Soil Carbon Pools, Carbon and Nitrogen Storage Pattern in Soil Aggregate Fractions under Long-term Application of Organic and Synthetic Fertilizers in Rice-Wheat System: A Review

Soil organic matter (SOM) has long been recognized as an important indicator of soil productivity. The SOM refers to the organic fraction of undecayed plant and animal residues. The preservation of SOM is crucial to ensure long-term sustainability of agricultural ecosystems. OM plays a critical role in the global carbon balance that is thought to be the major factor affecting global warming. Overall, adequate amounts of SOM maintain soil quality and reduce environmental pollution. SOC concentrations and storage to 60 cm depth are significantly influenced due to long-term fertilization. The SOC storage in 0–60 cm in NP+FYM (farmyard manure), NP+S, FYM and NP treatments were increased as compared to the CK treatment. The concentration of particulate organic carbon (POC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in organic manure plus inorganic fertilizer treatments (NP+S and NP+FYM) in 0–60 cm depth increased linearly with increasing SOC content. Light fraction organic carbon (LFOC) was also significantly higher following the treatments including organic amendment than following applications solely of chemical fertilizers. Application solely of chemical fertilizers had no significant effects on LFOC and KMnO4C fractions compared with unfertilized control plots. Carbon pools were significantly correlated with SOC, which increased with application of organic amendments. Threshold C input of 3.3 MgCha-1 yr-1 was needed to maintain the SOC stock even at the low antecedent level. This review study will be helpful in crafting sustainable nutrient management programs in the future to enhance crop productivity with high efficiency and minimum nutrient loss. Therefore, fertilization strategies that include organic manure can increase the pool of stable C in the surface soil layer, while at the same time increasing concentrations and proportions of labile C. Organic manure use contributes to improved nutrient cycling services and higher soil quality in rice-wheat system.