Abstract
The gradual increase in the consumption of mineral nitrogen is leading to heightened levels of harmful air pollutants, particularly N2O emissions from the agriculture sector. A potential solution to address the issues arising from the excessive use of urea in wheat is the substitution of conventional urea with nano urea. This study aimed to quantify the effects of nano urea, both independently and in conjunction with prilled urea, under various agroclimatic and sowing conditions in India. To achieve this objective, a multi-location field experiment on nano and prilled urea was conducted under irrigated conditions across 21 locations with 13 different treatments during the agricultural seasons of 2021–2022 and 2022–2023. The experiments followed a randomized block design with three replications, covering diverse agro-climatic regions of India. Analysis of combined data from multiple years and locations revealed that applying the recommended dose of nitrogen (RDN), i.e., 150 kg/ha in NWPZ (North western plains zone) and NEPZ (North eastern plains zone), and 120 kg/ha in CZ (Central zone) and PZ (Peninsular zone), along with two sprays of nano urea, resulted in a significant increase in grain yield 7.6%, 8.0%, 5.5%, and 9.1% in NWPZ, NEPZ, CZ, and PZ, respectively, compared to RDN alone. Notably, using 75% RDN along with either two sprays of nano urea or 5% urea showed a non-significant (P ≥ 0.05) difference in grain yield compared to the full RDN. From the perspective of higher net benefits, the combination of RDN and two sprays of 5% urea emerged as the most favourable option. On the other hand, considering the higher marginal rate of return (MRR), the combination of 75% RDN and two sprays of 5% urea proved to be more advantageous for farmers across the zones. In conclusion, environmentally friendly practices such as two sprays of nano urea or 5% urea combined with 75% RDN present promising alternatives for Indian farmers seeking to enhance wheat grain yield. Thus, this practice can save 25% of nitrogen (1.02 billion kg) which can reduce 5.06 billion kg CO2 equivalent emissions annually over recommended practice and can play a significant role in achieving the goal of net zero emissions by 2070 in India.
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Introduction
Wheat stands as one of the most extensively cultivated food crops globally, covering an expansive 222.21 million hectares and yielding a staggering 779.03 million metric tons on a worldwide scale1. In the context of India, wheat takes the position of the second most crucial cereal crop, trailing only behind rice. It is cultivated across an extensive 30.54 million hectares, contributing to a production volume of 106.84 million metric tons2. However, given the escalating demands on resources and the impact of climate change on rainfed crop production, there exists a pressing need to enhance the productivity and resource utilization efficiency of wheat cultivation in India3. Several tactics and practices, especially crop nourishment, should be implemented to raise wheat productivity4,5,6.
Nitrogen emerges as a pivotal primary nutrient, especially in the sandy loam soils of the Indo-Gangetic Plains (IGPs) in India, where its natural occurrence is scant, measuring less than 280 kg/ha. Under normal or stressed conditions, N applications had the potential to modulate and enhance yield-related parameters, hence boosting crop productivity7,8. To combat N deficiency, external fertilizer sources have long been utilized to supplement nitrogen in the soil9,10,11. Due to the positive correlation between N application and achievable productivity, the wheat growers tend to apply much more N fertilizers than the need to obtain the maximum returns12,13,14. Urea, in particular, has served as the primary nitrogen source nationwide for an extended period. However, the indiscriminate and excessive application of conventional urea, containing 46% nitrogen, has resulted in diminished soil responsiveness to fertilizers, elevated production costs, and heightened environmental concerns due to its low nutrient use efficiency.
Recent data from the Fertilizer Association of India15 reveals a substantial increase in nitrogen production in India, reaching 19.44 million tonnes—an impressive 71.9% surge over the past two decades. This spike in production is predominantly driven by the pursuit of heightened agricultural productivity and profitability. FAI reports also indicate that India’s total urea consumption during the same period amounted to 34.18 million tonnes, with a significant portion being imported. The central government’s substantial subsidies on urea reached 759,020 million rupees in 2021-22, underscoring the critical role of nitrogen in agriculture.
Regrettably, this subsidy-driven approach has led to excessive nutrient consumption, resulting in diminished profitability and environmental challenges. The overall efficiency of conventional fertilizers barely exceeds 30–35% for nitrogen, 18–20% for phosphorus, and 35–40% for potassium. Additionally, nitrogen use efficiency through urea is relatively low, ranging from 20 to 50% in most soils, and it decreases with higher nitrogen doses due to susceptibility to losses such as leaching, denitrification, and volatilization16.
The reliance on mineral fertilizers as the sole source for crop nutritional requirements has come under scrutiny due to their adverse impacts on the environment17,18,19. Nitrogen losses through nitrate leaching could reach as high as 46–66% under wet coarse-textured soil, posing a substantial environmental burden and contributing to the eutrophication of water bodies20,21. The nitrogen losses also contribute to greenhouse gas emissions and water pollution which also shows the importance of transitioning to foliar sprays through urea or nano urea.
Foliar fertilization demonstrates potential in enhancing crop nutrient use efficiency compared to traditional soil fertilizer applications, facilitating direct nutrient absorption into leaves22. Alternatively, urea can be applied through foliar spraying to enhance nutrient availability, especially nitrogen23. Recently, interest has grown in the use of nano-sized nutrient particles for foliar application, exploiting the high surface area to volume ratio for faster dissolution and nutrient absorption24,25. Nano-fertilizers, with dimensions ranging from 1 to 100 nm, are gaining attention for their ability to improve nutrient use efficiency26. These innovative fertilizers, such as nano urea containing 4% nitrogen, offer advantages over conventional fertilizers, including high solubility, stability, controlled release, targeted effectiveness, reduced eco-toxicity, and convenient modes of delivery and disposal27.
Nano urea, in particular, shows promise in providing nitrogen in a more eco-friendly and efficient manner than conventional urea fertilizer28. Despite its potential, there is limited field-scale research on the use of nano urea in wheat production29. Substituting conventional urea with nano urea emerges as a promising strategy to address challenges associated with the excessive use of traditional nitrogen fertilizers. Implementing an eco-friendly nano-nutrition strategy has the potential to conserve resources through optimized irrigation schedules and enhance productivity through more efficient foliar nitrogen application28,30.
However, it is crucial to carefully manage the dosage, as excessive use of nano-fertilizers can inhibit crop growth and yield. Determining the optimum dosage of nano-fertilizer is paramount for improving crop production, ensuring environmental sustainability, ecological balance, and economic stability, especially as a partial substitute for conventional urea. Nevertheless, systematic investigations are needed to improve resource use efficiency and environmental sustainability in wheat production. Therefore, this multilocation study was carried out with the objectives to identify and promote the best nitrogen management strategies which can empower farmers to enhance agricultural productivity with environmental safety across India.
Materials and methods
Experiment location
Wheat exhibits robust adaptability, thriving not only in tropical and sub-tropical zones but also in temperate and cold regions extending well beyond the 60⁰ North latitude. A series of field experiments was conducted under irrigated conditions at 21 locations. Geographically, the country is primarily categorized into four distinct spring wheat agroclimatic growing regions: North Western Plain Zone (NWPZ), North Eastern Plain Zone (NEPZ), Central Zone (CZ), and Peninsular Zone (PZ). The latitude and longitude coordinates of the experimental locations are visually represented in Fig. 1. Further details regarding the soil’s physico-chemical properties are provided in Supplementary Table S1. The soils of NPWZ were sandy loam, loamy sand and loam at different locations. The soils were non-saline and neutral to alkaline in nature and low in organic carbon at all the locations of NWPZ except Pantnagar where the organic carbon was medium (0.50–0.75%). The soils were low (< 280 kg/ha) in available nitrogen at all locations and medium in available phosphorus except at Pantnagar, Durgapura and Ludhiana having high available phosphorus (exceeding the values of 25 kg/ha). The available potassium was low (< 112 kg/ha) at Gurdaspur, medium (112–225 kg/ha) at Jammu, Karnal and Pantnagar and high (> 225 kg/ha) at Delhi, Durgapura and Hisar locations of NWPZ (Supplementary Table S1). In NEPZ, the sandy loam soils of Burdwan and Coochbehar were non-saline and acidic in nature with medium organic carbon, low available nitrogen, medium available phosphorus and low available potassium in Burdwan and medium in Coochbehar. The remaining three locations of NEPZ; Ranchi, Sabour and Varanasi were clay loam, loamy clay and sandy clay loam in texture, respectively with non-saline and slightly acidic to neutral in nature. These locations also had low available nitrogen, medium available phosphorus and medium available potassium except Varanasi which had high available potassium. In CZ, the black soils of Jabalpur and Junagarh had medium organic carbon and high in available nitrogen and potassium. However, the texture of soils in PZ was clay with low in available nitrogen and high in available potassium as presented in Supplementary Table S1.
21 locations at 4 wheat agroclimatic growing regions in India.
Weather conditions
In India, wheat is grown as a spring season crop, demonstrates remarkable adaptability. It can withstand severe cold and snow, resuming growth with the onset of warm spring weather, enabling cultivation from sea level up to an altitude of 3300 m. Ideal conditions for wheat cultivation include cool and moist weather during the vegetative growth stage, transitioning to dry and warm weather for grain maturation. The optimum temperature range for wheat seed germination is 20–25 °C, with warm and humid conditions being unfavorable31. Ripening necessitates an average temperature of 25–30 °C, while temperatures exceeding 25 °C during grain filling can adversely impact grain weight. Detailed weather parameters, including monthly maximum and minimum temperatures, and overall rainfall received by the wheat crop throughout the entire growing season at all locations, are provided in Supplementary Tables S2, S3 and S4 for both years of the study. The maximum temperature was higher during the months of March and April which is required during the dough stage whereas, the minimum temperature at all the growing locations was not lower than the 4.5℃ (Supplementary Tables S2 and S3). Except Gwalior during both years, and Vijapur and Durgapura during 2022-23, all the location received rainfall during the growing seasons and the remaining water requirement was accomplished through irrigation (Supplementary Table S4). Therefore, the weather parameters during both years of study were congenial for the wheat cultivation across all zones.
Treatment details, design and crop management
A field experiment was conducted under irrigated conditions at 21 locations across various wheat-growing regions of India (Table 1). Considering both environmental and technological factors, the country is primarily categorized into four wheat agroclimatic growing regions, namely the North Western Plain Zone (NWPZ; encompassing Punjab, Haryana, Western Uttar Pradesh, and some parts of Rajasthan) with an acreage of approximately 12.33 million hectares, the North Eastern Plain Zone (NEPZ; covering Eastern Uttar Pradesh, Bihar, West Bengal, Orissa, and Eastern states) with an acreage of about 8.85 million hectares, the Central Zone (CZ; including Madhya Pradesh, Gujarat, Southern Rajasthan, and the Bundelkhand region of Uttar Pradesh) spanning approximately 6.84 million hectares, and the Peninsular Zone (PZ; comprising Maharashtra and Karnataka) occupying about 0.71 million hectares32. The growing period of wheat varies across these agroclimatic zones, impacting both vegetative and grain-filling durations and ultimately leading to differences in attainable yields. The maximum wheat growing duration is observed in NWPZ, while it is minimum in PZ.
The experiment was conducted using a randomized block design with three replications at eight locations in NWPZ, five locations in NEPZ, five locations in CZ, and three locations in PZ, incorporating a total of 13 treatments. The study investigated three levels of recommended dose of nitrogen (RDN) at 100%, 75%, and 50% for the respective wheat-growing regions. The treatments included two water sprays at tillering (40–45 days after sowing; DAS) and jointing (60–65 DAS), one spray of nano urea at tillering, two sprays of nano urea at tillering and jointing, and two sprays of urea (5%) at tillering and jointing. For comparison, one treatment served as an absolute control (no nitrogen), resulting in a total of 13 treatments.
The experiment utilized a recommended high-yielding and disease-resistant wheat variety for each zone, sown between November 5th −11th in NWPZ and PZ, and November 12th −18th in NEPZ and CZ. The name of the high-yielding and disease-resistant wheat varieties used at every location are given in Supplementary Table S4. Uniform seed rate of 100 kg/ha with a row-to-row distance of 20 cm, adjusted to a 1000-grain weight of 38 g, was applied during the agricultural seasons of 2021–2022 and 2022–2023. Sowing was carried out using a calibrated seed cum fertilizer drill at all study locations.
At the time of sowing, one-third of the recommended dose of nitrogen (RDN) in the form of urea, 60 kg P2O5 ha−1 in the form of diammonium phosphate, and 40 kg K2O ha−1through muriate of potash were applied as a basal dose. These fertilizer recommendations for wheat are given by ICAR-IIWBR33. Subsequently, one-third of nitrogen was applied at the GS31 stage (first node visible), and the remaining one-third nitrogen was applied at the jointing stage. The wheat crops received six irrigations at critical stages, including crown root initiation (CRI), tillering, jointing, flowering, milk, and dough stages.
Nano urea was applied at a rate of 4 ml per liter of water at respective stages, utilizing a double boom flat fan nozzle in 500 L of water per hectare. Similarly, 5% urea was also sprayed according to the treatment. For weed control in wheat, narrow and broad-leaved weeds were managed by applying sulfosulfuron at 25 g/ha and metsulfuron at 4 g/ha, respectively, in 500 L of water at 30–35 days after sowing across all wheat-growing environments. Approximately 7–10 days after reaching physiological maturity, a net plot of 9.8 m² was manually harvested using sickles in the mid of April in NWPZ and NEPZ, while in the March in CZ and February in PZ, excluding border rows and the half-meter at both ends of the wheat field. All other recommended agricultural practices were followed. Yield and yield attributing characters were assessed using methods described by Bell and Fischer (1994)34.
Observations
Approximately 7–10 days post-physiological maturity, the manual harvesting of wheat in each net plot (9.8 m²) involved cutting plants just above ground level in both experiments. Above-ground biomass data were collected after 1–2 days of sun-drying the harvested crops, utilizing an electronic weighing balance. These biomass measurements were then extrapolated to tons per hectare to standardize yield measurement to a hectare unit to calculate the harvest index.
For grain yield data collection, the sun-dried bundles underwent threshing through a mechanical thresher. The resultant grains were subjected to winnowing and weighed to determine the grain yield for each treatment. To facilitate accurate comparisons, grain yield measurements were adjusted to accommodate a moisture content of 14%. The harvest index (HI) was calculated by dividing grain yield by the biomass of the respective treatments.
The number of spikes which also represent effective tillers of one meter row length were counted manually at two locations in each plot and then averaged and converted to per m² by multiplying with a factor of 5 as the row to row spacing was 20 cm. The thousand-grain weight (TGW) was determined by randomly selecting grain samples, counting them using a Contador electronic seed counter (Pfeuffer, Germany), and weighing them. The number of grains per earhead and grains per m² were calculated following the procedure outlined by Bell and Fischer (1994)34. This standardized procedure was consistently applied in both experiments across all locations.
The agronomic N use efficiency was calculated by subtracting the grain yield in control plot from the grain yield of fertilized plot and then divided by nitrogen supplied35. It is multiplied by 100 to express in %.
Economic analysis
The wheat grain yield was multiplied by the minimum support price (MSP) of $245.7 per ton, while the wheat straw yield was similarly multiplied by the market rate of $48.7 per ton. The resulting values were summed to calculate the gross return. The cost of cultivation included various factors such as field preparation, seed, fertilizer, irrigation, transportation, herbicide application, harvesting and threshing costs, management charges, land rental, interest on fixed capital, and depreciation of implements and farm buildings. Net returns were determined by subtracting the cost of cultivation from gross returns. To express these values in US dollars, the gross return, cost of cultivation, and net return were divided by the prevailing exchange rate (US$ = INR 82).
Partial budget analysis
To assess the economic advantages of diverse cropping systems concerning both grain and straw yields, we performed a partial budget analysis. This method involved evaluating the economic feasibility of different treatments by estimating their costs and benefits using prevailing market prices. It is essential to recognize that experimental yields may occasionally surpass what farmers achieve in real-world scenarios with identical treatments, as observed in previous studies36. Gross and net benefits were computed using the following formulas:
*Total variable cost was computed by subtracting the fixed land cost of from total cost of cultivation.
Marginal rate of return (MRR) and dominance analysis (DA)
The calculation of the marginal rate of return (MRR) was performed by dividing the change in net benefit by the change in variable cost, indicating the additional return obtained from increasing the input. Prior to computing the MRR, we conducted a simplified dominance analysis, following the approach outlined by Program (1988)36, to identify treatments pertinent for farmers in terms of earnings. A treatment is considered dominated if, despite incurring higher costs, it fails to yield a greater increase in net benefits. In such instances, it is dominated by at least one other treatment with equal or lower costs that generates higher benefits. For this analysis, treatments were arranged in ascending order of variable costs, and comparisons were made to assess whether an increase in costs corresponded to a proportionally greater increase in net benefits.
Statistical analysis
Pooled analysis was performed as randomised block design over the years and locations. The analysis of variance (ANOVA) was utilized to determine the significance of distinctions among the treatments. Subsequently, post hoc analysis using Tukey’s Honestly Significant Difference (HSD) test37 was performed to differentiate the means of treatments at a significance level of 0.05 (5%). All statistical analyses were executed using the General Linear Model (GLM) Procedure in SAS® version 9.3 (6.1.7061) for Windows, developed by SAS Institute Inc. in Cary, NC, in 2012.
Results
Yield and yield attributes
North Western plain zone
The combined analysis of eight locations over the years revealed a significant effect of treatment (P ≤ 0.05) on grain yield, biomass, spikes/m², and number of grains/m², while showing non-significant (P ≥ 0.05) impact on harvest index (HI), 1000 grain weight, and number of grains/spike (Fig. 2). The T3 treatment (RDN + two sprays of nano urea) exhibited the highest grain yield (5.24 t/ha) and biomass (13.13 t/ha), surpassing RDN (T1) by 7.6% and 5.1%, respectively, followed by the T4 treatment (RDN + two sprays of 5% urea). The increased grain yield in the T3 treatment was primarily attributed to the rise in the number of spikes/m² (4.5%) and grains/m² compared to T1 (RDN). It is noteworthy that the treatments involving 75% RDN, either with one or two sprays of nano urea, or with two sprays of 5% urea, or water spray, showed a non-significant (P ≥ 0.05) difference in grain yield compared to RDN (T1).
Effect of nano and prilled urea on wheat yield and yield attributes in NWPZ.
North Eastern plain zone
Upon conducting an analysis spanning two years and five locations, it was observed that the treatment effect was significant (P ≤ 0.05) for grain yield, biomass, spikes/m², number of grains/m², 1000 grain weight, and grains/spike, while being non-significant (P ≥ 0.05) for harvest index (HI) (Fig. 3). The highest grain yield was recorded under the T3 treatment, i.e., RDN + two sprays of nano urea (4.84 t/ha), followed by T4, i.e., RDN + two sprays of 5% urea (4.79 t/ha), which were 8.0% and 6.8% higher than T1 (RDN). The increase in grain yield in the T3 treatment was attributed to the rise in spikes/m² (5.1%) and the number of grains/m² (5.9%) compared to T1 (RDN).
Interestingly, treatments involving 75% RDN, either with one or two sprays of nano urea, or with two sprays of 5% urea, exhibited a non-significant (P ≥ 0.05) difference in grain yield compared to RDN (T1), but were significantly (P ≤ 0.05) higher than 75% RDN + water spray at tillering and jointing (T5). A similar trend was observed for biomass.
Effect of nano and prilled urea on wheat yield and yield attributes in NEPZ.
Central zone
Analysis across two years and five locations revealed a significant treatment effect (P ≤ 0.05) for grain yield, biomass, spikes/m², grains/spike, harvest index (HI) and number of grains/m², while showing non-significance (P ≥ 0.05) for 1000 grain weight (Fig. 4). The T3 treatment (RDN + two sprays of nano urea) recorded the highest grain yield, biomass, number of spikes/m², and grains/m². The corresponding increases in these parameters were 5.5%, 3.5%, 4.8%, and 4.3% in T3 over T1, respectively. A similar trend was observed for T4, i.e., RDN + two sprays of 5% urea. Notably, the treatments involving 75% RDN, either with two sprays of nano urea or two sprays of 5% urea, showed a non-significant (P ≥ 0.05) difference in grain yield compared to RDN (T1) but were significantly (P ≤ 0.05) higher than 75% RDN + water spray at tillering and jointing (T5).
Effect of nano and prilled urea on wheat yield and yield attributes in CZ.
Peninsular zone
Upon conducting a pooled analysis over two years and three locations, the data revealed a significant treatment effect (P ≤ 0.05) for grain yield, biomass, and number of grains/m², while showing non-significance (P ≥ 0.05) for harvest index (HI), spikes/m², grains/spike, and 1000 grain weight (Fig. 5). The T3 treatment (RDN + two sprays of nano urea) exhibited increases of 9.1%, 5.9%, and 9.3% in grain yield, biomass, and number of grains/m², respectively, compared to T1 (RDN). The substantial increase in grain yield was primarily attributed to increased biomass and number of grains/m². The next most effective treatment from a yield perspective was T4 (RDN + two sprays of 5% urea), which also increased yield by 7.1% and the number of grains/m² by 5.5% when compared to T1 (RDN). It is noteworthy that all treatments (T1 to T12) of 100%, 75%, and 50% RDN combinations produced non-significant (P ≥ 0.05) differences in biomass and grain yield among themselves, except for the control (T13).
Effect of nano and prilled urea on wheat yield and yield attributes in PZ.
Economic analysis
North western plain zone
Examination of data from Table 2 revealed that treatments T5, T6, T10, and T11 were excluded based on dominance analysis. The highest net benefit was observed in the T4 treatment (RDN + two sprays of 5% urea), followed by the T3 treatment (RDN + two sprays of nano urea), which was 8.9% and 8.0% higher than T1 (RDN), respectively. These treatments also exhibited positive marginal rate of return (MRR). When considering the highest MRR, the T8 treatment (75% RDN + two sprays of 5% urea) emerged as more favorable to farmers than others (Table 2).
North Eastern plain zone
Similar to NWPZ, in this zone, treatments T5, T6, T10, and T11 were excluded based on dominance analysis. The highest net benefit was observed in the T4 treatment (RDN + two sprays of 5% urea), followed by the T3 treatment (RDN + two sprays of nano urea), which was 10.4% and 7.6% higher than T1 (RDN), respectively. These treatments also exhibited positive marginal rate of return (MRR). Considering the highest MRR, the T8 treatment (75% RDN + two sprays of 5% urea) proved to be more beneficial from the farmers’ point of view (Table 3).
Central zone
Similar to the earlier two mega-environments, in this zone as well, treatments T5, T6, T10, and T11 were excluded based on dominance analysis. The highest net benefit was observed in the T4 treatment (RDN + two sprays of 5% urea), followed by the T2 treatment (100% RDN + one spray of nano urea), which was 2.7% and 2.3% higher than T1 (RDN), respectively. These treatments also resulted in positive marginal rate of return (MRR). Considering the highest MRR, T1 (RDN) followed by T4 (RDN + two sprays of 5% urea) is a better option for farmers (Table 4).
Peninsular zone
Similar to the earlier three mega-environments, in this zone as well, treatments T5, T6, T10, and T11 were excluded based on dominance analysis. The highest net benefit was observed in the T3 treatment (RDN + two sprays of nano urea), followed by the T4 treatment (RDN + two sprays of 5% urea), which was 10.6% and 7.8% higher than T1 (RDN), respectively. These treatments also resulted in positive marginal rate of return (MRR). Considering the highest MRR, T8 (75% RDN + two sprays of 5% urea) emerged as a better option for farmers compared to others (Table 5).
Agronomic N use efficiency
The agronomic efficiency of nitrogen was highest in CZ, followed by NWPZ, and NEPZ and PZ on cumulative average basis of all the treatments (Fig. 6). The highest agronomic N use efficiency was observed in treatment having 50% RDN + two spray of nano urea at tillering and jointing (T11) acoss all the zones. Decreasing nitrogen doses led to an increase in agronomic nitrogen use efficiency, and foliar spray of nano urea, either with one or two sprays, further enhanced agronomic nitrogen use efficiency compared to the application of two sprays of 5% urea. This improvement can be attributed to the additional nitrogen application (23 kg/ha) facilitated by the two sprays of 5% urea.
Agronomic efficiency of nano urea with prilled urea in various zones of India.
Environmental impacts
A country like India, whose economy is primarily driven by agriculture, imported a substantial quantity of urea (9.36 million tons) during the 2021-22 financial year to meet nitrogen consumption in agriculture. The wheat area in India was approximately 31.8 million hectares during the 2022-23 period, with around 28.73 million hectares under irrigated conditions. Extrapolating a 25% nitrogen saving only in irrigated conditions, which is achievable through one or two sprays of nano urea, across all four mega-environments under study, would result in saving approximately 2.22 million tons of urea or 1.02 million tons of nitrogen in wheat crops annually (Fig. 7) as compared to recommended dose of urea or nitrogen. This will also save 5.06 million tons of CO2 emission annually from the wheat fields by reducing the amount of nitrogen application. This is based on 4.96 kg CO2emission/kg N used in agriculture38. This represents a significant stride towards environmental conservation, reduces the country’s urea import burden, and saving foreign exchange.
On the contrary, applying two sprays of 5% urea, considering the entire wheat area, which yields similar results, would lead to an additional consumption of 1.41 million tons of urea or 0.65 million tons of nitrogen annually. This will ultimately result in an additional annual 3.22 million tons of CO2 emissions from wheat fields as compared to recommended dose of nitrogen. This would exacerbate environmental pollution, which is already a pressing issue, increase the country’s import burden, and ultimately diminish foreign exchange reserves. It’s important to note that the additional fuel consumed by the transportation of the extra added urea was not included in this analysis.
From an energy perspective, considering 22.2 gigajoules (GJ) of energy consumed per ton of urea production39, the application of nano urea would result in saving 46.62 million GJ of energy. In contrast, the application of two sprays of 5% urea would lead to an additional consumption of 35.29 million GJ of energy annually.
Annual nitrogen uses and CO2 emission by irrigated wheat area in India.
Discussion
Yield and yield attributes
Nitrogen plays a pivotal role in influencing the growth and development of wheat40. In our agricultural system, the primary method of nitrogen application is through conventional urea (46% N). However, the nitrogen use efficiency with urea is notably low, ranging from 20 to 50%, depending on agronomic practices16. With increasing nitrogen doses, efficiency tends to decrease due to various losses such as leaching, denitrification, and volatilization41,42.
To address the challenge of nitrogen volatilization, nano-fertilizers emerge as a promising solution. These fertilizers offer variable solubility, increased effectiveness, high consistency, controlled release, and improved targeted activity at optimal concentrations26. The application of nano-fertilizers through foliar spraying allows penetration through the epidermis or stomata, followed by translocation through apoplast or symplast pathways43. This mode of application holds the potential for enhancing nitrogen use efficiency in plants.
In our study, the combined analysis of data over the years and locations revealed that the recommended dose of nitrogen (RDN), i.e., 150 kg/ha in NWPZ and NEPZ, and 120 kg/ha in CZ and PZ, along with two sprays of nano urea, increased grain yield by 7.6%, 8.0%, 5.5%, and 9.1% in NWPZ, NEPZ, CZ, and PZ, respectively (Figs. 2, 3, 4 and 5). This improvement in grain yield was primarily attributed to a significant enhancement in spikes/m2 and the number of grains/m2 through the application of 5% nano urea. The number of grains/spike were calculated a result of grain yield divided by number of effective tillers/m2and thousand grain weight by taking units of measurement into consideration34. Notably, the application of 75% RDN, along with either two sprays of nano urea or 5% urea, resulted in statistically similar grain yields compared to RDN alone. Recently, Tripathi et al. (2024)44, in a similar kind of study in India, reported that RDN with two sprays of nano urea improved the yield under restricted irrigation condition (only two irrigations i.e., first at crown root initiation stage and 2nd at flag leaf stage).
Crop yield, encompassing both grain and straw, is influenced by various growth parameters and yield attributes associated with productivity. These include the number of grains/spike, spike/m2, grains/m2, and 1000-grain weight. The provision of nutrients through urea nanoparticles to plants, ensuring ample supply without significant environmental loss, can impact plant yield attributes and overall yield45. The controlled release of nutrients through nano sources has been demonstrated in previous studies, such as the utilization of nano-zeolite as a carrier for urea to deliver nitrogen to maize plants46.
However, these attributes were significant over the control due to increased nitrogen absorption in highly fertilized plots, leading to translocation into the economical parts of plants and thereby enhancing these attributes. Similar findings were reported by Mehta and Bharat (2019)47, Rawate et al. (2022)48and Singh et al. (2023)45.
Economic analysis
In the current study, the application of RDN + two sprays of 5% urea proved to be the most beneficial in terms of achieving higher net benefits across all zones in India (Tables 3, 2, 4 and 5). The increase in each monetary input corresponds to a rise in the overall cost of cultivation49. Treatments with minimal or no fertilizer application demonstrated lower cultivation costs compared to those with higher fertilizer doses. This can be attributed to the escalated expenses associated with higher fertilizer levels and the corresponding application costs in the plots50.
Due to the lower cost of urea used for spraying, in contrast to the higher cost of nano urea, while maintaining equal application costs, the production expenses were reduced. This reduction in production costs contributed to increased net benefits in all regions of India. From a higher marginal rate of return (MRR) perspective, 75% RDN + two sprays of 5% urea are more favourable for farmers than other options across the zones. This is attributed to the additional profit gained from the application of two sprays of 5% urea, in addition to 75% of the recommended dose of nitrogen (RDN), at a lower cost compared to applying 100% RDN. This highlights the higher efficiency and profitability resulting from incremental changes in input levels through the foliar application of urea. These results are in line with Singh et al. (2023)45and Upadhyay et al. (2023)51.
Agronomic N use efficiency
As per Fig. 6, it is evident that the agronomic efficiency of nitrogen was highest for CZ, followed by PZ, NWPZ, and NEPZ in all treatments under irrigated conditions. The results suggest that applying nitrogen at lower doses contributes to an enhancement in agronomic nitrogen use efficiency. In the case of foliar application, one and two foliar sprays of nano urea demonstrated improved agronomic nitrogen use efficiency compared to the application of two sprays using 5% urea. This improvement can be attributed to the additional nitrogen application (23 kg/ha) associated with the two sprays of 5% urea. Comparable results were documented by Solomon and Anjulo (2017)52and Boulelouah et al. (2022)53. Previous research consistently indicates that the application of high nitrogen amounts leads to a decline in agronomic efficiency. This decrease is attributed to the heightened loss of nitrogen42,45,54.
Environmental impacts
In the current study, the highest energy input was observed under RDN + two sprays of urea across the four mega-environmental zones in India under investigation, as it involved the highest nitrogen consumption per hectare (168.4 kg in NWPZ and NEPZ, and 138.4 kg for CZ and PZ). Adopting the practice of applying 75% of the recommended dose of nitrogen (RDN, 150:60:40:: N: P:K) through urea and the remaining dose through one or two sprays of nano urea has the potential to save 25% of nitrogen. If implemented exclusively in irrigated conditions across all four mega-environments under investigation, this practice could result in an estimated annual nitrogen savings of approximately 1.02 million metric tons in wheat crop. On the basis of calculations suggested by Yadav et al. (2018)38, it can reduce 5.06 million tons CO2equivalent emissions by nitrogen saving from wheat crop annually in the country. The controlled release mechanism of nano urea reduces nitrogen runoff, minimizing water pollution and eutrophication26,51. Its targeted delivery enhances nutrient uptake, reduces overall nitrogen application and mitigates soil and groundwater contamination. Additionally, the lower application rates contribute to a reduction in greenhouse gas emissions associated with traditional urea production51,55. The efficient utilization of nano urea promotes sustainable agriculture, minimizing adverse environmental impacts linked to excessive nitrogen use50. The long-term use of nano urea shows promising potential in improving nitrogen use efficiency, reducing greenhouse gas emissions, and promoting soil health51. By foliar spray, nano urea allows crops to absorb nutrients more efficiently, reducing the need for higher nitrogen inputs and contributing to significant nitrogen savings. Additionally, it can minimize nitrogen losses through volatilization and denitrification, leading to a reduction in the release of nitrous oxide, a potent greenhouse gas. This not only lowers the environmental impact of nitrogen-based fertilizers but also mitigates one of agriculture’s major contributors to greenhouse gas emissions.
Furthermore, the reduced nitrogen load from using nano urea can help prevent soil degradation, such as acidification and nutrient leaching, which are often associated with excessive use of traditional fertilizers56. This can improve soil health by promoting microbial activity and nutrient cycling, supporting the long-term fertility of the land. Beyond the soil, nano urea’s efficient nitrogen delivery reduces the risk of nitrogen runoff into water bodies, lowering the incidence of eutrophication and benefiting aquatic ecosystems. Overall, the long-term use of nano urea offers a sustainable approach to nitrogen management, with positive implications for the environment, soil health, and agricultural productivity.
Conclusion
Conclusions from a two-year study conducted at various locations across four wheat-growing zones suggest that applying the recommended dose of nitrogen (RDN), along with two sprays of nano urea, resulted in significant increases in grain yield by 7.6% in NWPZ, 8.0% in NEPZ, 5.5% in CZ, and 9.1% in PZ as compared to the RDN alone. Notably, combinations involving 75% of the recommended dose of nitrogen with either two sprays of nano urea or 5% urea showed no significant differences in grain yield compared to the recommended dose of nitrogen alone. From a net benefit perspective, the combination of the recommended dose and two sprays of 5% urea was found to be the most profitable. However, considering the marginal rate of return, the combination of 75% recommended dose and two sprays of 5% urea is more favorable for farmers across the zones. Adopting a practice where 75% of the RDN is applied through urea and the remaining dose through one or two sprays of nano urea has the potential to save 25% of nitrogen, amounting to approximately 2.22 and 5.06 million tons of urea and CO2 emissions annually, respectively in wheat crops. In conclusion, both environmentally and economically, two sprays of nano urea and two sprays of 5% urea with 75% recommended dose of nitrogen are recommended options for Indian farmers to enhance wheat grain yield.
Data availability
All the data will be available on request to corresponding author.
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Acknowledgements
Authors are highly thankful to ICAR-IIWBR for providing certified wheat seeds to centers.
Funding
The research work was funded by Indian Council of Agricultural Research at Indian Institute of Wheat and Barley Research, Karnal − 132001, Karnal, Haryana, India.
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SCT conceptualized idea, coordinated the conduct of experiments, drafted and edited the manuscript, NK calculated dominance analysis and MRR and edited, KV analyzed data, made graphs and edited.
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Tripathi, S.C., Kumar, N. & Venkatesh, K. Nano urea’s environmental edge and economic efficacy in boosting wheat grain yield across diverse Indian agro-climates. Sci Rep 15, 3598 (2025). https://doi.org/10.1038/s41598-024-83616-9
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DOI: https://doi.org/10.1038/s41598-024-83616-9
