Soil Quality Responses to Gypsum and Cover Crops in No-Till Soybean–Corn Rotations Across the Midwest and Southeast U.S

Soil quality (SQ) refers to the soil’s capacity, as influenced by management practices, to sustain productivity, maintain environmental quality, and provide essential ecosystem services. The impacts (2012–2016) of gypsum application, cover cropping, and crop rotation on SQ were evaluated under rainfed no-till (NT) systems at sites in Shorter, Alabama; Farmland, Indiana; and Hoytville and Piketon, OH, USA. Experimental treatments were arranged in a randomized complete block design in a factorial combination of gypsum (0, 1.1, and 2.2 Mg ha−1), cover crop [cereal rye (Secale cereale) or no cover], and crop rotations as follows: soybean (Glycine max; SS), corn (Zea mays)–soybean (CS), and soybean–corn (SC). Composite soil samples were collected at 0–15 and 15–30 cm depths and analyzed for biological, chemical, and physical properties to compute a comprehensive SQ index (SQIComp). Principal component analysis identified a minimum dataset (MDS), including microbial biomass, organic carbon, and mean weight diameter, used to compute SQIMDS. Applying gypsum at 2.2 Mg ha−1 increased SQIComp by 3–7% and SQIMDS by 7–17% at most sites compared with the control. The CS rotation produced the highest SQ, exceeding SS by 5–10%. Cover crops had minimal overall effects on SQ, except in Indiana. When averaged across all sites, SQ differences between depths were 19% for SQIComp and 33% for SQIMDS. Significant linear relationships between SQIMDS and SQIComp indicate that SQIMDS accounted for most of the variability (R2 = 0.77–0.94) in SQIComp. Overall, gypsum application at 2.2 Mg ha−1 and the CS rotation improved surface SQ under NT systems, and SQIMDS is better suited for relative comparisons than for absolute quantification.