Soil carbon sequestration and agronomic productivity of an Alfisol for a groundnut-based system in a semiarid environment in southern India

Soil organic carbon (SOC) is a strong determinant of soil quality and agronomic productivity especially under harsh arid and semiarid environments of the tropics. Thus, a 20-year experiment was used to assess the impact of rainfed groundnut (Arachis hypogeae) monocropping, fertilization and manuring on soil quality, SOC sequestration, and crop yield sustainability on an Alfisol in southern India. Five treatments with 4 replications were: (1) control (no fertilizer or manure), (2) 100% recommended dose of fertilizer (RDF, 20:40:40 kg ha−1 of N:P2O5:K2O), (3) 50% RDF + 4 Mg ha−1 of groundnut shells (GNS), (4) 50% RDF + 4 Mg ha−1 of farmyard manure (FYM) and (5) 5 Mg ha−1 of FYM. The SOC concentration to 1-m depth increased from 2.3 to 3.5 g kg−1 (52.2%) in 50% RDF + 4 Mg ha−1 GNS over control and mean SOC sequestration rate was 0.57 Mg C ha−1 yr−1. Higher mean pod yield of groundnut (Mg ha−1) was obtained with 50% RDF + 4 Mg ha−1 FYM (1.03). The rate of increase in groundnut pod yield was 13 kg ha−1 yr−1 for every one Mg increase in profile SOC stock. A minimum of 1.12 Mg C ha−1 yr−1 input was needed to maintain the zero change in SOC. Hence, combined use of chemical fertilizers and organic manure is essential to enhancing SOC sequestration in monocrop regions in semi arid tropical conditions.

► Soil organic C is a strong determinant of soil quality and agronomic productivity.
► Prevailing high temperatures rapidly oxidized soil organic C with intensive tillage.
► Information available on soil C sequestration in semi arid tropics is rather little.
► Locally available organic materials are useful for improvement of SOC.
► One of the first few reports on critical C input requirement in tropical conditions.