Soil microbiological properties during decomposition of crop residues under conventional and zero tillage

Abstract

Field experiments were conducted to correlate decomposition of red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and wheat (Triticum aestivum) residues, and soil organic C (SOC), under zero tillage and conventional tillage, with soil microbial biomass C (MBC), bacterial functional diversity and microbial activity (CO2 evolution). A greenhouse experiment was also conducted to relate crop residue quality to soil microbial characteristics. Zero tillage increas ed MBC only in the 0- to 5-cm soil layer. Soil MBC decreased more with soil depth than either microbial diversity or total SOC. Legume GM residues induced greater initial CO2 evolution than the other residues. This means that results that do not include the initial flush of microbial activity, e.g., by sampling only in the season(s) following residue placement, probably underestimate gas evolution from legume crop residues. Residue N, P and K contents were positively correlated with microbial functional diversity and activity, which were positively correlated with crop residue decomposition. Therefore, microbial functional diversity and activity were good indicators of microbial decomposition processes. Residue C/N and C/P ratios (i.e., high C content) were positively correlated with MBC, which was positively correlated with SOC. Therefore, soil MBC was a good indicator of soil quality (soil organic matter content). Key words: Biological soil quality, crop residues, crop rotation, microbial activity, microbial biomass, microbial diversity