegetation period. Studies by Lewandowski and Kircherer (1997) [42] showed that miscanthus leaves have a higher ash content than stems, which is also confirmed by own research. The content of potassium in the aboveground part of plants ranges from 4.3 to 10.5 g kg DM [22]. According to Borzecka-W ˛ alker ’s (2010) [31] study, the potassium content in the aerieal parts of miscanthus plants ranged from 2.7 to 9.9 g kg DM on heavy black soil and from 1.6 to 9.4 g kg DM on medium heavy black soil, depending on the genotype and year of cultivation. In the research of Kalembasa et al. (2019) [22] the mean potassium content in mischanthus grass biomass was 15.66 g kg D.M. Further- more, Lewandowski et al. 2000 [43] presented a review of potassium content obtained in field studies by several authors for some locations in Europe. Potassium concentration was significantly influenced during harvest time. According to Jensen et al. (2017) [38], potassium content decreased over the three harvests from June (2009) to February (2010) with the highest concentration during the summer. As expected, delaying the harvest by three to four months improved the combustion quality by reducing potassium content from 9 to 4 g kg DM. Agriculture 2021, 11, 76 13 of 16 Their experiment indicated that many genotypes of Mischanthus are characterised by higher concentrations of potassium in autumn. According to Beale and Long (1997) [24], potassium concentrations in the aboveground dry matter decreased from 32 to 12.0 g kg during whole vegetation period. In our study, the potassium content also decreased from summer till the end of vegetation in aboveground part of plants. Kalembasa et al. (2019) [22] proved that potassium was transferred from the aboveground parts of plants to rhizomes at the end of the growing season. According to Christian et al. (2008) [44] transfer of potassium from leaves and stem to rhizomes is 14–30%. The uptake of macronutrients is strongly dependent on the yield. The higher obtained yield, the higher the uptake of the following element [44]. In the Christian et al. (2008) [44] experiment between 1993 and 1995, the mineral uptake increased when the yield increased rapidly. The translocation of the elements during harvest depends on many external factors, especially weather conditions. While Mischanthus is characterised by higher dry yields (about 30 Mg ha ) from a three-year old crop, Beale and Long (1997) [24] found high potassium uptake gaining 38.0 g m . Nassi o Di Nasso et al. (2011) [45] obtained potassium 2 2 uptake of around 27.0 g m . In our research potassium uptake was around 24.8 gm . Greater uptake of potassium in the Roncucci et al. (2015) [28] study was found in autumn (16.0 gm ), and uptake was lower during wintertime. In this research, potassium uptake by the aboveground part of miscanthus at wintertime had values corresponding to around 33% of those recorded at autumn harvest. The time of harvest was the most relevant factor influencing miscanthus nutrient uptake in own experiments and those by Roncucci et al. (2015) [28]. Aerial parts of grasses accumulated mostly calcium, potassium and magnesium. The issue of calcium content in the rhizomes was undertaken by Stypczynska ´ et al. (2017) [21]. The concentration of this element in their study in the rhizomes was 1.5 g kg DM. In turn, Nassi di Nasso et al. 2010 [45] studied calcium content in the rhizomes and obtained values of 0.5–1.4 g kg DM which are confirmed in our research. The content of calcium was affected by the following factors: genotypes, geographical location of plantation and weather conditions, according to Helios (2018) [46]. In the lack of calcium fertilisation the content of this element relies on age of the plantation. In a 12-year study by Helios (2018) [46], the calcium content ranged from 3.1 g kg DM while calcium uptake 2 1 amounted to 0.45 g m in the first year of experiment to 0.5 g kg DM, while the calcium uptake was 1.2 g m in the tenth year of cultivation. In studies by Baxter et al. (2014) [15] and Stypczynska ´ et al. (2017) [21], leaves of miscanthus were characterised by higher calcium content compared to the stems, which is confirmed by our research. In conducted experiments by Lewandowski and Kicherer [42], the calcium concentrations in the leaves ranged from 2.3 to 3.7 g kg DM while that in the stems ranged from 0.5 to 1.1 g kg DM. In our research, the trends of changes in calcium content during vegetation were similar to those of Kotecki et al. (2010) [41] who showed that the content of this element in the aboveground part of the plant was decreasing until summer and then it increased. Sulphur plays an important role during the combustion process. Sulphur compounds that are formed during this process lead to corrosion and are emitted into the atmo- sphere [30]. In Lewandowski and Kicherer ’s [42] research no definite effect of nitrogen fertilisation on sulphur concentration in the leaves and stems was found. In our experiment, the content of this element in the stems was dependent on examined factor (p = 0.0485) while the nitrogen fertilisation had no significant impact on sulphur content in the leaves. For the entire vegetation period of miscanthus, Spiak et al. (2012) [29] showed that almost half the sulphur content is present in the stems compared to that in the leaves. In the study by Baxter et al. (2014) [15], on the other hand, the opposite results were obtained. In our study, the highest sulphur content was found in the rhizomes and there was less in the leaves and stems. The sulphur content in the leaves (0.64 g kg DM) and stems (0.65 g kg DM) was similar. Concentration of this element in aboveground parts of mis- canthus amounted to 0.72 g kg DM. In research by Kotecki (2010) [41], sulphur content in aerial parts of plants was 0.5–0.8 g kg DM. Agriculture 2021, 11, 76 14 of 16 In our field experiment, the highest content of this component was found in young plants. As the vegetation progressed, the sulphur content decreased in the aboveground part of plants by around 50%. In contrast to the content, the sulphur uptake was signifi- cantly higher in stems than in leaves. The uptake of sulphur in the aboveground part and whole plants with an increased trend was observed until the end of the vegetation season. A similar tendency was observed in rhizomes from July to December. 5. Conclusions Because of the need to reduce emissions, and to avoid worsening the air quality by producing the compounds during combustion of, e.g., hard coal for heating purposes in many Polish cities and other Central and Eastern European countries, the low content of mineral components in Miscanthus giganteus biomass is very desirable and may constitute an alternative source of biomass for energy purposes. While the research hypothesis was verified, it should be stated that only ash content in rhizomes and aboveground part of plants depended significantly on nitrogen fertilisation, while potassium (except in leaves), calcium and sulphur content (except in stems and aboveground parts) were not significantly influenced by this factor. The uptake of the studied elements was significantly dependent on nitrogen fertilisation in the case of ash, potassium, sulphur and calcium (except for stems). K and S concentrations were highest at the beginning of the growing period and decreased clearly during the growing season. The ash content was significantly higher under the influence of nitrogen fertilisation 2 2 in leaves at 58.3 g m and the lowest in stems at 42.2 g m , and the highest intake by 2 2 stems at 60.1 g m and the lowest in leaves at 46.3 g m . Significantly higher sulphur uptake was found in stems under the influence of nitrogen fertilisation at the amount of 1.28 g m . Author Contributions: Conceptualization: A.J.-R., I.G.-B., W.H.; Methodology: A.K., M.K., W.H.; Software: I.G.-B., W.H., A.J.-R.; Validation: A.K., M.K.; Investigation: I.G.-B., W.H., A.K.; Formal Analysis: I.G.-B., W.H., A.J.-R.; Writing: I.G.-B., W.H., A.J.-R.; Review: M.K., A.K., A.J.-R. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. 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Published: Jan 18, 2021

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