Effect of ten years of reduced tillage and recycling of organic matter oncrop yields, soil organic carbon and its fractions in Alfisols of semi aridtropics of southern India

Abstract

Reducing tillage intensity and retaining residues are important components of conservation agriculturebut in small holder systems in developing countries where crop residues have alternate uses such asfodder and fuelwood, recycling or external additions of organic matter may be a possible option.Information on impacts of long term reduced tillage on soil carbon, labile organic carbon fractions andtheir depth distribution is scant in drylands of semi arid regions. The effect of tillage intensity (CT—conventional tillage; RT—reduced tillage and MT—minimum tillage) and sources of nitrogen (100% OS:100% of recommended N through organic source; 50% OS +50%IOS: 50% N through organic source and 50%N through inorganic source and 100% IOS: 100% N through inorganic source) on crop yields, soil organiccarbon and C fractions in an Alfisol was assessed at the end of a 10 year long term experiment. Fingermillet yields decreased significantly with reduction in tillage intensity (29%). Among N sources, highestyields were recorded with substitution of 50% of the N through organic source. After 10 years, the soilorganic carbon (SOC) in 0–20 cm soil layer with MT was 11% higher than with CT. The labile fractions ofcarbon, viz. particulate organic carbon (POC), microbial biomass carbon (MBC) and permanganateoxidizable carbon (KMnO4-C) under MT were 47%, 16% and 43% higher, respectively, in comparison to CTin the 0–20 cm soil layer. The total carbon (TC) and total organic carbon (TOC) with MT were higher by28% and 27% over CT and higher by 20% and 20% with 100%OS over 100% IOS. Labile carbon fractionsrevealed differential sensitivity and POC, MBC and KMnO4-C are sensitive indicators to detect short termmanagement effects. Reducing tillage intensity and applying various N sources enhanced SOC marginallyand the C sequestration rate varied from 62 to 186 kg ha 1yr 1. Based on the study it can berecommended for substitution of 50% of the recommended N with organic source as it increases cropyields and soil carbon and could be a potential alternative for residue retention for crops which havefodder value. Reducing the tillage intensity can enhance the SOC in semi arid rainfed systems but lowercrop yields under MT is a concern which needs to be addressed in order to make these systems acceptableto the farming community.