Effect of nitrogen and hydrogel levels on nutrient concentration and nutrient uptake by wheat (Triticum aestivum L.) under climatological-based irrigation schedule

Introduction

Wheat is the most extensively cultivated cereal crop globally. In India, it is a key rabi season crop, grown on 32.8 million ha., with a production of 117.9 million tons and a productivity of 3.60 tons/ha. (Anonymous, 2026). The principal wheat producing states viz., Uttar Pradesh, Madhya Pradesh, and Punjab. Wheat is highly nutritious, comprising 60-68% carbohydrates, 8-15% protein, 1.5-2% fat, 2-3% sugar, 2-2.5% cellulose, and 1.5-2% minerals (Singh et al., 2011) [15] . It is also rich in amino acids namely niacin and thiamine. The high gluten content in wheat provides the structural framework i.e., necessary for the spongy cellular structure of bread, chapatti, and other baked products (Shewry et al., 2002) [14] . Water management has become increasingly critical and occupies a central role in global political and economic discussions. Water use efficiency remains a significant constraint to achieving agricultural growth, sustainability, and future food security. In India's central zone, monsoon rainfall governs groundwater recharge and water harvesting in ponds, which are subsequently used for irrigation in wheat during the rabi season, significantly influencing productivity (Sharma and Solanki, 2025) [13] . Understanding groundwater dynamics and its contribution to evapotranspiration under varying water table levels is essential for effective crop irrigation and nutrient management (Singh et al., 2005) [17] . Enhancing wheat production remains challenging due to climatic variability, declining soil health, and the increasing incidence of diseases and insect-pest infestations. Addressing these challenges requires integrating innovative technologies that can improve the sustainability of current cropping systems. Notably, advancements such as the use of the irrigation water to cumulative pan evaporation ratio, optimized nitrogen fertilization, and hydrogel application are receiving increased attention in modern agricultural practices. For irrigation scheduling, a climatological approach utilizing the IW/CPE ratio has proven most effective. This method integrates all relevant weather parameters affecting crop water use and can potentially increase production by 15-20%. Wheat productivity is influenced by multiple factors, with mineral nutrition, particularly nitrogen, playing a predominant role (Anonymous, 2020). Nitrogen is required throughout the cropping period for growth and development, from the vegetative stage to harvest. Generally, wheat productivity increased with increasing nitrogen and water supply (Mon et al. 2016, Tari, 2016) [8,19] up to a certain threshold, N is both essential for achieving greater wheat yields and susceptible to losses through leaching in heavy rainfall areas and volatilization in arid regions. Consequently, nitrogen use efficiency in wheat is often compromised, resulting in reduced yields and increased environmental impact. Hydrogels are bio-degradable, three-dimensional, hydrophilic polymeric networks capable of retaining water for extended periods, thereby hydrating crops and gradually releasing water (Kaewpirom and Boonsang, 2006) [6] . Pusa hydrogel, a novel semi-synthetic super-absorbent polymer developed by the Indian Agricultural Research Institute, New Delhi, has proven potential for increasing yields per unit input. This hydrogel exhibits a swelling capacity ranging from a minimum of 350 to over 500 times its own weight in pure water. The swelling ratio of Pusa hydrogel increases with temperature up to 50°C without compromising the polymer matrix structure. Pusa hydrogel enhances crop productivity per unit of available water and nutrients, particularly under moisture stress conditions. It also improves soil physical properties, seed germination, seedling emergence rate, root density, and root growth, thereby enabling plants to withstand prolonged moisture stress (Ekebafe et al., 2011) [15] .

Materials and Methods

The present study was conducted during the winter (rabi) seasons of 2021-22 and 2022-23 at Farm of Agricultural Research of R.B..S College, Bichpuri, Agra. The experimental site is located at 27°02' N latitude and 77°09' E longitude, at an altitude of 163 meters above mean sea level. The research farm is classified as North-Western Plain Zone, class II, in terms of land capability. The mean annual rainfall is 628 mm, with July to August being the wettest months. The soil at a depth of 0-15 cm was sandy loam, characterized by an alkaline pH of 8.46, electrical conductivity (EC) of 1.67 dS/m, low organic carbon (0.41%), low available nitrogen (187.31 kg/ha), high available phosphorus (27.68 kg/ha), and also high available potassium (292.02 kg/ha). The experiment was conducted using a split-plot design with three replications, involved 24 treatment combinations. The main-plot treatments consisted three irrigation regimes (0.50, 0.75, and 1.00 IW/CPE ratios) and two nitrogen rates (75% and 100% RDN). The sub-plot treatments included of four hydrogel levels: control (no hydrogel), Pusa hydrogel @ 2.5 kg/ha, 5.0 kg/ha, and 7.5 kg/ha. The doses of recommended nitrogen, phosphorus, and potassium were 150:60:50 kg/ha applied according to the treatments. Full doses of phosphorus and potassium were applied as basal at the time of sowing using di-ammonium phosphate (DAP) and muriate of potash (MOP). Half of the nitrogen dose was applied as basal at the time of sowing by Urea, and the remaining half was applied in two split top-dressings after the first and second irrigations. The wheat variety HD 3086 was sown with seed rate @ 100 kg/ha on 18 th and 21 st November during the 2021 and 2022, respectively, in gross plots measuring 4 × 3 m with 20 cm row-to-row spacing and sowing depth of 5 cm. Finally, wheat was harvested manually on 12 th and 15 th April during the 2022 and 2023, respectively. All observations were recorded in accordance with standard procedures. After harvest, the crop was sun-drying for one-week time, then bundled, tagged, weighed and transported to the threshing yard. Grain yield was obtained after threshing and converted into t/ha. In laboratory, total N, P, and K contents in wheat grain and straw were determined using standard procedures. N, P and K uptake by grain and straw of wheat was calculated as:

All experimental data statistical analysis using a split-plot design following the methods of Gomez and Gomez (1984). Significant differences among treatments were assessed using the 'F' (variance) test and means were separated at P<0.05 using Fisher's protected least significant difference (LSD test).

Results and Discussion

Nutrient content in grain and straw of wheat: Irrigation at 1.00 IW/CPE ratio resulted in significantly higher nutrient contents (N, P, and K) in both grain and straw compared to irrigation at 0.75 IW/CPE ratio. Adequate water supply facilitates nutrient availability in the soil solution, thereby supporting plant growth and development. The increased N, P, and K contents observed with at 1.00 and 0.75 IW/CPE ratios were attributed to improved solubilization of applied nutrients, leading to greater nutrient availability and uptake. Lower N, P, and K contents under the 0.50 IW/CPE ratio were due to reduced nutrient uptake, resulting from limited root growth and development and insufficient nutrient solubilization in the absence of favourable moisture conditions (Pratap et al., 2024) [10] . Maximum N, P, and K contents in both grain and straw were observed under 100% RDN, which was significantly higher than 75% RDN. This was attributed to increased nutrient availability resulting from an ample and balanced nutrient supply with 100% RDN, aligning with crop requirements throughout the growing period. Lower N, P, and K contents in wheat grain and straw with 75% RDN were due to reduced nutrient availability and uptake, likely caused by imbalanced synchrony between crop demand and N supply. Application of Pusa hydrogel @ 7.5 kg/ha resulted in higher N, P, and K contents in both grain and straw, significantly surpassing the control but remaining statistically similar to the Pusa hydrogel @ 5.0 kg/ha treatment. This improvement was primarily attributed to increased nutrient uptake, facilitated by hydrogelretained water in the root zone, which provided continuous moisture and enhanced nutrient solubilization. Lower N, P, and K contents in control were due to insufficient water retention in the root zone, resulting in reduced nutrient uptake and limited root growth and development under moisture-deficit conditions, which disrupted the balance between water and nutrient supply and demand (Barihi et al., 2013, Roy et al. 2019) [3,12] . N, P, and K uptake by grain and straw of wheat: Irrigation regimes, nitrogen and hydrogel levels significantly affected N, P, and K uptake by wheat grain and straw during both study years (Verma et al., 2015) [15] . The highest uptake of N, P, and K was observed under the 1.00 IW/CPE irrigation regime, followed by irrigation at 0.75 and 0.50 IW/CPE ratios. The increased nutrient uptake under irrigation at 1.00 IW/CPE regime by frequently supply of water was attributed to higher grain and straw yields.

Lower N, P, and K uptake under irrigation at 0.75 and 0.50 IW/CPE regimes interval led to water stress conditions and lower grain and straw production. Application of 100% RDN resulted in approximately 20.0%, 27.2%, and 19.4% greater total N, P, and K uptake by grain and straw, respectively, compared to 75% RDN (Patra and Singh, 2018) 98] . The higher grain and straw yields with 100% RDN expedited increased nutrient absorption. Lower yields with 75% RDdN led to reduced N, P, and K uptake by grain and straw (Reena et al., 2017, Kumar et al., 2023) [11,7] . Application of Pusa hydrogel @ 7.5 kg/ha resulted in the highest N, P, and K uptake by grain and straw, followed by 5.0 kg/ha, 2.5 kg/ha and control. The increased nutrient uptake under the Pusa hydrogel @ 7.5 kg/ha treatment was attributed to the highest grain and straw yields (Singh, 2015). Lower N, P, and K uptake in control was due to reduced grain and straw yields. In summary, the two-year field investigation proved that irrigating wheat at 1.00 IW/CPE ratio, combined with the application of 100% RDN and Pusa hydrogel @ 7.5 kg/ha, can enhance the grain yield, N, P and K content in grain, N, P and K uptake and quality of wheat. However, under conditions of limited water availability, it can have advocated to wheat cultivation with 100% RDN and Pusa hydrogel @ 5.0 kg/ha under irrigation at 0.75 IW/CPE regime.

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