Soil macrofaunal activity, microbial catabolic limitations and nutrient cycling in cropping systems amended with woody residues and nitrogen inputs

Abstract Agroecological practices are emerging as efficient alternatives to address the challenge of sustainable agriculture. The objective of this study was to examine whether plant residue amendments from stems and leaves (SL) of an agroforestry shrub (Piliostigma reticulatum) enriched with nitrogen (N) sources improve nutrient cycling in Soudano-Sahelian cropping systems. The experimental design was organized into four replicates with six treatments consisting of two treatments of SL residue amendments (amended and non-amended) in combination with three treatments including additional N sources (natural soils, urea, and cowpea as intercrop). The results showed that the activity of termites (Nasutitermes torquatus) and ants (Messor galla and Pachycondyla rufipes) was 12 to 13 and 2 to 3 times higher in the SL amended soils than in non-amended soils, respectively. The activity of earthworms (Millsonia inermis) was highest in the SL amended soils associated with the cowpea intercrop, and was significantly lower in the urea enriched soils. SL amendments and N enrichments had no effect on soil basal respiration. The substrate-induced respiration with N substrates (L-alanine and L-arginine) was 25 and 52% higher in the SL amended soils than in the natural soils without any N inputs, indicating N limitation of microbial activity. This corroborates the higher C/N ratio (14.3) observed in the SL amended soils compared to the natural soils without any inputs (10.3). The N enrichment decreased the C/N ratio of the SL amended soils but was not efficient to alleviate microbial catabolic limitations, likely by switching from N to C limitation. Overall, the SL amendments with or without N enrichments triggered temporarily the soil macrofaunal activity, increased the NH4-N availability compared to that of NO3-N, and improved crop performance.