Optimization of sowing date and nitrogen-zinc nutrition for enhancing the growth of wheat (Triticum aestivum L.)

Introduction

India currently ranks as the world's second-largest wheat producer. Wheat production during 2023-24 is estimated to reach a record level of about 109.52 million tonnes, compared to 107.86 million tonnes in the previous year (Economics times, 2024). Wheat is one of the most widely traded cereal crops in the world, and the demand for Indian wheat has been increasing globally. During 2023-24, India exported about 20.88 lakh metric tonnes of wheat worth nearly ₹4,037.60 crore, with major export destinations including Nepal, Bangladesh, the United Arab Emirates, Sri Lanka, and Yemen. In India, the major wheat-producing regions are mainly located in the northern states such as Uttar Pradesh, Haryana, and Punjab. (APEDA). The climate of Uttar Pradesh is mainly humid subtropical with dry winters, while some western parts of the state experience semi-arid conditions. Climate variability is considered one of the major factors affecting crop productivity, even in regions with advanced agricultural practices and high-yield production systems (Bhan and Behera, 2014) [3] . Rising temperatures and moisture stress during the reproductive stage adversely affect winter wheat productivity. Terminal heat stress can reduce plant growth, increase spikelet sterility, and restrict embryo development, ultimately lowering grain number and yield. Higher temperatures during the reproductive phase also increase respiration losses, which further affects crop performance. Therefore, adoption of suitable crop management practices is essential to minimize the negative effects of terminal heat stress on wheat production.

With rising global temperatures, wheat crops are likely to become more fragile in the future. Temperature increases have the potential to drastically lower yields (Aggarwal and Rani, 2009) [1] . Nitrogen has been identified as the most limiting component in plant development and growth, and therefore in crop output, out of all the important nutrients for plants (Ullah et al., 2020) [23] .

Nucleic acids, amino acids, Nitrogen is a component of proteins, enzymes, and photosynthetic pigment, which are all essential components of cells (Pandey et al., 2023) [16] . Chlorophyll, the key pigment involved in photosynthesis, contains nitrogen as an essential constituent. A major portion of leaf proteins responsible for photosynthesis also depends on nitrogen, which promotes leaf expansion and overall plant growth. Hence, nitrogen plays a direct role in improving crop development and yield. In wheat, split application of nitrogen not only supplies nutrients during critical growth stages but also enhances grain protein content. Studies have shown that applying nitrogen in two split doses can improve both yield and nitrogen use efficiency (Rahman et al., 2002) [17] . Fertilizer applied to the leaves is more effective than fertilizer applied to the soil because it circumvents many of the possible pathways for nitrogen loss linked to nitrogen delivery to the soil. Rahman et al. (2014); Mosali et al. (2006) [13,18] . It is commonly recognized that foliar N treatment and uptake during anthesis is better than soil urea applications because it enables more efficient and quick N transfer to the grain (50 percent absorption in 6 hours) (Wagan et al., 2017) [24] .

Human zinc deficiency is now well recognized as a severe nutritional issue. It is more common in areas where grain consumption is high and animal product consumption is low (Roohani et al., 2013) [19] . Zinc has a crucial role in subcellular metabolism. In every enzyme classification, it is a necessary part of the catalytic site or sites of at least one enzyme (Fierke, 2020) [7] . Considering that more than 33 percent of people globally are zinc deficient, and that most of those afflicted live in impoverished nations (Crook, 2011) [4] . According to Singh (2016) [21] , zinc deficiency in Indian soils is predicted to increase from 49 to 63 percent by 2025. Hard wheat is valued for its characteristic golden colour and strong gluten content, making it well suited for bread and pasta production (APEDA). In wheat flour, both the quantity and quality of gluten are key determinants of end-use quality. Gluten, a viscoelastic protein complex in wheat, is responsible for the dough's physical properties, including its elasticity and extensibility, which ultimately influence processing and baking quality (Curic et al., 2001) [5] . Gluten content is assumed to rise with any increase in the flour's total protein concentration. By applying nitrogen at the right time and in the right amount, total protein content may be raised. By increasing the grain's protein content, zinc may be applied both foliarly and basally, increasing gluten and the gluten index (Kinaci and Kinaci, 2019) [9] . By influencing the glutenin interlinking chain, zinc supplementation can change the structural and rheological characteristics of wheat (Liu et al., 2015) [11] . Growth stage scales such as Feekes, Zadoks, and Haun are widely used in agriculture to determine the appropriate timing for input applications in crops. Among these, the Zadoks scale provides a more detailed description of wheat development. It classifies the wheat growth cycle into 10 main stages, which are further divided into finer sub-stages, resulting in a numerical scale from 00 to 99 that covers the entire life cycle of the wheat plant.

Materials and Methods

The field experiment was conducted during the Rabi season of 2025 at Agronomy Research farm of Rama University, Kanpur Uttar Pradesh. The soil of the experimental field was sandy clay loam in texture, neutral in reaction (pH 7.2), which is common in the district's alluvial soils. The soil was low in available nitrogen (246.60 kg ha⁻¹) as determined by the alkaline permanganate method (Subbiah and Asija, 1956). The available phosphorus content was medium (14.5 kg ha⁻¹), estimated by Olsen's method (Olsen et al., 1954). The soil was found medium to moderately high in available potassium (294.40 kg ha⁻¹), determined through the flame photometric method (Metson, 1956) at 0-15 cm soil depth prior to the initiation of the experiment. These fertility levels are generally representative of the Indo-Gangetic alluvial soils of the district. No.1 show the data on Plant height increased progressively with crop age, showing rapid growth at early stages and a gradual increase thereafter up to harvest. Sowing time significantly influenced plant height across growth stages, with maximum growth observed during mid-November. Nitrogen effect was nonsignificant up to 90 DAS but became significant at harvest, where N2 recorded higher plant height than N1. Overall, plant height showed consistent improvement with crop advancement and management practices. Similar result reported by (Asseng et al., 2011), (Kumar 2013) [2,10] . Different zinc management practices significantly influenced plant height over time. Z2 (2.5 kg ha⁻¹ Zn as basal application) resulted in the tallest plants at 30 and 60 DAS, while Z1 (no zinc) recorded the lowest plant height. Treatments Z3 and Z4 were statistically similar, with Z3 showing the maximum plant height at 90 DAS and at harvest.Similar result stated by (Xue et al., 2021), (Nie et al., 2017) [15,25] . Significant interaction effects were observed among sowing time, nitrogen, and zinc management at different growth stages. At 60 DAS, D1Z2 recorded the tallest plants, while at 90 DAS and harvest, D1Z3 showed the maximum plant height. The interaction effect of nitrogen and zinc was also significant, with N2Z2 performing better at 60 DAS compared to N1Z2 and N1Z3. At harvest stage, the highest plant height was recorded in the combinations D1N2, D1Z3, and N2Z3. Sowing time significantly influenced tiller production, with maximum increase observed during the second fortnight of November. Nitrogen effect was non-significant up to 90 DAS but became significant at harvest, where N2 recorded higher tiller numbers compared to N1, although both were statistically similar up to 90 DAS. Similar result reported by (Mishra et al. 2002), (Kumar 2013) [10,12] . The data indicate that zinc management significantly affected the total number of tillers at different growth stages. Across both years, Z2 (2.5 kg ha⁻¹ Zn as basal application) recorded the highest number of tillers at 30 and 60 DAS. However, at 90 DAS and harvest, Z3 showed the maximum tiller production, while Z1 (no zinc application) consistently recorded the lowest number of tillers. Similar result reported by (Sehgal et al., 2018), (Farooq et al., 2014) [6,20] . Significant interaction effects were observed between nitrogen and zinc management as well as between sowing time and zinc management. At 60 DAS, the highest tiller number was recorded in D1Z2 and N1Z2, while at 90 DAS and harvest, D1Z3 and N1Z3 showed maximum tiller production. (g m -1 ) Shoot dry matter accumulation increased progressively from 30 DAS up to harvest under the influence of sowing time, nitrogen, and zinc management. Sowing during the second fortnight of November resulted in higher dry matter accumulation. Although N1 showed comparatively higher values at 30, 60, and 90 DAS, the effect of nitrogen management remained non-significant up to 90 DAS but became significant at harvest. Similar result reported by (Gholami et al., 2011), (Statkevičiūtė et al., 2022) [8,22] . Significant differences in shoot dry matter accumulation were observed across all growth stages due to zinc management. Z2 (2.5 kg ha⁻¹ Zn as basal application) recorded the highest values at 30 and 60 DAS, while Z3 showed the maximum shoot dry matter accumulation at 90 DAS and at harvest. Similar result reported by (Neenu and Ramesh, 2020), (Farooq et al., 2014) [6,14] .

No. of tillers per running meter

Shoot dry matter accumulation

Leaf area index

Leaf area index increased from 30 to 60 DAS and then showed a slower rate of increase from 60 to 90 DAS. Sowing during the second fortnight of November resulted in notable variation in LAI. Although N1 showed comparatively higher values at 30, 60, and 90 DAS, the effect of nitrogen management on leaf area index was non-significant when treatments were compared. Similar result reported by (Neenu and Ramesh, 2020), (Farooq et al., 2014) [6,14] . Significant variation in leaf area index was observed across all growth stages due to zinc management. Z2 (2.5 kg ha⁻¹ Zn as basal application) recorded the highest values at 30 and 60 DAS, while Z3 showed the maximum leaf area index at 90 DAS. Similar trends have also been reported in earlier studies. (Xue et al., 2021), (Nie et al., 2017) [15,25] . At different phases of growth, the interaction impact was shown to be substantial; nevertheless, in the majority of situations, the results were found to be comparable.

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