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Effect of Potassium Budget on Evolution of Soil Potassium in Different Crop Sequences and Site Conditions

Effect of Potassium Budget on Evolution of Soil Potassium in Different Crop Sequences and Site... Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 DOI: 10.1515/agri-2015-0001 MIKULÁS MADARAS Crop Research Institute, Prague MADARAS, M.: Effect of potassium budget on evolution of soil potassium in different crop sequences and site conditions. Agriculture (Ponohospodárstvo), vol. 60, 2014, no. 4, pp. 121­131. The influence of six different crop sequences on the dynamics of topsoil available and fixed potassium (K avail and K fix ) was studied within a 4-year period at 6 sites of different soil and climatic conditions. The highest K offtakes were recorded for 3-year alfalfa / clover cropping followed by winter wheat (151 kg K/ha/year) and for the crop sequence including one year of sugar beet / potato (124 kg K/ha/year). K avail and K fix were significantly decreased especially at crop sequence with alfalfa / clover cropping, compared to other crop sequences. At three sites of lower Kfix content (340830 mg K/kg), differences in K avail and K fix between crop sequences were more frequent, whereas almost no significant differences between treatments were observed at sites of higher K fix content (1,0001,380 mg K/kg). Changes of both K forms and K budget correlated significantly at sites of lower K fix content. At these sites, K avail decreased at the rate of 0.045 mg K per 1 kg/ha of K offtake; the rate of K fix decrease was 0.059 mg K per 1 kg/ha of K offtake. At sites of higher K fix , no significant relation between K forms and K budget was observed. The results show an importance of K fix as a K source in intensive agricultural systems with low or no K inputs. Key words: fertilisation, nutrients, budget, balance, non-exchangeable potassium Although the use of potassium (K) fertilisers increased by 25% since 1980 in global scale (Zörb et al. 2014), their application decreased dramatically in northern and western Europe (Öborn et al. 2005). In the Czech Republic, the use of K fertilisers dropped after 1989 from the level of ca. 70 kg K2O/ha to the level as low as ca. 10 kg K2O/ha (Grzebisz et al. 2010). Recent K input to agricultural soils is at the level of 5 kg K/ha in the form of mineral fertilisers. In addition, 18 kg K/ha is applied in the form of manures (Anonymous 2013). Overall field K offtake by harvested products is estimated to 71 kg K/ha on average (Klír et al. 2008); the exact offtake depends on the selection of crops and their yields. With insufficient external K input, plant demand for K is fulfilled by previously bound fertiliser K and by internal soil K sources. K content in soils ranges from 0.4 to 30 g/kg. Only 210% of soil K is available to plants, the main pool is present as hardly available structural K in K-bearing feldspars and layer silicates (Huang 2005; Zörb et al. 2014). The term "available K" (Kavail) is often used in agronomy for the pool consisting predominantly of water-soluble and exchangeable K. Non-exchangeable K is another significant pool available to plants, too. This pool, called also reserve K, interlayer K or fixed K (Kfix), is neither bonded covalently within the crystal structures of mineral particles nor is exchangeable. Its relation to exchangeable and water-soluble K is weak (Torma 1999). Kfix is moderately to less available to plants, depending on soil properties (Martin & Sparks 1985). A release of Kfix to easily available forms is forced by plant K removal, microbial activity and by K leaching (Moritsuka et al. 2004; Martin & Sparks 1985). The measurement of Kfix is often suggested to improve prediction of K availability RNDr. Mikulás Madaras, PhD., Crop Research Institute, Drnovská 507, 16106 Prague 6 ­ Ruzyn, Czech Republic. E-mail: madaras@vurv.cz Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 to plants (Neuberg 1980; Rees 2013; Edmeades et al. 2014), but in the Czech Republic these analyses were not included within the common testing of agricultural soils. As it is known from long-term field fertilisation experiments, non-use of K fertilisers leads first to the decrease of Kavail and afterwards to the stabilisation of Kavail at a certain level ranging from 30 to 120 mg K/kg (Blake et al. 1999). At this stage, further K uptake is compensated by K release from Kfix. Our previous research concerning long-term experiments with graduated K input indicated at some sites that the more negative is K budget, the more intensive is depletion of both Kavail and Kfix (Madaras et al. 2014). The decrease of Kfix can have the same magnitude as the decrease of Kavail. In some cases, the whole K offtake can originate from Kfix pool (Øgaard & Hansen 2010). The experimental design of graduated fertiliser rates is common in short-term and long-term field fertilisation experiments, while other factors such as crop sequence are usually uniform for all trial plots (Blake et al. 1999; Øgaard & Hansen 2010; Hejcman et al. 2013; Madaras et al. 2014). However, crops differ in their nutrient uptake, which consequently have an influence on the nutrient budget. Some crops have also specific mechanisms or adaptations by which they can increase the uptake from Kfix (Rengel & Damon 2008). To study the influence of different crop plants on short-term soil K changes in agricultural systems without K input, we established the 4-year field experiment where different crop sequences were included as treatments. The objective of the research presented in this paper is to evaluate the influence of selected typical crop plants and their sequences on evolution of soil K. MATERIAL AND METHODS Experimental design Field small-plot experiment was established at 6 sites with different climatic and soil conditions (Table 1). Sites were selected from the research station network of the Crop Research Institute, Prague. At each site, the experiment consisted of 24 plots of the size 3 × 10 m. An experimental design included 6 treatments, differing by the sequence of typical crop plants (Table 2). Treatments were replicated four times at each site. The same crop varieties and the same fertilisation scheme were used at all sites, with respect to particular crop production region. At colder sites, sugar beet was replaced by potato and alfalfa was replaced by clover. Treatments A, B, C and D differed only by the crop in the 2nd year of the experiment. Treatment E represented fodder production and included crops with high K uptake (alfalfa / clover). Treatment F was soil without vegetation cover within the first 3 years, weeds were suppressed chemically or mechanically when it was necessary. Exceptions of the uniform design were (1) the use of mustard or spring rapeseed instead of winter rapeseed after damage in winter 2010/2011 and (2) cropping of winter triticale instead of winter T a b l e 1 Basic characteristics of experimental sites and soils A [m] 220 265 290 345 530 670 T [oC] 9.2 8.1 8.0 7.9 7.1 6.0 R [mm] 548 597 696 472 559 1,000 Clay [%] 24 14 16 19 9 13 Cox [%] 2.2 1.2 1.1 1.5 1.1 2.1 pH (KCl) Site Ivanovice na Hané Hnvceves (HK) Kostelec n. Orlicí Prague (Ruzyn) Pernolec (Tachov) Vysoké n. Jizerou Soil type Chernozem Luvisol Luvisol Luvisol Cambisol Cambisol Reg SB SB SB SB POT FOD Kavail 186 173 145 187 99 207 Kfix [mg/kg] 1,050 800 500 1,010 1,350 350 Pavail 177 73 62 62 71 12 A altitude, T mean air temperature, R annual sum of rainfall, Reg production regions (SB sugar beet, POT potato, FOD-fodder crop), Clay fraction <0.002 mm, K avail and P avail available nutrients (Mehlich III extraction), K fix fixed K Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 wheat in site Vysoké. Overview of the weather conditions during the experiment is presented in Figure 1 and Table 3. Sampling and analyses Plant main product and by-products were harvested each year. Harvested material was weighed at actual moisture. Representative samples of the plant material were taken for further laboratory analyses, which includes determination of moisture content (drying at 105oC until a constant weight) and total K content (total microwave digestion). K offtake by harvested material was expressed in kg/ha. Because none K was applied in fetrilisers during the experiment, K offtake is equal to the K budget. Soil samples of the plough horizon (020 cm) were taken from each plot after the harvest of the last crop. Each sample consisted of 58 subsamples. Samples were dried at room temperature and sieved through 2 mm mesh. Two pools of soil K were analyzed. Kavail was extracted by the Mehlich 3 method (Mehlich 1984). Kfix was calculated as K extracted by 1 mol/l HCl (1:10 w/v, incubation 20 h at 50oC; adapted from Scheffer & Schachtschabel 1976) subtracted by Kavail. Extracts were analyzed twice by AAS GBC 908AA. Statistical evaluation of the results was performed using the STATISTICA 12 software (Statsoft). T a b l e 2 Crop sequences and fertilisation [kg nutrient/ha] Sequence code A B C D E 2010 Crop ww ww ww ww alf / clo* N1+N2 50+50 50+50 50+50 50+50 0 Crop ww pea sb / pot* rap / mus* alf / clo* 2011 N1+N2 40+60 0+30 60+40 40+30 0 Crop bar bar bar bar alf / clo* 2012 N1+N2 50+50 50+50 50+50 50+50 0 P 30 30 30 30 0 Crop ww ww ww ww ww 2013 N1+N2 40+60 40+60 40+60 40+60 40+60 P 40 40 40 40 40 F fallow 0 fallow 0 fallow 0 0 ww 40+60 40 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap / mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou T a b l e 3 Overview of the weather conditions during the experiment 2010 Site Ivanovice Hnvceves Kostelec Prague Pernolec Vysoké IXII R 826 792 900 679 693 1,231 T 8.4 8.4 8.2 8.9 7.1 5.8 IVIX R 637 591 696 531 382 733 T 15.6 15.6 14.9 15.4 13.9 12.8 IXII R 438 552 672 605 554 984 T 9.5 9.4 9.3 9.6 8.7 7.3 2011 IVIX R 350 361 508 437 361 598 T 16.4 16.0 15.7 16.2 15.0 13.7 IXII R 482 772 656 563 459 1,127 T 9.6 9.1 9.0 9.8 8.3 6.2 2012 IVIX R 331 518 415 437 278 529 T 16.7 15.9 15.7 16.3 14.6 13.7 IXII R 551 615 680 731 554 969 T 9.2 8.9 8.8 8.3 7.7 6.6 2013 IVIX R 379 424 465 559 372 534 T 15.7 15.3 15.0 15.3 13.9 12.7 R annual sum of rainfall, T mean air temperature Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Rainfall Temperature Ivanovice Ivanovice Vysoké Vysoké Kostelec Kostelec 200 Temperature [ oC] Rainfall [mm] 10 150 0 100 -10 0 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 2010 2011 2012 Figure 1. Overview of the weather conditions during the experiment (selected sites) -20 RESULTS Yields and K uptake Crop yields differed widely among experimental sites (Table 4). On average, they reached or exceeded average yields in the Czech Republic in particular years. The only exception was very low yield of rapeseed in 2011 due to the unfavourable late-winter and spring weather conditions at sites Hnvceves, Prague and Ivanovice. High intensity of weed attack (e.g. Apera spica-venti) was one of the main reasons of low yields of winter wheat in Pernolec. Low rainfall caused decreased alfalfa yields in Ivanovice, especially in 2012. Calculated K uptake by crops is shown in Table 5. The highest annual uptake (327 kg K/ ha on average in 2011) was recorded for sugar beet / potato cropping, with maximum of 415 kg K/ha in Hnvceves. By-products (leaves of sugar beet, stems and leaves of potato) accounted for 56% of K uptake. The second largest annual K uptake was recorded for alfalfa / clover during the 2nd and 3rd year of the experiment. On average, 244 kg K/ha was taken up annually by three cuts of hay. The lowest uptake was recorded for spring barley and for rapeseed. In the latter case, low uptake was caused both by low yield and by naturally low K concentration in the rapeseed biomass. Average annual K uptake by winter wheat was 59 kg K/ha; 41% of it accounted for grain. Triticale, as a replacement of winter wheat in Vysoké, showed more than 2-times higher K uptake compared to winter wheat because of higher straw K content (1.1% K in triticale straw, 0.6% K in winter wheat straw). The crop variations in K uptake are reflected in average K budgets for treatments. The most negative K budget was calculated for treatment E (184 kg K/ha/year; average of 2011, 2012 and 2013), which was followed by the treatment C (150 kg K/ha/year). In order of increasing K budget, next crop sequences were B (59 kg K/ha/year), A (54 kg K/ha/year), D (53 kg K/ha/year) and F (26 kg K/ha/year; here only K uptake by winter wheat in 2013 was accounted). Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Figure 2. Available K contents at sites of fixed K < 1,000mg K/kg (arithmetic mean and standard deviation). In particular years, significant differences (P < 0.05) between treatments A, C, E and F are marked by different letters. Figure 3. Fixed K contents at sites of fixed K < 1,000mg K/kg (arithmetic means and standard deviation). In particular years, significant differences (P < 0.05) between treatments are marked by different letters. Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Soil available potassium Remarkable changes of Kavail were observed especially in Vysoké, Kostelec and Hnvceves (Figure 2). At these 3 sites, Kavail of the treatment E was clearly different from other treatments. In Hnvceves, Kavail at crop sequence E was significantly lower than at other crop sequences in years 2012 and 2013 (P < 0.01 for almost all Student tests between treatments); however there were no significant differences among other crop sequences. During the experiment, Kavail remained approximately at the same level, with exception of the continuous decrease by alfalfa cropping within 2010 and 2012 at treatment E. In Kostelec, a significant decrease of Kavail was observed for all treatments between 2010 and 2013 (P < 0.001). Since 2011, Kavail of treatments C and E was lower than that of other treatments (P < 0.05). In 2013, a slight increase of Kavail was observed for treatment E compared to the contents in 2012 (P = 0.01). T a b l e 4 Overview of crop yields at experimental sites in main product (MP) and by-product (BP) [t/ha]. Moisture: cereals / rapeseed / pea 14%; sugar beet / potato actual moisture at harvest; alfalfa and clover ­ yields in dry matter. In brackets ­ standard deviations. Site MP Ivanovice BP MP Hnvceves BP MP Kostelec BP MP Prague BP MP Pernolec BP MP Vysoké BP Average MP 2010 ww 6.4 (1.0) 4.0 (0.7) 10.2 (0.5) 11.9 (0.9) 8.3 (0.5) 4.4 (0.2) 7.6 (0.5) 3.8 (0.4) 2.2 (0.5) 1.7 (0.4) 8.4 (0.3) 8.5 (0.3) 7.2 alf / clo* 2.7 (0.6) ­ 3.3 (0.5) ­ 4.0 (0.5) ­ 5.7 (1.0) ­ 1.0 (0.2) ­ 3.1 (0.4) ­ 3.3 ww 7.4 (0.5) 7.9 (0.8) 11.1 (0.3) 8.4 (0.5) 7.0 (0.8) 3.1 (0.2) 5.6 (0.2) 2.1 (0.3) 2.9 (0.2) 2.3 (0.2) 6.3 (0.3) 8.3 (0.3) 6.7 pea 4.0 (0.7) 3.5 (0.6) 4.5 (0.1) 4.1 (0.1) 2.6 (0.5) 2.3 (0.4) 2.9 (0.0) 2.6 (0.1) 2.7 (0.2) 2.5 (0.3) 6.3 (0.3) ­ 3.3 26.7 (0.7) ­ 43 (1.0) ­ 83 / 35 82 (11.5) 41 99 (6.2) 50 89 (9.7) 45 2011 sb / pot* rap / mus alf / clo* 61 (21) 31 0.9 (0.2) 2.2 (0.4) 1.0 (0.1) 2.0 (0.4) 3.3 (0.1) 4.2 (0.2) 0.7 (0.1) 2.0 (0.3) 1.4 (0.1) ­ 4.8 (0.4) ­ 1.5 7.4 (0.5) ­ 15.9 (2.1) ­ 9.1 (1.9) ­ 19.7 (1.7) ­ 13.2 (0.4) ­ 12.0 (0.7) ­ 12.9 bar 3.5 (0.4) 3.9 (0.6) 6.3 (0.5) 6.4 (1.7) 6.6 (0.7) 3.0 (0.3) 3.2 (0.5) 2.1 (0.3) 4.1 (0.4) 2.2 (0.2) 5.9 (0.3) 6.2 (0.3) 4.9 2012 alf / clo* 3.2 (0.2) ­ 18.3 (1.1) ­ 9.3 (0.3) ­ 15.3 (1.8) ­ 11.4 (0.2) ­ 9.8 (0.8) ­ 11.2 2013 ww 7.6 (0.4) 9.3 (0.6) 6.6 (1.4) 7.4 (1.6) 10.6 (0.8) 9.1 (0.7) 10.7 (0.7) 5.4 (0.5) 4.1 (1.0) 3.2 (0.8) 6.3 (0.4) 6.4 (0.4) 7.7 BP 5.7 ­ 5.4 3.0 44 / ­ 2.6 ­ 4.0 ­ 6.8 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap / mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 In Vysoké, the courses of K avail were very similar to those in Kostelec. A significant decrease of K avail was observed for all treatments between 2010 and 2013 (P < 0.001). K avail of treatment E was significantly lower than that of other treatments in 2011 and 2012 (P < 0.05). In 2013, however, there were no significant differences among the treatments because of the increase of K avail in treatment E. Trends of Kavail at sites of higher Kfix (Prague, Ivanovice and Pernolec) were not so straightforward (Table 6). In 2013, there were no significant differences between treatments at these sites, with exception of significantly higher Kavail of treatment F compared to treatments A, B and C in Ivanovice (P < 0.05). This treatment in Ivanovice had the highest Kavail level during the whole experiment. Soil fixed potassium In general, Kfix differences between treatments were less significant than those of Kavail (Figure 3). Partially it was due to the higher variability of Kfix T a b l e 5 Potassium uptake at experimental sites [kg/ha/year] by main product (MP), by-product (BP) and total biomass (TB). In brackets standard deviations. Site MP Ivanovice BP MP Hnvceves BP MP Kostelec BP MP Prague BP MP Pernolec BP MP Vysoké BP MP Average BP 2010 ww 19 (3) 18 (1) 32 (2) 67 (5) 26 (2) 21 (2) 24 (2) 22 (3) 7 (2) 8 (2) 31 (1) 97 (3) 23 35 alf / clo* 57 (11) 70 (3) 87 (4) 67 (10) 21 (1) 70 (15) 73 ww 25 (2) 35 (6) 34 (2) 39 (3) 24 (3) 10 (1) 19 (1) 11 (2) 12 (1) 19 (2) 30 (2) 75 (8) 23 29 pea 31 (6) 30 (5) 34 (2) 32 (4) 21 (4) 19 (4) 22 (1) 21 (0) 25 (2) 20 (2) 116 (10) 30 27 2011 sb / pot* rap / mus 66 (16) 154 192 (22) 223 135 (15) 248 111 (14) 205 113 (3) 102 c 189 (11) 171 c 144 183 5 (1) 36 (6) 6 (1) 43 (5) 5 (1) 32 (3) 6 (1) 31 (4) 12 (1) 50 (9) 6 36 alf / clo* 131 (11) 325 (53) 211 (32) 262 (23) 305 (21) 309 (34) × 259 bar 13 (2) 17 (3) 23 (2) 35 (9) 24 (2) 12 (2) 12 (2) 12 (2) 18 (2) 11 (1) 28 (1) 31 (2) 21 20 2012 alf / clo* 58 (4) 365 (23) 220 (8) 202 (24) 258 (5) 248 (21) 229 2013 ww 27 (1) 41 (3) 24 (5) 45 (10) 39 (3) 43 (3) 38 (2) 32 (0) 16 (4) 15 (4) 27 (2) 73 (5) 29 37 TB 59 73 53 57 327 42 259 41 229 66 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap/mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou, c calculated Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 contents within replications. In Hnvceves, Vysoké and Kostelec, alfalfa / clover cropping (treatment E) led to the lowest Kfix, whereas crop sequence with cereals (treatment A) had the highest Kfix. In Hnvceves, Kfix decreased markedly in all treatments during the experiment (P < 0.001), but this trend was not recorded at other sites. In Prague and Pernolec, no significant differences of Kfix were indicated within the whole experimental period. In Ivanovice, significant differences were recognized only in 2012 between Kfix of treatment D and treatments B, E and F (P < 0.05), but this difference did not appear in other years. K budget vs. soil K A clear trend was found between total K budget and change in soil Kavail within 2010 and 2013 for sites of lower Kfix (Vysoké, Kostelec, Hnvceves, P = 0.002), but no trend was found for sites of higher Kfix (Figure 4). The same holds also for the change of Kfix, which is significant only for sites of lower Kfix (P = 0.007). As can be seen from the steepness of the Kavail and Kfix regression lines, a decrease of Kfix per a K budget unit was slightly but insignificantly higher (56%) than the decrease of Kavail (44% of the decrease of both forms). DISCUSSION K budgets The highest K uptake was recorded for sugar beet, which is known for its high K demand and high K content in leaves (on average 4.5% K in dry matter; Neuberg et al. 1980). Potato represents also a large sink of soil K, as majority of this element is present in tubers. Sugar beet can utilize less-available forms of K (Vank et al. 2007). This was confirmed only by K fix trend from Kostelec (Figure 3). In several European long-term fertilisation experiments, annual K budgets in conventional agricultural systems including sugar beet and potato are in the range from 23 to 75 kg K/ha (Blake et al. 1999; Andrist-Rangel et al. 2007). Our K budget for treatment C is therefore lower; for a 4-year period it is 124 kg K/ha/year. It is due to harvesting all by-products, as the intent of the experiment was to keep K budget as low as possible. Leaves of sugar beet are however usually not harvested in recent agricultural practice. They represent an important K source and thus compensate high K offtake; Onderka et al. (2001) reported that by post-harvest incorporation of sugar beet leaves, 148 kg K/ha was applied back to soil. Permanent grasslands are also known for their highly negative K budget, which is given by high K concentration in grass/clover biomass (1.22.7% in dry matter; Öborn et al. 2005). Asdal and Bakken (1999) reported that total K budgets were in the range from 228 to 527 kg K/ha in a 6-year crop rotation with 50% of clover Figure 4. Relation between 3-year budget and change of available and fixed K contents for lower K fix sites (sites of fixed K fix < 1,000 mg K/kg ­ Vysoké, Kostelec, Hnvceves) and higher K fix sites (K fix > 1,000 mg K/kg ­ Ruzyn, Pernolec, Ivanovice) Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 T a b l e 6 Available (K avail ) and fixed (K fix ) potassium contents [mg/kg] during the experiment at sites of higher fixed K. In brackets standard deviations. Site Treatment A Prague C E F A Ivanovice C E F A Pernolec C E F Kavail 2010 181 (7) 186 (2) 170 (10) 190 (13) 162 (7) 159 (3) 177 (9) 189 (17) 96 (11) 85 (7) 109 (15) 105 (7) 2011 186 (8) 148 (4) 156 (11) 176 (15) 168 (8) 179 (13) 180 (18) 193 (17) 120 (6) 99 (5) 106 (14) 104 (14) 2012 168 (5) 165 (2) 155 (3) 181 (13) 160 (14) 156 (10) 188 (22) 207 (28) 78 (8) 76 (7) 111 (33) 106 (11) 2013 175 (7) 178 (8) 158 (23) 179 (9) 153 (5) 147 (4) 157 (6) 90 (7) 81 (4) 86 (7) 2010 991 (22) 1,015 (21) 994 (33) 1,003 (24) 1,075 (14) 1,087 (15) 1,069 (21) 1,475 (96) 2011 1,009 (20) 992 (26) 979 (41) 1,007 (30) 1,067 (14) 1,076 (18) 1,059 (21) 1,089 (31) 1,463 (88) Kfix 2012 1,000 (17) 1,014 (7) 986 (23) 1,018 (22) 1,024 (33) 1,027 (17) 992 (35) 1,013 (11) 1,451 (96) 2013 1,032 (75) 997 (66) 1,008 (24) 1,008 (41) 1,047 (3) 1,057 (9) 1,060 (48) 1,036 (5) 1,432 (64) 180 (17) 1,083 (32) 1,393 (175) 1,370 (170) 1,347 (235) 1,312 (167) 1,338 (177) 1,343 (174) 1,347 (260) 1,303 (248) 94 (17) 1,376 (209) 1,373 (224) 1,371 (269) 1,322 (289) ley; maximum annual K uptake reached 175 kg K/ha in the first year of clover. Our results are even higher; in Hnvceves the K offtake by alfalfa reached 365 kg K/ha in 2012. Such high offtake is not unrealistic. Øgaard and Krogstad (2005) reported that in non-K-fertilised soils in Norway, annual K offtake in the first year of grassland exceeded 300 kg K/ha in some cases. Soil K pools Our results show that Kavail and Kfix dynamics depends on the Kfix level, as majority of significant differences appeared for sites of lower Kfix content (Vysoké, Kostelec and Hnvceves). Vopnka and Machácek (1985) found that Kfix level have an influence on relation between Kavail and K budget. In soils of Kfix higher than 1200 mg K/kg, Kavail increased even when the budget was negative; in soils of Kfix lower than 600 mg K/kg, Kavail usually decreased even when the budget was positive. This can explain why almost no significant differences in Kavail were found in Prague, Ivanovice and Pernolec. Possible differences might be also masked by high Kfix variability in soils of Prague and Pernolec. Øgaard and Hansen (2010) studied changes of Kavail and Kfix in 6 grassland fertilisation experiments without K fertilisation. They found large differences between the sites in K uptake from Kfix. In all sites, Kavail contributed to total K uptake (40183 kg K/ha) by less than 40 kg K/ha and majority of K uptake was fulfilled from Kfix. This was observed in Hnvceves, where Kfix decreased rapidly, whereas Kavail remained without significant changes for 5 of 6 treatments. Øgaard and Krogstad (2005) found that K uptake from Kfix pool (`interlayer K') during 3 years of grass cropping increased with the percentage of clay in the soil consisting of 1 to 34% clay. For soils containing >12% clay, Kfix release covered 43% of the K uptake. In our data, the relation with clay content was not observed, which might be due to a narrower range of clay content in soil. CONCLUSION Negative nutrient budget represents potential risk for intensive agricultural systems. We showed that K budget can be very negative in case of K demanding crops. However, by-products are often not harvested in common agricultural praxis, as well as sub-optimal K application rates replace a part of removed soil K. According to the actual data about K inputs and outputs in the agricultural Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 soils of the Czech Republic, a reasonable estimate of average K budget is in the range from about 50 kg K/ha/year (main and by-product harvested) to about 20 kg K/ha/year (only main product harvested). Therefore, based on the linear regressions found, potentially available K reserve (Kavail + Kfix) decreases annually approximately by from 17 to 32 mg K/kg in topsoils with Kfix <1,000 mg K/kg. Approximately half of this depletion originates from Kfix. Therefore, by simple calculation, available K reserve can be exhausted within 3 to 4 decades in soils of lower Kfix content. However, such fast `potassium mining' is not realistic because the plant available pool is continuously replenished from structural K by weathering of soil minerals. With respect to K availability, susceptible agricultural soils are soils of low Kfix used for production of crops with high K offtake, e.g. forage, potato and sugar beet. In these soils, Kfix dynamics should be monitored for preventing the risk of decreased K availability, which can result in yield or quality drop, e.g. in case of a drought stress. Acknowledgements: The work was supported by the Ministry of Agriculture of the Czech Republic, projects QI91C118 and RO0414. EDMEADES, D.C. MORTON, J.D. WALLER, J.E. METHERELL, A.K. ROBERTS, A.H.C. CAREY P. 2014. The diagnosis and correction of potassium deficiency in New Zealand pastoral soils: a review. In New Zealand Journal of Agricultural Research, vol. 53, pp. 151173. DOI:10.1080/00288233.2010. 482954. GRZEBISZ, W. DIATTA, J. HARDTER, R. CYNA K. 2010. Fertilizer consumption patterns in Central European countries effect of actual yield development trends in 19862005 years a comparative study of the Czech Republic and Poland. In Journal of Central European Agriculture, vol. 11, no.1, pp.7382. DOI:10.5513/JCEA01/11.1.809. HEJCMAN, M. BERKOVÁ, M. KUNZOVÁ, E. 2013. Effect of long-term fertilizer application on yield and concentrations of elements (N, P, K, Ca, Mg, As, Cd, Cu, Cr, Fe, Mn, Ni, Pb, Zn) in grain of spring barley. In Plant, Soil and Environment, vol. 59, no. 7, pp. 329­334. HUANG, P.M. 2005. Chemistry of potassium in soils. In TABATABAI, M.A. SPARKS, D.L. (Eds.). Chemical processes in soils. Madison: SSSA, pp. 227292. ISBN 0-89118-843-6. KLÍR, J. KUNZOVÁ, E. CERMÁK, P. 2008. Rámcová metodika výzivy rostlin a hnojení [Frame methodology of plant nutrition and fertilization]. Prague: Crop Research Institute, 48 pp. ISBN 978-8087011-61-4. MADARAS, M. KOUBOVÁ, M. SMATANOVÁ, M. 2014. Long-term effect of low potassium fertilization on its soil fractions. In Plant, Soil and Environment, vol. 60, 2014, no. 8, pp. 358363. MARTIN, H.W. SPARKS, D.L. 1985. On the behaviour of nonexchangeable potassium in soils. In Communications in soil science and plant analyses, vol. 16, pp.133162. DOI:10.1080/00103628509367593. MEHLICH, A. 1984. Mehlich-3 soil test extractant: a modification of Mehlich-2 extractant. In Communications in soil science and plant analyses, vol. 15, pp. 1409­1416. DOI:10.1080/00103628409367568. MORITSUKA, N. YANAI, J. KOSAKI, T. 2004. Possible processes releasing nonexchangeable potassium from the rhizosphere of maize. In Plant and Soil, vol. 258, pp. 261268. DOI:10.1023/B:PLSO.0000016556.79278.7f. NEUBERG, J. 1980. Komplexní metodika výzivy rostlin [The Complex Methodology of Plant Nutrition]. Prague: UVTIZ, 327 pp. ÖBORN, I. ANDRIST-RANGEL, Y. ASKEKAARD, M. GRANT, C.A. WATSON, C.A. EDWARDS, A.C. 2005. Critical aspects of potassium management in agricultural systems. In Soil Use and Management, vol. 21, no.1, pp. 102112. DOI:10.1111/j.1475-2743.2005. tb00114.x. ØGAARD, A.F. HANSEN, S. 2010. Potassium uptake and requirement in organic grassland farming. In Nutrient Cycling in Agroecosystems, vol. 87, no. 1, pp.137149. DOI:10.1007/s10705-009-9320-5. ØGAARD, A.F. KROGSTAD, T. 2005. Release of interlayer potassium in Norwegian grassland soils. In Journal of Plant Nutrition and Soil Science, vol. 168, pp. 8088. DOI:10.1002/jpln.200421454. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Agriculture de Gruyter

Effect of Potassium Budget on Evolution of Soil Potassium in Different Crop Sequences and Site Conditions

Madaras, Mikuláš
Agriculture , Volume 60 (4) – Dec 1, 2014
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Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 DOI: 10.1515/agri-2015-0001 MIKULÁS MADARAS Crop Research Institute, Prague MADARAS, M.: Effect of potassium budget on evolution of soil potassium in different crop sequences and site conditions. Agriculture (Ponohospodárstvo), vol. 60, 2014, no. 4, pp. 121­131. The influence of six different crop sequences on the dynamics of topsoil available and fixed potassium (K avail and K fix ) was studied within a 4-year period at 6 sites of different soil and climatic conditions. The highest K offtakes were recorded for 3-year alfalfa / clover cropping followed by winter wheat (151 kg K/ha/year) and for the crop sequence including one year of sugar beet / potato (124 kg K/ha/year). K avail and K fix were significantly decreased especially at crop sequence with alfalfa / clover cropping, compared to other crop sequences. At three sites of lower Kfix content (340830 mg K/kg), differences in K avail and K fix between crop sequences were more frequent, whereas almost no significant differences between treatments were observed at sites of higher K fix content (1,0001,380 mg K/kg). Changes of both K forms and K budget correlated significantly at sites of lower K fix content. At these sites, K avail decreased at the rate of 0.045 mg K per 1 kg/ha of K offtake; the rate of K fix decrease was 0.059 mg K per 1 kg/ha of K offtake. At sites of higher K fix , no significant relation between K forms and K budget was observed. The results show an importance of K fix as a K source in intensive agricultural systems with low or no K inputs. Key words: fertilisation, nutrients, budget, balance, non-exchangeable potassium Although the use of potassium (K) fertilisers increased by 25% since 1980 in global scale (Zörb et al. 2014), their application decreased dramatically in northern and western Europe (Öborn et al. 2005). In the Czech Republic, the use of K fertilisers dropped after 1989 from the level of ca. 70 kg K2O/ha to the level as low as ca. 10 kg K2O/ha (Grzebisz et al. 2010). Recent K input to agricultural soils is at the level of 5 kg K/ha in the form of mineral fertilisers. In addition, 18 kg K/ha is applied in the form of manures (Anonymous 2013). Overall field K offtake by harvested products is estimated to 71 kg K/ha on average (Klír et al. 2008); the exact offtake depends on the selection of crops and their yields. With insufficient external K input, plant demand for K is fulfilled by previously bound fertiliser K and by internal soil K sources. K content in soils ranges from 0.4 to 30 g/kg. Only 210% of soil K is available to plants, the main pool is present as hardly available structural K in K-bearing feldspars and layer silicates (Huang 2005; Zörb et al. 2014). The term "available K" (Kavail) is often used in agronomy for the pool consisting predominantly of water-soluble and exchangeable K. Non-exchangeable K is another significant pool available to plants, too. This pool, called also reserve K, interlayer K or fixed K (Kfix), is neither bonded covalently within the crystal structures of mineral particles nor is exchangeable. Its relation to exchangeable and water-soluble K is weak (Torma 1999). Kfix is moderately to less available to plants, depending on soil properties (Martin & Sparks 1985). A release of Kfix to easily available forms is forced by plant K removal, microbial activity and by K leaching (Moritsuka et al. 2004; Martin & Sparks 1985). The measurement of Kfix is often suggested to improve prediction of K availability RNDr. Mikulás Madaras, PhD., Crop Research Institute, Drnovská 507, 16106 Prague 6 ­ Ruzyn, Czech Republic. E-mail: madaras@vurv.cz Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 to plants (Neuberg 1980; Rees 2013; Edmeades et al. 2014), but in the Czech Republic these analyses were not included within the common testing of agricultural soils. As it is known from long-term field fertilisation experiments, non-use of K fertilisers leads first to the decrease of Kavail and afterwards to the stabilisation of Kavail at a certain level ranging from 30 to 120 mg K/kg (Blake et al. 1999). At this stage, further K uptake is compensated by K release from Kfix. Our previous research concerning long-term experiments with graduated K input indicated at some sites that the more negative is K budget, the more intensive is depletion of both Kavail and Kfix (Madaras et al. 2014). The decrease of Kfix can have the same magnitude as the decrease of Kavail. In some cases, the whole K offtake can originate from Kfix pool (Øgaard & Hansen 2010). The experimental design of graduated fertiliser rates is common in short-term and long-term field fertilisation experiments, while other factors such as crop sequence are usually uniform for all trial plots (Blake et al. 1999; Øgaard & Hansen 2010; Hejcman et al. 2013; Madaras et al. 2014). However, crops differ in their nutrient uptake, which consequently have an influence on the nutrient budget. Some crops have also specific mechanisms or adaptations by which they can increase the uptake from Kfix (Rengel & Damon 2008). To study the influence of different crop plants on short-term soil K changes in agricultural systems without K input, we established the 4-year field experiment where different crop sequences were included as treatments. The objective of the research presented in this paper is to evaluate the influence of selected typical crop plants and their sequences on evolution of soil K. MATERIAL AND METHODS Experimental design Field small-plot experiment was established at 6 sites with different climatic and soil conditions (Table 1). Sites were selected from the research station network of the Crop Research Institute, Prague. At each site, the experiment consisted of 24 plots of the size 3 × 10 m. An experimental design included 6 treatments, differing by the sequence of typical crop plants (Table 2). Treatments were replicated four times at each site. The same crop varieties and the same fertilisation scheme were used at all sites, with respect to particular crop production region. At colder sites, sugar beet was replaced by potato and alfalfa was replaced by clover. Treatments A, B, C and D differed only by the crop in the 2nd year of the experiment. Treatment E represented fodder production and included crops with high K uptake (alfalfa / clover). Treatment F was soil without vegetation cover within the first 3 years, weeds were suppressed chemically or mechanically when it was necessary. Exceptions of the uniform design were (1) the use of mustard or spring rapeseed instead of winter rapeseed after damage in winter 2010/2011 and (2) cropping of winter triticale instead of winter T a b l e 1 Basic characteristics of experimental sites and soils A [m] 220 265 290 345 530 670 T [oC] 9.2 8.1 8.0 7.9 7.1 6.0 R [mm] 548 597 696 472 559 1,000 Clay [%] 24 14 16 19 9 13 Cox [%] 2.2 1.2 1.1 1.5 1.1 2.1 pH (KCl) Site Ivanovice na Hané Hnvceves (HK) Kostelec n. Orlicí Prague (Ruzyn) Pernolec (Tachov) Vysoké n. Jizerou Soil type Chernozem Luvisol Luvisol Luvisol Cambisol Cambisol Reg SB SB SB SB POT FOD Kavail 186 173 145 187 99 207 Kfix [mg/kg] 1,050 800 500 1,010 1,350 350 Pavail 177 73 62 62 71 12 A altitude, T mean air temperature, R annual sum of rainfall, Reg production regions (SB sugar beet, POT potato, FOD-fodder crop), Clay fraction <0.002 mm, K avail and P avail available nutrients (Mehlich III extraction), K fix fixed K Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 wheat in site Vysoké. Overview of the weather conditions during the experiment is presented in Figure 1 and Table 3. Sampling and analyses Plant main product and by-products were harvested each year. Harvested material was weighed at actual moisture. Representative samples of the plant material were taken for further laboratory analyses, which includes determination of moisture content (drying at 105oC until a constant weight) and total K content (total microwave digestion). K offtake by harvested material was expressed in kg/ha. Because none K was applied in fetrilisers during the experiment, K offtake is equal to the K budget. Soil samples of the plough horizon (020 cm) were taken from each plot after the harvest of the last crop. Each sample consisted of 58 subsamples. Samples were dried at room temperature and sieved through 2 mm mesh. Two pools of soil K were analyzed. Kavail was extracted by the Mehlich 3 method (Mehlich 1984). Kfix was calculated as K extracted by 1 mol/l HCl (1:10 w/v, incubation 20 h at 50oC; adapted from Scheffer & Schachtschabel 1976) subtracted by Kavail. Extracts were analyzed twice by AAS GBC 908AA. Statistical evaluation of the results was performed using the STATISTICA 12 software (Statsoft). T a b l e 2 Crop sequences and fertilisation [kg nutrient/ha] Sequence code A B C D E 2010 Crop ww ww ww ww alf / clo* N1+N2 50+50 50+50 50+50 50+50 0 Crop ww pea sb / pot* rap / mus* alf / clo* 2011 N1+N2 40+60 0+30 60+40 40+30 0 Crop bar bar bar bar alf / clo* 2012 N1+N2 50+50 50+50 50+50 50+50 0 P 30 30 30 30 0 Crop ww ww ww ww ww 2013 N1+N2 40+60 40+60 40+60 40+60 40+60 P 40 40 40 40 40 F fallow 0 fallow 0 fallow 0 0 ww 40+60 40 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap / mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou T a b l e 3 Overview of the weather conditions during the experiment 2010 Site Ivanovice Hnvceves Kostelec Prague Pernolec Vysoké IXII R 826 792 900 679 693 1,231 T 8.4 8.4 8.2 8.9 7.1 5.8 IVIX R 637 591 696 531 382 733 T 15.6 15.6 14.9 15.4 13.9 12.8 IXII R 438 552 672 605 554 984 T 9.5 9.4 9.3 9.6 8.7 7.3 2011 IVIX R 350 361 508 437 361 598 T 16.4 16.0 15.7 16.2 15.0 13.7 IXII R 482 772 656 563 459 1,127 T 9.6 9.1 9.0 9.8 8.3 6.2 2012 IVIX R 331 518 415 437 278 529 T 16.7 15.9 15.7 16.3 14.6 13.7 IXII R 551 615 680 731 554 969 T 9.2 8.9 8.8 8.3 7.7 6.6 2013 IVIX R 379 424 465 559 372 534 T 15.7 15.3 15.0 15.3 13.9 12.7 R annual sum of rainfall, T mean air temperature Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Rainfall Temperature Ivanovice Ivanovice Vysoké Vysoké Kostelec Kostelec 200 Temperature [ oC] Rainfall [mm] 10 150 0 100 -10 0 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 2010 2011 2012 Figure 1. Overview of the weather conditions during the experiment (selected sites) -20 RESULTS Yields and K uptake Crop yields differed widely among experimental sites (Table 4). On average, they reached or exceeded average yields in the Czech Republic in particular years. The only exception was very low yield of rapeseed in 2011 due to the unfavourable late-winter and spring weather conditions at sites Hnvceves, Prague and Ivanovice. High intensity of weed attack (e.g. Apera spica-venti) was one of the main reasons of low yields of winter wheat in Pernolec. Low rainfall caused decreased alfalfa yields in Ivanovice, especially in 2012. Calculated K uptake by crops is shown in Table 5. The highest annual uptake (327 kg K/ ha on average in 2011) was recorded for sugar beet / potato cropping, with maximum of 415 kg K/ha in Hnvceves. By-products (leaves of sugar beet, stems and leaves of potato) accounted for 56% of K uptake. The second largest annual K uptake was recorded for alfalfa / clover during the 2nd and 3rd year of the experiment. On average, 244 kg K/ha was taken up annually by three cuts of hay. The lowest uptake was recorded for spring barley and for rapeseed. In the latter case, low uptake was caused both by low yield and by naturally low K concentration in the rapeseed biomass. Average annual K uptake by winter wheat was 59 kg K/ha; 41% of it accounted for grain. Triticale, as a replacement of winter wheat in Vysoké, showed more than 2-times higher K uptake compared to winter wheat because of higher straw K content (1.1% K in triticale straw, 0.6% K in winter wheat straw). The crop variations in K uptake are reflected in average K budgets for treatments. The most negative K budget was calculated for treatment E (184 kg K/ha/year; average of 2011, 2012 and 2013), which was followed by the treatment C (150 kg K/ha/year). In order of increasing K budget, next crop sequences were B (59 kg K/ha/year), A (54 kg K/ha/year), D (53 kg K/ha/year) and F (26 kg K/ha/year; here only K uptake by winter wheat in 2013 was accounted). Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Figure 2. Available K contents at sites of fixed K < 1,000mg K/kg (arithmetic mean and standard deviation). In particular years, significant differences (P < 0.05) between treatments A, C, E and F are marked by different letters. Figure 3. Fixed K contents at sites of fixed K < 1,000mg K/kg (arithmetic means and standard deviation). In particular years, significant differences (P < 0.05) between treatments are marked by different letters. Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 Soil available potassium Remarkable changes of Kavail were observed especially in Vysoké, Kostelec and Hnvceves (Figure 2). At these 3 sites, Kavail of the treatment E was clearly different from other treatments. In Hnvceves, Kavail at crop sequence E was significantly lower than at other crop sequences in years 2012 and 2013 (P < 0.01 for almost all Student tests between treatments); however there were no significant differences among other crop sequences. During the experiment, Kavail remained approximately at the same level, with exception of the continuous decrease by alfalfa cropping within 2010 and 2012 at treatment E. In Kostelec, a significant decrease of Kavail was observed for all treatments between 2010 and 2013 (P < 0.001). Since 2011, Kavail of treatments C and E was lower than that of other treatments (P < 0.05). In 2013, a slight increase of Kavail was observed for treatment E compared to the contents in 2012 (P = 0.01). T a b l e 4 Overview of crop yields at experimental sites in main product (MP) and by-product (BP) [t/ha]. Moisture: cereals / rapeseed / pea 14%; sugar beet / potato actual moisture at harvest; alfalfa and clover ­ yields in dry matter. In brackets ­ standard deviations. Site MP Ivanovice BP MP Hnvceves BP MP Kostelec BP MP Prague BP MP Pernolec BP MP Vysoké BP Average MP 2010 ww 6.4 (1.0) 4.0 (0.7) 10.2 (0.5) 11.9 (0.9) 8.3 (0.5) 4.4 (0.2) 7.6 (0.5) 3.8 (0.4) 2.2 (0.5) 1.7 (0.4) 8.4 (0.3) 8.5 (0.3) 7.2 alf / clo* 2.7 (0.6) ­ 3.3 (0.5) ­ 4.0 (0.5) ­ 5.7 (1.0) ­ 1.0 (0.2) ­ 3.1 (0.4) ­ 3.3 ww 7.4 (0.5) 7.9 (0.8) 11.1 (0.3) 8.4 (0.5) 7.0 (0.8) 3.1 (0.2) 5.6 (0.2) 2.1 (0.3) 2.9 (0.2) 2.3 (0.2) 6.3 (0.3) 8.3 (0.3) 6.7 pea 4.0 (0.7) 3.5 (0.6) 4.5 (0.1) 4.1 (0.1) 2.6 (0.5) 2.3 (0.4) 2.9 (0.0) 2.6 (0.1) 2.7 (0.2) 2.5 (0.3) 6.3 (0.3) ­ 3.3 26.7 (0.7) ­ 43 (1.0) ­ 83 / 35 82 (11.5) 41 99 (6.2) 50 89 (9.7) 45 2011 sb / pot* rap / mus alf / clo* 61 (21) 31 0.9 (0.2) 2.2 (0.4) 1.0 (0.1) 2.0 (0.4) 3.3 (0.1) 4.2 (0.2) 0.7 (0.1) 2.0 (0.3) 1.4 (0.1) ­ 4.8 (0.4) ­ 1.5 7.4 (0.5) ­ 15.9 (2.1) ­ 9.1 (1.9) ­ 19.7 (1.7) ­ 13.2 (0.4) ­ 12.0 (0.7) ­ 12.9 bar 3.5 (0.4) 3.9 (0.6) 6.3 (0.5) 6.4 (1.7) 6.6 (0.7) 3.0 (0.3) 3.2 (0.5) 2.1 (0.3) 4.1 (0.4) 2.2 (0.2) 5.9 (0.3) 6.2 (0.3) 4.9 2012 alf / clo* 3.2 (0.2) ­ 18.3 (1.1) ­ 9.3 (0.3) ­ 15.3 (1.8) ­ 11.4 (0.2) ­ 9.8 (0.8) ­ 11.2 2013 ww 7.6 (0.4) 9.3 (0.6) 6.6 (1.4) 7.4 (1.6) 10.6 (0.8) 9.1 (0.7) 10.7 (0.7) 5.4 (0.5) 4.1 (1.0) 3.2 (0.8) 6.3 (0.4) 6.4 (0.4) 7.7 BP 5.7 ­ 5.4 3.0 44 / ­ 2.6 ­ 4.0 ­ 6.8 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap / mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 In Vysoké, the courses of K avail were very similar to those in Kostelec. A significant decrease of K avail was observed for all treatments between 2010 and 2013 (P < 0.001). K avail of treatment E was significantly lower than that of other treatments in 2011 and 2012 (P < 0.05). In 2013, however, there were no significant differences among the treatments because of the increase of K avail in treatment E. Trends of Kavail at sites of higher Kfix (Prague, Ivanovice and Pernolec) were not so straightforward (Table 6). In 2013, there were no significant differences between treatments at these sites, with exception of significantly higher Kavail of treatment F compared to treatments A, B and C in Ivanovice (P < 0.05). This treatment in Ivanovice had the highest Kavail level during the whole experiment. Soil fixed potassium In general, Kfix differences between treatments were less significant than those of Kavail (Figure 3). Partially it was due to the higher variability of Kfix T a b l e 5 Potassium uptake at experimental sites [kg/ha/year] by main product (MP), by-product (BP) and total biomass (TB). In brackets standard deviations. Site MP Ivanovice BP MP Hnvceves BP MP Kostelec BP MP Prague BP MP Pernolec BP MP Vysoké BP MP Average BP 2010 ww 19 (3) 18 (1) 32 (2) 67 (5) 26 (2) 21 (2) 24 (2) 22 (3) 7 (2) 8 (2) 31 (1) 97 (3) 23 35 alf / clo* 57 (11) 70 (3) 87 (4) 67 (10) 21 (1) 70 (15) 73 ww 25 (2) 35 (6) 34 (2) 39 (3) 24 (3) 10 (1) 19 (1) 11 (2) 12 (1) 19 (2) 30 (2) 75 (8) 23 29 pea 31 (6) 30 (5) 34 (2) 32 (4) 21 (4) 19 (4) 22 (1) 21 (0) 25 (2) 20 (2) 116 (10) 30 27 2011 sb / pot* rap / mus 66 (16) 154 192 (22) 223 135 (15) 248 111 (14) 205 113 (3) 102 c 189 (11) 171 c 144 183 5 (1) 36 (6) 6 (1) 43 (5) 5 (1) 32 (3) 6 (1) 31 (4) 12 (1) 50 (9) 6 36 alf / clo* 131 (11) 325 (53) 211 (32) 262 (23) 305 (21) 309 (34) × 259 bar 13 (2) 17 (3) 23 (2) 35 (9) 24 (2) 12 (2) 12 (2) 12 (2) 18 (2) 11 (1) 28 (1) 31 (2) 21 20 2012 alf / clo* 58 (4) 365 (23) 220 (8) 202 (24) 258 (5) 248 (21) 229 2013 ww 27 (1) 41 (3) 24 (5) 45 (10) 39 (3) 43 (3) 38 (2) 32 (0) 16 (4) 15 (4) 27 (2) 73 (5) 29 37 TB 59 73 53 57 327 42 259 41 229 66 ww winter wheat (triticale was used instead of winter wheat in all cases at Vysoké nad Jizerou), alf / clo alfalfa / clover, sb / pot sugar beet / potato, rap/mus rapeseed / mustard, bar spring barley * latter crop was used in Pernolec and Vysoké nad Jizerou, c calculated Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 contents within replications. In Hnvceves, Vysoké and Kostelec, alfalfa / clover cropping (treatment E) led to the lowest Kfix, whereas crop sequence with cereals (treatment A) had the highest Kfix. In Hnvceves, Kfix decreased markedly in all treatments during the experiment (P < 0.001), but this trend was not recorded at other sites. In Prague and Pernolec, no significant differences of Kfix were indicated within the whole experimental period. In Ivanovice, significant differences were recognized only in 2012 between Kfix of treatment D and treatments B, E and F (P < 0.05), but this difference did not appear in other years. K budget vs. soil K A clear trend was found between total K budget and change in soil Kavail within 2010 and 2013 for sites of lower Kfix (Vysoké, Kostelec, Hnvceves, P = 0.002), but no trend was found for sites of higher Kfix (Figure 4). The same holds also for the change of Kfix, which is significant only for sites of lower Kfix (P = 0.007). As can be seen from the steepness of the Kavail and Kfix regression lines, a decrease of Kfix per a K budget unit was slightly but insignificantly higher (56%) than the decrease of Kavail (44% of the decrease of both forms). DISCUSSION K budgets The highest K uptake was recorded for sugar beet, which is known for its high K demand and high K content in leaves (on average 4.5% K in dry matter; Neuberg et al. 1980). Potato represents also a large sink of soil K, as majority of this element is present in tubers. Sugar beet can utilize less-available forms of K (Vank et al. 2007). This was confirmed only by K fix trend from Kostelec (Figure 3). In several European long-term fertilisation experiments, annual K budgets in conventional agricultural systems including sugar beet and potato are in the range from 23 to 75 kg K/ha (Blake et al. 1999; Andrist-Rangel et al. 2007). Our K budget for treatment C is therefore lower; for a 4-year period it is 124 kg K/ha/year. It is due to harvesting all by-products, as the intent of the experiment was to keep K budget as low as possible. Leaves of sugar beet are however usually not harvested in recent agricultural practice. They represent an important K source and thus compensate high K offtake; Onderka et al. (2001) reported that by post-harvest incorporation of sugar beet leaves, 148 kg K/ha was applied back to soil. Permanent grasslands are also known for their highly negative K budget, which is given by high K concentration in grass/clover biomass (1.22.7% in dry matter; Öborn et al. 2005). Asdal and Bakken (1999) reported that total K budgets were in the range from 228 to 527 kg K/ha in a 6-year crop rotation with 50% of clover Figure 4. Relation between 3-year budget and change of available and fixed K contents for lower K fix sites (sites of fixed K fix < 1,000 mg K/kg ­ Vysoké, Kostelec, Hnvceves) and higher K fix sites (K fix > 1,000 mg K/kg ­ Ruzyn, Pernolec, Ivanovice) Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 T a b l e 6 Available (K avail ) and fixed (K fix ) potassium contents [mg/kg] during the experiment at sites of higher fixed K. In brackets standard deviations. Site Treatment A Prague C E F A Ivanovice C E F A Pernolec C E F Kavail 2010 181 (7) 186 (2) 170 (10) 190 (13) 162 (7) 159 (3) 177 (9) 189 (17) 96 (11) 85 (7) 109 (15) 105 (7) 2011 186 (8) 148 (4) 156 (11) 176 (15) 168 (8) 179 (13) 180 (18) 193 (17) 120 (6) 99 (5) 106 (14) 104 (14) 2012 168 (5) 165 (2) 155 (3) 181 (13) 160 (14) 156 (10) 188 (22) 207 (28) 78 (8) 76 (7) 111 (33) 106 (11) 2013 175 (7) 178 (8) 158 (23) 179 (9) 153 (5) 147 (4) 157 (6) 90 (7) 81 (4) 86 (7) 2010 991 (22) 1,015 (21) 994 (33) 1,003 (24) 1,075 (14) 1,087 (15) 1,069 (21) 1,475 (96) 2011 1,009 (20) 992 (26) 979 (41) 1,007 (30) 1,067 (14) 1,076 (18) 1,059 (21) 1,089 (31) 1,463 (88) Kfix 2012 1,000 (17) 1,014 (7) 986 (23) 1,018 (22) 1,024 (33) 1,027 (17) 992 (35) 1,013 (11) 1,451 (96) 2013 1,032 (75) 997 (66) 1,008 (24) 1,008 (41) 1,047 (3) 1,057 (9) 1,060 (48) 1,036 (5) 1,432 (64) 180 (17) 1,083 (32) 1,393 (175) 1,370 (170) 1,347 (235) 1,312 (167) 1,338 (177) 1,343 (174) 1,347 (260) 1,303 (248) 94 (17) 1,376 (209) 1,373 (224) 1,371 (269) 1,322 (289) ley; maximum annual K uptake reached 175 kg K/ha in the first year of clover. Our results are even higher; in Hnvceves the K offtake by alfalfa reached 365 kg K/ha in 2012. Such high offtake is not unrealistic. Øgaard and Krogstad (2005) reported that in non-K-fertilised soils in Norway, annual K offtake in the first year of grassland exceeded 300 kg K/ha in some cases. Soil K pools Our results show that Kavail and Kfix dynamics depends on the Kfix level, as majority of significant differences appeared for sites of lower Kfix content (Vysoké, Kostelec and Hnvceves). Vopnka and Machácek (1985) found that Kfix level have an influence on relation between Kavail and K budget. In soils of Kfix higher than 1200 mg K/kg, Kavail increased even when the budget was negative; in soils of Kfix lower than 600 mg K/kg, Kavail usually decreased even when the budget was positive. This can explain why almost no significant differences in Kavail were found in Prague, Ivanovice and Pernolec. Possible differences might be also masked by high Kfix variability in soils of Prague and Pernolec. Øgaard and Hansen (2010) studied changes of Kavail and Kfix in 6 grassland fertilisation experiments without K fertilisation. They found large differences between the sites in K uptake from Kfix. In all sites, Kavail contributed to total K uptake (40183 kg K/ha) by less than 40 kg K/ha and majority of K uptake was fulfilled from Kfix. This was observed in Hnvceves, where Kfix decreased rapidly, whereas Kavail remained without significant changes for 5 of 6 treatments. Øgaard and Krogstad (2005) found that K uptake from Kfix pool (`interlayer K') during 3 years of grass cropping increased with the percentage of clay in the soil consisting of 1 to 34% clay. For soils containing >12% clay, Kfix release covered 43% of the K uptake. In our data, the relation with clay content was not observed, which might be due to a narrower range of clay content in soil. CONCLUSION Negative nutrient budget represents potential risk for intensive agricultural systems. We showed that K budget can be very negative in case of K demanding crops. However, by-products are often not harvested in common agricultural praxis, as well as sub-optimal K application rates replace a part of removed soil K. According to the actual data about K inputs and outputs in the agricultural Agriculture (Ponohospodárstvo), 60, 2014 (4): 121-131 soils of the Czech Republic, a reasonable estimate of average K budget is in the range from about 50 kg K/ha/year (main and by-product harvested) to about 20 kg K/ha/year (only main product harvested). Therefore, based on the linear regressions found, potentially available K reserve (Kavail + Kfix) decreases annually approximately by from 17 to 32 mg K/kg in topsoils with Kfix <1,000 mg K/kg. Approximately half of this depletion originates from Kfix. Therefore, by simple calculation, available K reserve can be exhausted within 3 to 4 decades in soils of lower Kfix content. However, such fast `potassium mining' is not realistic because the plant available pool is continuously replenished from structural K by weathering of soil minerals. With respect to K availability, susceptible agricultural soils are soils of low Kfix used for production of crops with high K offtake, e.g. forage, potato and sugar beet. In these soils, Kfix dynamics should be monitored for preventing the risk of decreased K availability, which can result in yield or quality drop, e.g. in case of a drought stress. Acknowledgements: The work was supported by the Ministry of Agriculture of the Czech Republic, projects QI91C118 and RO0414. EDMEADES, D.C. MORTON, J.D. WALLER, J.E. METHERELL, A.K. ROBERTS, A.H.C. CAREY P. 2014. The diagnosis and correction of potassium deficiency in New Zealand pastoral soils: a review. 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Agriculture – de Gruyter

Published: Dec 1, 2014

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