Soil organic carbon sequestration in relation to organic and inorganic fertilization in rice–wheat and maize–wheat systems

Soil organic carbon (SOC) pool is the largest among the terrestrial pools. The restoration of SOC pool in arable lands represents a potential sink for atmospheric CO2. The management and enhancement of SOC is important for sustainable agriculture. The cropping system and soil type influence crop biomass under different fertilization. Data from two long-term field experiments on rice–wheat and maize–wheat systems in progress since 1971, were analyzed to assess the impact of fertilization practices on SOC stocks in sandy loam soils (typic ustipsament). The treatments in rice–wheat included (i) farmyard manure (FYM alone @ 20 t ha−1, applied at the time of pre-puddling tillage), (ii) N120P30K30 (120 kg N, 30 kg P2O5 and 30 kg K2O ha−1), (iii) N120P30 (same as in (ii) except that K application was omitted), (iv) N120 (same as in (ii) except that P and K application was omitted) and (v) control (without any FYM or inorganic fertilizer). Similar treatments were studied in maize–wheat except that the amounts of N, P2O5 and K2O were 100, 50 and 50 kg ha−1, respectively. In rice–wheat system, the SOC concentration at different depths in 0–60 cm soil profile was higher (1.8–6.2 g kg−1) in FYM-treated plots followed by 1.7–5.3 g kg−1 in NPK plots, compared to 0.9–3.0 g kg−1 in unfertilized plots. Balanced fertilization improved the SOC concentration. Similar trend was found in maize–wheat system. In the 60-cm soil profile the total SOC stocks in both the cropping systems were highest in FYM (31.3 and 23.3 Mg ha−1 in rice–wheat and maize–wheat system) followed by balanced fertilization (29.6 and 21.3 Mg ha−1) and lowest in unfertilized control (21.4 and 18.7 Mg ha−1). The SOC concentration in rice–wheat soils was 54 and 30% higher in FYM and NPK plots than in maize–wheat system. Improved SOC content enhances soil quality, reduces soil erosion and degradation, and increases soil. The soils under rice–wheat sequestered 55% higher SOC in FYM plots and 70% higher in NPK plots than in maize–wheat. These results document the capacity of optimally fertilized rice–wheat system to sequester higher C as compared to maize–wheat system.