Assessing carbon and nitrogen stocks of no-till systems in Oklahoma

Intensive tillage during the last century has greatly reduced organic carbon contents of Oklahoma cropland. Increased public interest in carbon sequestration and the potential for carbon storage in no-till soils to offset CO2 emissions has brought about the need for accurate estimates of carbon sequestration in Oklahoma. Eight locations across Oklahoma were soil sampled to determine the impact of no-till farming practices on soil carbon storage. Locations consisted of side by side no-till and tilled fields sampled at four sites in each field. Samples were divided into 0-10, 10-20, 20-40, 40-70, and 70-110 cm depths and analyzed for organic carbon (OC) and total nitrogen (TN). Averaged across locations and depth, the concentration of organic carbon (OC) was 0.7 g kg(-1) greater in no-till compared to tilled fields. As expected, differences between no-till and conventional till were dependent on length of time in no-till and annual precipitation. The greater the time in no-till management and the higher the annual precipitation, the greater the carbon stocks compared to conventional till fields. Despite the high degree of variation among sample locations, the mass of OC was significantly (p = 0.07), greater in the NT compared to that found in the CT fields, with the average difference being 8.6 Mg ha(-1). The highest OC accumulation was observed in Miami with an average of 3.5 Mg ha(-1) year(-1), while at Lahoma 2 and Goodwell no accumulation of OC was observed. Eliminating tillage operations can increase OC accumulation with the presence of adequate rainfall and an extended period of time. (C) 2011 Elsevier B.V. All rights reserved.