Multivariate assessment of soil quality indicators for crop rotation and tillage in Illinois

- Principal component analysis was used to identify soil quality indicators in Illinois.
- Soil C and N indicators were most effective at separating rotation and tillage.
- Other important parameters included soil pH and pH-affected nutrient contents.
- Only the two continuous-cropping sequences were able to be readily separated from one another.

The long-term implementation of crop rotation and tillage influences the soil environment through inputs and disturbance of the soil, which in turn, impact soil quality (SQ). A vital component of developing sustainable agronomic practices is to evaluate their effect on SQ. The objective of this study is to address the first step in this process by identifying soil parameters that are sensitive to changes in the soil and indicative of soil functions. Soil samples were collected from two Illinois sites with cropping systems and tillage treatments in place for more than 16 years. Crop rotation and tillage were evaluated with separate principal component analyses (PCA) of 20 soil parameters. Six principal components accounted for 74% of variability among rotations. The soil parameters loaded within these components highlighted the strong influence on carbon and nitrogen cycling indicated by greater soil organic carbon, total nitrogen, microbial biomass, and aggregate stability under crop rotations with high C:N residues and biomass production. Other strongly loaded parameters, such as soil pH and nutrient contents, are likely related to the use of nitrogenous fertilizers in grass species. Rotations with only a single contrasting crop were able to be differentiated readily while the multi-species crop rotations were only marginally able to be separated. The PCA for tillage explained 73% of variability with six principal components; of those, three were able to separate no-till from conventional tillage. As with rotation, the choice of tillage practice can have a large influence on the cycling of carbon and nitrogen, as decomposition of residues and soil organic matter are accelerated by tillage. No-till was also associated with stratification of pH and other nutrients. Soil parameters relating to carbon and nitrogen cycling have the greatest potential as SQ indicators while other measures relating to nitrogen fertilization, such as shifts in soil pH and nutrient contents, can also prove useful in comparing SQ under crop rotation and tillage in Illinois.