Combined application of nano-DAP and conventional fertilizers improved agronomic and economic performance of rainfed maize, nutrient and energy use efficiency

Efficient nitrogen (N) and phosphorus (P) management enhances crop yield while minimizing environmental impact. Nano-fertilizers are reported to ensure sustained nutrient release, optimize nutrient absorption and improve nutrient use efficiency, leading to higher crop productivity and profitability. A two year field trial was conducted under semi-arid conditions in India to evaluate the effect of foliar-applied nano-DAP on the growth, productivity, profitability and nutrient use efficiency of rainfed maize. The treatments comprised conventional fertilizers at varying N and P levels [0, 50, 75, and 100% recommended dose of N and P] with and without foliar application of nano-DAP. Application of 100% recommended NPK (90-45–45 N-P-K kg ha^-1) through conventional fertilizers along with foliar sprays of nano-DAP (N₁₀₀P₁₀₀K+ nano-DAP) resulted in higher grain yield (3058 kg ha^-1) and economic returns (US $ 473 ha^-1). Notably, the N₇₅P₇₅K + nano-DAP treatment produced yield and economic returns comparable to those obtained with 100% recommended NPK, either alone or in combination with nano-DAP. This demonstrates that two foliar sprays of nano-DAP can reduce N and P inputs by 25% without compromising on yield or profitability. Higher agronomic use efficiency of N (26.9%) and P (48.4%), apparent recovery efficiency of N (42.6%) and P (11.3%) were also observed under N₇₅P₇₅K + nano-DAP. Furthermore, N₇₅P₇₅K + nano-DAP treatment reduced greenhouse gas (GHG) emissions by 24.5% and energy consumption by 15.4%, highlighting its potential for sustainable maize production with reduced environmental impact compared to N₁₀₀P₁₀₀K treatments.

1 Introduction

Maize (Zea mays L.) is a versatile crop with wide adaptability across diverse agro-climatic conditions. In India, it is ranked as the third most important food crop after paddy and wheat (Rathore et al., 2022). It is cultivated in an area of 11.24 million hectares, with the kharif/rainy season accounting for 7.57 million hectares (67.3%). However, maize productivity remains relatively low at 2,671 kg ha^-1 in kharif compared to 5,529 kg ha^-1 in rabi/winter (Anonymous, 2024). Despite being known as the “Queen of Cereals” for its high genetic yield potential, maize often faces low productivity in rainfed regions due to several constraints such as monsoon variability, soil degradation, low soil organic carbon, multi-nutrient deficiencies, limited access to improved seeds, lack of irrigation, inadequate pest and disease management (Aakash et al., 2022). As a nutrient-intensive crop, maize requires efficient nutrient management, which is particularly challenging in rainfed systems due to fluctuating soil moisture, unpredictable monsoons, and abiotic and biotic stresses. The impracticality of fertilizer application at critical growth stages further hampers nutrient uptake leading to suboptimal yields. Therefore, effective nutrient management in rainfed maize cultivation is crucial for maximizing productivity, maintaining soil health, and promoting sustainable agriculture.

Among essential nutrients, nitrogen and phosphorus are the most critical for maize production. Nitrogen, a key component of nucleic acids, amino acids, phytohormones and chlorophyll, is the most deficient nutrient in Indian soils (Asha et al., 2024). Furthermore, improper management practices such as excessive fertilizer application, surface broadcasting without incorporation, single-dose application at the start of the season, neglecting weather conditions, improper irrigation practices, lack of soil testing and inadequate nutrient analysis lead to nitrate leaching and greenhouse gas emissions (Maryam, 2024). Phosphorus, essential for root development, energy transfer (via ATP) and grain filling, faces even greater inefficiencies due to soil fixation particularly in alkaline or acidic soils where it binds to iron, aluminum or calcium, rendering up to 80% unavailable (Zhang et al., 2016, 2023).

In 2023–24, India’s fertilizer consumption reached 35.78 million MT of urea, 10.81 million MT of DAP and 4.54 million MT of SSP (FAI, 2023-24). Farmers usually apply urea, DAP, and SSP to meet crop nutrient demands, though these fertilizers often have low use efficiency (Asha et al., 2024). Farmers tend to apply excess N through granular urea and DAP to boost grain yield (Kaufman et al., 2013). This practice enhances productivity; with a trade-off for lower nutrient use efficiency (35-40% for N and 15-20% for P) leading to significant nutrient losses and environmental concerns (Qiao et al., 2022). For instance, excessive N use leads to eutrophication in water bodies, while P runoff contributes to algal blooms (Wani et al., 2021). Moreover, the low N and P use efficiencies highlight systemic flaws in current agronomic practices (Ladha et al., 2005). Emerging solutions such as controlled-release fertilizers (CRFs), foliar micronutrient supplementation, and precision soil testing-could mitigate these losses. For example, CRFs have shown promise in reducing N leaching by 30-50% while maintaining yields, and foliar Zn application has been demonstrated to improve maize kernel weight and starch content (Wani et al., 2021).

Another promising solution to overcome these challenges is the adoption of smart nutrient delivery systems, such as nanotechnology-based fertilizers, which enhance soil health and improve agricultural output (Poudel et al., 2023). Nano-fertilizers are fertilizers that contain nutrients inside nano-porous materials covered with polymer films, or given as nano-scale emulsions or particles (Rai et al., 2012). Nano-fertilizers regulate the nutrient release depending on the crop requirement, making them more efficient than normal fertilizers (Liu and Lal, 2015). Unlike the conventional fertilizers, the nutrient use efficiency of nano-fertilizers is 51-58% (Poudel et al., 2023). Application of nano-fertilizers through foliar spray serves as an effective supplement to soil fertilization, ensuring nutrient availability during critical growth stages while offering a cost-effective alternative to conventional methods (Janmohammadi et al., 2016). The foliar application of nano N and P optimizes nutrient management, minimizing N losses and P immobilization in the soil (Mejias et al., 2021). Nano-DAP liquid fertilizer containing 8% nitrogen and 16% phosphorus aims to address nutrient deficiencies, reduce mineral fertilizer use and enhance crop growth and productivity (Mahalakshmi et al., 2024). Recent studies have also demonstrated the effectiveness of nano-DAP in improving crop yields. Asha et al. (2024) reported that application of 75% of the recommended dose of fertilizers (RDF) combined with foliar spray of nano-DAP significantly increased yield of maize. Similarly, Sahoo et al. (2024) observed that integrating 50% of the soil test dose (STD) of conventional fertilizers with nano-DAP maintained yields comparable to 100% STD while recording higher nitrogen and phosphorus agronomic use efficiency in paddy. Jayara et al. (2024) reported that integrating conventional fertilizers with nano-fertilizers reduced GHG emissions and increased the energy ratio in wheat. These findings suggest that nano-DAP can help in replacing a certain percentage of conventional DAP and urea, if used judiciously.

Given these insights, the present study was undertaken to determine the optimal combination of conventional fertilizers and nano-DAP for maximizing the performance of kharif/rainy season maize in rainfed conditions. Specifically, this study aimed to evaluate the effects of integrating nano-DAP with conventional fertilizers on growth, nutrient uptake, yield, nutrient use efficiency, profitability, GHG emissions and energy dynamics of rainfed maize under semi-arid conditions of India.

2 Materials and methods

2.1 Experimental site

The present study was conducted at Gungal Research Farm (GRF) of ICAR-Central Research Institute of Dryland Agriculture, Hyderabad, Telangana, India during rainy season (June-September) of 2021 and 2022. Hyderabad is situated at an altitude of 542 m above mean sea level (MSL). It is located at latitude 17.40° N and longitude of 78.47° E. The mean weekly minimum and maximum temperature during cropping period fluctuated from 19.7 to 22.9°C and 22.3 to 31.2°C during 2021. Whereas, the weekly mean minimum and maximum temperature varied between 21.0 to 24.0°C and 28.3 to 33.4°C during 2022. An amount of 753.5 and 691.3 mm was received in 45 and 36 rainy days during the crop growth period of 2021 and 2022. The soil of experimental plot wassandy loam, slightly acidic (pH 6.51), normal EC (0.05-0.07 dS m^-1), low in organic carbon (0.43%) and available N (179.1 kg ha^-1), high in available P (24.7 kg ha^-1) and medium in available K (218.1 kg ha^-1).

2.2 Experiment details

The experiment comprising of 8 treatments (Table 1) was laid out in a randomized complete block design (RCBD) with three replications. Nutrients were applied as per the recommended dose 90-45–45 i.e., 90 kg of N (three splits), 45 kg of P₂O₅ (basal) and 45 kg K₂O (basal) per hectare according to the treatment plan using urea, DAP and MOP, respectively. Sprayer calibration was done using water in the sprayer tank. The sprayer was operated at a constant pressure and speed, and spray volume used to cover a unit area was measured. Nano-DAP was foliar applied @ 2 ml liter^-1 water twice at (800 ml ha^-1) V₆-V₈ and (1000 ml ha^-1) V₁₁-V₁₂ stages of crop as per the treatment, using a battery-operated power sprayer. Spraying operations were carried out during morning hours when wind speed was low and there was no rainfall. In other treatments, only water was sprayed. The technical description of IFFCO nano-DAP is provided in Supplementary Table S1 (GoI, 2023).

Table 1

Table 1. Details of the treatments.

2.3 Crop management

The field was initially ploughed for primary tillage, followed by secondary tillage using a cultivator to ensure fine tilth. Finally, the field was levelled with rotavator for optimal crop establishment. Tractor-drawn seed drill was used to sow the crop at a spacing of 60 cm × 20 cm. The hybrid DHM 111, developed by Professor Jayashankar Telangana State Agricultural University, is a medium-duration variety (90–95 days) with high yield potential (6.25–7.5 t ha^-1). It is suitable for both irrigated and rainfed conditions and is one of the popular hybrids cultivated in Telangana State. In treatments involving nano-DAP, seeds were treated with nano-DAP at 5 ml per kg of seed. Thinning and gap filling was done at 10–15 days after sowing (DAS), as required. Atrazine 50% WP @ 2.5 kg ha^-1 was sprayed at 2 DAS as pre-emergence spray followed by Tembotrione 42% SC @ 286 ml ha^-1at 15–20 DAS or 4 leaf stage as post emergence to control the growth of weeds. Intercultivation was done once at 35 DAS to control late emerging weeds. For the control of fall army worm, Carbofuran 3G granules @ 7.5 kg ha^-1was placed in leaf whorls at 25–30 DAS. Spraying of Emamectin benzoate 5% SG @ 0.4 g litre^-1 was done as required during the crop growth period. The entire crop was grown under rainfed conditions. Crop was harvested manually at physiological maturity stage.

2.4 Field data collection

Five representative plants from each net plot area were randomly selected and tagged for measuring plant height (cm). The height was measured using a graduated straight scale from the base of the shoot at the soil surface to the base of the tassel. Dry matter production was recorded by following the destructive sampling technique. While, leaf area index (LAI) was determined by using following formula (Watson, 1952).

$$\text{LAI }=\text{ Total leaf area }({\text{m}}^2)/\text{Land area }({\text{m}}^2)$$

The maximum quantum yield of Photosystem II (Fv/Fm) was measured using the Handy PEA fluorometer (Hansatech Instruments Ltd., UK). Leaves were dark-adapted for 15 minutes using leaf clips, a duration standardized through preliminary tests where no further increase in Fv/Fm was observed beyond this time. A saturating light pulse of 3000 μmol m^-²s^-¹ was applied to the leaf surface, and Fv/Fm was recorded. Measurements were conducted at ambient temperature with a time resolution of 10 μs, using short, intense pulses from an array of LEDs.

Five cobs were randomly selected from each net plot area to record length of the cob (cm), single cob weight (g) and number of grains cob^-1. For 100 grain weight (g), all the cobs from each net plot were threshed and one hundred grains were counted from the yield of each net plot and then weighed. The mean of various parameters were computed and used for statistical analysis. Cobs harvested from each net plot were sun-dried before being threshed with a maize thresher and then grain output was recorded. The grain yield was adjusted to a moisture content of 12%. After removing the cobs, leftover plant material, including the husk, was sun dried and weighed for stover yield.

2.5 Plant analysis

Nitrogen (N) content in plant samples was estimated by modified Kjeldhal method (Jackson, 1967) using Automatic Kelplus distillation unit after digesting the plant sample in conc. H₂SO₄ and H₂O₂ (Piper, 1966). Phosphorus and potassium content were estimated after digesting the plant samples with di-acid mixture consisting of HNO₃ and HCIO₄ in 9:4 ratio. Phosphorus content in the digested plant sample was estimated using the vanadomolybdophosphoric acid yellow color method in a nitric acid medium, with color intensity measured at 660 nm using a spectrophotometer (Jackson, 1958). Potassium content in the plant sample digest was measured by atomizing the diluted acid extract in a flame photometer (Jackson, 1958).

Nutrient uptake by grain and stover of maize crop was calculated by using the following formula.

$${\text{Nutrient uptake (kg ha}}^{-1})=\frac{\text{Nutrient content (}\%\text{) in grain}/\text{stover}\times \text{grain}/\text{stover yield} ({\text{kg ha}}^{-1})}{100}$$

2.6 Soil analysis

After the crop harvest in 2022, the soil samples were collected from all the treatments (0–15 cm depth) in polythene bags. The post harvested soil samples were dried under shade, ground with pestle and mortar and sieved through 2 mm sieve. The alkaline KMnO₄ method (Subbaiah and Asija, 1956), Olsen’s P method (Olsen et al., 1954), and neutral normal ammonium acetate method (Jackson, 1973) were employed to estimate the available N, P₂O₅, and K₂O, respectively.

2.7 Nutrient use efficiency

2.7.1 Agronomic use efficiency

It is the additional increasing yield per unit of input as influenced by kg of grain per kg of supplied nutrient, is calculated using following formula (Yoshida, 1981).

$$\text{AUE}=\frac{\text{Grain yield in the treated plot }({\text{kg ha}}^{-1})-\text{Grain yield in the control plot }({\text{kg ha}}^{-1})}{\text{Quantity of nutrients applied }({\text{kg ha}}^{-1})}$$

2.7.2 Apparent recovery efficiency

It specifies the proportion of nutrients absorbed from externally applied nutrient or fertilizer sources. It is expressed in terms of kg of nutrient uptake per kg of nutrient applied (Mitra et al., 2023).

$$\text{RE}=\frac{\text{Total nutrient uptake in the treated plot }({\text{kg ha}}^{-1})-\text{Total nutrient uptake in the control plot }({\text{kg ha}}^{-1})}{\text{Quantity of nutrients applied }({\text{kg ha}}^{-1})}\times 100$$

2.7.3 Relative agronomic efficiency

It is estimated as the ratio of the yield response with the test nutrient to the respective yield responses of the reference (100% RDF) nutrient and it was calculated using following formula (Akinrinde et al., 2005).

$$\text{RAE}=\frac{\text{Grain yield in treated plot }({\text{kg ha}}^{-1})-\text{Grain yield in control plot }({\text{kg ha}}^{-1})}{\text{Grain yield in\hspace{0.17em} }100 \%\text{ RDF plot }({\text{kg ha}}^{-1})-{\text{Grain yield in control plot(kg ha}}^{-1})}\times 100$$

2.8 Economic analysis

The economic analysis included assessing the cost of cultivation, gross returns, net returns, and benefit:cost (B:C) ratio in different treatments. The cost of cultivation was calculated for all treatments with the prevailing market prices of inputs and was worked out by considering all the expenses incurred in the crop cultivation and summed up with the common costs of various operations and inputs (Supplementary Table S2). Gross returns were calculated by multiplying the grain and stover yield with their respective minimum support price of grain and prevailing market price of stover during respective years of the study. Net returns were calculated by subtracting the total cost of cultivation from the gross returns (US $ ha^-1). B:C ratio was calculated as the ratio of gross return to the cost of cultivation. Further, economic analysis was also carried out by considering the cost of non-subsidized urea and DAP (US $ 0.61 and 1.04 kg^-1, respectively) as against the subsidized cost (US $ 0.06 and 0.34 kg^-1, respectively) (FAI, 2021-22).

2.9 Energy budgeting

All inputs (fertilizers, seeds, fuel, human, agro-chemicals, implements, machine etc.) and outputs (main and by-product) were considered for energy budgeting. Physical unit of inputs were translated into energy units by multiplying with energy equivalents (Supplementary Table S3) for the estimation of energy inputs. Similarly, energy output was calculated by multiplying the amount of grain and stover yield by its corresponding energy equivalents. The net energy, energy ratio and energy intensiveness were calculated as described below (Singh et al., 2016).

$$\text{Net energy }({\text{MJ ha}}^{-1})=\text{Energy output }({\text{MJ ha}}^{-1})-\text{Energy input }({\text{MJ ha}}^{-1})$$

$$\text{Energy intensiveness}=\frac{\text{Energy input}}{\text{cost of cultivation}}$$

$$\text{Energy ratio}=\frac{\text{Energy output}}{\text{Energy input}}$$

2.10 GHG emissions

Greenhouse gas (GHG) emissions from various treatments were estimated using reference emission values. The reference values used for the calculations were 5.15 kg CO₂-eq kg^-1 product for urea (Upadhyay et al., 2023b), 2.03 kg CO₂-eq kg^-1 product for DAP, 0.25 kg CO₂-eq kg^-1 product for MOP, and 0.242 kg CO₂-eq liter^-1 for nano-DAP (Jayara et al., 2024).

2.11 Statistical analysis

The data were subjected to analysis of variance (ANOVA) of a RCBD and tested at 5% level of significance using SPSS. Post-hoc mean separation was done using Duncan’s Multiple Range Test.

3 Results

3.1 Crop growth

Combined application of 100% N, P and recommended K along with foliar sprays of nano-DAP significantly improved the growth parameters of maize (Table 2). Higher plant height and dry matter production was recorded with N₁₀₀P₁₀₀K + nano-DAP which were found on par with N₁₀₀P₁₀₀K and N₇₅P₇₅K+ nano-DAP during both the years of study. A similar trend was observed for the leaf area index, where N₁₀₀P₁₀₀K + nano-DAP recorded the highest values, which were statistically at par with N₁₀₀P₁₀₀K and N₇₅P₇₅K+ nano-DAP. Whereas, the lowest plant height, dry matter production and leaf area index were observed in N₀P₀K and N₀P₀K + nano-DAP. The highest quantum yield (QY) values in both years were also recorded in treatments receiving Nano-DAP with higher NPK levels (Table 2). Specifically, N₁₀₀P₁₀₀K + nano-DAP and N₇₅P₇₅K + nano-DAP exhibited superior performance with QY values of 0.84 ± 0.007 and 0.83 ± 0.007 in 2021 (CLD “a” and “ab”), and 0.85 ± 0.004 in 2022 (CLD “a”). Moderately high QY values were observed in the N₁₀₀P₁₀₀K treatment without nano-DAP followed by N₇₅P₇₅K. Lower QY values were observed in nutrient-deficient treatments (N₀P₀K + nano-DAP and N₀P₀K). The consistent ranking across both years highlights the positive effect of nano-DAP in improving photosynthetic efficiency, especially when combined with optimal nutrient levels.

Table 2

Table 2. Effect of nutrient management on growth parameters of maize.

3.2 Yield attributes and yield

Foliar application of nano-DAP significantly increased the yield attributes of maize (Table 3). The cob length, no. of grains per cob, single cob weight and 100 grain weight of maize were significantly superior with application of 100% RDF along with foliar sprays of nano-DAP (N₁₀₀P₁₀₀K + nano-DAP) than other treatments except N₁₀₀P₁₀₀K and N₇₅P₇₅K + nano-DAP during both the years.

Table 3

Table 3. Effect of nutrient management on yield attributes of maize.

The maximum grain yields of 2909 kg ha^-1 in 2021 and 3206 kg ha^-1 in 2022, along with stover yields of 5979 kg ha^-1 and 6182 kg ha^-1, respectively, were recorded with N₁₀₀P₁₀₀K + nano-DAP, which were statistically on par with the treatments N₁₀₀P₁₀₀K and N₇₅P₇₅K + nano-DAP (Figure 1). Application of 100% RDF through soil combined with foliar sprays of Nano-DAP, resulted in a 62% increase in grain yield and a 55% increase in stover yield compared to the treatment without N and P application. Whereas, the treatments receiving only 50% of the recommended N and P, regardless of nano-DAP application, resulted in significantly lower grain yields by 27% and 38.5% compared to N₁₀₀P₁₀₀K + Nano-DAP.

Figure 1

Figure 1. Effect of nutrient management on yield of maize (2021 and 2022). The lowercase letters above each bar indicate variability and statistical significance among treatments.

3.3 Nutrient uptake by maize at harvest

Different levels of conventional fertilizers with and without Nano-DAP had a significant effect on the uptake of NPK (Table 4). Significantly higher N uptake by grain and stover were observed with application of 100% recommended NPK with foliar spray of nano-DAP (N₁₀₀P₁₀₀K + Nano-DAP) which were on par with N₇₅P₇₅K + nano-DAP and N₁₀₀P₁₀₀K during both years. Similarly, N₁₀₀P₁₀₀K + Nano-DAP also resulted in higher P and K uptakes over other treatments which were again on par with N₇₅P₇₅K + nano-DAP and N₁₀₀P₁₀₀K. The lower nutrient uptake values by grain and stover were obtained in N₀P₀K treatment during both 2021 and 2022.

Table 4

Table 4. Effect of nutrient management on nutrient uptake (kg ha^-1) by maize at harvest.

3.4 Nutrient use efficiencies

Higher agronomic use efficiency of nitrogen and phosphorus were recorded with the application of 75% of the recommended NP along with foliar spray of nano-DAP (N₇₅P₇₅K + nano-DAP), followed by N₅₀P₅₀K + nano-DAP (Figure 2). Significantly higher recovery efficiency of N and P were also observed with the application of N₇₅P₇₅K + nano-DAP over other treatments. However, the relative agronomic efficiency was highest with the application of N₁₀₀P₁₀₀K + Nano-DAP but was on par with N₇₅P₇₅K + Nano-DAP and N₁₀₀P₁₀₀K.

Figure 2

Figure 2. Effects of nutrient management on Agronomic use efficiency (AUE), apparent recovery efficiency (RE), and relative agronomic efficiency (RAE) of maize. The lowercase letters above each bar indicate variability and statistical significance among treatments.

3.5 Post-harvest soil available nutrients

The available soil N values ranged from 149.4 to 187.8 kg ha^-1 (Table 5). The lowest was observed in N₀P₀K, whereas a significantly highest value was recorded with N₁₀₀P₁₀₀K among all treatments except N₁₀₀P₁₀₀K + nano-DAP and N₇₅P₇₅K + nano-DAP. Similarly, higher soil available P was recorded in the plots under N₁₀₀P₁₀₀K, and the lowest value was recorded withN₀P₀K. However, the highest available soil K was recorded in the plots under N₀P₀K.

Table 5

Table 5. Effect of nutrient management on post-harvest soil nutrient status after maize.

3.6 Economics

The cost of cultivation with subsidized urea and DAP was comparatively lower than non-subsidized urea and DAP while net returns and B:C was higher (Table 6). The cost of cultivation was highest for N₁₀₀P₁₀₀K + nano-DAP compared to other treatments (US $ 42 ha^-1and US $ 59 ha^-1 with and without subsidy, respectively), whereas the lowest cost of cultivation was observed for N₀P₀K treatment. The highest gross returns and net returns per hectare with subsidy were recorded with N₁₀₀P₁₀₀K + nano-DAP, which were comparable with N₁₀₀P₁₀₀K and N₇₅P₇₅K + nano-DAP. While the net returns were higher for N₇₅P₇₅K + nano-DAP without subsidy. The lowest returns were recorded with N₀P₀K. The highest B:C ratio were recorded with N₇₅P₇₅K + nano-DAP, which was on par with N₁₀₀P₁₀₀K + nano-DAP and N₁₀₀P₁₀₀K. The lowest B:C ratio was observed under N₀P₀K.

Table 6

Table 6. Effect of nutrient management on economics of maize(mean data of two years).

3.7 Energy budgeting

Higher energy input and energy intensiveness were recorded under N₁₀₀P₁₀₀K + nano-DAP and N₁₀₀P₁₀₀K treatments (Table 7). Energy output and net energy returns were significantly higher under N₁₀₀P₁₀₀K + nano-DAP over rest of the treatments but remained at par with N₁₀₀P₁₀₀K and N₇₅P₇₅K + nano-DAP. While, energy ratio was significantly higher under N₀P₀K + nano-DAP over rest of the treatments.

Table 7

Table 7. Effect of nutrient management on energetics of maize (mean data of two years).

3.8 Greenhouse gas emissions

Among the treatments, the highest GHG emissions were recorded with N₁₀₀P₁₀₀K (1134.3 kg CO₂-eq ha^-1) and N₁₀₀P₁₀₀K + Nano-DAP (1134.7 kg CO₂-eq ha^-1) than other treatments (Table 8). The additional emissions due to foliar application of nano-DAP were negligible, amounting to only 0.4 kg CO₂-eq ha^-1compared to treatments without nano DAP application. However, a 25% reduction in the nitrogen and phosphorus dose combined with nano-DAP application (N₇₅P₇₅K + Nano-DAP) resulted in lower GHG emissions (856.7 kg CO₂-eq ha^-1) compared to the N₁₀₀P₁₀₀K treatment.

Table 8

Table 8. Effect of nutrient management on greenhouse gas (GHG) emissions.

4 Discussion

4.1 Growth attributes

The combined application of conventional fertilizers at optimal dosages along with nano-DAP as a foliar spray enhanced nutrient (N and P) availability, boosts enzyme activity and auxin metabolism, promoting cell division, elongation, and protein synthesis (Keerthana et al., 2024; Reddy et al., 2024) which ultimately resulted in taller plants in treatments N₁₀₀P₁₀₀K + Nano-DAP, N₇₅P₇₅K + Nano-DAP, and N₁₀₀P₁₀₀K. The basal application of conventional fertilizers to the soil along with foliar spray of nano-DAP significantly enhanced total dry matter production, which may be attributed to vigorous growth leading to an expanded photosynthetic surface, increased chlorophyll formation, greater nutrient uptake, and biomass accumulation. The nano-fertilizers also helped in proper supply of nutrients and accumulation of dry matter in leaves and improved the overall growth of the plant. These results are in conformity with Mahachandramuki et al. (2023); Keerthana et al. (2024); Reddy et al. (2024) who reported improved growth attributes in cotton, tomato and paddy with combined application of conventional fertilizers and nano-DAP.

The results highlight the critical role of nano particle-enhanced nutrient management in optimizing photosynthetic efficiency. The superior performance of treatments combining Nano-DAP with NPK (N₇₅P₇₅K + Nano-DAP) likely stems from improved nutrient solubility and uptake efficiency, a phenomenon documented in studies on nano-fertilizers (Pudhuvai et al., 2024). The decline in QY (Quantum Yield) for treatments like N₅₀P₅₀K highlights the limitations of suboptimal NPK application without nano-fertilizer supplementation. Recent studies show that nanoparticles of<50 nm in size can bypass traditional nutrient uptake barriers, maintaining optimal photosynthetic performance even under reduced fertilizer applications (Singh, 2025). The observed variation in Fv/Fm across nutrient treatments offers valuable insights into the functional status of Photosystem II under differing nutrient regimes. Treatments supplemented with nano-DAP, particularly when combined with 75% or 100% of the recommended NPK dose, exhibited higher Fv/Fm values indicating optimal photochemical efficiency and minimal PSII damage. This suggests that nano-DAP likely facilitated a more balanced and sustained nutrient release, enhancing chloroplast function and protecting the photosynthetic apparatus under rainfed conditions. In contrast, lower Fv/Fm in the nutrient-deficient treatments points to PSII photoinhibition, possibly due to nutrient-limited synthesis of repair proteins and antioxidants necessary to counteract photooxidative stress. Thus, the data imply that nano-DAP not only improves nutrient use efficiency but also plays a role in maintaining PSII integrity under sub-optimal growing conditions, contributing to better overall photosynthetic resilience in maize.

4.2 Yield attributes and yield

Better vegetative growth has also led to better yield attributes. Higher yield attributes of maize were observed with N₁₀₀P₁₀₀K + Nano-DAP, N₇₅P₇₅K + Nano-DAP, and N₁₀₀P₁₀₀K, which can be attributed to the application of conventional fertilizers along with two foliar sprays of nano-DAP. Foliar spray of nano-DAP facilitated nutrient absorption through the stomatal opening, leading to optimal development of plant parts and enhanced metabolic processes such as photosynthesis, ultimately resulting in increased accumulation and translocation of photosynthates to the plant’s economic portions (Upadhyay et al., 2023a). These findings are also consistent with those of Sahoo et al. (2024), who reported higher yield-attributing characteristics in paddy with two foliar sprays of nano-DAP due to improved nutrient absorption and translocation within the plant.

Grain and stover yield of maize was significantly higher with N₁₀₀P₁₀₀K + Nano-DAP than other treatments except N₁₀₀P₁₀₀K and N₇₅P₇₅K + Nano-DAP. The combined effect of conventional soil-applied fertilizers and foliar-applied nano-DAP ensured optimal and balanced nutrient availability for plant uptake throughout the crop growth period, especially during the critical stages of crop. Nitrogen, being a crucial component of amino acids such as glutamic acid and glycine, plays a fundamental role in chlorophyll formation and vegetative tissue development. The foliar application of nano-DAP at v₆-v₈ and v₁₁-v₁₂ stages (25 and 45 DAS) might have helped in increased rate of photosynthesis, resulting in greater dry matter accumulation in plants (Rajesh et al., 2021). Additionally, increased leaf area and prolonged leaf senescence further enhanced dry matter production and facilitated the efficient translocation of photosynthates from source to sink. Although the available phosphorus in the experimental plot was high, factors such as soil pH, limited soil moisture during critical periods, and phosphorus fixation reduced its availability to the crop (Chtouki et al., 2022). However, foliar application allowed rapid phosphorus absorption through stomata and cuticular pores, bypassing soil fixation mechanisms and ensuring its availability for critical physiological functions like ATP synthesis and root development (Fageria et al., 2010; Henningsen et al., 2023). By improving the availability of these key elements, nano-DAP enhanced the synthesis of vital proteins and enzymes, such as Rubisco, which facilitate carbon fixation, ultimately leading to improved photosynthetic efficiency and higher energy production (Jiaying et al., 2022). This in turn results in greater accumulation of photosynthates and their translocation to the plant’s yield components (Liu and Lal, 2015), thereby increasing grain and stover yields. Reddy et al. (2024); Mahalakshmi et al. (2024); Sahoo et al. (2024) also reported higher yields in rice and maize with combined application conventional fertilizers and nano-DAP.

4.3 Nutrient uptake

Significantly higher nutrient uptake (N, P, and K) at harvest by grain and stover was recorded with N₁₀₀P₁₀₀K + Nano-DAP, N₁₀₀P₁₀₀K, and N₇₅P₇₅K + Nano-DAP, primarily due to the increased and more efficient availability of nutrients through both soil application and foliar spraying. The foliar application of nano-DAP prolonged the availability of nitrogen and phosphorus, ensuring a steady nutrient supply over an extended period (Poudel et al., 2023). This, in turn, facilitated efficient nutrient absorption by plants, leading to higher nutrient concentrations. The increase in nutrient uptake can be attributed to the synchronization of nutrient release with the active crop growth stages, ensuring a sustained supply for optimal utilization and dry matter production (Sahoo et al., 2024). Similarly, potassium uptake was enhanced due to the improved availability and efficient utilization of nutrients, facilitated by the application of either 100% or 75% of the recommended NP fertilizer dosage along with nano-DAP. In contrast, conventional urea application may have resulted in nitrogen loss through leaching and volatilization, DAP application in soil may have resulted in immobilization of phosphorus leading to reduced nitrogen and phosphorus availability for plants and, consequently, lower nitrogen and phosphorus uptake compared to the Nano-DAP treatment. Additionally, the lack of an optimal nutrient supply in N₀P₀K and N₅₀P₅₀K treatments led to inadequate nutrient availability, further contributing to decreased nutrient uptake by grain and stover. Comparable findings were reported by Deo et al. (2022); Prakash et al. (2023), who documented improved nutrient uptake in rice and soybean with the integrated application of conventional fertilizers and foliar spray of nano-DAP.

4.4 Nutrient use efficiencies

Higher agronomic use efficiency (AUE) for nitrogen and phosphorus, along with higher apparent recovery efficiency (RE) of these nutrients was recorded with N₇₅P₇₅K + Nano-DAP. These results can primarily be attributed to the lower levels of nitrogen and phosphorus applied to the soil coupled with the resulting higher yield. The application of nano-DAP in this treatment enhanced nutrient utilization by the plants. Due to the smaller size of the nutrients, which are smaller than stomatal pores and possess a higher surface area, they remained available to the plants for a longer period, thus increasing productivity (Patil et al., 2020). It has been observed that recovery efficiency tends to decrease with an increase in fertilizer levels, as excessive fertilizer application can reduce nutrient uptake efficiency. Plants can only absorb nutrients up to a specific limit, beyond which excess nutrients are lost (Hulmani et al., 2022).Therefore, applying lower fertilizer levels, such as 75% of recommended N, P, and the recommended K, along with foliar sprays of nano-DAP can minimize nutrient loss and improve nutrient use efficiency, while saving 25% of fertilizers. The higher relative agronomic efficiency (RAE) in N₁₀₀P₁₀₀K + Nano-DAP, N₇₅P₇₅K + Nano-DAP and N₁₀₀P₁₀₀K was mainly due to the higher yield observed in these treatments. These results are in line with the findings of Asha et al. (2024); Sahoo et al. (2024) who recorded higher nutrient use efficiencies in maize and paddy with combined application of conventional DAP and urea along with foliar spray of nano-DAP.

4.5 Post harvest soil nutrient status

The enrichment of available nitrogen and phosphorus levels in the post-harvest soil of N₁₀₀P₁₀₀K + Nano-DAP, N₁₀₀P₁₀₀K, and N₇₅P₇₅K + Nano-DAP can be attributed to the optimal supply of nutrients through soil. In contrast, available soil K levels were reduced in these treatments compared to the N₀P₀K treatment. This reduction can be attributed to the fact that the same dosage of potassium was supplied to all treatments, but the N₀P₀K treatment, being deprived of nitrogen and phosphorus, had lower nutrient absorption, resulting in less dry matter production and reduced potassium uptake from the soil. The results are in agreement with the findings of Prakash et al. (2023).

4.6 Economics

Application of nano-DAP in combination with N₇₅P₇₅K (based on subsidized urea and DAP prices) incurred an additional expense of US $ 14 per hectare compared to the N₁₀₀P₁₀₀K treatment. This marginal increase is largely due to the government subsidy on conventional urea, which offsets the cost of soil-applied fertilizers. However, under non-subsidized conditions, the use of N₇₅P₇₅K along with two foliar sprays of nano-DAP resulted in a cost saving of US $ 29 per hectare, highlighting the economic advantage of integrating nano-fertilizers. Although N₁₀₀P₁₀₀K + nano-DAP resulted in high returns, the cost of cultivation was also higher due to the soil application of nitrogen, phosphorus, and potassium at 100% recommended dose, along with the additional foliar spray of nano-DAP. This increased input cost reduced the overall profitability compared to N₇₅P₇₅K + Nano-DAP, where fertilizer savings contributed to a better economic return. Similar findings were reported by Sachin et al. (2024) in rainfed pigeon pea and Sahoo et al. (2024) in rice, where higher net returns were observed with the combined application of conventional fertilizers and foliar spray of nano-DAP.

4.7 Energetics

Energy input was highest for N₁₀₀P₁₀₀K + nano-DAP treatment followed by N₁₀₀P₁₀₀K and the difference between these two treatments was only 87 MJ ha^-1 due to addition of nano-DAP. This suggests that nano-DAP production requires relatively low energy, making it an energy-efficient technology. The energy equivalent for producing 500 ml of nano-DAP is only 1.93 MJ (Upadhyay et al., 2023b), whereas the energy requirement for producing 1 kg of conventional nitrogen is 60.6 MJ and phosphorus is 11.1 MJ (Upadhyay et al., 2023b). While, higher energy ratio was recorded under N₀P₀K + nano-DAP over rest of the treatments mainly due to the complete omission of conventional nitrogen and phosphorus, substantially reducing input energy. However, the energy ratio under N₇₅P₇₅K + nano-DAP was higher over other treatments due to the reduction of 25% dose of N, P and statistically similar yields with that of N₁₀₀P₁₀₀K + nano-DAP and N₁₀₀P₁₀₀K treatments. Energy intensiveness values were higher under N₁₀₀P₁₀₀K mainly due to the application of 100% of recommended N and P fertilizers which have high energy equivalents which leads to significantly higher energy input per hectare. Whereas, reducing 25% of N and P fertilizers has reduced the energy cost without compromising on yield. Based on these findings, N₇₅P₇₅K + nano-DAP emerge as the most energy-efficient alternative compared to N₁₀₀P₁₀₀K-based treatments. Higher energy use efficiency was also reported by Upadhyay et al. (2023b) in maize and by Jayara et al. (2024) in wheat with the combined application of conventional fertilizers and nano-fertilizers.

4.8 Greenhouse gas emissions

Comparatively higher GHG emissions were observed in N₁₀₀P₁₀₀K treatments compared to N₇₅P₇₅K treatments. This was primarily due to the 25% reduction in nitrogen and phosphorus doses through conventional fertilizers. The additional emissions due to foliar application of nano-DAP were negligible. Since nano-DAP has a lower GHG emission factor than urea and DAP, the production of urea and DAP emits more GHGs over nano-DAP. Therefore, replacing a portion of conventional fertilizers with nano-DAP effectively reduced overall emissions, highlighting its potential role in mitigating the environmental impact of nitrogen and phosphorus fertilization. The N₇₅P₇₅K + Nano-DAP treatment lowered GHG emissions while maintaining a yield comparable to N₁₀₀P₁₀₀K. Jayara et al. (2024) also reported that the integration of mineral-based products with nano-DAP led to lower GHG emissions compared to the sole application of 100% recommended nutrients through synthetic fertilizers.

5 Conclusion

Based on findings from the study, it may be concluded that application of nano-DAP combined with conventional fertilizers has a significant impact on growth, yield, nutrient uptake, economic returns, energetics and GHG emissions in rainfed maize. Application of 75% recommended dose of NP + recommended K along with two foliar sprays of nano-DAP (N₇₅P₇₅K + Nano-DAP) resulted in grain yield and net returns comparable to that of 100% recommended NPK with or without nano-DAP spray (N₁₀₀P₁₀₀K + Nano-DAP and N₁₀₀P₁₀₀K). Additionally, nutrient use efficiency (NUE) and net energy returns were significantly higher with N₇₅P₇₅K + nano-DAP treatment compared to conventional fertilization regimes. Notably, this treatment also exhibited lower greenhouse gas (GHG) emissions than the N₁₀₀P₁₀₀K treatments, largely attributable to the 25% reduction in conventional nitrogen and phosphorus inputs. This indicates that the nano-DAP formulation, by enabling a more synchronized nutrient release and better availability, minimizes nutrient losses through volatilization and leaching-key contributors to GHG emissions and inefficiency in rainfed systems. These findings collectively position nano-DAP not merely as a substitute but as a strategic advancement over traditional urea and DAP, especially in optimizing input use, reducing environmental impact, and enhancing sustainability in dryland agriculture. However, long-term studies are needed to assess the impacts of nano-fertilizer use on soil health and crop quality. Furthermore, these findings need to be validated across diverse crops, environmental stress conditions and agro-ecological zones before being translated into recommendations for farmers.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author contributions

KG: Investigation, Writing – original draft, Visualization. VV: Investigation, Writing – review & editing. VS: Writing – review & editing, Visualization, Investigation. AS: Writing – review & editing, Investigation. KR: Visualization, Writing – review & editing. SK: Formal analysis, Writing – original draft. GC: Visualization, Writing – review & editing. BB: Writing – review & editing. BR: Writing – original draft, Formal analysis. NL: Formal analysis, Writing – original draft. PC: Writing – original draft, Formal analysis. MK: Writing – review & editing, Resources. TS: Resources, Writing – review & editing.

Funding

The author(s) declared that financial support was received for this work and/or its publication. The work was funded by Indian Farmers Fertilizer Cooperative Limited (IFFCO), New Delhi, India.

Conflict of interest

MK and TS were employed by the company IFFCO.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The handling editor VP declared a past co-authorship with the author(s) VS.

Generative AI statement

The author(s) declare that no Generative AI was used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fagro.2025.1723814/full#supplementary-material

Supplementary Table 1 | Specifications of IFFCO Nano DAP (Liquid) (GoI, 2023).

Supplementary Table 2 | Cost of resources used in the present study.

Supplementary Table 3 | Energy equivalent of inputs and outputs in agricultural production.

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