Mulch quality regulates soil fertility and microbial communities during a crop cycle

Context The benefits of plant-based mulch extend beyond improving soil physical properties as mulches hold value as a fertiliser and in maintaining robust soil microbial communities throughout the crop cultivation period. Aims We investigated the impact of plant-based mulch quality (comprising contrasting hemicellulose, cellulose, and lignin components) sourced from single and diverse species mixtures on soil fertility, microbial communities, crop yield, and seed quality by growing barley from seed to maturity in rhizotrons. Methods The treatments consisted of residue mixtures containing 17, 12, 6, and 1 grassland plant species, as well as wood chips, with a control group receiving no residues. Soil samples were collected at two time points, 69 and 195 days after mulch application, for nutrient and microbial phospholipid fatty acid analysis. Residues were analysed for hemicellulose, cellulose, and lignin content. Key results We found that high-quality residues, with low carbon:nitrogen ratio, low recalcitrance, and the highest nitrogen content decomposed most quickly and increased available soil potassium concentrations compared to residues of lower quality. The lower-quality residues retained a greater proportion of their initial fertilisation capacity, which was released gradually. There was a concomitant increase in soil microbial biomass at later stages of decomposition in residues of lower quality. Residue quality significantly affected crop seed quality but not yield. Conclusions Lower-quality residues can maintain their fertilisation capacity over a longer time horizon than higher-quality residues. Plant residue mulch can influence soil microbial biomass throughout the cultivation period, regardless of its initial quality, and can affect crop quality although this effect is slow and not always readily detectable. Implications These findings emphasise the importance of considering plant-based mulch quality in enhancing soil fertility and crop quality.