Soil management and grass species effects on the hydraulic properties of shrinking soils

In this study, we explored the effect of the roots of different forage grasses on soil hydraulic properties at the plot scale. To achieve this, we set up a field experiment in which six different grass cultivars were grown on replicated field plots at North Wyke, UK. We used tension infiltration measurements to assess soil hydraulic properties and structure. These measurements were made over two consecutive seasons. Measurements of shrinkage, water repellence, and the water release characteristic on soil samples taken from the North Wyke site were also made. We also wanted to compare the effects of different grasses on soil structure with the effects of differences in soil management; we therefore made tension infiltration measurements on fallow soil, permanent grassland, and arable land on a long-term experiment at Rothamsted, Harpenden, UK. Our data showed that the saturated hydraulic conductivity of the capillary matrix of the soil sown with grass depended on the grass species. Grass species affected the characteristic pore size estimated from tension infiltration data. At the Rothamsted site, we were able to infer that the development of macropore structure can be ranked grassland > arable > fallow (from the greatest to the least amount of macropores). In the North Wyke site, all the grass plots showed evidence of a macropore structure, consistent with the grassland site at Rothamsted, but there did not appear to be any variation between grass species. We concluded that changes to soil structure were probably due to physical rearrangement of soil particles by shrinkage.