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 @ 20tha⁻¹, applied at the time of pre-puddling tillage), (ii) N₁₂₀P₃₀K₃₀ (120kg N, 30kg P₂O₅ and 30kgK₂Oha⁻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 50kgha⁻¹, respectively. In rice-wheat system, the SOC concentration at different depths in 0-60cm soil profile was higher (1.8-6.2gkg⁻¹) in FYM-treated plots followed by 1.7-5.3gkg⁻¹ in NPK plots, compared to 0.9-3.0gkg⁻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 23.3Mgha⁻¹ in rice-wheat and maize-wheat system) followed by balanced fertilization (29.6 and 21.3Mgha⁻¹) and lowest in unfertilized control (21.4 and 18.7Mgha⁻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.