How can we make better use of crop residues?

Crop residues are a widely available on-farm resource that contain calories, carbon and other nutrients. However, decomposition of crop residue soil amendments does not always translate into greater SOM levels, increased nutrient availability, or improved soil structure. Therefore, a better understanding of the decomposition processes involved is needed to improve the management of crop residues in arable and horticultural cropping systems. In this thesis, an extensive literature review and an investigation of the link between aboveground crop diversity and belowground soil biota suggested two strategies to increase SOM accumulation with crop residue amendments. The potential of these strategies was assessed in two experiments underpinned by ecological theories that have previously been observed in natural systems: (1) a test of the applicability of the home-field advantage (HFA) hypothesis (i.e. litter decomposes faster in soil in which it was grown, home, compared to a different soil, away) to arable cropping systems; and (2) a trial to exploit litter-mixing effects observed in forest ecosystems, in which crop residues of different chemical qualities were applied as mixtures and as individual residues to a horticultural soil. Different abundances of soil fauna were observed at the different stages of an arable crop rotation. However, no HFA effect could be detected within this same crop rotation. Soil amendment with mixtures of chemically contrasting crop residues, on the other hand, led to non-additively greater SOM and available N levels within a short time frame (44 days). Crop-residue mixing may therefore be a more suitable strategy to make better use of crop residues in arable and horticultural systems. This strategy may have practical implications, because it would involve the removal, mixing and re-application of crop residues, rather than simply returning them to the soils they were grown in. There is a need for a more mechanistic understanding of HFA effects, which may help explain why no HFA effect was found in this research project. Therefore, I envision a future HFA microcosm experiment in which possible factors that drive HFAs are controlled.