There are few reliable data sets to inspire confidence in policymakers that soil organic carbon (SOC) can be measured on farms. We worked with farmers in the Tamar Valley region of southwest England to select sampling sites under similar conditions (soil type, aspect and slope) and management types. Topsoils (2–15 cm) were sampled in autumn 2015, and percentage soil organic matter (%SOM) was determined by loss on ignition and used to calculate %SOC. We also used the stability of macroaggregates in cold water (WSA) (‘soil slaking’) as a measure of ‘soil health’ and investigated its relationship with SOC in the clay-rich soils. %SOM was significantly different between management types in the order woodland (11.1%) = permanent pasture (9.5%) > ley-arable rotation (7.7%) = arable (7.3%). This related directly to SOC stocks that were larger in fields under permanent pasture and woodland compared with those under arable or ley-arable rotation whether corrected for clay content (F = 8.500, p <.0001) or not (F = 8.516, p <.0001). WSA scores were strongly correlated with SOC content whether corrected for clay content (SOCadj R2 =.571, p <.0001) or not (SOCunadj R2 = 0.490, p =.002). Time since tillage controlled SOC stocks and WSA scores, accounting for 75.5% and 51.3% of the total variation, respectively. We conclude that (1) SOC can be reliably measured in farmed soils using accepted protocols and related to land management and (2) WSA scores can be rapidly measured in clay soils and related to SOC stocks and soil management.
Bibliographical noteFunding Information:
Special thanks are given to the farmers of the Tamar Valley Organic Group (TVOG) who precipitated in the development of the project and participated as case study farms. We thank the Westcountry Rivers Trust for providing funding for Tim Bearder who provided technical support for soil sampling and laboratory analysis and for funding laboratory analysis at North Wyke. We also thank Tim Harrod and David Hogan (formerly of the Soil Survey of England and Wales) for help with the development of the soil sampling technique and training. SC and MJ were supported in part by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2013‐68002‐20525, and SC's travel was funded by the Global Farm Platform project ( www.globalfarmplatform.org ). JD was funded by BBSRC‐funded institute strategic programme (2012–2017) at Rothamsted Research on Maximising Carbon Retention in Soils (BBS/E/C/00005214).
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- aggregate stability
- carbon sequestration
- management type
- soil health