Effects of cover crops on soil quality: Part II. Soil exchangeable bases (potassium, magnesium, sodium, and calcium), cation exchange capacity, and soil micronutrients (zinc, manganese, iron, copper, and boron)

Maintaining and conserving essential soil nutrients using soil management practices, such as incorporating cover crops and no-tillage into crop rotation, has the potential to improve soil quality and fertility as well soil productivity. The effects of cover crops in a no-tillage seed maize (Zea mays L.) production system on soil exchangeable bases and soil micronutrients were investigated in Beaver Crossing (Seward County), Nebraska. The main objective of the research was to investigate the effects of growing cover crops under conservation tillage on soil exchangeable bases (potassium [K], magnesium [Mg], calcium [Ca], and sodium [Na]), cation exchange capacity (CEC), and soil micronutrients (zinc [Zn], copper [Cu], boron [B], iron [Fe], and manganese [Mn]). Extensive field research was conducted in four cover crop growing seasons (2012 to 2013, 2013 to 2014, 2014 to 2015, and 2015 to 2016) on three center pivot-irrigated seed maize or soybean (Glycine max L.) and cover crop rotation large-scale production fields. While extensive soil samples were taken to quantify and analyze the changes in soil exchangeable bases and soil micronutrients from the beginning of 2012 to the end of 2015, all large-scale production fields had cover crops in either seed maize or soybean rotation since 2002. Thus, it is anticipated that the changes in soil exchangeable bases, CEC, and micronutrients are a result of long-term (from early 2002 to late 2015) cover crop impacts on soil in all three research fields. The treatment effects exhibited variation not only between the treatments, but also between the soil layers for the same treatment. Cover crops in seed maize or soybean treatment (SCCC) had a significant effect on soil exchangeable K in the topsoil (0 to 5 cm soil layer). Cover crops did not affect exchangeable K concentration below the 5 cm soil layer. Exchangeable Ca concentrations were unaffected by any land cover treatment imposed in this research. Incorporating cover crops into a no-tillage seed maize or soybean cropping system (SCCC) might help in maintaining the exchangeable Mg concentration more effectively than no cover crop treatment (SC), especially in the 20 to 40 cm soil layer. Cover cropping has significant effects on CEC in the 5 to 40 cm soil depth. At the 5 to 20 cm soil depth, the SCCC treatment resulted in increased CEC by 8.4%, whereas bare soil, cover crop only without seed maize or soybean residue (CC), and SC treatments resulted in 10%, 4.1%, and 21% reduction in CEC, respectively. The SCCC treatment reduced the concentration of micronutrients in the topsoil (0 to 5 cm soil layer). Overall, cover crops (SCCC) have the potential in maintaining the optimum levels of Zn, B, Fe, and Mn in the topsoil (0 to 5 cm soil layer) as compared to the SC treatment. The results of this research suggest that cover cropping has the potential to alter several very important soil chemical properties (and significantly in some cases); however, the impacts primarily occur in the topsoil.