Cover crops, crop rotation, and gypsum, as conservation practices, impact Mehlich-3 extractable plant nutrients and trace metals

Conservation practices are encouraged to improve soil health and sustain agronomic crop production. Mehlich-3 is often used as a multi-nutrient extractant to determine soil fertility status. A study investigated the impacts of the conservation practices of gypsum, cover crops, and crop rotation on 28 Mehlich-3 extractable elements, of which 11 were considered plant nutrients, from soil at three midwestern US locations. Soil was collected from 0 to 15 and 15–30 cm depths 5 years after implementing the conservation practices. Treatments consisted of (1) with and without cereal rye (Secale cereale L.) winter cover, (2) continuous soybean [Glycine max (L.) Merr.] vs. soybean-corn (Zea mays L.) rotation, and (3) annual gypsum application (0, 1.1, and 2.2 Mg ha−1). Differences were observed by site, depth, and conservation practice depending on the element evaluated. Minimal interactive effects were observed among treatments. The most consistent effect was observed for crop rotation across sites. Gypsum only affected the site with the greatest clay content, where more Ca and S were retained, and Mg and Mn displaced. Cover crop only affected elements at this high clay site, where different elements were positively or negatively affected. Results suggest that not one practice fits all, and optimum conservation practices must be tailored for the site.