Long-term influence of leguminous cover crops on the biochemical properties of a sandy clay loam Fluventic Sulfaquent in a humid tropical region of India

Cover crops grown in the interspaces of plantations may influence soil properties, especially biochemical properties related to organic matter turnover and nutrient cycling. In this study leguminous crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides and Pueraria phaseoloides grown as soil cover individually in the interspaces of a 19-year-old coconut (Cocos nucifera L.) plantation in S. Andaman (India) were assessed for their influence on biochemical properties of a sandy clay loam soil after the end of 10 years. In all the years, P. phaseoloides, followed by A. scarabaeoides had consistently higher biomass (10.2 and 9.0 Mg ha−1 per year, respectively), followed by C. pubescens and C. mucunoides (4.4 and 3.8 Mg ha−1 per year, respectively). The total C, N and carbohydrate additions for the 10-year period also exhibited marked variations and was significantly higher for P. phaseoloides followed by A. scarabaeoides. In general, incorporation of leguminous cover crops significantly enhanced organic C by 1.9–4.6 g kg−1 and total N by 0.52–0.78 g kg−1 after the 10-year period. The Bray P and K levels were also increased by 1.3–2.3 and 3.2–4.2 mg 100 g−1, respectively. Consequently, all the biochemical variables related to microbial activity (biomass C and N, N flush, CO2 evolution, qCO2, ATP, N mineralization and activities of dehydrogenase and catalase) were at significantly greater levels, thereby reflecting the response of greater organic matter inputs to the soil. Likewise, all the hydrolytic enzymes (acid phosphomonoesterase, phosphodiesterase, casein-protease, BAA-protease, β-glucosidase, CM-cellulase, invertase, urease and arylsulfatase) were activated to varying degrees in soils with cover crops which suggested that cover cropping significantly enhanced microbial activity, enzyme synthesis and accumulation due to increased C turnover and nutrient availability. The study further revealed that P. phaseoloides and to some extent A. scarabaeoides were better suited as cover crops compared to C. pubescens and C. mucunoides for the humid tropics.