Clay–organic complexes (COC) impart chemical and physical protection to soil carbon (C). In the present study, the aim was to assess the long-term effects of different organic amendments on C stability in COC, distribution of the aggregates, C concentration in the aggregates and labile organic C fractions in the inceptisols located at the research farm situated in the semi-arid sub-tropical climate of India. The results showed that the COC, the percentage of large macroaggregates (LMA) (>2 mm) and the C associated with the aggregates decreased through the soil depths, whereas the other size fractions of soil aggregates (<2 mm) showed an increasing trend. The COC was significantly higher (4.4 times) in soil treatments where farmyard manures (FYM), green manure (GM) and biofertilizers (BF) were applied together (FYM + GM + BF). The organic amendments increased the proportion of LMA over control (no application of organic amendments) to a magnitude of 83 to 101% and the C associated with LMA to a magnitude of 0.48 to 9.8% over control in surface soil. On average, the combined application of FYM, GM and BF exhibited higher C accumulation in almost all soil aggregate fractions, except microaggregates (mA), i.e., (0.25–0.053 mm) size fractions, where application of FYM alone recorded the highest value. Averaged over soil depths, the particulate organic C (POC), dissolved organic C (DOC) and potassium permanganate oxidizable C (POXC) were significantly higher under integrated organic treatments than individual amendments. The significantly higher correlation between COC and the percentage of LMA and aggregate-associated C implied their direct role in soil aggregate formation and their stability. The carbon stability, i.e., retention time of humus in soil, was significantly correlated with soil organic carbon, dissolved organic carbon, particulate organic carbon, potassium permanganate oxidizable C, C mineralization (C_min), glomalin-related soil protein (GRSP), macroaggregate (MA)-associated C and rice equivalent yield (REY). Overall, the data suggest that the combined application of FYM + GM + BF promotes soil quality under rice–wheat rotation in inceptisols in semi-arid sub-tropical India.

This study was undertaken to address how near-surface soil water content (SWC) patterns have varied across diverse agroecological regions (AERs) of mainland India from 1979 to 2022 (44 years) and how these variations relate to environmental factors. Grid-wise trend analysis using the Mann–Kendall (MK) trend test and Sen’s slope was conducted to determine the trends and their magnitudes. Additionally, we used Spearman’s rank correlation (ρ) to explore the relationships of ESA CCI’s near-surface SWC data with key environmental variables, including rainfall, temperature, actual evapotranspiration, and the normalized difference vegetation index (NDVI). The results revealed significant variations in SWC patterns and trends across different AERs and months. The MK trend test indicated that 17.96% of the area exhibited a significantly increasing trend (p < 0.1), while7.6% showed a significantly decreasing trend, with an average annual Sen’s slope of 0.9 × 10⁻⁴ m³ m⁻³ year⁻¹ for mainland India. Areas with the highest decreasing trends were AER-16 (warm per-humid with brown and red hill soils), AER-15 (hot subhumid to humid with alluvium-derived soils), and AER-17 (warm per-humid with red and lateritic soils). In contrast, increasing trends were the most prominent in AER-5 (hot semi-arid with medium and deep black soils), AER-6 (hot semi-arid with shallow and medium black soils), and AER-19 (hot humid per-humid with red, lateritic, and alluvium-derived soils). Significant increasing trends were more prevalent during monsoon and post-monsoon months while decreasing trends were noted in pre-monsoon months. Correlation analysis showed strong positive correlations of SWC with rainfall (ρ = 0.70), actual evapotranspiration (ρ = 0.74), and NDVI (ρ = 0.65), but weak or negative correlations with temperature (ρ = 0.12). This study provides valuable insights for policymakers to delineate areas based on soil moisture availability patterns across seasons, aiding in agricultural and water resource planning under changing climatic conditions.

The present investigation evaluated the effect of continuous application (>43 years) of organic and inorganic fertilisers on soil aggregate stability, aggregate size distribution, aggregate-associated carbon and its fractions, and total macro-nutrient content under the soybean–wheat cropping system in vertisols of the semi-arid region. Seven contrasting treatments consisted of T₁ (50% NPK), T₂ (100% NPK), T₃ (150% NPK), T₄ (100% NP), T₅ (100% N), T₆ (100% NPK + FYM) and T₇ Control (crop raised without addition of any nutrient). The highest and lowest percentage of large macroaggregates (11.3%) was found in T₆ and T₇ treatments. The NPK + FYM (T₆) treatments substantially increased the proportion of the macroaggregate fractions (>2 mm and 2–0.25 mm) than other treatments. However, different manure and fertilisation treatments did not affect the proportion of silt + clay aggregates. Long-term application of 100% NPK + FYM increased mean weight diameter (MWD) and stable water aggregates (WSA) by 35.7 and 6.01% over control. The aggregate-associated SOC followed the trend of large macroaggregates > microaggregates > small macroaggregates > silt + clay fractions. Application of long-term manure plus inorganic fertiliser (T₆) has also increased Walkley Black soil organic carbon (WBSC), permanganate oxidisable carbon (KMnO₄-C), soil microbial biomass carbon (SMBC), carbon mineralisation (CM), total soil carbon (TSC), total soil N (TSN), total soil phosphorus (TSP) and total soil potassium (STK) by 82.1, 71.6, 182, 42.4, 23.9, 41.6, 117 and 18.4%, respectively, over control (T₇). The lowest metabolic quotient (MetQ) value of 5.13 mg CO₂–C mg⁻¹ MBC h⁻¹ was obtained in the control treatment (T₇). The lowest MetQ was recorded in the integrated application of manure + inorganic fertiliser, i.e., 100% NPK + FYM (T₆). Similarly, microbial quotient (MiQ) was also higher in treatment T₆ (100% NPK + FYM) and lower in T₇ (control). It is concluded that the application of inorganic fertiliser alone is insufficient to maintain soil health and sustainability so, combined application of manure plus inorganic fertilisation is the most important nutrient management practice for long-term soil sustainability because it maintains SOC levels in soils for long periods and ultimately ensures the soil health of soybean–wheat cropping systems in the vertisols of semi-arid 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.

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.