Wind erosion reduces soil organic carbon sequestration falsely indicating ineffective management practices

Improved management of agricultural land has the potential to reduce greenhouse gas emissions and to reduce atmospheric CO2 via soil carbon sequestration. However, SOC stocks are reduced by soil erosion which is commonly omitted from calculations of crop production, C cycling, C sequestration and C accounting. We used fields from the wind eroded dryland cropping region of Western Australia to demonstrate the global implications for C sequestration and C accounting of omitting soil erosion. For the fields we previously estimated mean net (1950s-1990) soil erosion of 1.2 +/- 1.0 t ha(-1) y(-1). The mean net (1990-2013) soil erosion increased by nearly four times to 4.4 +/- 2.1 t ha(-1) y(-1). Conservation agriculture has evidently not reduced wind erosion in this region. The mean net (1990-2013) SOC erosion was up to 0.2 t C ha(-1) y(-1) across all sampled fields and similar to measured sequestration rates in the region (up to 0.5 t C ha(-1) y(-1); 10 years) for many management practices recommended for building SOC stocks. The minimum detectable change (MDC; 10 years) of SOC without erosion was up to 0.2 t C ha(-1) y(-1) whilst the MDC of SOC with erosion was up to 0.4 t C ha(-1) y(-1). These results illustrate the generally applicable outcome: (i) if SOC erosion is equal to (or greater than) the increase in SOC due to management practices, the change will not be detectable (or a loss will be evident); (ii) without including soil erosion in SOC sequestration calculations, the monitoring of SOC stocks will lead to, at best the inability to detect change and, at worst the false impression that management practices have failed to store SOC. Furthermore, continued omission of soil erosion in crop production, C accounting and C sequestration will most likely undermine confidence in policy designed to encourage adoption of C farming and the attendant benefits for soil stewardship and food security. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.