Long-term Cropping, Fertilization and Manuring Effects on Carbon Pools, Carbon Sequestration and Yield Sustainability in Semiarid Tropical Conditions of Western India

The impact of rainfed perlmillet-clusterbean-castor sequence, fertilization and manuring on crop yield, soil organic carbon (SOC) pools and SOC buildup was investigated in a long term fertility experiment carried out over 18 years under semiarid conditions. Conjunctive use of chemical fertilizer along with FYM could be used as a soil amendment to obtain higher yields, improved SOC pools as well as higher SOC buildup as compared to cropping without amendments. Higher mean seed yield of pearlmillet (809 kg ha⁻¹), clusterbean (576 kg ha⁻¹), castor (827 kg ha⁻¹) over six cropping seasons were obtained as well as highest crop residues C (6.6 Mg ha⁻¹) and total C (33.5 Mg ha⁻¹) inputs were added 50% N (Fertilizer) + 50% N (FYM) treatment. Rainfall received during each month was positively correlated with the seed yield except for the month of September in case of pearlmillet and castor (R² = 0.34 to 0.99; n=18). Highest SOC (2.7 g kg⁻¹), total N (0.044%), MBC (135.5 μg g⁻¹ soil) and POC (0.14%) were observed in in surface (0–0.2m) soil of 50% N (Fertilizer) + 50% N (FYM) treatment. These parameters decreased in lower depth. The amount of SOC build up was in proportion to the carbon (C) inputs (R²=0.93; P<0.05). Carbon pools such as microbial biomass carbon (MBC) and particulate organic carbon (POC) were significantly correlated (P<0.05) with SOC, which increased with organic amendments.