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Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 doI: 10.2478/agri-2021-0012 original paper The role of nano-silicon and oTher soil condiTioners in improving physiology and yield of droughT sTressed cropbarley 1* 2 1 Abdel W AhAb M. MAhMoud , hAssAn A.Z.A , shAdy Abdel Mott Aleb , 3 1 MohAMed M. RoWeZAk And AZZA M. sAlAMA Cairo university, Giza, egypt soil, Water & environment Institute, Agriculture Research Center, Giza, egypt College of science, Juof university, kingdom of saudi Arabia Mahmoud, A.W.M., A.Z.A., h., Mottaleb, s.A., Rowezak, M.M., and salama, A.M.(2021). the role of nano-silicon and other soil conditioners in improving physiology and yield of drought stressed barley crop. Agriculture (Poľnohospodárstvo), 67(3), 124 – 143. A field experiment was conducted in sandy soil to assess the effect of different sources of soil conditioners on barley (Hordeum vulgare l. cv. Giza 137) growth and its yield under drought stress. Plants were exposed to two levels of drought stress until grain maturity: (A) drought at 75% available water (AW) with nPk as control (treatment, t1); (b) mild drought stress at 50% AW with foliar spray of nano-silicon at 75 ppm (treatment, t2), foliar spray of nano-zeolite at 75 ppm (treatment, t3), perlite at 4 tons/h (treatment, t4), natural zeolite at 600 kg/ha (treatment, t5), bentonite at 4 tons/h (treatment, t6), and a combined treatment of t2+t3+t4+t5+t6 at the half amount of each material (t7). All the treatments received the recommended doses of organic matter. Vegetative growth and yield characters as well as anatomical characters were recorded. the physical and chemical soil properties were significantly improved by both foliar and soil conditioners application. The nutrients content of the barley crop were augmented under combined treatment (t7) as compared to other treatments. under that treatment, barley crop chemical components, i.e. protein, ash, chlorophylls, amino acids, vitamins, and fibre were significantly higher compared to other treatments. In addition, gibberellic acid (GA ) and abscisic acid (AbA) content besides antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) activities were significantly affected by all treatments. The economical profits were achieved, as reflected by an investment factor value equal to or higher than 3, and this was achieved for all tested nano- silicon, zeolite, and soil conditioners indicated the effectiveness and profitability of studied treatments. key words: nanoparticles, soil conditioners, drought stress, anatomy, physio-chemical soil properties, economical evaluation the main obstacle to sustainable agriculture in stress is estimated to cause severe damages to the arid and semi-arid areas is the limited water resourc- global crop production reaching up to 30% by 2025, es available for agricultural production. the inade - accounting for the current yield (Raza et al. 2019). quate moisture content together with bad manage- drought-resistant crops are an obvious choice to be ment of available resources is considered a serious used in cultivation in these types of affected lands. problems that must be tackled for proper agriculture barley (Hordeum vulgare l.), for example, is an im- land management and utilisation. harsh drought portant extensively cultivated annual grain cereal in Abdel Wahab M. Mahmoud (*Corresponding author), shady Abdel Mottaleb, Plant Physiology division, botany department, Faculty of Agriculture, Cairo university, Giza, 12613, egypt. e-mail: Mohamed.firstname.lastname@example.org hassan A.Z.A, soil, Water & environment Institute, Agriculture Research Center, Giza, egypt Mohamed M. Rowezak, biology department, College of science, Juof university, kingdom of saudi Arabia Azza M. salama, Plant t axonomy division, Agricultural botany department, Faculty of Agriculture, Cairo university, Giza, 12613, egypt © 2021 Authors. this is an open access article licensed under the Creative Commons Attribution-nonComercial-noderivs license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 124 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 arid areas due to its rich contents of carbohydrates, or horticulture, providing an environmentally safe minerals, and vitamins. It is mostly cultivated in arid method to ameliorate soils affected by abiotic stress zones owing to its stress tolerance nature (sánchez- acting as an ecosystem-friendly soil conditioner díaz et al. 2002). drought stress has more impact to amend salt-affected soils (hassan & Mahmoud on barley during and just before spike emergence 2015). similarly natural zeolite has many impor - (samarah 2005). Another peak of barley sensitivi - tant properties that boost soil quality. The clinop- ty to drought is reported to be during anthesis and tilolite-rich zeolite is extensively used to improve the initial stages of grain development. Moreover, water and air quality because of its large specific the severity of drought stress from the beginning of surface area and cation exchange capacity (CeC), grain filling to maturity may be detrimental to grain low cost, and mechanical strength (Mahmoud et al. development (grain abortion) and yield (Rajala et al. 2017). In addition, the physical and chemical prop- 2011). During the grain-filling period, drought stress erties of zeolite minerals make them an appropri- reduces the net photosynthetic rate of the flag leaf, ate soil amendment and regulator of plant nutrients but under a high vapour pressure deficit, it also had (Mahmoud & swaefy 2020). Another useful soil an insignificant effect on the grain-filling rate. The conditioner is perlite, which is a siliceous mineral flag leaf and ear are the main photosynthetic organs formed during volcanic eruptions. Perlite has sev- to provide assimilate for grain filling, particularly in eral advantages such as its relatively low price and environments where drought is encountered at the is mainly used to increase the aeration and drainage end of the plants life cycle (Rajala et al. 2011). the of the soil because of its lightness and uniformity capacity to remobilise vegetative reserves seems to (Grillas et al. 2001). Finally, bentonite is stretchy be responsible for maintaining the grain growth rate clay collected mostly from montmorillonite and its under drought stress. Middle to late drought stress surface has permanent negative charges and, thus, promoted leaf senescence, shortened the grain-fill - can be used as an adsorbent for several inorganic ing period, and decreased grain yield and individual and organic contaminants present in water (li et al. grain weight of barley (Fischer & Maurer 1978). 2010). this is especially evident in its capability of Many soil amendments and foliar treatments adsorbing some heavy metals (sen & Gomez 2011). have been documented in the literature to ameliorate the objective of this work was to study the ef- drought stress in plants (Rekaby et al. 2020; Mot- fects of two foliar sprays (nano-si and nano-zeolite) taleb et al. 2021). For example, Xie et al. (2012) and three soil conditioners (natural zeolite, perlite, stated the nano-silicon (nano-si) sprays augmented and bentonite), and their combination, on amelio- the chlorophyll contents and improved gas exchange rating drought stress imposed on barley and subse- parameters of stressed plants such as photosynthetic quent effects on plant growth, yield and grain-filling rate, transpiration rate, stomatal conductance, and period, as well as their anatomical and biochemical photochemical efficiency. Furthermore, Mahmoud characters. et al. (2020) reported that nano-si improved the nutritional quality of salt-stressed potatoes. More- MAteRIAl And Methods over, nano-Si spray significantly enhanced some growth parameters such as plant height, stem diam- Land preparation and plant material eter, ground cover, canopy spread, and the number An experimental field trial was initiated at Wadi of achenes in the capitulum (Janmohammadi et al. el-natron el-behera Governorate, egypt longitude 2016). Another beneficial foliar spray reported in 28°54’ e, latitude 28°20 n, and Altitude 130 m, the literature is nano-zeolite. this molecule has an through two winter seasons (2017/18 and 2018/19). exclusive cation exchange, adsorption, soil remedi- barley grains (Hordeum vulgare cv. Giza 137) were ation, hydration-dehydration, and catalytic proper- th th planted in sandy soil on the 18 and 10 of novem- ties. All these properties enable nano-zeolite to be st nd ber in the 1 and the 2 seasons, respectively. the loaded with macro and micronutrients and act as relevant physical and chemical properties of the in- a slow-release fertiliser (Mahmoud et al. 2020). na- vestigated soil area were determined according to no-zeolite can be used in conservative agriculture 125 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 Page et al. 1982 and klute 1965 as shown in t able environment Research Institute (sWeRI) of the Ag- ricultural Research Center (ARC), egypt and was as barley grains were obtained from the Agriculture follows: organic matter (oM) = 34.8%, total nitro- Research station, Faculty of Agriculture, Cairo uni- gen (n) =1.6, carbon to nitrogen (C:n) ratio =18:1, versity. the experiment was laid out in split plots ph = 6.5, electrical conductivity (eC) = 3.23, ds/m, design with four replicates. the grains were sown potassium (k) = 0.76%, phosphorus (P) = 0.87%, in plots of 2 × 5 m size with 1 m alleys among rep- iron (Fe) = 452 ppm, manganese (Mn) = 29.5 ppm, lications at a rate of 350 grains/m . the treatments zinc (Zn) = 16.5 ppm, copper (Cu) = 11.2 ppm. consisted of two irrigation regimes (main plots) and Treatments six foliar and soil conditioners (sub-plots) as will be the treatments of irrigation water regimes and detailed below. t wo drought stress treatments were the applied foliar sprays or soil conditioners were imposed on the plants: 75% of available water (AW) as follow: as a control and 50% AW (mild stress), The field capacity was calculated under dripping irrigation T1 ‒ nitrogen, phosphorus and potassium (NPK) + when zones of water overlap each other on the line. 75% AW as control. the applied rates of n (urea 48%), P (calcium T2 ‒ nano-silicon [75 ppm] + 50% AW (applied 4 superphosphate 15.5%) and k (potassium sulphate times with 25 days intervals after one week from 48%) were 100, 50 and 100 kg/Fadden (one Fad- sowing date). den = 4,200 m ), respectively. urea was applied as T3 ‒ nano-zeolite [75 ppm] + 50% AW (applied 4 basal fertiliser in one-third (40 kg) at land prepara- times with 25 days intervals after one week from tion, the second one (40 kg) after 30 days from the sowing date). first, and the last one after 2 months later. Calcium T4 ‒ perlite [4 ton/ha] + 50% AW. and potassium were added in the form of top dress- T5 ‒ natural zeolite [600 kg/ha] + 50% AW. ing one month before the tillering and flowering T6 ‒ bentonite [4 ton/ha] + 50% AW. stages of barley, respectively. Moreover, farmyard T7 ‒ combined treatment of T2+T3+T4+T5+T6 but manure was applied as base fertilisers during land at half concentration each mentioned above + 50% preparation at the rate of 10 m /ha. the analyses of AW. farmyard manure were performed at soil, Water and t a b l e 1 Physical and chemical soil properties of the experimental site soil properties Particle size distribution [%] Soil moisture content [%] sand silt Clay t exture saturation FC WP AW 85.00 11.55 3.45 sandy 29.00 12.50 7.20 5.30 Physical ph EC [dS/m] CaCo [%] OM [%] 7.87 0.28 8.13 0.10 Soluble cations [meq/l] Soluble anions [meq/l] 2+ 2+ + + 2− − − 2− Ca Mg k na Co hCo Cl so 3 3 4 3.50 2.60 0.43 2.25 0.00 1.81 0.93 6.04 Chemical Total [mg/100 g soil] Available micronutrients [ppm] n P k Fe Mn Zn Cu 16.00 10.20 18.00 8.70 4.20 2.03 4.28 Note: FC ‒ field capacity; WP ‒ wilting point; AW ‒ available water; EC – electrical conductivity; OM ‒ organic matter. 126 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 Nano-silicon and nano-zeolite synthesis Anatomical studies leaf samples were taken 90 days after sowing the silicon nanomaterial was synthesized in the th from the 4 internodes from stem apex. samples non-transferred ARC plasma system from com- were killed and fixed in F.A.A. solution (50 ml 95% mercial silicon powder (40 microns, Aldrich). the ethyl alcohol + 10 ml formalin + 5 ml glacial acetic synthesis of nano silicon was carried out according acid + 35 ml distilled water) for 48 hours. thereaf - to y asar-Inceoglu et al. (2012). the synthesis of ter, samples were washed in 50% ethyl alcohol, de- nano zeolite was prepared according to hassan and hydrated, and cleared in tertiary butyl alcohol series, Mahmoud (2015). the average sizes of silicon and embedded in paraffin wax (melting point 54 ‒ 56°C). zeolite nanoparticles were 4.87 nm and 4.93 nm, re- Cross-sections, 20 μm thick, were cut by a rotary spectively. microtome, double stained with crystal violet/eryth- Composition of perlite rosine, cleared in xylene, and mounted in Canada t ables 2, 3, and 4 show the physical and chemi- balsam (nassar & el-sahhar 1998). Measurements were done using a micrometer eyepiece and an av- cal properties of perlite, natural zeolite, and benton- erage of 10 readings was calculated. examination ite, respectively. and photomicrographs were taken at botany de- Morphological and yield characters partment, Faculty of Agriculture, Cairo university, In both seasons, Random samples of five plants egypt. were taken 90 days after sowing and at harvest time Analysis of grains minerals content to record the measurements of morphological char- t otal nitrogen concentration was determined us- acters and yield components of individual plants as ing the modified Kjeldahl method (Cottenie et al. follows: 1982). Phosphorus was measured after dry ashing 1 ‒ plant height [cm]; according to the Vanadate-molybdate method (Page 2 ‒ number of tillers/plants; et al. 1982). Potassium was determined by using 3 ‒ fresh weight of shoot [g/plant]; flame photometer apparatus. The concentrations of 4 ‒ dry weight of shoot [g/plant]; 5 ‒ total number of spikes/plant; 6 ‒ length of spikes [cm] [spikes with grains/plant]; t a b l e 2 7 ‒ grains and total grain weight/plant; Physical and chemical properties of perlite 8 ‒ harvest index. Random samples of five plants were taken 120 Characters Perlite days after sowing in both seasons to record the fol- Bulk density [g/cm ] 0.39 lowing yield characters: Particle density [g/cm ] 2.26 1 ‒ number of spikes/plant; ph 8.24 2 ‒ spike length [cm]; Electrical conductivity [dS/m] 0.10 3 ‒ weight of 1,000 grain [g]; 4 ‒ grain yield [g/plant]. Carbonates [%] 0.79 t a b l e 3 Chemical composition of natural zeolite loss of sio ti o Al o F o Feo Mno Mgo Cao na o k o sro P o 2 2 2 3 2 3 2 2 2 5 Chemical ignition composition [%] 45.6 2.85 13.49 5.45 8.26 0.56 6.25 9.57 2.78 0.80 0.20 0.76 3.38 ba Ca Cr se Cu Zn Zr nb ni Rb y ‒ ‒ Trace elements [ppm] 11 1.30 34 0.84 20 64 249 15 53 18 23 ‒ ‒ 127 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 iron, zinc, magnesium, and copper were determined of spectrophotometry. Concentration for each amino using flame atomic absorption spectrometry (Shi- acid was estimated by a standard curved line for gly- madzu AA.670, Japan). cine (t rajkovic et al. 1983; Džamić 1989). Analysis of total protein, ash, starch, chlorophylls Vitamins (a, b), fiber, and water contents extraction and determination of vitamins e was Total proteins, ash, starch, and fiber were meas- estimated calorimetrically, whereas the high-perfor- ured in grains according to katoch (2011). Chloro- mance liquid chromatography (HPLC) technique as phylls (a, b) were measured in leaves with a spec- described by batifoulier et al. (2005) was used for trophotometer (helios uVG1702e, england) ac- the separation and quantification of vitamins B1, cording to the method of lichtenthaler & Wellburn b2, b6, and folic acid using a new reversed-phase (1983). Water contents (WC) of five different leaves chromatographic method. per treatment were monitored using a lICoR 6400 Endogenous phytohormones (lincoln, nebraska, usA) infrared gas analyzer the analysis of endogenous phytohormones (IRGA) according to t urner (1981). was performed according to Fales et al. (1973) Analysis of total amino acids in leaves for the determination of gibberellic acid Grain samples of barley were prepared for anal- ) and abscisic acid (ABA). The quantification (GA of the endogenous phytohormones was carried out ysis of total amino acid concentrations. the total with Ati-Unicum gas-liquid chromatography (610 amino acids extracted using 80% of ethanol and Series), equipped with flame ionization detector ac- precipitation liquefied proteins by chloroform (Gru- cording to the method described by Vogel (1975), jić-Injac 1962). Identification of amino acids was at the end freeze-dried plant herbs (equivalent 6 g done by using the method of chromatography and t a b l e 4 Physical and chemical properties of bentonite Physical properties Chemical properties Particle size distribution [%] Soluble cations [meq/l] 2+ Coarse sand [2,000‒200 µm] 0.98 Ca 14.98 2+ Fine sand [200‒20 µm] 3.97 Mg 21.56 Silt [20‒2 µm] 21.85 k 0.30 Clay [<2µm] 73.20 na 146.90 Bulk density[g/cm ] 1.26 Soluble anions [meq/l] 2− Total porosity [%] 54.50 Co nil Pore size distribution as [%] of total porosity hCo 2.65 Macro (drainable) pores [>28.8 µm] 45.85 Cl 152.80 2− Micro pores [<28.8 µm] 54.15 so 28.29 Water holding capacity [WHC]* 83.05 Electrical conductivity [EC] dS/m 16.95 Field capacity [FC]* 50.62 pH [1:2.5] soil: water suspension 7.87 Wilting percentage [WP]* 32.43 t otal CaCo [%] 0.24 Available moisture [FC-WP]* 18.19 Organic matter [%] 0.29 hydraulic conductivity m/day 0.150 *% on a weight basis 128 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 FW) were ground to a fine powder using a mortar Hydro physical soil properties and soil conditioner additives and pestle. the powdered material was extracted Representative soil samples (0 ‒ 30 cm depth) three times (one time for 3 h.- and then 2 times for 1 were collected to determine some hydro-physical h.) with methanol (80% v/v, 15 ml/g F.W.), supple- properties and soil conditioner additives. soil bulk mented with butylated hydroxytoluene (2,6-di-tret- density was determined by the core method (Page butyl-p-cresol) as an antioxidant, at 4°C in darkness. 1982). t otal soil porosity was calculated using the the extract was centrifuged at 4,000 rpm. the su- data of bulk density and pore size distributions pernatant was transferred into flasks wrapped with (loveday 1974). the hydraulic conductivity was aluminium foil and the residue was twice extracted measured under constant head (constant water sup- again. the supernatants were combined and the vol- ply) (klute 1965). ume was reduced to 10 ml at 35°C under vacuum. The aqueous extract was adjusted to pH 8.6 and Economical evaluation extracted three times with an equal volume of pure the total yield was calculated and economic ethyl acetate. the combined alkaline ethyl acetate analysis was performed using the following equa- extract was dehydrated over anhydrous sodium sul- tions (sarwar et al. 2007; Mubashir et al. 2010): phate then filtered. The filtrate was evaporated to dry- • Gross income = yield × price; ness under vacuum at 35°C and re-dissolved in 1 ml • Profitable return [PR] = gross income-total pro- absolute methanol, Samples (50 μl) were then duction cost; analyzed by chromatography. • PR% over control = [PR] ‒ control treatments; • Benefit cost ratio [BCR] = PR % over con- Enzymes activity trol / total production cost; • Investment factor [IF] = gross income / total Catalase activity production cost. the spectrophotometric method by bergmeyer (1970) was selected for the determination of catalase Statistical analysis activity (CAt) in the green biomass of plants. this data were subjected to statistical analysis using method is based on the measurement of the decline analysis of variance (ANOVA) test at a 5% signifi- in absorbance upon hydrogen peroxide cleavage at cance level. the difference between treatments was 240 nm. the measured difference in absorbance per then analysed using duncan’s multiple range test minute is then a value of catalase activity expressed (dMR t) at 5% (duncan 1955). data were analysed in units (u). using the statistical analysis system (sAs) software. superoxide dismutase activity superoxide dismutase (sod) activity was as- Results And dIsCussIon sessed using the method adapted for the determina- tion of this antioxidant enzyme in a plant material Morphological and yield characters (belcrediová et al. 2007). the assay principle was All tested growth characters of barley plants were based on the use of xanthine and xanthine oxidase significantly boosted by foliar application of both to generate superoxide radicals which react with nano-zeolite or silicon at 50% available water (AW) 2-(4-iodophenyl)-3-(4-nitrophenol)-5-phenyltetra- compared to the untreated plants (t able 5). nano ze- zolium chloride to form a red formazan dye. sod olite was the most effective treatment in increasing activity was measured spectrophotometrically by plant height, tillers number, and shoot fresh and dry monitoring the inhibition of this reaction at 37°C weights by 50, 92.3, 128.7, and 186.9%, respective- ly. As to the effect of soil conditioners at 50% AW, and wavelength of 505 nm. nano-zeolite treatment realized the highest values the CA t and sod values determined in fresh for the mentioned growth characters followed by mass were recalculated to dry matter and expressed perlite then bentonite compared to the control (t able in the international units (Iu) per gram in dry matter 5). Application of zeolite increased the plant height, (u/g). 129 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 number of leaves, and shoot fresh and dry weights number of spikes, spike length, 1,000 grains weight, by 43.1, 69.2, 83.8, and 130.4%, respectively com- and grain yield also showed maximum values under pared to the control treatment (t able 5). t7 treatment (t able 6). Application of si was docu- the combined treatment (t7) of nano-si, na- mented to have several beneficial effects on cere- no-zeolite, perlite, natural zeolite, and bentonite also al´s morphological characters. For example, when had a positive effect on plant growth. It increased si was applied to drought stressed wheat plants, it plant height and tillers number by 52.9 and 66.7%, led to a higher leaf weight ratio and specific leaf respectively compared to control (t1). It was no- area compared with untreated plants (Gong et al. ticed that foliar application or soil conditioners sig- 2003). similarly zeolite improved plant height and nificantly enhanced the shoot fresh and dry weight yield components of plants under abiotic stress by of barley plants by 152.2 and 217.4%, respectively increased the water retention capacity of soils (by- (t able 5). Moreover, yield characters such as the bordi 2016). Zeolite significantly increased the wa- t a b l e 5 effect of different soil conditioners on morphological characters of barley plants under drought stress Morphological characters t reatments Plant height shoot fresh weight shoot dry weight no. of tillers [cm] [g] [g] d d d d T1: [NPK + 75% AW] 51.0 ± 0.2 15.0 ± 0.2 13.6 ± 0.3 2.3 ± 0.05 a a a a T2: [Nano-silicon + 50% AW] 76.5 ± 0.1 22.0 ± 0.4 31.1 ± 0.4 6.6 ± 0.06 a a b b T3: [Nano-zeolite + 50% AW] 75.0 ± 0.3 24.0 ± 0.1 28.4 ± 0.2 5.8 ± 0.07 b b b b T4: [Perlite + 50% AW] 73.0 ± 0.2 20.0 ± 0.5 25.0 ± 0.1 5.3 ± 0.12 c b c c T5: [Natural zeolite + 50% AW] 65.0 ± 0.4 19.0 ± 0.4 22.2 ± 0.5 4.4 ± 0.02 d c d c T6: [Bentonite + 50% AW] 53.0 ± 0.3 17.0 ± 0.3 17.6 ± 0.4 3.7 ± 0.03 a a a a T7: [T2 + T 3 + T4 + T5 + T6 + 50% AW] 78.0 ± 0.1 25.0 ± 0.1 34.3 ± 0.3 7.3 ± 0.05 Means with the same letters in a column are not significantly different by DMRT 5%. Each value is an average of two seasons. Note: AW ‒ available water; DMRT ‒ Duncan’s multiple range test. t a b l e 6 y ield characters of barley plants as affected by different soil conditioners under drought stress y ield characters t reatments spike length 1,000 grains Grain yield no. of spikes harvest index [cm] weight [g] [t/ha] b d d e a T1: [NPK + 75% AW] 3 ± 0.01 15.5 ± 0.2 30.4 ± 0.4 3.25 ± 0.03 1.41 ± 0.01 b b b d c T2: [Nano-silicon + 50% AW] 4 ± 0.02 19.5 ± 0.3 42.3 ± 0.1 3.40 ± 0.01 0.51 ± 0.03 b b b c b T3: [Nano-zeolite + 50% AW] 4 ± 0.01 19.1 ± 0.4 40.5 ± 0.2 3.55 ± 0.02 0.61 ± 0.01 b b c c b T4: [Perlite + 50% AW] 4 ± 0.02 19.0 ± 0.2 38.8 ± 0.3 3.50 ± 0.01 0.66 ± 0.04 b b c b b T5: [Natural zeolite + 50% AW] 4 ± 0.03 18.0 ± 0.1 36.0 ± 0.2 3.65 ± 0.02 0.82 ± 0.02 b c d b a T6: [Bentonite + 50% AW] 3 ± 0.01 17.5 ± 0.3 33.3 ± 0.1 3.70 ± 0.04 1.00 ± 0.02 a a a a c T7: [T2 + T3 + T4 + T5 + T6 + 50% AW] 5 ± 0.01 20.0 ± 0.2 44.6 ± 0.3 3.80 ± 0.04 0.52 ± 0.03 Means with the same letters in a column are not significantly different by DMRT 5%. Each value is an average of both seasons. Note: AW ‒ available water. 130 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 ter-holding capacity of the soil cultivated with wa- ite (t7), a clear synergistic effect was observed, as ter-stressed barley, which improved plant growth expected, due to a further enhancement of soil prop- parameters including plant height, leaf area, number erties and water retention. of spikes, total plant fresh weight, and total plant drought was documented to decrease yield dry biomass (Albusaidi et al. 2011). When nano-si and can generally weaken spring barley production and zeolite were combined with perlite and benton- regardless of soil conditions (t rnka et al. 2007). th Figure 1. t ransverse sections through the 4 leaf of barley of treatments: 1 ‒ control [T1]; 2 ‒ nano-Si [T2]; 3 ‒ nano-zeolite [T3]; 4 ‒ perlite [T4]; 5 ‒ natural zeolite [T5]; 6 ‒ bentonite [T6]; 7 ‒ combined treatment [T7] [X40%]. 131 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 Stomatal closure is the first line of defense against by Petrov et al. (2012) in barley plants. using foliar drought, where plants regulate water loss through sprays treatments (t2 and t3) as well as applica - precise control of stomatal opening. Moreover, the tion of soil conditioners (t4, t5, and t6) or their accumulation of osmolytes diminished cell water combination (T7) led to a significant increase in all loss and to sustained tissue turgor. In addition, pho- tosynthetic membranes were protected against reac- tive oxygen species (Ros), which were generated as a response to water potential decrease, by the pro- duction of carotenoids to decrease the degradation process (Munné & Alegre 2000). Prolonged drought caused the above defensive mechanisms to fail and consequently led to impaired photosynthesis. There- fore, soil conditioners are used to mitigate drought stress due to their action in retaining soil water and nutrients for a long time to complete the plant sur- vival, so plant growth and yield are not further af- fected (hassan et al. 2020). Grain yield parameters were reported to be decreased under drought stress in and wa- wheat plants due to diminishing of net Co ter uptake assimilation rate (Gong et al. 2005). Fur- thermore, drought majorly affects plant flowering, pollination, and grain-filling. These negative effects are due to shortages in water and nutrient absorption by plants, which consequently decreases CO assim- ilation rate and transport of assimilates to reproduc- tive organs. Increased water retention, due to zeo- lite application, increased required carbohydrates for metabolical processes, which in turn enhanced grain yield and harvest index of plants (Al-busaidi et al. 2008). It is also evident that nano-si and zeo- lite boosted the beneficial effects achieved by perlite and bentonite (t7), due to a further enhancement of soil properties and water retention. Anatomical studies th Anatomical characters of the 4 leaf of barley at age 90 days grown under drought stress and affected by different treatments are illustrated in t able 7 and Figure 1. Results revealed that water deficit generally de- creased the thickness of midvein, xylem vessels, and mesophyll, in addition to the diameter of midvein bundle and upper and lower epidermis of barley leaf. de souza et al. (2013) found in maize that the effect of drought stress could be attributed to the de- crease in size induced in the mesophyll thickness, as well as in the length and width of vascular bundles. these results are in agreement with those obtained t a b l e 7 Anatomical characters of barley leaf under drought stress as affected by foliar or terrestrial conditioners individual or in the mixture Xylem Midvein Mesophyll Midvein Vb upper lower upper lower bulliform vessel t reatments thickness thickness diameter sclerenchyma sclerenchyma epidermis epidermis cells diameter [mm] [mm] [mm] [mm] [mm] [mm] [mm] [mm] [mm] T1: [NPK + 75% AW] 1,125 500 277.5 60.0 510 280 53 60 60 T2: [Nano-silicon + 50% AW] 1,670 735 325.0 80.0 825 480 60 80 75 T3: [Nano-zeolite + 50% AW] 1,500 705 322.5 77.5 770 440 57 75 73 T4:[Perlite + 50% AW] 1,465 670 317.5 75.0 720 415 55 70 70 T5: [Natural zeolite + 50% AW] 1,450 560 310.0 67.5 705 370 53 68 67 T6: [Bentonite + 50% AW] 1,405 530 295.0 65.0 690 360 52 65 65 T7: [T2 + T3+ T4 + T5 + T6 + 50% AW] 1,890 820 330.0 90.0 1,050 540 70 85 80 Note: VB – vascular bundle; NPK ‒ nitrogen, phosphorus, potassium; AW ‒ available water. Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 −143 anatomical leaf characters. Regarding foliar treat- worth mentioning that the upper and lower epider- ment, the results revealed that nano-si spray (t2) mis increased by 27.2 and 41.6% more than con- increased thickness of midvein and mesophyll, mid trol. Finally, bulliform cells recorded higher and in- vascular bundle diameter, and upper sclerenchyma creased by 33.3% over untreated plants. si applica - tissue thickness by 48.4, 54.7, 16.2, and 61.7%, re- tion to drought-stressed wheat led to the formation spectively, over the control (t1). on the other hand, of thicker leaves, which might reduce the loss of spraying nano-zeolite (t3) increased xylem vessels water due to transpiration as well as keeping higher diameter, lower sclerenchyma tissue, and upper and relative water content in cells and tissues (Gong et lower epidermis thickness by 33.3, 51.7, 9.1, and al. 2003). Moreover, t ripathi et al. (2014) report- 25%, respectively, compared to the control (t1). ed that si application to plants affected by abiotic Concerning soil conditioners, application of perlite stress increased the length of its leaf epidermal cells, (t4) increased the thickness of midvein, mesophyll, making these plants more tolerant to stress. When and upper scalerenchyma tissue by 33.3, 33.0, and nano-si and zeolite were combined with perlite and 50.9%, respectively, over the control (t1). Whereas bentonite (t7), a clear synergistic effect was ob- soil application of natural zeolite (t5) increased mid served which enhanced the leaf anatomical features vascular bundle diameter and bulliform cells thick- due to additional amendment of soil properties and ness by 17.1 and 25%, respectively, more than con- water retention. trol, moreover the effect of bentonite (t6) showed a similar trend. Interestingly, the results of the pres- Minerals contents ent study revealed that the combination of foliar and Water stress and different soil conditioners soil conditioners (t7) was the most effective treat - showed interesting effects on grains content of ni- ment in increasing the leaf thickness of barley over trogen (n) (t able 8). nitrogen content increased in the control (t able 7 and Figure 1). the presence of soil conditioners with water stress the increased percentages occurred by this com- and the highest n content was achieved under the bination were 68 and 18.9% for midvein and vascu- combined treatment (t7). the trend towards less lar bundle diameter over control, respectively. the concentration of n in grains in response to applied diameter of xylem vessels inside the mid vascular irrigation, might be due to the diminishing or un- bundle increased by 50% over the untreated plants. available soil minerals particularly under control on the other hand, upper and lower scheleranchy - conditions (t1). these results are in harmony with ma tissue recorded a higher increase of 105.8 and those obtained by barczak (2008). 92.8% over control, respectively. Moreover, it is t a b l e 8 effects of drought stress and different soil conditioners treatments on minerals concentrations of barley grains n P k Fe Zn Mn Cu t reatments [mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] b c d e c d c T1: [NPK + 75% AW] 21,590 ± 10 3,630 ± 11 1,560 ± 8 53.90 ± 0.1 56.70 ± 0.2 22.54 ± 0.2 15.40 ± 0.1 b c d e c d c T2: [Nano-silicon + 50% AW] 21,690 ± 12 3,680 ± 10 1,587 ± 9 56.80 ± 0.1 58.50 ± 0.4 22.75 ± 0.1 15.79 ± 0.3 b c c d c c b T3: [Nano-zeolite + 50% AW] 21,764 ± 15 3,689 ± 12 2,023 ± 7 60.45 ± 0.2 59.50 ± 0.6 23.65 ± 0.1 16.45 ± 0.2 b b c d c c b T4: [Perlite + 50% AW] 21,875 ± 13 3,700 ± 13 2,015 ± 10 60.67 ± 0.5 59.88 ± 0.8 23.55 ± 0.3 16.12 ± 0.5 b b b c b b a T5: [Natural zeolite + 50% AW] 21,970 ± 11 3,700 ± 16 2,056 ± 12 63.90 ± 0.6 65.90 ± 0.9 25.60 ± 0.4 17.56 ± 0.5 a a b b b b a T6: [Bentonite + 50% AW] 22,030 ± 12 3,809 ± 18 2,076 ± 6 65.89 ± 0.8 63.70 ± 0.1 25.77 ± 0.5 17.05 ± 0.3 a a a a a a a T7: [T2 + T3 + T4 + T5 + T6 + 50% AW] 22,243 ± 15 3,850 ± 13 2,098 ± 10 70.89 ± 0.3 70.65 ± 0.3 27.80 ± 0.7 17.90 ± 0.2 Means with the same letters in a column are not significantly different by DMRT 5%. Each value is the average of both seasons. Note: NPK ‒ nitrogen, phosphorus, potassium; AW ‒ available water; DMRT ‒ Duncan’s multiple range test. 133 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 126 −145 Moreover, using soil conditioners under drought Regarding micronutrients, iron (Fe) absorption stress had a significant effect on phosphorus (P) was affected by water stress and soil conditioners concentration in barley grain. P concentration fol- (t able 8). It reached its highest level under the com- lowed an increasing trend with increased water bined treatment (T7). A significantly higher con- stress particularly under all treatments; its concen- centration of Fe was observed under drought stress tration was higher in treatments (t2, t3, t4, t5, combined with foliar sprays or soil conditioners (t2, and t6) compared to control (t1). In particular, P t3, t4, t5, and t6) treatments compared to control concentration was significantly affected and record- (t1). the Fe concentration in the grain was aug- ed its highest level under the combined treatment mented with increasing drought stresses and supple- t7 (t able 8). higher P concentration in treatment mentation of different soil conditioners. Moreover, (T7) among other treatments indicated high efficien- zinc (Zn) levels in grain were significantly affected cy of the mixture soil conditioners which consisted by water stress and soil conditioners supplied, with of high P levels in their minerals skeleton such as combined treatment (t7) achieved the highest level bentonite, natural zeolite, nano-zeolite, and perlite. of Zn (t able 8), compared with control (t1) which A similar trend was observed in the results of po- was the lowest. t reatments t2, t3, t4, t5, and t6 tassium (k). under drought stress, the grain k ab- also caused higher Zn accumulation in grains over sorption showed an increasing trend in treatments the control plants (t1), but to a lesser extent than the (t2, t3, t4, t5, and t6) which was more obvious combined treatment (t7); the trend of Zn increment in the combined treatment (t7), which recorded the under the combined treatment (t7) was more pro- highest k absorption 34.5% compared to control nounced, and Zn concentration reached a maximum (t1). the mineralization rate would be accelerated level of 70.65 mg/kg. the high concentration of Zn because of the high oxidation rate at drought stress in treatments t2 and t7 could have resulted from conditions. Moreover, the high level of (k) content the remobilization of Zn to the grain. Manganese inside the skeleton of bentonite, natural zeolite, and (Mn) concentration also increased with water stress perlite might cause a high absorption rate by grain intensity and soil conditioners; combined treatment barley. these results were in agreement with those (t7) realized the highest level of Mn in both seasons obtained by Andersen et al. (1992) who stated that (t able 8). While at 75% AW and nPk fertilisers k and P are generally decreased in plants as a result (t1) the lowest level of Mn in grain in both seasons of harmful effects of abiotic stress. Plants supplied was noticed compared to the rest of the treatments with later amounts of k are less vulnerable to wa- (t2, t3, t4, t5, and t6). the maximum Mn absorp- ter deficit. Applying Si to plants subjected to abiotic tion of 27.80 mg/kg was attained under combined stress boosted the contents of these macro-and mi- treatment (t7) when 50% AW drought stress was cronutrients by stimulating the root transport activ- combined with foliar sprays and soil conditioners. ity of these plants (Mahmoud et al. 2020). Moreo- Copper (Cu) concentration behaved similarly to ver, Ali et al. (2018) reported that si enhanced the all microelements. Cu concentration was increased uptake of sulfur and ammonium in tomato drought with increasing water stress and applying different -stressed tomato plants. Zeolite is known for its ca- soil conditioners (t able 8). Application of different pacity of enhancing the retention of plant nutrients soil conditioners will have a long-term effect on soil and/or providing micronutrients to the a soil (Ayan chemical and physical properties, and water deficit et al. 2008). Application of zeolite as soil amend- during grain filling augmented grain protein, N, P, ment to barley plants affected by abiotic stress led and k, and micronutrient absorptions (t rnka et al. to higher concentrations of k, Mg, and Ca under sa- 2007). It can be deduced from the results of the pres- line water in the upper soils (Al-busaidi et al. 2008). ent study that water deficit might be capable of aug- Moreover, foliar nano-zeolite boosted the content menting the nutritious value of barley under drought of micro-and macronutrients in salt-stressed potato stress if combined with the appropriate foliar sprays plants (Mahmoud et al. 2020). this is majorly re- and/or soil conditioners. these treatments, including flected in the proper metabolic and physiological nano-si and nano zeolite, perlite, bentonite, natural performance of the plants under such stresses. zeolite, and their combination have the capability to 134 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 provide successful mitigation to drought-stressed ferent available water contents and soil conditioners. soils, which might improve sustainable agricultural t reatment t1 gave 9.75 g protein/100 g grains while systems in arid and semi-arid regions. at 50% AW with different foliar sprays and soil con- ditioners (treatments t2-t6), it was slightly high- Total protein, ash, starch, chlorophylls (a, b), fibre, er and varied from 10.20 to 10.86 g protein/100 g and water content grains. the combined treatment (t7), on the other t otal grain protein was slightly affected by dif- hand, realized the maximum value of 10.95 g pro- tein/100 g grains. the same trend was true for t7 treatment where ash and total starch contents were increased, under drought stress (t able 9). the 100 g dry grain of barley produced 1.75 g ash under con- trol conditions (t1) while applying nano-zeolite, na- no-si, natural zeolite, perlite and bentonite achieved a value of 1.80, 2.00, 2.15, 2.30, 2.55 g ash, respec- tively (t able 9). the same trend was true for starch at different water stress and soil conditioners. starch was reported to increase with increased si concen- tration in barley by modulating glycolytic and tCA pathways (hosseini et al. 2017). As for leaf contents of chlorophylls (a, b), these were not affected by drought stress under any treat- ment (t2-t7). Relative water content was slightly decreased under drought stress and the application of different soil conditioners. Combined treatment (t7) produced 64% chlorophyll (a) and 55% chlo- rophyll (b) over control, while relative water content was slightly decreased by 11% as compared to con- trol. Zeolite alleviates drought stress by increasing water retention in the soil, which boosts photosyn- thesis to normal levels and increases starch, and pro- tein accumulation. In this concern, bybordi (2016) reported a decrease in respiration of salt-stressed canola plants when the zeolite is applied, which he concludes it provides evidence of the successful role of zeolite in combating saline and water stress. A similar trend was achieved for fibre content under drought stress and different treatments. Fibre con- tents recorded the highest values (13.65 g/100 g) under combined treatment (t7) compared to the control (t1) which was the lowest (12.95 g/100 g). these results were in agreement with those obtained by hassan and Mahmoud (2013) and hassan et al. (2020). these authors reported the ability of natural zeolite and bentonite minerals in the ratio of 1:10 (w/w) to amend soil chemical, hydro-physical char- acteristics as well as morphological growth param- eters and yield production of faba bean and corn, which were boosted under drip irrigation system and natural drainage conditions. t a b l e 9 the effect of drought stress and different soil conditioners on components of barley leaves and grains t otal protein Ash starch Chlorophyll-a Chlorophyll-b Fibre Water content t reatments [g/100 g seeds] [g/100 gseeds] [g/100 g seeds] [mg/g FW] [mg/g FW] [g/100 g] [%] c c c c b a T1: [NPK + 75% AW] 9.75 ± 0.01 1.75 ± 0.02 60 ± 0.3 4.22 ± 0.05 1.80 ± 0.04d 12.95 ± 0.3 80 ± 0.1 b c b c b T2: [Nano-silicon + 50% AW] 10.20 ± 0.02 1.80 ± 0.03 62 ± 0.4 4.50 ± 0.01 1.95 ± 0.02d 12.98 ± 0.4b 75 ± 0.1 b b b b b T3: [Nano-zeolite + 50% AW] 10.35 ± 0.01 2.00 ± 0.01 63 ± 0.6 5.35 ± 0.03 2.59 ± 0.01c 13.10 ± 0.1a 76 ± 0.2 b b b b a T4:[Perlite + 50% AW] 10.65 ± 0.03 2.15 ± 0.02 65 ± 0.2 5.70 ± 0.04 2.80 ± 0.03c 13.25 ± 0.2a 79 ± 0.4 a a a b b T5: [Natural zeolite + 50% AW] 10.78 ± 0.05 2.30 ± 0.05 67 ± 0.1 5.85 ± 0.06 3.00 ± 0.03b 13.35 ± 0.2a 75 ± 0.2 a a a a b T6: [Bentonite + 50% AW] 10.86 ± 0.04 2.55 ± 0.06 68 ± 0.5 6.25 ± 0.01 3.15 ± 0.02a 13.50 ± 0.3a 77 ± 0.5 a a a a c T7: [T2 + T 3+ T4 + T5 + T6 + 50% AW] 10.95 ± 0.02 2.69 ± 0.02 70 ± 0.4 6.55 ± 0.02 3.25 ± 0.04a 13.65 ± 0.1a 72 ± 0.1 Means with the same letters in a column are not significantly dif ferent by DMRT 5%. Each value is the average of both seasons. Note: NPK ‒ nitrogen, phosphorus, potassium; AW – available water; FW – fresh weight; DMRT – Duncan's multiple range test. Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 Total amino acids analysis are used for biosynthesis of sucrose. In gliadin stor- data presented in t able 10 show the analysed age proteins, glutamic acid is an important source of amino acids in barley grains under treatments of nitrogen for germ nutrition. Interestingly, the high- drought stress and soil conditioners. All treatments est the concentration of glutamic acid was found led to increased total amino acid contents, being the in barley (Dukić et al. 2005). under the treatments maximum under the combined treatment t7, closely of this study, concentration of proline varied from followed by natural zeolite (t5) and natural benton- 0.89 – 0.97 mg/100 mg dry weight (t able 10). the ite (t6) treatments. high proline content affected the secondary structure the amino acid proline was documented to be of gliadin polypeptides because the formation of al- accumulated in barley to support plants in tolerating pha-helices is hindered by proline side chains. there drought stress. Moreover, tryptophan was very im- are large differences in the total amino acids com- portant for the synthesis of indole acetic acid, while position of cytoplasmic and storage proteins (t able threonine and lysine were limiting essential amino 10). storage proteins are characterised by a high acids. barley contains more lysine than other cere - proportion of glutamic acid and proline and a low als, and glutamic acid and proline are the principal proportion of lysine, methionine, and tryptophan. In amino acids in all cereal protein fractions. Glutamic some cases gliadine glutamic acid content is over acid is very important for nitrogen metabolism in 50%, while contents of s-containing amino acids the cell. Products of degradation of glutamic acid are low. the low level of lysine, arginine, and his- t a b l e 10 The effect of different soil conditioners and drought stress on distribution of amino acids [mg/100 mg dry weight] in barley grains t reatments t1 t2 t3 t4 t5 t6 t7 Amino acids c b b b a a a Alanine 0.28 ± 0.1 0.30 ± 0.2 0.31 ± 0.2 0.31 ± 0.2 0.33 ± 0.3 0.33 ± 0.3 0.34 ± 0.3 c c c b b b a serine 0.29 ± 0.2 0.31 ± 0.1 0.31 ± 0.1 0.33 ± 0.2 0.34 ± 0.1 0.34 ± 0.1 0.36 ± 0.2 d c c c b b a Proline 0.89 ± 0.2 0.90 ± 0.1 0.91 ± 0.1 0.92 ± 0.1 0.94 ± 0.2 0.94 ± 0.2 0.97 ± 0.3 d c c c b a a t yrosine 0.19 ± 0.2 0.21 ± 0.1 0.21 ± 0.1 0.22 ± 0.1 0.24 ± 0.1 0.26 ± 0.2 0.27 ± 0.1 e d c c b b a Aspartic acid 0.43 ± 0.2 0.45 ± 0.1 0.47 ± 0.2 0.48 ± 0.1 0.50 ± 0.2 0.50 ± 0.1 0.52 ± 0.2 c c b b b b a Glycine 0.26 ± 0.1 0.27 ± 0.1 0.28 ± 0.3 0.29 ± 0.3 0.29 ± 0.3 0.30 ± 0.2 0.32 ± 0.2 c b b b a a a threonine 0.23 ± 0.2 0.25 ± 0.1 0.26 ± 0.1 0.26 ± 0.1 0.28 ± 0.2 0.28 ± 0.2 0.29 ± 0.1 b b b a a a a Glutamic acid 1.95 ± 0.2 1.96 ± 0.2 1.98 ± 0.1 2.00 ± 0.3 2.00 ± 0.2 2.10 ± 0.2 2.30 ± 0.1 d c b b b a a Valine 0.34 ± 0.5 0.36 ± 0.1 0.37 ± 0.2 0.37 ± 0.2 0.38 ± 0.1 0.39 ± 0.3 0.40 ± 0.2 c c b a a a a l ysine 0.27 ± 0.1 0.28 ± 0.1 0.29 ± 0.3 0.30 ± 0.2 0.30 ± 0.2 0.31 ± 0.1 0.33 ± 0.3 d c b b b a a Isoleucine 0.25 ± 0.3 0.27 ± 0.2 0.28 ± 0.3 0.29 ± 0.2 0.30 ± 0.1 0.32 ± 0.2 0.33 ± 0.2 b b b a a a a Methionine 0.13 ± 0.1 0.13 ± 0.1 0.14 ± 0.1 0.15 ± 0.4 0.16 ± 0.3 0.16 ± 0.2 0.17 ± 0.1 c c b b a a a t ryptophan 0.10 ± 0.2 0.11 ± 0.1 0.12 ± 0.3 0.13 ± 0.2 0.14 ± 0.3 0.14 ± 0.3 0.15 ± 0.2 c c b b b a a nor-leucine 0.27 ± 0.2 0.28 ± 0.3 0.29 ± 0.1 0.30 ± 0.2 0.30 ± 0.4 0.32 ± 0.3 0.32 ± 0.3 c c c b b b a Phenylalanine 0.40 ± 0.5 0.41 ± 0.2 0.42 ± 0.1 0.43 ± 0.2 0.44 ± 0.1 0.44 ± 0.1 0.46 ± 0.2 c b b b a a a l-Cysteine 0.15 ± 0.1 0.16 ± 0.2 0.16 ± 0.2 0.17 ± 0.1 0.19 ± 0.2 0.19 ± 0.2 0.20 ± 0.1 d c c c b b a Arginine 0.34 ± 0.1 0.36 ± 0.2 0.37 ± 0.1 0.37 ± 0.1 0.39 ± 0.1 0.39 ± 0.1 0.41 ± 0.3 d d d c c b a histidine 0.15 ± 0.2 0.16 ± 0.1 0.16 ± 0.1 0.17 ± 0.2 0.18 ± 0.1 0.20 ± 0.1 0.22 ± 0.2 Means with the same letters in a line are not significantly different by DMRT 5%. Each value is average of both seasons. 136 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 tidine and low level of free carboxyl groups makes Vitamin e is a crucial biological antioxidant that these proteins among the least charged proteins. on scavenges free radicals and prevents lipid peroxida- the contrary to storage proteins, metabolically ac- tion. the values of vitamin e were ranged between 8.90 to 9.60 Iu/kg (t able 11). the lowest value of tive proteins contain considerably less glutamic acid vitamin e was found in the control treatment (t1) and proline and have higher proportions of lysine while the highest value was found in the combined and arginine which give these proteins a higher nu- treatment (t7). It could be hypothesized that the role tritive value but lower functional (bread making) of foliar sprays and soil conditioners might have properties. barley, sorghum, rye, and oat proteins maintained the water content in soil and supplied the have lower digestibility (77 ‒ 88%) than those of barley crop in all its growth stages with adequate rice, maize, and wheat (95 ‒ 100%). The biological amounts of water, which led to an increase in the value and net protein utilization of cereal proteins amount of vitamin e on a dry weight basis. More- are relatively low due to deficiencies in essential over, folate ranged between 16 to 20 mcg/100 g, amino acids and low protein availability (y ilmaz et where the lowest values were recorded under control al 2018). si application to drought-stressed plants (t1) and nano-si foliar spray (t2), while the highest lead to higher production of amino acids including value was observed under the combined treatment serine and methionine Ali et al. (2018). the authors (t7). In rice shoots, the folate/biopterin transporter hypothesized that this was due to a higher accumu- gene was documented to be down-regulated under lation of sulphur and ammonium in the plants treat- drought and salinity stress, which was speculated to ed with exogenous si. When nano-si and zeolite are have a role in conferring drought stress tolerance to combined with perlite and bentonite (t7), a clear these plants (Zhou et al. 2007). this is evident in synergistic effect was observed, as expected, due to control plants where the folate content was severely a further enhancement of soil properties and water reduced compared to other treatments which allevi- retention. ated drought stress. In addition, vitamin A ranged from 18 to 24 Iu/kg, where the minimum value was Vitamins content recorded under control (t1), while the maximum Results presented in t able 11 showed that con- value was achieved under the combined treatment trol treatment (t1) recorded the lowest amounts of (t7). these results were in agreement with those vitamins b1, b2, and b6, while combined treatment reported by Wrigley (2010). barley and wheat are (t7) had the highest amount of these vitamins in famous to be a good resource of vitamins, especially barley grains. thiamine, niacin, vitamin b6, and folate. Moreover, t a b l e 11 effect of different soil conditioners and drought stress on vitamins in barley grains b1 b2 b6 A Folate e t reatments [mg/100g] [mg/100g] [mg/100g] [IU/kg] [mcg/100g] [IU/kg] e f c d c c T1: [NPK + 75% AW] 0.340 ± 0.001 0.125 ± 0.003 0.253 ± 0.001 18 ± 0.1 16 ± 0.3 8.90 ± 0.6 d e b c c b T2: [Nano-silicon + 50% AW] 0.344 ± 0.003 0.128 ± 0.002 0.258 ± 0.001 20 ± 0.3 16 ± 0.2 8.94 ± 0.2 c d b c c b T3: [Nano-zeolite + 50% AW] 0.347 ± 0.004 0.130 ± 0.001 0.259 ± 0.002 20 ± 0.3 17 ±0.1 8.98 ± 0.3 c d b b c b T4: [Perlite + 50% AW] 0.347 ± 0.003 0.131 ± 0.005 0.259 ± 0.003 21 ± 0.1 17 ± 0.1 9.00 ± 0.4 b c a b b a T5: [Natural zeolite + 50% AW] 0.350 ± 0.001 0.133 ± 0.004 0.261 ± 0.001 21 ± 0.2 19 ± 0.2 9.10 ± 0.2 b b a b a a T6: [Bentonite + 50% AW] 0.351 ± 0.005 0.135 ± 0.001 0.263 ± 0.002 22 ± 0.1 20 ± 0.4 9.30 ± 0.2 a a a a a a T7: [T2 + T 3+ T4 + T5 + T6 + 50% AW] 0.356 ± 0.002 0.137 ± 0.003 0.265 ± 0.001 24 ± 0.2 21 ± 0.6 9.60 ± 0.4 Means with the same letters in a column are not significantly dif ferent by DMRT 5%. Each value is the average of both seasons. Note: NPK ‒ nitrogen, phosphorus, potassium; AW ‒ available water. 137 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 cereals are a moderate resource of vitamin e giving need. Moreover, the vital role of silicon provides 6 ‒ 20 mg of a-tocopherol equivalent per gram. An rigidity, mechanical strength, plant growth, and evident improvement in the accumulation of vita- development, and induced plant resistance against mins was observed when nano-si and zeolite were many abiotic stresses such as salinity, drought, combined with perlite and bentonite (t7), which heavy metal toxicities, high temperature, and cold might be due to a further improvement of soil prop- stress as well (Vasanthi et al. 2014). earlier stud- erties and water retention. to some ies revealed that application of nano-sio plants in non-stressed conditions increased vege- Hormones content and enzymes activity tative growth traits, chlorophylls content, nutrients the results of the hormones and enzymes analy - content, soluble protein, free amino acids, antioxi- sis presented in t able 12 revealed that barley plants dant enzymes activity, stomatal regulation, and gas are greatly affected by different treatments of soil exchange (Janmohammadi et al. 2016). Moreover, conditioners. perlite and its role as preserver of water and boosting the augmentation of growth parameters might aeration within the soil, hence perlite was generally be associated with high levels of growth promoter used as a soil additive (Grillas et al. 2001). Further- GA and low levels of AbA. therefore, it was found more, bentonite (or swelling bentonite) was charac- that combined treatment (t7) treatment gave the terised by its expansion capacity up to 15 times of significantly highest content of GA over all other original volume when exposed to water and, thus, treatments including control treatment (t1); the in- had a large specific surface area that provides strong crease in GA hormone was about 36.5% over the adsorption, hygroscopicity, and expansibility (Zhou control plants. on the other hand, control treatment et al. 2015). (t1) recorded higher 20% AbA than combined the most important antioxidant protective sys- treatment (t7), while the highest amount of AbA tems are enzymatic defences such as (sod) and resulted from nano-si treatment (t2). Increased si (superoxide radi- (CAt) which convert the toxic o accumulation improved AbA homeostasis where it cal) and h o to water and molecular oxygen (o ), 2 2 2 significantly increased compared to control plants thus preventing the cellular damage under unfa- and, consequently, boosted drought stress toler- vourable conditions such as drought stress (t an et ance (hosseini et al 2017). the synergistic effects al. 2006). based on those facts, the results in t able of combined treatment (t7) might be attributed to 12 declared that the highest activities of CAt and a variety of reasons. Zeolite can retain water and sod enzymes were recorded from t2, t4, and t6 most essential elements to supply plants in time of t a b l e 12 effect of different treatments on hormones content and enzymes activity GA AbA sod CAt t reatments [mmg/g fresh weight] [mmg/g fresh weight] [Unit mg protein] [Unit mg protein] b d c c T1: [NPK + 75% AW] 4.1 ± 0.03 0.5 ± 0.02 43 ± 0.1 73 ± 0.3 d a b a T2: [Nano-silicon + 50% AW] 1.3 ± 0.01 4.6 ± 0.03 51 ± 0.1 85 ± 0.1 c c b b T3: [Nano-zeolite + 50% AW] 2.7 ± 0.03 1.0 ± 0.01 49 ± 0.3 74 ± 0.1 d b b a T4: [Perlite + 50% AW] 1.4 ± 0.04 1.1 ± 0.02 50 ± 0.2 89 ± 0.3 c c a b T5: [Natural zeolite + 50% AW] 2.2 ± 0.02 1.1 ± 0.01 48 ± 0.2 75 ± 0.1 d b a a T6: [Bentonite + 50% AW] 1.1 ± 0.01 2.1 ± 0.03 51 ± 0.1 90 ± 0.2 a e a d T7: [T2 + T3 + T4 + T5 + T6 + 50% AW] 5.6 ± 0.05 0.4 ± 0.02 41 ± 0.2 65 ± 0.2 Means with the same letters in a column are not significantly different by DMRT 5%. Each value is the average of both seasons. Note: NPK ‒ nitrogen, phosphorus, potassium; AW – available water; GA – gibberellic acid; AbA – abscisic acid; SOD – superoxide dismutase; CAT ‒ catalase; DMRT ‒ Duncan's multiple range test 138 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 while significantly the lowest activity of mentioned also reported a higher activity when zeolite was enzymes resulted from t7. the activities of CA t combined with some micronutrients such as seleni- and sod enzymes were higher in t1 (control) by um. 11%, and 4.6% than t7, respectively. similar results Soil texture were found with t an et al. (2006) who mentioned Results in t able 13 showed that the increase in that both CAt and sod enzymes cooperated dur - the finest soil fractions (silt and clay), observed un- ing water deficits. However, reports on the effects of der perlite, zeolite, bentonite treatments and their stresses on CAT activities fluctuate; increased, de- combination (t7), could be attributed to the addi- creased, or unchanged CAt activities under drought tion of clay deposits (Al-omran et al. 2004; 2005). stress were reported (Jiang & huang 2001). the Moreover, soil texture, in consequence, was sandy lowest amount of previous enzymes recorded with in all treated soil and remained unchanged. t7 may be due to alleviating drought stress and change adverse conditions to favourable ones. the Bulk density and total porosity activities of sod and CA t in stressed barley plants Results in t able 13 showed noticeable improve- were significantly stimulated by Si spray (Gong et ment in both soil bulk density and total porosity rank al. 2003). sod is an important Ros scavenger that because of applying different soil conditioners. the its increased activity was usually followed by an in- values of bulk density were slightly decreased com- crease in CAt activity to aid the breakdown of h 2 2 pared to control (t1) by 7.0, 7.0, 4.0, 6.0, 5.0, and (Wu & t iedemann 2002). Application of zeolite to 4.0% for nano zeolite, nano-silicon, zeolite, perlite, stressed canola plants induced higher activity of bentonite, and the combination of all, respectively. CAt and sod in plant tissues, which relieved the these results could be attributed to the redistribu - harmful effects of Ros (bybordi 2016). the author tion of soil particles, the decrease in bulk soil vol- t a b l e 13 soil physical properties with different soil conditioners additives under different drought stress Physical properties t1 t2 t3 t4 t5 t6 t7 Particle size distribution [%] a a a b b b b Coarse sand 2,000 ‒ 200 µm 72.20 ± 0.2 73.16 ± 0.2 74.99 ± 0.3 71.90 ± 0.1 70.34 ± 0.2 69.39 ± 0.3 70.45 ± 0.1 a a b b b b b Fine sand 200 ‒ 20 µm 22.88 ± 0.3 21.14 ± 0.3 19.05 ± 0.4 20.10 ± 0.2 19.67 ± 0.2 19.61 ± 0.3 20.55 ± 0.2 b b b a a a a Silt 20 ‒ 2 µm 3.12 ± 0.2 3.70 ± 0.1 3.85 ± 0.1 4.50 ± 0.3 5.95 ± 0.1 5.99 ± 0.1 4.85 ± 0.2 d c c b a a a Clay <2µm 1.80 ± 0.2 2.00 ± 0.1 2.15 ± 0.1 3.50 ± 0.2 4.05 ± 0.2 5.01 ± 0.1 4.15 ± 0.2 3 a b b a b a a Bulk density [g/cm ] 1.76 ± 0.3 1.65 ± 0.2 1.65 ± 0.2 1.70 ± 0.4 1.67 ± 0.1 1.68 ± 0.2 1.69 ± 0.3 c c c b a a a Total porosity [%] 54.80 ± 0.1 54.90 ± 0.1 54.82 ± 0.1 56.45 ± 0.1 57.45 ± 0.3 58.12 ± 0.2 58.80 ± 0.1 Pore size distribution as % of total porosity a a b b c c c Macro (drainable) pores [>28.8 µm] 54.15 ± 0.3 55.13 ± 0.1 53.90 ± 0.2 52.88 ± 0.2 51.90 ± 0.1 50.04 ± 0.2 49.80 ± 0.2 c d c b b a a Micro pores [<28.8 µm] 45.85 ± 0.2 44.87 ± 0.2 46.10 ± 0.1 47.12 ± 0.2 48.10 ± 0.2 49.96 ± 0.1 50.20 ± 0.2 d d d c c b a Water holding capacity [WHC]* 29.48 ± 0.3 30.40 ± 0.3 30.75 ± 0.2 35.05 ± 0.3 35.25 ± 0.2 37.18 ± 0.2 39.80 ± 0.1 c b b a a a a Field capacity [FC]* 9.51 ± 0.2 10.25 ± 0.2 11.65 ± 0.1 12.65 ± 0.4 13.30 ± 0.3 13.82 ± 0.2 13.79 ± 0.1 c b b b a a a Wilting percentage [WP]* 3.46 ± 0.1 4.10 ± 0.3 5.00 ± 0.3 5.70 ± 0.2 6.25 ± 0.1 6.13 ± 0.1 7.76 ± 0.2 b b b b a a b Available moisture [FC-WP]* 6.05 ± 0.3 6.15 ± 0.3 6.65 ± 0.3 6.90 ± 0.2 7.05 ± 0.1 7.69 ± 0.1 6.03 ± 0.3 c b a d d d d hydraulic conductivity m/day 0.76 ± 0.2 0.83 ± 0.2 0.90 ± 0.5 0.105 ± 0.3 0.110 ± 0.3 0.112 ± 0.3 0.115 ± 0.1 Means with the same letters in a line are not significantly different by DMRT 5%. * ‒ % on a weight basis. 139 Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 ume, and the binding action of bentonite and zeolite, Economic evaluation and investment factor ($/ha) which aided in improving soil structure, mainly by Based on the USD exchange rate in 2018 ‒ 2019, aggregate formation. These findings are very close the control treatment (t1) realized the least produc- to those obtained by Al-omran et al. (2002). this tion cost during both seasons (215 $/ha). on the increase in parameters of soil moisture retention is other hand, bentonite the treatment (t6) recorded considered the greatest goal in the reclamation of sandy soils, where water deficit is very common to occur. these may be rendered to the increase in the content of fine particles (clay fraction) result- ing from bentonite and natural zeolite application, which act as water moderators that absorb water up to 55% of their weight. the impact of these results may save a lot of irrigation water, which can be used to reclaim, cultivate new areas and to enhance the water use efficiency of most crops. These results were in agreement with those obtained by hassan and Mahmoud (2013) who reported that the ability of natural zeolite and bentonite minerals in the ratio of 1:10 (w/w), successfully amended soil chemical and hydro-physical characteristics. Pore size distribution soil conditioners affected the pore size distri- bution of sandy soil. It is apparent that micro-pores (<28.8µm), especially those responsible for the available moisture such water-holding pores (WhP 28.8 ‒ 0.19 µm), progressively increased in contrast to the macro ones, which represent the total draina- ble pores (TDP > 28.8µm). On the other hand, fine capillary pores (FCP) which retain soil moisture at the wilting percentage, were slightly increased. these results may be attributed to the redistribution of solid particles after the application of bentonite and the swelling and bending action resulted from the applied zeolite in treatment t5 and t7. In that case, soil aggregates can be established, hence, the water-holding pores increased, and consequently the availability of moisture in the treated soils in- creased as well. Saturated hydraulic conductivity “K” the values of saturated hydraulic conductivity (k), measured for the surface layer, were sharply decreased by soil conditioner application (t4-t6) as well as in the combined treatment (t7) compared to control (t1) (t able 13). the reverse trend was observed by the foliar application of nano-zeolite or nano-silicon, since k values increased by 9.21 and 18.42% in the treatments (t2) and (t3), respective - ly, compared to the control (t1). t a b l e 14 economical evaluation of barley crop under different soil conditioners and drought stress t otal Profitable PR over PR% t otal yield Gross income t reatments production return [PR] control increase bCR IF [Ton/ha] [$/ha] cost [$/ha] [$/ha] [$/ha] [$/ha] e d e f c T1: [NPK + 75% AW] 3.26 ± 0.3 215.0 ± 0.2 619.4 ± 0.2 404.4 ± 0.3 ‒ ‒ ‒ 2.88±0.2 d d d e d d b T2: [Nano-silicon + 50% AW] 3.42 ± 0.2 216.0 ± 0.1 649.8 ± 0.1 433.8 ± 0.1 29.3 ± 0.2f 6.75 ± 0.2 0.13 ± 0.2 3.10 ± 0.3 c b c c d c c b T3:[Nano-zeolite + 50% AW] 3.57 ± 0.3 223.5 ± 0.4 678.3 ± 0.3 454.8 ± 0.3 50.0 ± 0.3 10.99 ± 0.1 0.22 ± 0.3 3.03 ± 0.4 c b c d e c d c T4: [Perlite + 50% AW] 3.54 ± 0.3 226.6 ± 0.2 672.6 ± 0.1 446.0 ± 0.2 41.6 ± 0.2 9.32 ± 0.2 0.18 ± 0.1 2.97 ± 0.1 b a b c c b c b T5: [Natural zeolite + 50% AW] 3.66 ± 0.3 230.0 ± 0.2 695.4 ± 0.2 463.5 ± 0.2 59.1 ± 0.3 12.75 ± 0.2 0.26 ± 0.2 3.02 ± 0.3 a a a b b b b b T6: [Bentonite + 50% AW] 3.73 ± 0.1 233.0 ± 0.1 708.7 ± 0.3 475.7 ± 0.4 71.3 ± 0.1 14.98 ± 0.2 0.31 ± 0.1 3.04 ± 0.3 a c a a a a a a T7: [T2 + T 3+ T4 + T5 + T6 + 50% AW] 3.84 ± 0.2 219.0 ± 0.3 729.6 ± 0.1 510.6 ± 0.1 106.2 ± 0.2 20.80 ± 0.1 0.48 ± 0.2 3.33 ± 0.2 Means with the same letters in a column are not significantly different by DMRT 5%. Based on the USD exchanging rate in 2018 and 2019. Note: NPK ‒ nitrogen, phosphorus, potassium; AW – available water; BCR ‒ benefit-cost ratio; IF – investment factor; PR ‒ profitable return; DMRT ‒ Duncan's multiple range test. Agriculture (Poľnohospodárstvo), 67, 2021 (3): 124 − 143 the highest amount of production cost (233 $/ha). ReFeRenCes Furthermore, the highest gross income (729.6 $/ha) Al-busaidi, A., y amamoto, t ., t anigawa, t . and Rahman, h.A. was achieved by the combined treatment (t7) com- (2011). use of zeolite to alleviate water stress on subsurface pared to the rest of treatments. these results show drip irrigated barley under hot environments. Irrigation and Drainage, 60, 473 ‒ 480. DOI:10.1002/ird.595. exceptional results of different sources of soil condi- Al-busaidi, A., y amamoto, t ., Inoue, M., eneji, A.e., Mori, tioners and offer positive venues of profitable return y . and Irshad, M. 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Agriculture – de Gruyter
Published: Oct 1, 2021
Keywords: nanoparticles; soil conditioners; drought stress; anatomy; physio-chemical soil properties; economical evaluation
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