Conservation Effects on Soil Quality Indicators in the Missouri Salt River Basin.

The Salt River Basin in the Central Claypan Region of Missouri was selected as a benchmark watershed to assess long-term effects of conservation practices on soil quality as part of the Conservation Effects Assessment Project and the Long-Term Agroecosystem Research Network. Fifteen management systems, including annual crop rotations with varying nutrient management, cover crop, and tillage (i.e., no-till, mulch-till, and intensive tillage) practices as well as perennial systems with legumes and/or cool- and warm-season grasses managed within Conservation Reserve Program, prairie restoration, or working grassland (i.e., pasture, forage, and hay production) systems were evaluated. Soil samples were collected in 2008 from surface (0-5 cm) and subsurface (5-15 cm) layers and analyzed for 11 biological, physical, chemical, and nutrient soil quality indicators (SQI). An overall soil quality index was quantified using the Soil Management Assessment Framework (SMAF). Soil quality index (SQI) values varied with soil functional group and depth. Management systems with permanent, vegetative cover and living roots in the surface layer had the highest SMAF scores, ranging from 88 to 98 of the soil’s inherent potential. Annual cropping systems scored from 76 to 87% with: no-till plus cover crops (87.4%) = mulch-till with cover crops (87.4%) > no-till without cover crops (84.5 – 84.9%) > mulch-till or intensive tillage without cover crops (76.0 – 83.9%). Biological and physical indicators were the most influential factors affecting all SQI values. Biological soil quality under the diversified no-till system with cover crops was 11% greater than under no-till alone, and 20% greater than mulch-till without cover crops. In the subsurface layer, no-till cropping systems scored lower (60 – 64%) than mulch-till systems (65 – 72%). Overall, our results demonstrate the influence of vegetative cover and living roots on surface soil quality, and emphasize the importance of diversified cropping systems that reduce soil disturbance and maximize soil cover.