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

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 m² (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 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 (m³ 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.

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.

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 (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.

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) (Eq. 1).

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.

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 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).

There were insignificant variations between potassium silicate and control treatments for macronutrient (Table 3) and micronutrient (Table 4) uptake of wheat grains in both seasons, 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.

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.