Abstract/Summary

Plant-based mulches can improve soil physical conditions. In addition, shredded mulches of high quality are shown to enrich soil nutrients more than those of lower quality in a short term. However, the effect of size and quality of diverse mulches on soil nutrients and soil microbiology at later stages of decomposition has not been properly investigated. I hypothesized that, at later stages of decomposition, long size diverse residue mulch maintains higher fertilization capacity than short residues, and residue quality affects soil microbiology due to changes in decomposition rates, influencing soil nutrients and crop quality, but not crop yield. Two rhizotron and one field experiments were conducted to evaluate the effect of mulch residue size (<1.5 cm vs >30 cm) and diversity on soil chemistry and microbiology at later stages of decomposition, and on crop yield, crop quality, and residue quality at the end of the growing season. Residue mixes of 17, 12, 6, and 1 plant species, wood chips and control treatment with no residues were used. Residue biomass loss was not affected by its size, but it was higher in residues of higher quality. Long residues retained higher fertilization capacity than short residues at harvest. Residues of lower quality had higher fertilization capacity than those of higher quality at a timepoint long after harvest. In field, the remaining residues mixed with crop residues at harvest produced residues of higher quality than the crop residues alone. Residue quality affected crop quality but not yield. Soil nutrients were affected by both residue size and residue quality. There were indications that residue quality affected soil microbial biomass, at later stages of decomposition, although differences were not significant, and Arbuscular Mycorrhizal fungi root colonization was increased with increasing residue plant species richness. Generally, mulches of diverse residues can maintain soil fertility throughout cultivation period. Soil chemistry can be affected by both residue size and quality, and possibly soil microbiology can be affected either by residue quality or by residue diversity. Further investigation is needed with continuous applications of mulches to evaluate their long-term benefits.