Evaluating the impacts of upland grazing management on soil carbon stocks
Dr Sheila Palmer and Prof Pippa Chapman
The British uplands are important areas for domestic grazing animals and producing fodder crops, typically as semi-improved and unimproved grassland. The soils in these areas are organo-mineral, with an organic surface horizon overlying mineral soils of variable depth. Hence these soils are also important stores of carbon. Before the intensification of sheep farming in the mid-20th century, these grasslands were managed by low-intensity grazing in spring and autumn, and cut for species-rich hay during summer. A return to this method of farming has been encouraged during the last 20 years via government farm payment schemes, primarily to improve biodiversity but also to preserve a cultural landscape. The impacts of these management changes on soil sustainability have not quantified, and indeed very little research has been conducted on upland grassland soils since the 1980s when intensification was encouraged via liming and fertilizing to improve grass biomass. The recent initiatives to reduce livestock pressure and increase in biodiversity now have the potential to fundamentally alter soil resources, and improve soil carbon stocks, in many ways:
- Increasing the return of organic matter to soil as leaf litter due to reduced biomass removal;
- Promoting the growth of deeper-rooting plant species such knapweed, which will deliver organic matter to deeper soil layers where it is more likely to be protected from decomposition by interaction with soil minerals;
- Reducing surface soil compaction by livestock trampling, thereby improving water infiltration and percolation, and facilitating organic matter transfer from the surface to deeper soil layers.
This project will evaluate the impacts on soil carbon contents and bulk density of three types of upland grazing management currently being practiced in the Yorkshire Dales: 1) conventional year-round grazing on semi-improved pasture; 2) hay meadow and reduced grazing on semi-improved pasture; 3) conservation winter-only grazing on unimproved pasture. The approach will involve field sampling, field soil depth measurements, laboratory analysis for soil organic matter, soil carbon, and dry bulk density, and subsequent calculation of soil carbon stocks and statistical analysis for management effects. There is scope for the student to design and develop (with our support) a sampling strategy that encompasses soil heterogeneity: a) at the farm scale (between-field); b) vertically by depth and/or genetic soil horizon; c) across two different soil types typical of the region (calcareous brown earth and acidic poorly-drained gleysol).