Intensive agriculture to semi-natural grassland: evaluating changes in ecosystem service provision to help determine costs and benefits of agri-environment schemes
Horrocks, Claire Alice
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Intensive agriculture has led to an increase in production; however this has often coincided with a decline in the provision of other Ecosystem Services (ES). ES affected include those regulated by soil chemical, physical and biological properties such as biodiversity provision and the regulation of nutrient cycling, water quality and rates of greenhouse gas emissions. A growing awareness of the value of nonproduction ES to human health and wellbeing has encouraged the funding of agrienvironment schemes in the UK, through which farmers receive funding to alter management practices to increase the provision of certain ES. One particular management change encouraged through agricultural payments is the creation of species rich grassland (SRG) on former intensively managed (IM) arable or grassland sites. Under these schemes farmers are required to carry out an extensification of management practices by reducing or ceasing fertiliser application, grazing and cultivation, or removing the existing crop or sward and sowing a specified seed mix of desired grassland species. Despite the commitment of substantial sums of money and land to extensification schemes, there has been little research into the extent to which they enhance provision of multiple ES and the potential for the legacy of intensive agriculture to limit ES provision and greatly reduce the value of extensification. This study aimed to: 1) compare soil properties between sites remaining under intensive management and those that had undergone extensification; 2) relate soil properties to; fluxes of the greenhouse gas nitrous oxide (N2O), plant diversity, soil microbial diversity and concentrations of nutrients in leachate from intensively and extensively managed sites in order to determine potential benefits of extensification. Paired field plots were established on working farms in south east Scotland and at Rothamsted Research North Wyke in south west England. Each of the four plot pairs in Scotland consisted of a newly created SRG on former arable land and an adjacent IM plot. The SRG plots ranged in age from 3 to nine years old in 2010. Soil samples were collected from the Scottish sites twice yearly in 2010 and 2011, alongside regular measurements of N2O fluxes from soil and assessment of plant diversity. At North Wyke four replicated SRG plots, forming part of an existing experiment on former intensive grassland, were each paired with an IM plot. Soil samples were analysed for their chemical and physical properties and for the concentration of certain phospholipid derived fatty acids (PLFA) biomarkers to compare the composition and size of the soil microbial community. Soil N2O fluxes and the nitrogen (N) and phosphorus (P) concentrations of soil water samples measured in 2010 and 2011. Results from more intensive N2O flux measurements, conducted in 2012, were compared to model output from the UK-DNDC model to assess its potential for predicting changes in N2O emissions following extensification. No significant difference was found in any soil chemical or physical properties between paired IM and SRG plots in Scotland, although soil bulk density tended to be lower in the older SRG plots relative to the paired IM plots. Nitrous oxide emissions were low from all plots with only an occasional emissions peak being recorded and overall there was no significant effect of management intensity on soil N2O fluxes. The UK-DNDC model outputs were generally of a similar order of magnitude but poorly correlated with measured N2O fluxes and soil water and available N content. Botanical diversity was enhanced in the SRGs compared to the IM plots, though plant species were mostly of low conservation value and indicative of a high nutrient environment and the diversity of the SRG plots was low, compared to long-established semi-natural grassland elsewhere in Europe. Total soil PLFA concentration was significantly higher in the IM plots but the fungal concentration and the ratio of Gram positive:Gram negative bacteria were no greater in the SRG, suggesting it had begun to resemble long-term unimproved grassland. Despite limited success at obtaining soil water samples, at North Wyke concentrations of mineral N in soil water were lower from the SRG plots than the IM plots, although there were no consistent differences in total P or organic N concentrations, organic N contributed over 80% of the total N in soil water samples from the SRG plots. This study has shown that the legacy of intensive agriculture continues to affect soil properties for at least 10 years following extensification. The results suggest that the potential for newly created SRGs to provide enhanced ES’ could be limited and may not justify the reduction in productivity and the financial input associated with shortterm extensification schemes.