Response of irrigated wheat to nitrogen management using nano and prilled urea

Introduction

Wheat (Triticum aestivum L.) is the leading cereal crop cultivated during the Rabi season in India. It is hexaploid (6n = 42) species belongs to Poaceae family, which plays a crucial role for feeding approximately 4.5 billion people, supplying 20% of their daily intake of protein and calories (Shewry and Hey, 2015) [20] . Globally wheat is the leading cereal crop which constitutes nearly 30% of total cereal production and is an essential food for about close to 10 billion people in 43 different countries. The global wheat cultivated area is about 240 million hectares, producing an output of 777 million metric tonnes (FAO, 2023) [3] . Nevertheless, China stands out as the leading wheat producer worldwide, reaching a historic output of 137 million tonnes, with India following closely behind (110.55 million tonnes), Russia (91.5 million tonnes) and the USA (49.1 million tonnes) (USDA, 2024) [24] , together they contribute about 58% of global wheat production which is around 449 million tonnes. In 2023-24, India recorded an unprecedented wheat output of 113.92 million tons from a cultivated area of 34.15 million hectares, achieving an average productivity of 3.31 tons per hectare (MoA and FW, 2024). Nutrient management plays a vital role in attaining self-sufficiency in food grain production. However, indiscriminate fertilizer application has led to increased nutrient usage and diminished profitability. The efficiency of conventional fertilizers has seen little improvement over the years, with nitrogen, phosphorus and potassium utilization rates remaining at approximately 30-35%, 18-20%and 35-40%, respectively (Umaret al., 2020) [23] . Nitrogen stands out as the most crucial and fundamental nutrient among all essential nutrients. It is a crucial nutrient necessary for the production of enzymes, DNA, RNA, amino acids and chlorophyll, making it essential for the growth and development of plants (Ohyama, 2010) [11] . The efficiency of nitrogen utilization diminishes with increasing nitrogen application rates, primarily due to its vulnerability to losses through processes like leaching, denitrification and volatilization (Zhao et al., 2006; Tana et al., 2015) [27,22] . The unbalanced and over-reliant use of standard urea, comprising 46% nitrogen, with the primary focus on boosting productivity and profitability, has caused a reduction in the soil's effectiveness in responding to fertilizer applications (Ladha et al., 2005) [9] . The Fertilizer Association of India has reported that the total consumption of urea in India was 34.18 million metric tons. The total amount comprised 25.08 million metric tons from domestic production and 9.14 million metric tons from imports. In recent years, there has been a growing interest in nanotechnology, particularly in the application of nano-fertilizers aimed at optimizing their efficiency. Nano-fertilizers are essential for enhancing crop resilience against various stress factors, boosting disease resistance, preserving the genetic traits necessary for other crops and augmenting the active compounds within plants. By utilizing the unique attributes of particles sized between 1 and 100 nano meters, these fertilizers can significantly boost nutrient use efficiency (Seleiman et al., 2020) [19] . Nanofertilizers are characterized by their favourable properties, such as superior solubility, stability, effectiveness, controlled release mechanisms, targeted application, reduced environmental toxicity and ease of delivery and disposal. A recent evaluation of nanofertilizers has confirmed their remarkable solubility, consistency, effectiveness, time-controlled release, targeted application and safe, easy methods for both delivery and disposal.The application of nanotechnology in agriculture has surfaced as a promising strategy for improving crop yields and reducing the environmental consequences associated with conventional farming methods. In this context, evaluating the efficacy of nanourea on wheat growth dynamics, grain yield, and crop physiology provides critical insights into integrating modern agrotechnology with sustainable nutrient management.

Materials and Methods

The field experiment was conducted during Rabi season of 2021-22 and 2022-23 at Wheat & Barley Section Research Area, Department of Genetics and Plant Breeding, CCS Haryana Agricultural University, Hisar (Haryana) situated at 291N Latitude and 7546 E Longitude with a height of 215.2 meters above mean sea level. The soil of experimental field was low in available nitrogen (143.5 kg/ha), medium in available phosphorus (12.1 kg/ha) and high in available potassium (252.6 kg/ha) with 0.45% organic carbon. It was moderately alkaline in reaction with pH 7.8 and electrical conductivity of 0.28 dS/m. The experiment was conducted in randomized block design (RBD) with 13 treatments: [T 1 = Recommended N doses (1/3 rd basal, 1/3 rd CRI, 1/3 rd tillering) + water spray at tillering (40-45 DAS) and jointing (60-65 DAS), T 2 = RDN + one spray of nano urea at tillering, T 3 = RDN + two spray of nano urea at tillering and jointing, T 4 = RDN + two spray of urea (5%) at tillering and jointing,T 5 = 75% N + water spray at tillering and jointing, T 6 = 75% N + one spray of nano urea N at tillering, T 7 = 75% N + two spray of nano urea at tillering and jointing, T 8 = 75% N + two spray of 5% urea at tillering and jointing, T 9 = 50% N + water spray at tillering and jointing, T 10 = 50% N + one spray of nano urea at tillering, T 11 = 50% N + two spray of nano urea at tillering and jointing, T 12 = 50% N + two spray of 5% urea at tillering and jointing and T 13 = Control (without N only)] and each treatment was replicated thrice. Wheat variety WH 1270 was sown with a seed rate of 100 kg/ha on 11 th and 12 th November during 2021 and 2022, respectively. Full dose of phosphorus and potash and 1/3 rd nitrogen was applied as basal dose as per treatments and the remaining 2/3 rd nitrogen as 1/3 rd at first irrigation and 1/3 rd at second irrigation wherever required as per treatment while recommended P and K were applied in all the treatments. Nano urea was sprayed @ 4 ml/litre of water with a quantity of water 400 l/ha. The process of data collection encompassed the measurement of various yield parameters including effective tillers/m 2 , grains/earhead, 1000 grains weight, grain yield and biological yield (q/ha) at the harvest stage, of randomly selected plants within each plot. Measurement of chlorophyll was done by using SPAD meter whereas, canopy temperature was measured using infrared thermometer.

Results and Discussion

Plant height

The perusal of plant height (Table 1) data recorded at maturity revealed that the significantly higher plant height (94.96 and 97.00 cm) was recorded with treatment RDN + two spray of urea (5%) at tillering and jointing as compared to other treatments, but was statistically at par with T 1 , T 2 , T 3 , T 6 , T 7 and T 8 during 2021-22 and 2022-23, respectively. It may be due to more availability and uptake of nitrogen which enhanced the process of synthesis of protoplasm, expansion, cell division, vigorous plant growth (Sisodiya et [21,6,7] .

Effective tillers/m 2

The data mentioned in the table 1, showed that different treatments had a significant effect on the numbers of effective tillers/m 2 and significantly higher effective tillers/m 2 was recorded in the treatment RDN + two spray of nano urea at tillering and jointing in 2021-22 (443) and with RDN + two spray of urea (5%) at tillering and jointing in 2022-23 (416) as compared to other treatments except T 1 , T 2 and T 3 during both the years. The increase in effective tillers/m 2 might be associated with higher nitrogen availability and prolonged nutrient release capability of nano fertilizers, which ensures constant supply of nutrients and positively influences plant growth. The application of nano urea resulted in enhanced uptake of nitrogen through both leaves and roots due to its better absorption. This resulted in more synthesis of carbohydrates into amino acids and proteins, which resulted in increased cell division and elongation. These results are in conformity with the findings of by Rani et al. (2024) [14] , Rawateet al. (2022) [15] , Yadav et al. (2023) [26] and Sarkar et al. (2023) [18] have reported similar findings.

Grains/earhead

The results presented in Table 1, showed that grains/earhead didn't showed any significant difference during the year 2021-22 but was recorded highest with the treatment RDN + two spray of nano urea at tillering and jointing (33.38) followed by RDN + two spray of urea (5%) at tillering and jointing (33.13). However, during 2022-23 maximum grains/earhead was recorded with RDN + two spray of urea (5%) at tillering and jointing (57.80), which was statistically at par with T 1 , T 2 , T 3 and T 7 . Foliar supplementation of nitrogen enhances chlorophyll synthesis, leaf area index (LAI) and photosynthetic. This leads to greater accumulation of photo-assimilates and efficient partitioning of carbohydrates toward the developing earhead (sink), resulting in higher grains/earhead. These results are similar with the findings of Gooding and Davies (1992) [4] and Kumar et al. (2021) [8] .

1000 grains weight

The perusal of data presented in Table 1, showed that 1000 grains weight didn't influenced significantly by different treatments during the year 2021-22 but was recorded highest with the treatment control (41.11) followed by 50% N + water spray at tillering and jointing (40.30). However, during 2022-23 1000 grains weight showed a significant variation among the treatments and was recorded highest with control (40.80) which was at par with T 9 , T 11 and T 12 . Nitrogen application increases tiller survival, effective panicles/unit area and the number of grains/earhead which ultimately results in increase in test weight of grains. These results are in conformity with Zhang et al. (2024) [28] and Vicentin and Canales (2024) [25] .

Grain yield

The data given in the table 2, showed that different treatments had a significant effect on the grain yield of wheat and higher grain yield (56.19 and 62.20 q/ha) was recorded with treatment T 3 (RDN + two spray of nano urea at tillering and jointing) which was significantly higher than other treatments except T 1 (54.25 and 59.06q/ha) , T 2 (55.03and 60.13 q/ha) and T 4 (55.95and 61.27 q/ha) in 2021-22 and 2022-23, respectively. This may be due the synergistic effect of nano fertilizer in combination with prilled urea that improved nutrient absorption efficiency, nutrient translocation, enhanced photosynthesis and finally increased the economic and biological yield. With the increase in growth and yield parameters due to foliar application of nano urea spray, there was increase in overall yield. These results are similar with the findings of Sisodiya et al. (2024) [21] , Rani et al. (2024) [14] , Sarkar et al., (2023) [18] , Ojha et al. (2023) [12] and Al-Juthery et al. (2018) [1] , Rahman et al. (2019) [13] and Al-Shamary and Ansari (2022) [2] .

Biological yield

The perusal of the data presented in the table 2, showed that different treatments had a significant effect on the biological yield and significantly higher biological yield (146 and 151 q/ha) was recorded in treatment T 3 (RDN + two spray of nano urea at tillering and jointing) which was significantly higher than other treatments except T 1 (142 and 147 q/ha) , T 2 (145 and148q/ha), T 4 (146 and149 q/ha) and T 7 (134 and 141q/ha) during 2021-22 and 2022-23, respectively. Nitrogen is a crucial component in plant tissues which plays vital role in cell division and cell elongation which reflected its synergistic effect on different growth parameters viz., plant height, number of leaves and dry matter accumulation (Srivani et al., 2022). Furthermore, the appropriate supply of nitrogen enhanced the meristematic activity and photosynthetic area which resulted in improved production and accumulation of more photosynthates which collectively resulted in higher yield. These results are in conformity with Sisodiya et al. (2024) [21] , Samui et al. (2022) [17] , Sarkar et al. (2023) [18] , Ojha et al. (2023) [12] and Al-Jutheryet al. (2018) [1] .

Harvest index

The data mentioned in table 2, revealed that the harvest index (%) didn't showed any significant variation among the treatments but was recorded highest (38.49 and 41.19%) in treatment RDN + two spray of nano urea at tillering and jointing followed by RDN + two spray of urea (5%) at tillering and jointing (38.32 and 41.12%) during 2021-22 and 2022-23, respectively.

Canopy Temperature (ºC)

The data presented in the table 3, showed that canopy temperature at 15 DAA (Days after anthesis) ranged from (21.1-25.5 o C and 24.0-26.9 o C) during 20221-22 and 2022-23, respectively which was found maximum with control (26.5 and 26.9 o C) and minimum (21.1 o C) with RDN + two spray of nano urea at tillering and jointing in 2021-22 and RDN + two spray of urea (5%) at tillering and jointing (24 o C) in 2022-23. Nitrogen plays a fundamental role in stomatal regulation and guard cell function. Foliar application of nano urea or conventional urea at tillering and jointing improves leaf N concentration, chlorophyll content and stomatal opening. Higher stomatal conductance facilitates greater transpiration rates, which produces transpirational cooling effect. This significantly lowers the canopy surface temperature relative to ambient air (Gupta, 2023) [5] .

NDVI

The perusal of the data presented in the table3, showed that NDVI at 15 days after anthesis (DAA) of different treatments ranged from (0.72-0.81 and 0.61-0.72) during 20221-22 and 2022-23, respectively. Significantly higher NDVI was found with treatment RDN + two spray of urea (5%) at tillering and jointinghaving (0.81) and equal in T 3 (0.72) and T 4 (0.72) whereas, lowest NDVI value was recorded in control (0.72 and 0.81) in 2021-22 and 2022-23, respectively. Applying supplemental nitrogen via foliar sprays at critical vegetative stages (tillering and jointing) boosts leaf nitrogen content. This extra nitrogen prevents premature chlorophyll degradation of flag leaves (Saleem et al., 2010) [16] .

SPAD Chlorophyll content

SPAD chlorophyll content (Table 3) at 15 days after anthesis (DAA) of different treatments ranged from (46.24-51.88 and 43.6-51.2) during 20221-22 and 2022-23, respectively. Significantly higher (51.88 and 51.2) chlorophyll content was found with treatment RDN + one spray of nano urea at tillering having whereas, lowest chlorophyll content was recorded in control (44.78 and 43.6) in 2021-22 and 2022-23, respectively. Applying supplemental nitrogen via foliar sprays at critical vegetative stages (tillering and jointing) boosts leaf nitrogen content. This extra nitrogen prevents premature chlorophyll degradation of flag leaves (Saleem et al., 2010) [16] .

Conclusion

Application of recommended dose of nitrogen (RDN) with two sprays of nano urea or two sprays of urea (5%) or one spray of nano urea were produced statistically similar grain yield with recommended dose of nitrogen (RDN) without any spray. The addition of two sprays of nano urea and urea at tillering and jointing stage with RDN brought an increase of 5.3 and 3.7% in grain yield over RDN, respectively.

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