A statistical comparison of spatio-temporal surface moisture patterns beneath a semi-natural grassland and permanent pasture: From drought to saturation

摘要

Some 60% of the agricultural land in the UK is grassland. This is mostly located in the wetter uplands of the west and north, with the majority intensively managed as permanent pasture. Despite its extent, there is a lack of knowledge regarding how agricultural practices have altered the hydrological behaviour of the underlying soils relative to the adjacent moorland covered by semi-natural grassland. Near-surface soil moisture content is an expression of the changes that have taken place and is critical in the generation of flood-producing overland flows. This study aims to develop a pioneering paired-plot approach, producing 1,536 moisture measurements at each of the monitoring dates throughout the studied year, that were subsequently analysed by a comparison of frequency distributions, visual cum geostatistical investigation of spatial patterns and mixed-effects regression modelling. The analysis demonstrated that the practices taking place in the pasture (ploughing, re-seeding and drainage) reduced the natural diversity in moisture patterns. Compared to adjacent moorland, the topsoil dried much faster in spring with the effects requiring offset with moisture from slurry applications in summer. With the onset of autumn rains, these applications then made the topsoil wetter than the moorland, heightening the likelihood of flood-producing overland flow. During the sampling within one such storm event, the adjacent moorland was almost as wet as the pasture with both visibly generating overland flow. These contrasts in soil moisture were statistically significant throughout. Further, they highlight the need to scale-up the monitoring with numerous plot pairs to see if the observed highly dynamic, contrasting behaviour is present at the landscape scale. Such research is fundamental to designing appropriate agricultural interventions to deliver sustainable sward production for livestock or methods of mitigating overland-flow incidence that would otherwise heighten flood risk or threaten water quality in rivers.