Rice-based cropping systems play crucial role in global food production (Samant et al., 2021). In India, rice is the major crop during the kharif season, but the land left fallow after rice cultivation is underutilized. There is significant potential to make productive use of this fallow land, offering an opportunity to address food and nutritional insecurity (Gumma et al., 2024). Pulses are sown under rice fallow conditions on about 2.6 lakh hectares in Tamil Nadu, which accounts for 30.8% of the total area under pulses in the state (Rathika and Ramesh, 2023). However, conventional flooded rice cultivation, which requires continuous submergence of field, lead to high water demand and creates anaerobic soil condition responsible for significant methane emission. With increasing concerns over water scarcity, declining groundwater level and the environmental impacts of methane release, there is a growing interest in alternative rice production systems that require less water and reduce greenhouse gas emission. Among these, aerobic rice cultivation has emerged as a promising option. Aerobic rice cultivation has been shown to reduce irrigation water use by 5-70% (Zhang et al., 2016) and decrease methane emissions by >90% (Sharma et al., 2016) compared to traditional anaerobic systems. Continuous cultivation of the cereal-cereal cropping system can be exhaustive and leads to the deterioration of the rhizosphere environment. This degradation could result in reduced nutrient availability and hinder root growth of the crops. To overcome this issue, the existing cropping systems is to be diversified by incorporating various leguminous crops into the rotation. The integration of pulses into rotations is a widely practiced strategy to improve system productivity (Sangothari and Radhamani, 2025).
       
The tropical climate prevailing in India results in low organic carbon content in the soil. Furthermore, unbalanced nutrient application lead to the degradation of soil health. Prolonged application of chemical fertilizers can substantially reduce crop yield potential and degrade the physico-chemical properties of the soil (Pahalvi et al., 2021). In the absence of organic fertilizers and biofertilizers, deficiencies in secondary nutrients and micronutrients lead to reduced soil productivity (Howe et al., 2024 and Rajitha et al., 2024). Consequently, there is a need to shift towards sustainable nutrient management as a crucial measure to sustain the productivity of cropping systems in the long term. Integration of AM fungi into sustainable nutrient management practices improve nutrient acquisition efficiency in rice cultivation and help maintain nutrient availability for subsequent crop within the cropping system (Wang et al., 2023). Incorporation of green manure into cropping systems improves soil health through multiple mechanisms viz., regulates soil pH, improves soil structure, increases water retention and contributes to nitrogen enrichment. The combined use of organic, inorganic, green manure and biofertilizer sources in nutrient management represents a highly effective strategy for reducing dependence on non-renewable energy resources, sustain soil fertility, enhance crop yield, improve farm profitability and minimize environmental pollution (Kharlukhi et al., 2024 and Saikia et al., 2018).
               
Based on the above concerns, the present investigation hypothesised that the integrated application of inorganic fertilizer, vermicompost, EFYM, AM fungi, green manure along with foliar supplementation of urea, zinc and iron in an aerobic rice-blackgram cropping system would prove to be a viable strategy to enhance production sustainability and optimize resource utilization. 

The present investigation on sustainable nutrient management in aerobic rice-blackgram cropping system was carried out during 2022 to 2023 at the wetland farm, Tamil Nadu Agricultural University, Coimbatore (11°01'06" N latitude, 76°58'21"E longitude and 426.7 m above mean sea level). The region of study comes under the western agro-climatic zone of Tamil Nadu. The average annual rainfall was 403 mm and 392 mm, received over 31 and 29 rainy days during 2022 and 2023, respectively. The top soil (0-15 cm) of the site belongs to the clay loam class (clay 45.45%, silt 16.82%, fine sand 15.81% and coarse sand 26.84%). Soil analysis at a depth of 0-15 cm revealed low organic carbon content (0.66 and 0.68 g ha^-1) and available nitrogen (210 and 222 kg ha^-1), moderate level of available phosphorus (20.2 and 21.7 kg ha^-1), high level of potassium (690 and 699 kg ha^-1) and pH values of 8.10 and 8.00, respectively during the two year study period. The experiment was conducted in a split-plot design (SPD) with and without green manure intercropping in the main plots and six nutrient management strategies in the sub-plots and replicated thrice. Details of the treatments imposed in the experiment are furnished in Table 1. Paddy seeds were sown directly in dry soil at a spacing of 20 × 10 cm. Dhaincha was sown simultaneously using an additive series (1:1 ratio) as per the treatment plan and the green manure was manually incorporated 25 days after sowing. The recommended dose of nitrogen (RDN) (150:50:50 kg/ha of N:P:K) was applied in four splits: 20% at 15 DAS, 30% at tillering and panicle initiation and the remaining 20% at flowering. Potassium was applied in two equal splits, with half at the basal stage and the rest at panicle initiation stage. After rice crop harvest, blackgram was directly sown into the rice stubble without any field preparation. No additional nutrients were applied and the succeeding crop solely depended on the residual nutrients from the fertilizers applied to the preceding rice crop.


 
Cropping system analysis
 
To compare the effectiveness of dhaincha incorporation and nutrient management practices, the economic yield of all treatments were converted into rice equivalent yield (REY) based on the prevailing market price. The following formulae were employed to work out the system productivity and profitability under aerobic rice-blackgram cropping sequence.
 
Rice equivalent yield (REY)

System productivity

System profitability analysis
 
Based on current market price of inputs such seeds, organic manures, fertilisers, pesticides and crop outputs, the cost of cultivation, gross return, net return and cost benefit ratio were calculated.
 
System profitability

 
Nitrogen balance
 
The nitrogen balance was computed as the difference between total nitrogen input and total nitrogen output, with a positive balance indicating a net nitrogen gain and a negative balance reflecting a deficit in the system (Raghuwanshi et al., 1991).
 
Statistical analysis
 
In the study, the normality of the parameters was assessed using R software (Version 4.2.0), revealing that all parameters exhibited a normal distribution. The means were distinguished through least significant difference (LSD) method with a significance level of P≤0.05.

Response on rice equivalent yield and system productivity
 
Rice intercropping with dhaincha (M₂) significantly increased rice equivalent yield (12.5, 12.6 and 12.6%) and system productivity (12.5, 11.9 and 13.1%) in the first, second year and pooled results, respectively compared to sole rice (M₁). In nutrient management strategies, plots treated with half dose of RDN from inorganic fertilizer, quarter dose of RDN from EFYM, quarter dose of RDN from vermicompost, AM fungi and foliar application of 0.5% urea, 1% FeSO₄  and 0.5% ZnSO₄ (S₆) recorded significantly higher rice equivalent yield (43.8, 41.8 and 42.7%) and system productivity (43.4, 41.7 and 42.5%) in the first, second year and pooled results, respectively compared to sole application of chemical fertilizer (S₂) (Fig 1). This might be due to a balanced supply of nutrients through organic and inorganic sources that contribute to providing the crop with the required elements for optimal growth and development. This balanced supply of nutrients might have played a crucial role in enhancing the grain yield of the crop as already reported by Dash et al., (2025). The presence of AM fungi extend their hyphal network into the soil, increasing the surface area for nutrient absorption and facilitating the uptake of phosphorus and other nutrients essential for rice and blackgram growth. They also might have improved the soil structure by binding soil particles, enhancing aeration, water retention capacity and root penetration, which benefit crop growth. By promoting a healthy environment surrounding the root system and maintaining soil fertility, AM fungi support the sustainability and productivity of the aerobic rice-blackgram cropping system over time (Panneerselvam et al., 2023). The incorporation of green manure in aerobic rice and its residue retention in blackgram improved soil fertility by enhancing nutrient availability, microbial activity and moisture retention. This facilitated better nutrient uptake and increased yield, thereby improving overall system productivity (Park and Lee, 2025). With regard to interaction effect dhaincha intercropping and nutrient management strategies on rice equivalent yield and system productivity was non-significant in both the years of study and pooled analysis results.




 
Response on system profitability
 
Rice intercropped with dhaincha recorded higher system profitability (28.6, 26.8 and 27.6 %) in the first, second year and pooled results, respectively compared to sole rice. Regarding, nutrient management strategies, plot received with half dose of RDN from inorganic fertilizer, quarter dose from EFYM, quarter dose from vermicompost, AM fungi and foliar nutrients of 0.5% urea, 1% FeSO₄ and 0.5% ZnSO₄ (S₆) resulted higher system profitability (51.2, 46.9 and 49.0%) across the first, second year and pooled results, respectively compared to sole application of chemical fertilizer (S₂) (Fig 2). The higher grain and straw yields attained in the aerobic rice-blackgram cropping system contributed to increased system profitability. This could be attributed to the improved productivity of both rice and blackgram crop and enhanced profitability (Nagarjuna et al., 2023). The judicious application of fertilizers along with organic manures not only enhances farm profitability but also lowers cultivation expenses through efficient residue recycling, ultimately improving net returns (Mangaraj et al., 2023b). The interaction effect between dhaincha intercropping and nutrient management strategies on system profitability was significant in both years and pooled results.
 
Response on economics
 
Rice intercropping with dhaincha and application of combined application of inorganic fertilizer, enriched FYM, vermicompost, AM fungi and foliar application of nutrients (M₂S₆) registered higher total cost of cultivation (71,868, 71,443 and 71,656 Rs. ha^-1, respectively ), gross returns (133,085, 137,655 and 135,370 Rs. ha^-1, respectively), net returns (71,868, 62,212 and 63,715 Rs. ha^-1, respectively) and Benefit Cost Ratio (BCR) (1.85, 1.93 and 1.89 respectively) under aerobic rice-blackgram cropping sequence during first, second year and pooled results. The lowest total cost of cultivation, gross returns, net returns and BCR were recorded in control plot (M₁S₁) during both the years and pooled results. Economics of aerobic rice-blackgram cropping system increased with sustainable nutrient management strategies as compared to application of recommended dose of fertilizer alone (Table 2). This might be due to higher grain and straw yield obtained from sustainable nutrient management strategies in turn increased the economics of aerobic rice-blackgram cropping system (Mangaraj et al., 2023a).


 
Nitrogen balance in soil
 
Sustainable nutrient management practices to aerobic rice-blackgram cropping sequence positively influenced the net balance of nitrogen in soil at the end of the cropping system in both the years (Table 3 and 3a).




       
During first and second year, net gain of soil nitrogen (22 and 24 kg ha^-1, respectively) was maximum by dhaincha intercropping along with combined application of half dose of RDN by inorganic fertilizer + quarter dose of RDN by EFYM + quarter dose of RDN by VC + AM fungi + foliar nutrients of 0.5% Urea +1% FeSO₄ + 0.5% ZnSO₄ (M₂S₆) than all other nutrient management practices. The lowest net gain of soil nitrogen (3.0 and 6.0 kg ha^-1, respectively) was recorded in treatment M₁S₁. Sustainable nutrient management strategies and rotation with legume increased the net gain of soil nitrogen status under aerobic rice- blackgram cropping sequence. This might be due to crop rotation with legume and the integration of various nutrient sources could have a positive impact on the multiplication of beneficial microbes in the soil. These microbes might have played a crucial role in converting organically bound nitrogen from organic residues, such as crop residues and organic manures, into inorganic forms of nitrogen that are readily available for plant uptake. As a result of this microbial activity, higher net gain was observed in available nitrogen in the soil, making it more accessible to the subsequent crops in the rotation (Midya et al., 2021).

In accordance with the results of the present investigation, adoption of sustainable nutrient management strategies viz., green manure, organic manures, inorganic fertilizers, micronutrients and biofertilizer increased the system productivity by 42.5 per cent and profitability by 49.0 per cent compared to the recommended dose of fertilizer in aerobic rice-blackgram cropping system. Therefore, the shift from exclusive reliance on inorganic fertilizers to the integrated use of diverse nutrient sources in the aerobic rice-blackgram cropping system can be considered as a sustainable alternative, particularly under the conditions of the Western Zone of Tamil Nadu, India. However, further investigations are necessary to evaluate the broader effects of sustainable nutrient management strategies on ecosystem services, resource use efficiency and system performance under varying crop diversification practices.

All authors declare that they have no conflicts of interest.