Soil quality assessment of tillage impacts in Illinois

Successful soil quality assessment strategies are needed to improve our ability to manage soils sustainably. Our objective was to use a multivariate data set to determine whether recent adoption of no-tillage (NT) practices had altered soil quality in Illinois. In 1995 and 1996, we sampled thirty-six farm fields under conventional tillage (CT) or NT practices and relatively nondisturbed (ND) areas. Soils were Mollisols or Alfisols. Tillage or region affected 20 of the 23 parameters characterized. Soil chemical parameters were less variable than biological or physical measures. Principal component analysis (PCA) was used to assess soil quality overall. Principal component 1 (PC1) scores, which explained 39% of the total variance of the overall data set, were affected by tillage (ND > NT > CT) and increased with particulate and organic C and total N, biological activity, mineralizable N, and wet aggregate stability, and decreased with bulk density and dry aggregate mean weight diameter. The only significant factor contributing to PC2 was penetration resistance: PC2 explained 13% of the variance and decreased as follows: NT greater than or equal to ND > CT. Multivariate assessment of soil quality indicated use of NT practices improved the biological and physical condition of the soil (0-15 cm) despite increased consolidation. It also showed that those biological and physical aspects of soils influenced by organic matter were the properties most altered by agronomic practices. Particulate organic matter (POM) was identified as a promising soil quality measure. A next step is to determine the biological and environmental relevance of a refined set of soil quality measures in conjunction with soil processes of regional concern.