Open access publications in the SLU publication database

Abstract

Green manure is used as a nitrogen and carbon source in crop production, especially in organic cropping systems without access to farmyard manure. Decomposition and release of nutrients from the green manure is mediated by soil organisms. Consequently, increased understanding of how the biomass, activity and community composition of soil organisms are influenced by this resource input may contribute to improved plant nutrient management. The influence of different green manure forms and application methods on soil organisms, with emphasis on microbial community composition (described by phospholipid fatty acid analysis) and soil enzyme activity, was investigated in field trials. The green manure systems investigated were various red clover-based green manure forms (biogas slurry, compost, surface mulch and direct incorporation of a red clover ley) and long-term timothy grass amendments. In addition, C routes from decomposing green manure and the living plant roots into soil food webs were investigated using 13C labelling, which allowed differentiation between the two C sources. It was found that red-clover derived biogas slurry and mulch could provide alternatives to direct incorporation, enabling farmers to remove the green manure crop from their crop rotation and to adjust timing of application to crop nutrient requirements. Fresh green manure forms (direct incorporation, mulch) stimulated microbial growth and soil enzyme activity more than processed green manure forms (biogas slurry, compost), and also influenced microbial community composition differently. Long-term green manuring enhanced microbial biomass and soil enzyme activity and stimulated a different microbial community composition compared with other fertilizer regimes. In situ 13C labelling identified microbial groups specialised on decomposing green manure or rhizosphere C, respectively, and other microbial groups that were strongly linked to both C sources, indicating a general competitive ability. Different soil faunal taxa (Collembola, mites, enchytraeids and earthworms) were more linked to C from the green manure than the roots of the growing crop. To conclude, green manuring can be a useful management practice for enhancing microbial biomass and soil enzyme activity, but the green manure quality and application method needs to be considered.