Influence of in-situ green manure intercropping and nitrogen levels on soil microbial dynamics and enzymatic activities in a maize-maize cropping system under the southern transition zone of Karnataka

A field experiment was conducted during the Kharif and Rabi seasons of 2023-24 and 2024-25 at ZAHRS, Shivamogga, to assess the influence of in-situ green manure intercrops and nitrogen (N) levels on the soil microbial population and enzymatic activities in maize-maize sequence. The experiment followed a split-plot design with three nitrogen levels (75%, 100% and 125% RDN) and four green-manure based intercropping systems: sole maize, maize + cowpea, maize + horse gram and maize + sunhemp. Data indicated that 125% RDN produced the highest grain yield in all seasons, whereas 100% RDN resulted in superior microbial population and enzyme activities. Microbial populations and enzyme activities at harvest were consistently higher under sunhemp and lowest under sole maize. The interaction effects were non-significant across seasons; however, the combination of maize + sunhemp with 100% RDN registered the most favourable balance between productivity and soil microbial activity. Overall, in-situ incorporation of green manure—particularly sunhemp—proved effective in enhancing soil biological health and improving system sustainability in humid tropical maize production systems.