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How does change in land-use between set-aside and cropping impact soil biodiversity and function? - IF0138

Set-aside is an EU scheme introduced in 1992 in which farmers are paid a subsidy to remove land from arable production. The scheme was introduced as part of EU agricultural policy reforms to decrease grain surpluses across the EU. Land can be managed as rotational set-aside, in which different areas are set-aside each year, or permanent set-aside, in which there is a commitment to maintain land in set-aside for at least 5 years. Large amounts of land have been converted to set-aside, which in the mid 1990s amounted to 500 000 ha in England alone, which was equivalent to 11 % of all eligible arable land.

Set-aside has the benefits of potentially reducing soil erosion and halting or reversing declines in farmland biodiversity associated with conventional intensive agricultural production. Many studies have been conducted to investigate the impact of set-aside on above-ground biodiversity. However, limited information is available about the impact of change from arable cropping to set-aside on soil organic matter and soil microbial biodiversity. Soil organic matter (SOM) is crucial for sustaining crop production in agricultural soils and represents a large and important pool of carbon. Changes to the size and composition of SOM will affect C sequestration and the production of greenhouse gases. Soil microbes provide key ecosystem services in soil and are the agents responsible for driving biogeochemical cycling of carbon, nitrogen and phosphorus, contributing to SOM stabilisation, nutrient mineralisation and denitrification. The available evidence suggests that there may be rapid increases in both soil organic matter and soil biodiversity following change in land use to set-aside, although the extent to which this occurs varies between sites, possibly reflecting differences in soil type, climate, plant cover and management.

Increased demand for grain, resulting from the need to increase production of biofuel, combined with increased demand on the world market, is likely to result in a substantial return to cropping of former set-aside land both in the short and the longer term. However, no information is available about how soil organic mater and soil microbial biodiversity in set-aside will respond to conversion back to cropping, and how any loses of both soil organic matter and microbial diversity which may occur will impact on soil carbon storage and soil functioning, particularly at the landscape scale.

The aim of the current project is to investigate how reversion of land from set-aside to arable cropping impacts soil organic matter and soil microbial diversity. The project will use two approaches to determine the extent of the impact of land use change and the timescale over which changes are likely to occur. The first approach will be to set up a field experiment to convert existing set-aside land to cereal cropping, and vice-versa at a single site. The second approach will be to compare adjacent set-aside and cropped areas at a range of farms across England. Amounts of total and labile (light fraction) soil organic matter (SOM) will be determined. The amount and structure of microbial biomass will be determined using biochemical methods. To determine the effects of the land use change on soil microbial communities and soil functioning the quantity and diversity of bacterial, archaeal and fungal communities will be determined. We will also investigate populations of Arbuscular mycorrhizal fungi (AMF) as they are an important group involved in soil biogeochemical cycling and carbon flow and because methods for assessing their population sizes and diversity are relatively well established.

Data will be used to establish the timescales over which improvements to SOM and soil biodiversity take place following change to set-aside, and the rate of loss of any enhanced level of SOM or biodiversity in set-aside, following reversion to cropping. This will help determine whether management practices can be developed to reduce loss of SOM following reversion to set-aside, and will allow predictions of losses of CO2 to the atmosphere to be made following loss of set-aside. The data could also allow the effect of loss of set-aside other ecosystem services mediated by soil to be determined, particularly nutrient loss, and hence water quality. The extent to which soil properties and geographical location determines differences in SOM and microbial communities between set-aside and arable cropping will be elucidated. Using the experimental data, projections will be made for likely losses to SOM and changes to the amount and composition of total microbial populations and arbuscular fungi following conversion of set-aside to cropping, on different soil types and regions in England and Wales. Furthermore, the degree to which microbes show biogeograpical distribution will determined, allowing judgements to be made on the utility of soil microbes as generic bioindicators of soil quality, and the extent to which geography should be taken into account when interpreting data on microbial communities.
1. Characterise changes to organic matter and microbial community structure and diversity following change in land use between set-aside and cropping

a. Examine the dynamics of total and labile soil organic matter following conversion from non-rotational set-aside to arable cropping, and vice-versa, over a 3 year period
b. Determine changes to the size and structure of soil microbial biomass following conversion from non-rotational set-aside to arable cropping, and vice-versa, over a 3 year period
c. Investigate the impact of conversion between set-aside and arable cropping on the size and structure of the arbuscular mycorrhizal fungus community

2. Compare organic matter and microbial community structure and diversity at paired field sites under set-aside and cropping

a. Determine the amount of total and labile soil organic matter in set-aside and arable cropped soil at 15 sites
b. Characterise the size and structure of the microbial biomass in set-aside and arable cropped soil at 15 paired sites
c. Examine the extent to which the size and diversity of the arbuscular mycorrhizal fungus community differs between set-aside and cropping, at 15 paired sites, and the extent to which diversity is biogeographically distributed
d. Determine the extent to which inherent soil characteristics and time since change in land use affect the relative differences in organic matter and microbial characteristics between set-aside and arable cropping

Time-Scale and Cost
From: 2008

To: 2011

Cost: £270,000
Contractor / Funded Organisations
Warwick - HRI
Allocated - WHRI              
Integrated Farming Systems              
Sustainable Farming and Food Science              
Sustainable Farming Systems