Effects of different rotational legume crops and residue management regimes on soil microbial properties and functions in a sugarcane farming system

Abstract

Background: Legume crop rotation in sugarcane cropping systems can improve soil health and fertility. However, their impacts on soil microbial community composition and function have not been clearly understood to date. Aims: This study aimed to assess responses of soil biochemical properties and composition of microbial communities driving C and N transformations in soils to different legume crop rotations and crop residue management practices. Methods: We investigated the effects of two rotational legume crops (soybean and peanut) and six different crop residue management practices on soil physicochemical and microbial properties as well as biological activities including C and N mineralisation, nitrification capacity and denitrification potential, in a subtropical sugarcane cropping system. Results: Incorporating high-N soybean crop residues into soil significantly increased soil mineral N content in the first month compared to no-till; no significant tillage effects were recorded with low-N peanut residues. Both crop residues increased soil microbial biomass C, C mineralisation capacity and nitrification capacity. However, bacterial and archaeal composition and abundances of 16S rRNA and nitrification genes were not affected. Spraying a nitrification inhibitor (DMPG) onto the crop residues before tillage significantly suppressed soil nitrification capacity. Conclusions: Compared to peanut rotation, soybean rotation could supply significantly more N for the following sugarcane crop due to its much higher crop residue N inputs and faster N mineralisation. Spraying legume residues with DMPG before tillage may provide an effective strategy to inhibit NO3 - formation and thus reduce the risk of NO3 - losses through leaching or denitrification.