Search

Abstract Soil compaction is a major threat to agricultural soils. Heavy machinery is responsible for damaging soil chemical, physical and biological properties. Among these, organic matter decomposition, which is predominantly mediated by the soil biota, is a necessary process since it underpins nutrient cycling and the provision of plant nutrients. Understanding factors which impact the functionality of the biota is therefore necessary to improve agricultural practices. To better understand the effects of compaction on the soil system, we determined the effects of soil bulk density and soil penetration resistance on the decomposition rates of litter in three distinct field zones: a grass margin, sown at the edge of the field adjacent to the crop, tramlines in the crop:margin interface, and crop. Three litters of different quality (ryegrass, straw residues and mixed litter) were buried for 1, 2, 4 and 6 months in litter bags comprising two different mesh sizes (0.02 and 2 mm). Bulk density and soil penetration resistance were greater in the compacted tramline than in the margin or the crop. The greatest amount of litter remaining in the bags after 6 months was found in the tramline, and the least in the grass margin. Differences between treatments increased with burial time. No significant differences in mass loss between the two mesh sizes was detected before the fourth month, implying that microbial activities were the main processes involved in the early stages of decomposition. Decomposition in the tramline was clearly affected by the degradation of soil structure due to heavy compaction. This study shows that soil conditions at the edges of arable fields affect major soil processes such as decomposition. It also reveals the potential to mitigate soil degradation by managing the headland, the crop residues and the machinery traffic in the field. [ABSTRACT FROM AUTHOR]

Phylogenetic distances of coexisting species differ greatly within plant communities, but their consequences for decomposers and decomposition remain unknown. We hypothesized that large phylogenetic distance of leaf litter mixtures increases differences of their litter traits, which may, in turn, result in increased resource complementarity or decreased resource concentration for decomposers and hence increased or decreased chemical transformation and reduction of litter. We conducted a litter mixture experiment including 12 common temperate tree species (evolutionarily separated by up to 106 Myr), and sampled after seven months, at which average mass loss was more than 50%. We found no effect of increased phylogenetic distance on litter mass loss or on abundance and diversity of invertebrate decomposers. However, phylogenetic distance decreased microbial biomass and increased carbon/nitrogen (C/N) ratios of litter mixtures. Consistently, four litter traits showed (marginally) significant phylogenetic signal and in three of these traits increasing trait difference decreased microbial biomass and increased C/N. We suggest that phylogenetic proximity of litter favours microbial decomposers and chemical transformation of litter owing to a resource concentration effect. This leads to a new hypothesis: closely related plant species occurring in the same niche should promote and profit from increased nutrient availability. [ABSTRACT FROM AUTHOR]