Assessment of Near-Surface Soil Carbon Content Across Several U.S. Cropland Watersheds

Abstract

The Cropland Conservation Effects Assessment Project (CEAP) was initiated in the USA to provide a scientific basis for assessing effectiveness of conservation practices on water and soil quality. In 2006, sampling was initiated within a number of USDA-ARS experimental watersheds to measure and assess management impacts on near-surface (0–5 cm) soil quality indicators. Here, we focus on soil organic carbon (SOC) content because of its influence on key soil quality indicators. The sampling schemes for each of the 12 locations (<1,500 samples) in the states of Georgia, Iowa, Indiana, Maryland, Missouri, Mississippi, New Hampshire, Ohio, Oklahoma and Texas, were designed to address individual objectives. We used the Soil Management Assessment Framework (SMAF) to score the measured data so that climate and inherent soil properties would be taken into account. The SOC-SMAF scoring algorithms uses a more-is-better model reflecting SOC concentrations associated with high productivity and minimal environmental impact. Interactions include soil type, climate, and management practices such as tillage and crop rotation, which influence SOC content at each sampling site. Measured SOC contents ranged from 3.0 to 21.7 g kg−1 and SMAF-SOC scores ranged from 0.09 to 1.00, where 1.00 is an optimum level of SOC with regard to most soil functions. This assessment showed that SOC evaluations need to be soil- and site-specific because many factors, including environmental influences and inherent soil characteristics, influence SOC levels.