The present study aimed to evaluate the nutrient budget, apparent nutrient balance and quantify nutrient depletion and build-up resulting from 25 years of long term fertilization in a Vertisol of Subtropical India. The 150 % NPK recorded maximum positive apparent nitrogen (N) (3038 kg ha-1) and phosphorus (P) (1182 kg ha-1) balance, while minimum was recorded with absolute control (-1604 kg ha-1). The inclusion of green manure (GM) with 50 % NPK registered positive apparent N balance. The apparent P balance was positive with inclusion of P in fertilizer scheduling even under 50 % NPK and 50 % NPK + Blue green algae (BGA) treatments, indicating that 50 % P application fulfilled the crop P demand. The negative apparent K balance was recorded across almost all treatments with the average rate of -181 kg ha-1 yr-1 indicating luxury consumption of K by crops than its supplementation. The soil available N was depleted in all the treatments, however, depletion was minimum under 150 % NPK (10 kg ha-1) and 100 % NPK+FYM (13 kg ha-1). There was build-up of soil available P over initial status in all the imposed treatments (from 5 to 18 kg ha-1) even under sub-optimal dose of NPK, except in absolute control and 100 % N. However, a net negative soil available K was observed in almost all the treatments due to mining of soil K reserves to meet out crop demand. The findings underscore the critical necessity for strategic N and K fertilization in Vertisol under rice-wheat cropping system to sustain optimal nutrient equilibrium, managing soil fertility and maximize agronomic productivity.

The rice-wheat cropping system under Vertisol in sub-tropical regions of India faces significant challenges in maintaining soil health and achieving sustainable yields. This is primarily due to climatic variability and intensive agricultural practices, which accelerate the loss of soil organic carbon (SOC) and lead to soil degradation. There is a pressing need to adopt sustainable nutrient management, that not only maximize crop yields but also support climate change mitigation through carbon (C) sequestration and soil health management. In this context, a long-term fertilizer management (25 years) study was undertaken to assess crop productivity, C fractions, sequestration potential to achieve soil C 4 per mille under rice-wheat cropping system in sub-tropical Vertisol. The experiment was based on ten different fertilizer treatments either alone or in combination with organics. Grain yield, system productivity, and the sustainable yield index (SYI) were significantly higher under the 150%NPK and NPK + Farmyard manure (FYM) treatments compared to the unfertilized control. Relying on imbalanced fertilization (N) is inadequate for long-term sustainability. Long-term application of 100% NPK+FYM increased SOC content by up to 16%, whereas it decreased by 34% under absolute control relative to the initial value. Integrated nutrient management (INM) significantly enhanced the SOC pools, with higher proportion (57%) of total SOC in passive C pools. The increase in SOC stock was significantly correlated (R² = 0.76) with system productivity, requiring a minimum C input of 2.7 Mg C ha^-1 yr^-1 to maintain C equilibrium. The INM treatment achieved the highest C sequestration (2.27 Mg ha^-1), potential (7.04 Mg ha^-1) and rate (0.10 Mg C ha^-1 yr^-1) compared to NPK. In the present study, the C sequestration rate under NPK+FYM and 150%NPK surpassed the annual increment requirement of 0.4% SOC to achieve the target of the “4 per mille”. Over 25 years, application of 5 Mg ha^-1 FYM with NPK proved to be the most sustainable practice for SOC management. In addition to enhancing SOC stock, this practice maximizes crop productivity, thereby highlighting the potential of soil management as an effective voluntary carbon sequestration pathway for climate-change mitigation strategy in sub-tropical regions.

The rice–wheat cropping systems in sun-tropical Vertisols of India face major challenges in sustaining soil health and crop productivity due to climate variability and intensive agricultural practices, which accelerate soil organic carbon (SOC) depletion and soil degradation. Therefore, sustainable nutrient management that not only maximizes crop yields but also supports climate change mitigation through carbon (C) sequestration and soil health management is essential. In this context, a long-term fertilizer management (25 years) study was undertaken to assess crop productivity, C fractions, sequestration potential to achieve soil C 4 per mille under rice–wheat cropping system in sub-tropical Vertisol. The experiment was based on ten different fertilizer treatments including unfertilized control, varying levels of inorganic fertilizers, their combinations, and integrated nutrient management (INM) with organic amendments. Grain yield, system productivity, and the sustainable yield index (SYI) were significantly higher under the application of 150% of the recommended dose of nitrogen, phosphorus, and potassium (NPK) (150%NPK) and 100% of the recommended NPK dose with farmyard manure (FYM) (NPK + FYM) treatments compared to the unfertilized control. Long-term application of 100%NPK + FYM (NPK + FYM) increased SOC content by up to 16%, whereas SOC decreased by 34% under absolute control relative to the initial value. The increase in SOC stock was significantly correlated (R² = 0.76) with system productivity, requiring a minimum C input of 2.7 Mg C ha⁻¹ yr⁻¹ to maintain C equilibrium. The INM treatment achieved the highest C sequestration (2.27 Mg ha⁻¹), potential (7.04 Mg ha⁻¹) and rate (0.10 Mg C ha⁻¹ yr⁻¹) compared to NPK. In the present study, the C sequestration rate under NPK + FYM and 150%NPK surpassed the annual increment requirement of 0.4% SOC to achieve the target of the “4 per mille”. Over 25 years, application of 5 Mg ha⁻¹ FYM with NPK proved to be the most sustainable practice for SOC management. In addition to enhancing SOC stock, this practice maximizes crop productivity, thereby highlighting the potential of soil management as an effective voluntary carbon sequestration pathway for climate-change mitigation strategy in sub-tropical regions.