Effect of Potassium Silicate and Irrigation on Grain Nutrient Uptake and Water Use Efficiency of Wheat Under Calcareous Soils

In calcareous soil, two field experiments were conducted to investigate the effects of two potassium silicate treatments (with and without) and three irrigation levels (100, 80 and 60%, of crop evapotranspiration, abbreviated as IW100, IW80 and IW60, respectively) on wheat yield and nutrient uptake and water use efficiency (WUE). The experimental design was a strip plots design in randomized complete block arrangement with three replicates. Findings reveal that potassium silicate improved grain weight spike−1 by about 1.06 times whether with IW80 or IW60. Also, seed index increased by 1.03, 1.06 and 1.04 times owing to potassium silicate in the 1st season under IW100, IW80 and IW60 treatments, respectively. Application of potassium silicate surpassed the control treatment by about 1.05, 1.4 and 1.07 times for biological straw and grain yields under IW80. The interaction of IW80 × potassium silicate significantly equaled IW100 × potassium silicate for P, S Mg and Mn uptake in both seasons as well as N, K and Zn uptake in the 1st season and Fe uptake in the 2nd season. IW80 or IW60 with potassium silicate application were the efficient combinations for improving WUE in both growing seasons.


Introduction
Due to its contribution as the major staple food crop universally, wheat is ranked at the first position among cereals (Iqbal et al. 2021). However, crop yield potential is limited because of climate change impacts, especially abiotic stresses, including heat, salinity and drought (Saudy et al. 2020a;Yadav et al. 2020;Saudy et al. 2021a, c;El-Bially et al. 2022a, b).
In numerous field crops, deficit irrigation tactic is one of the practical strategies in crop irrigation programs to save water, however, crop productivity is negatively affected (El-Bially et al. 2018;Saudy et al. 2020a;El-Metwally et al. 2021. Water scarcity or deficit irrigation reduces plant growth and yield (Abd El-Mageed et al. 2021;Salem et al. 2021) due to production of reactive oxygen species (ROS), causing lipid peroxidation of membrane and interaction with other macromolecules (Bistgani et al. 2017). Under moderate or severe drought stress, plants close stomata and leaf pigments reduced causing reduction in photosynthesis rate and nutrient uptake (Yan et al. 2016;El-Metwally and Saudy 2021a;Saudy et al. 2021a).
Mineral nutrition plays a beneficial role in developing environmental stress tolerance in crop plants (Saudy 2014(Saudy , 2015Jan et al. 2017). Potassium (K + ) is a phyto-beneficial macro-element that performs a pivotal role in organizing physio-biochemical processes to support plant survival against abiotic stresses, including salinity (Merwad 2016;Abd El-Mageed et al. 2022). Adequate K + nutrition has been shown to mediate PM H + -ATPase activation to increase protons extrusion under abiotic stresses (Weng et al. 2020).
In several plant species, as wheat, the potentiality of silicon (Si) to reinforce the environmental stresses tolerance was obtained (Rodrigues et al. 2015). Si could enhance plant growth under normal and stress conditions (Saudy and Mubarak 2015). Application of Si increased water and osmotic potential in roots and leaves as well as alleviated water stress partially (Ming et al. 2012). Therefore, the current study aimed to investigate the potentiality of potassium silicate (as a source of K and Si) for alleviating the adverse impacts of drought stress in wheat through enhancing water use efficiency under calcareous soil conditions.

Study Site and Experimental Procedures
Two field experiments were implemented during winter seasons of 2019/20 and 2020/21 at Maryout experimental station, Desert Research Centre, Alexandria, Egypt. The soil was a calcareous and sandy loam in texture containing 92.0% sand, 2.1% silt, 5.9 clay, and 24.1% calcium carbonate with pH of 8.1 and 0.72 dS m -1 electrical conductivity. Sorghum (Sorghum bicolar L.) was the preceding crop in both seasons.
In a strip plots design based on randomized complete block arrangement using 3 replicates, two potassium silicate containing 0.05% Si (0 and 500 ml L -1 ) and three irrigation levels, were applied as ratio of crop evapotranspiration (100, 80 and 60%, abbreviated as IW100, IW80 and IW60, respectively) were tested. The experimental unit size was 10.5 m 2 (3 m × 3.5 m). On 19 November in 2019 and 2 December in 2020, wheat grains (cv. Giza-171) were sown in lines, 10 cm distance, at a rate of 150 kg grains ha -1 . During land preparation, single super phosphate (15.5% P2O5), at a rate of 240 kg ha -1 , and gypsum, as a soil conditioner, at a rate of 2.4 t ha -1 , were incorporated. At 30 days after sowing (DAS), ammonium nitrates fertilizer (33.5% N) at a rate of 450 kg ha -1 was applied.
Potassium silicate treatment was applied as foliar applications twice, 65 and 80 DAS. Irrigation water was applied equally to all irrigation treatments to increase the Fig. 1 Irrigation water amount applied under different irrigation levels in wheat during 2019/20 and 2020/21 seasons. IW100, IW80 and IW60: Irrigation at 100, 80 and 60% of crop evapotranspiration, respectively soil moisture up to field capacity until the 4-6 leaf growth stage (25 DAS); then, the irrigation treatments were started. Based on the meteorological data of the study area, reference evapotranspiration was calculated using FAO 56-Penman-Monteith method (formula 1) given by Allen et al. (1998). Using the formula 2 (Allen et al. 1998), wheat crop evapotranspiration was estimated. The irrigation water quantity (m 3 ha -1 ) received by wheat plants under different irrigation levels are illustrated in Fig. 1. Gated pipe irrigation system was exploited for crop irrigation. The PVC gated pipes were installed in irrigation channel against the upper end of the furrows, which convey the water based on the required flow rate (one gate per furrow). The temporary dam was used to keep a constant hydraulic head, to realize adequate inflow rate during irrigation events. The inflow rate was 90 lpm furrow -1 , which predetermined according to the technique of Merriam et al. (1983). The amount of water applied was estimated by a flow meter installed on the delivery line of the irrigation system. Soil surface slope was 0.20%. Irrigation cutoff was at 90% of furrow length and runoff was negligible, which the furrows were closed-ends. The water amount applied during each irrigation event was appropriate to the crop's growth stage as described by Dorrenbos and Pruitt (1977). Soil water content was measured by gravimetric method (Merriam et al. 1983) before and after irrigation events along furrow length to a depth of 1.0 m in depth increments of 0.2 m to evaluate the soil moisture distribution and irrigation performance.

Yield and Yield Components
At harvest (15th and 21st of April in 2020 and 2021 seasons, respectively), spike number m -2 was measured. Moreover, ten plants were randomly obtained from each plot to measure grains number spike -1 , grains weight spike -1 and seed index. Furthermore, whole plants of each plot were collected to estimate biological, straw and grain yields ha -1 .

Grain Nutrients Uptake
At Central Laboratory, Soil and Water Unit, Faculty of Agriculture, Ain Shams University, representative samples of grains were obtained to estimate the chemical analysis. Total nitrogen (N) was determined by micro Kjeldahl using 5% boric acid and 40% NaOH as described by Chapman and Pratt (1961). Total phosphorus (P) was estimated using Spectrophotometer according to the method described by Watanabe and Olsen (1965). Total potassium (K) was measured using Flame photometer (Chapman and Pratt 1961). Sulphur (S), magnesium (Mg), iron (Fe), zinc K (Zn), and manganese (Mn) were determined using ICP Mass Spectrometry (Benton 2001). After that, nutrient uptake was computed by multiplying the element concentration by grain yield ha -1 .

Water Use Efficiency
Based on the calculated applied irrigation water quantities for IW100, IW80 and IW60 in 2019/20 and 2020/21 seasons ( Fig. 1), water use efficiency (WUE) was estimated according to Jensen (1983)

Statistical Analysis
Data of the two seasons was subjected to analysis of variance (ANOVA) according to Casella (2008). Costat software program, Version 6.303 (2004) was used for carrying out ANOVA. Means were separated using Duncan's multiple range test only when the F-test indicated significant (p ≤ 0.05) differences among the treatments.

Wheat Yield Components
Potassium silicate significantly influenced grain weight spike -1 in 2019/20 and 2020/21 seasons and seed index in 2019/20 season (Table 1). Application of potassium silicate (500 ml L -1 ) enhanced grain weight spike -1 by 4.7 and 5.1% in 1st and 2nd seasons, respectively, and seed index by 4.2% in 1st season. Full irrigation (IW100) achieved the maximum values of yield components in wheat in both growing seasons. While, reducing water amount by 40% (IW60) caused the maximum reductions. Moderate water deficit (IW80) caused 4.4, 4.9, 11.4 and 7.1% decreases (averages of the two seasons) in spike number m -2 , grains number spile -1 , grain weight spile -1 and seed index, respectively, compared to no deficit water.
Interaction effect of potassium silicate and irrigation water revealed that potassium silicate applied in full irrigated plots showed the highest values of all yield parameters (Table 1). However, under each irrigation level, no noticeable differences between potassium silicate and tap water were obtained for all yield components in both seasons, except grain weight spike -1 and seed index in the 1st season. Herein, potassium silicate improved grain weight spike -1 by about 1.06 times whether with IW80 or IW60. Also, seed index was increased by 1.03, 1.06 and 1.04 times owing to potassium silicate in the 1st season under IW100, IW80 and IW60 treatments, respectively.

Wheat Yields
Wheat yields markedly responded to potassium silicate application in both growing seasons, except biological and straw yields in the 2nd season (Table 2). In the first season, increases in biological and straw yields due to potassium silicate were 5.7 and 6.1%, respectively. Moreover, increases in grain yield were 5.2 and 3.6% in the 1st and 2nd seasons, respectively. As shown in Table 2, supplying wheat plants with IW100 recorded the highest yields, while, reductions associated lower water supply. Accordingly, as averages of the two seasons, reductions in biological, straw and grain yields were approximately 10.8, 9.2 and 12.4% with IW80 as well as 28.9, 24.6 and 33.6% with IW60, respectively.
The impact of potassium silicate on wheat yields was more pronounced under lowering water supply. In this respect, significant differences in biological straw and grain yields between addition or no addition of K2Si4 under IW60 or IW80. For instance, in the first season, application of potassium silicate surpassed the control treatment by about 1.05, 1.4 and 1.07 times for biological straw and grain yields under IW80. Moreover, with irrigation by IW60 the corresponding increases reached 1.11, 1.16 and 1.05, respectively (Table 2).

Grain Nutrient Uptake
There were insignificant variations between potassium silicate and control treatments for macronutrient (Table 3) and micronutrient (Table 4) uptake of wheat grains in both sea-K  sons, except K uptake in the second season and Mg uptake in the first season. Due to application of potassium silicate grain K uptake increased by 6.9% in 2020/21 season and grain Mg uptake increased by 95.0% in 2019/20 season. All nutrients uptake recorded with IW80 were similar to those measured with IW100 in both growing seasons, except N uptake in 2020/21 season and Fe uptake in 2019/20 season. Also, all irrigation treatments statistically equaled in S uptake in the 1st season as well as Mg uptake and Zn uptake in both seasons.
Macro-and micro-nutrients uptake significantly responded to the interaction between potassium silicate and irrigation in both seasons, except S and Mg uptake in the 2nd season (Table 3) and Zn uptake in the 1st season (Table 4). Superiority of full irrigation (IW100) still pronounced with potassium silicate for enhancing grain nutrients uptake of wheat. However, IW80 x potassium silicate significantly equaled IW100 x potassium silicate for P, S Mg and Mn uptake in both seasons as well as N, K and Zn uptake in the 1st season and Fe uptake in the 2nd season.

Water Use Efficiency
Potassium silicate surpassed the control for WUE in the first season causing 5.6% increase (Fig. 2). There was no significant difference among the studied irrigation treatments in WUE of wheat (Fig. 3). Concerning the interaction, Fig. 4 depicted that IW80 or IW60 with potassium silicate application were the efficient combinations for improving WUE in both growing seasons.

Discussion
Wheat productivity is severely hampered by drought, owing to its negative impacts on crop growth and development. Deficit water caused serious reduction in yield productivity and quality (Saudy and El-Bagoury 2014;Saudy and El-Metwally 2019). Owing to drought, reductions in stomatal conductance, photosynthesis and transpiration rates were observed, and consequently CO2 assimilation rates declined (Farooq et al. 2012). Low water supply caused reduction in leaf pigments and soluble sugars, hence dry matter accumulation and nutrient uptake decreased El-Metwally 2019, 2022). The significant reduction in relative water content of leaves positively correlated with soil water availability under different irrigation treatments (Kalariya et al. 2015). Also, drought adversely influences the absorption and use of mineral nutrients shackling plant growth and production (Sun et al. 2012;Mubarak et al. 2021). Because of drought plant nutrient uptake capacity was reduced (Sanaullah et al. 2012;Abd-Elrahman et al. 2022). Low water supplies reduced plant growth and development by influencing uptake, transport, and partitioning of nutrients (Gessler et al. 2017;Saudy et al. 2020a). Also, reducing water supply caused severe depression in plant physiological, anatomical, and agronomic traits (El-Metwally et al. 2021;Makhlouf et al. 2022). Accordingly, in crop production management, all tools reduced water lost should be adopted.
Supplying of crop plants in appropriate quantities and forms of nutrients certainly promotes growth and development both under favorable and unfavorable conditions (Saudy et al. , 2020bEl-Metwally and Saudy 2021b;Saudy et al. 2021b). The current study proved that potassium silicate alleviated, partially at least, the hazards of drought with enhancing yield traits (Tables 1 and 2), nutrients uptake (Tables 3 and 4) and water use efficiency (Fig. 3). In this respect, Debona et al. (2017) and Luyckx et al. (2017) stated that Si fertilization had can improve plant tolerance to drought. Si also can enhance the anti-oxidative defense mechanisms thus, avoid damage from reactive oxygen species produced by various abiotic stresses (Maghsoudi et al. 2019). Si promotes the plant growth by modulating the nutrient (Na, Mg and Si) uptake and phytohormone levels and alleviating plant stress levels (Gong et al. 2008). On the other hand, potassium is an essential nutrient for growth with maintaining cell turgor and regulating the water content plant cells (Rengel and Damon 2008). Moreover, potassium supply plays an important role in regulating osmotic potential, increasing water uptake ability and avoiding K + depletion (Zengin et al. 2009). Also, K may help in maintaining a normal balance between carbohydrates and proteins (Monreal et al. 2007). It is a major nutrient for photosynthesis and the transport of assimilates (Wang et al. 2015). Potassium affects the osmotic adjustment of the plant and by enhancing the translocation of assimilates and maintaining osmotic charge (Marschner 1995;Mubarak et al. 2016). Therefore, providing wheat plants with potassium silicate is regarded as a crucial action for keeping productivity particularly under adverse conditions as drought (Salem et al. 2022).

Conclusion
It could be concluded that in calcareous soils, providing potassium silicate to wheat plants is seen as a critical measure for maintaining productivity, commonly under suitable conditions, or particularly in adverse situations such as lack of irrigation water. Moreover, farmers can mitigate drought stress effects and improve water use efficiency by using judicious application of potassium silicate and a moderate irrigation level (80% of crop evapotranspiration) in their fields, thus saving the applied water by 20%. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4. 0/.