The Production of Organic Vegetables in the Southeastern United States in Reference to Sod-based Rotation and Strip versus Conventional Tillage

The Southeastern United States provides much of the nation’s spring, fall and winter vegetables, although it only represents only 0.3 % of the US organic production due to poor soils, high temperature/humidity/rainfall and high pest pressures. We have previously shown that two or more years of bahiagrass and strip tillage increase organic matter and reduce fertilizer and water inputs. The purpose of this study is to transition to organic vegetable production by: 1) variable years in bahiagrass pretreatment, and; 2) strip-till versus conventional tillage. We utilized yearly crop rotation of oats/ryegrass (winter cover), green beans (spring cash crop), soybeans (summer cover) and broccoli (fall cash crop). We quantified the increase in soil quality and chemistry with consecutive years in bahiagrass and the depletion of soil quality indices with the vegetable crop rotations. Available soil N and P decreased with increased years in bahiagrass, especially in Year 3. Potential carbon mineralization was not affected by treatments, possibly due to vegetation inputs from cover crops and weed biomass. Yields of green beans and broccoli in our organic production system were usually comparable to that published for conventional production.  In the initial year of the study, yields were consistently higher in conventional compared to the strip tillage treatments. However, in subsequent years, tillage effects were less apparent and yields were well correlated with years in bahiagrass pretreatment. In a companion study, plots that had initially been in bahiagrass for over twenty years maintained high yields in vegetables until the third year of continued vegetable production suggesting that benefits in soil quality from bahiagrass may begin to diminish in the third year of vegetable production.  Increasing years in bahiagrass often reduced populations of Meloidgyne root-knot and Rotylenchus reniform nematodes. Weed communities were altered by bahiagrass pretreatment; rapid growth of grass and sedge species was more problematic in strip-till plots. Soil nutrient cycling enzymes and the soil microbial community were also studied.