Long-Term Cropping System Effects On Soil Properties and a Soil Quality Index.

Intensive row-crop production can lead to soil degradation over time if insufficient biomass return, intensive tillage, or excessive erosion lead to depletion of soil organic C. Soil quality may be improved by incorporating forage crops or grazing into the rotation, adding manure or other organic sources, and shifting to minimum tillage. We evaluated a range of physical, chemical, and microbial soil properties from six cropping systems in the WI Integrated Cropping Systems Trial after 18 years of continuous treatments. We sampled soils (0-5-cm and 5-20-cm depths) in Nov after the corn phase of five individual crop rotations (continuous corn (C), C-soybean (SB), organic grain (C-SB-wheat/red clover), alfalfa-corn (Alf-Alf-Alf-C), and organic dairy (C-oats/pea/Alf-Alf); at the end of the alfalfa phase of the alfalfa-corn and organic dairy cropping systems; and in the rotationally grazed grass-legume pasture. Extractable P and K, pH, total organic C (TOC), total N (TN), active soil C, potentially mineralizable N (PMN), water-stable aggregates (WSA), bulk density (BD), penetrometer resistance, and microbial biomass/diversity were measured, and the SMAF soil quality index (SQI) was determined. Cropping system treatments significantly affected all soil properties in the 0-5-cm soil depth and most in the 5-20-cm depth. The pasture treatment (0-5 cm) had the highest microbial biomass, TOC, TN, active C, PMN, and WSA. Active C and PMN were related to total C and N but were more sensitive to treatment. Forage phases had higher BD (0-5 cm) and penetrometer resistance than corn. Soil test P reflected net balance to the systems. Overall soil quality, as measured by the SMAF (Soil Management Assessment Framework) soil quality index, was higher in the surface layer, and there was a trend (0-20 cm) to higher SQI in most forage based systems.