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Comparison of soil carbon changes across England and Wales estimated in the Countryside Survey and the National Soil Inventory - SP1101

The extent of feedback between climate change and the terrestrial carbon cycle is one of the main uncertainties in predictions of future climate change. Soil carbon dynamics are a key element of this because soils contain two or three times the amount of carbon as in vegetation or the atmosphere.

In 2005 Cranfield published the results of the National Soil Inventory of England and Wales for changes in soil carbon during the 1980s and 90s. This showed gains in carbon in some soils, but large losses in others and overall a net loss of about 4 million tonnes per year during the survey. Because the losses occurred across all types of land use, a link to climate change was suggested. Subsequent studies have shown climate change probably was in part responsible, but the dominant cause was changes in land use and management, such as the conversion of grassland to crops after the war, and land drainage schemes. Whatever the reasons, such a large loss of carbon from soils has serious implications for the global carbon cycle, for the possibility of sequestering carbon in soils, and for the ability of soils to perform other environmental and agricultural functions.

More recently results from the Countryside Survey have been reported by CEH, and these fail to detect the changes in soil carbon observed in the NSI. The reaons for the differences are not yet clear. Given that the topsoils of England and Wales contain about 2 thousand million tonnes of carbon, detecting a change of even 4 million tonnes is challenging, and results are likely to be sensitive to the details of survey methods. In view of the significance of the earlier NSI findings, it is important to understand what is behind the differences, and which survey gives the truer picture of events.

This project will provide an independent evaluation of the findings of the two surveys by a statistical expert from a leading Swiss university, ETH Zurich, together with staff from Cranfield and CEH. Given that our datasets on soil carbon in England and Wales are among the most comprehensive in the world, the results will be of great interest nationally and internationally. In addition the results will inform the debate around soil protection for other environmental and agricultural functions.
The overall aim is to investigate why there appears to be a difference between the Countryside Survey (CS) estimate and National Soil Inventory (NSI) estimate of change in the amount of organic carbon in the soils of England and Wales between the late 1970s and late 1990s. Our specific objectives are to answer the following six questions:
1. What is the best, unbiased estimate of change in topsoil carbon by each survey for England and Wales from 1978 to 1998 and with what error/precision?

2. What is the best, unbiased estimate of change in topsoil carbon from each survey stratified by land categories (arable and rotational grass; permanent grass; woodlands/forest; everything else) in England and Wales during 1978–1998 and with what error/precision?

3. What is the best, unbiased estimate of change in topsoil carbon estimated by each survey stratified by soil carbon quantities (0–30, 30–100, 100–300, > 300 g C kg-1, averaged over the 1978 to 1998 period) in England and Wales during 1978–1998 and with what error/precision?

4. What are the answers to Questions 1–3 if the CS results for 2007 are included in the analysis?

5. In the cases (Q1 to Q3) where there are differences between the estimates of change in soil carbon between the two surveys, what is the most likely cause of these differences?

6. Are new measurements needed to help substantiate the conclusions from Questions 1–4?
Project Documents
• EVID4 - Final project report : SP1101 final report   (1771k)
Time-Scale and Cost
From: 2010

To: 2010

Cost: £28,009
Contractor / Funded Organisations
University - Cranfield
Environmental Protection