Impact of Management on Plant-soil-livestock Interactions in Upland Permanent Pasture

Abstract

Improved permanent pastures in the uplands are currently degraded yet have the potential to be important ecosystem service providers. Subsequent to CAP reforms in 2003, subsidies are now decoupled from production, freeing up farmers to reduce inputs and livestock numbers. This presents an opportunity to tailor pastoral activity to facilitate ecosystem service provision, yet the consensus as to which services to focus on is divided. Ecosystems develop over time and so any management undertaken needs to consider conditions decades from the point of initiation and plan for the long term. Using a set of long-term improved permanent pasture grassland plots in the uplands of mid-Wales with 25 years of development behind them, this study explored the long-term effects of reduced management on key ecosystem service indicators. Biomass production and quality, root production, estimated greenhouse gas emissions from biomass, soil carbon stocks and decomposition parameters were analysed. The control treatments were grazed and had inorganic NPK at a rate of 60 10 10 kg/ha-1 anually and liming to maintain a pH of 6.0. Other treatments were grazed (Gr +/-), hay-cut (Hay +/-) and hay-cut with aftermath grazing (HayGr +/-), all with and without lime. Results show that biomass quality and quantity were significantly reduced under all treatments relative to control which maintained historic management, and that withdrawal of NPK and lime have reduced the potential grazing days (-249 and -34 GD yr-1 respectively) and nutritional value of the forage (DOMD -27 and -35 g/kg respectively), impacting on stocking potential. In vitro GHG production was also reduced, particularly in species rich hay-cut plots (CH4 - 40.6 ml/g). Soil carbon however was not affected by management and maintained an average of 42.3 T ha-1 across treatments. Rates of stabilisation S for SOM was reduced under lime cessation (-0.06) and hay-cutting (-0.04) however, indicating that labile C has a short residence time. Provisioning and supporting services were considerably inhibited by NPK cessation. Lime removal reduced provisioning and regulating service potential. Converting to hay-cutting reduced production but enhanced floristic diversity. The study concluded that provisioning and regulating ecosystem services are negatively affected by extensive management options but there is strong potential to manage for floristic diversity under a hay-cutting and late-season grazing based pastoral system. These findings support a rotational grazing system in which livestock is weaned in the lowlands over the spring & summer before being grazed in the uplands from early August until the onset of autumn, coupled with silage production from floristically diverse grasslands would have the greatest benefit to ecosystem services.

Date of Award	2019
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Mariecia Fraser (Supervisor) & Niall McNamara (Supervisor)