2018 ASHS Annual Conference

Agricultural land management influences the physical, chemical, and biological characteristics of soil, including the structure of the community of soil microorganisms. In turn, the community of soil microorganisms directly influences processes such as nutrient cycling and water infiltration and retention, which shape the long-term fertility and productivity of the soil. The purpose of this study was to examine the effects of cover cropping on the soil biological and chemical features that contribute to soil fertility. The study looked at two summer cover crops – cowpea (Vigna unguiculata) and sorghum-sundangrass (Sorghum bicolor) in comparison with no-cover control – and their effects on soil respiration, soil organic matter and nitrogen availability, and fall lettuce production under black plastic mulch. Using soil samples taken from the in-field experiment, a parallel laboratory aerobic incubation study examined the effects of the cover crop on the transformation of nitrogen over five weeks. Both cover crops increased soil organic matter, total organic carbon, potassium, and magnesium by over 20%, 21%, 27%, and 35%, respectively, compared to the no-cover crop control. There were no differences in C/N ratio. Cowpea increased extractable soil nitrate by 97% and soil respiration rate by three fold compared to the no-cover control. In contrast, sorghum-sudangrass decreased extractable soil nitrate concentration to 21% of the control no-cover, but the increase in respiration was not different from the control. Lettuce growth and production as measured by both fresh weight and leaf area were reduced after sorghum-sudangrass, but were not different between cowpea and the control. In conclusion, the study found that sorghum-sudangrass and cowpeas both increased soil organic matter, but only cowpea increased extractable inorganic N, and that sorghum-sudangrass was detrimental for fall lettuce production under plastic mulch in the Eastern Shore of Virginia.