Crop Rotation Effects on Sweet Potato Yield and Quality

As the suite of fungicides, pesticides, and fumigants available to vegetable producers continues to shrink, growers may begin to reexamine crop rotations as an alternative method of disease, weed, and pest control. Although many studies have examined field crop rotations, relatively few have examined a vegetable crop as a part of that rotation. In 1985 a study was initiated to evaluate the effect of various crop rotations on sweet potato (Ipomoea batatas L.) yield and quality. Specific rotations were: (i) continuous sweet potato, (ii) sweet corn (Zea mays L. var. rugosa) and sweet potato, (ii) soybean [Glycine max (L.) Merr.] and sweet potato, (iv) 2 yr sweet corn and one yr sweet potato, (v) 2 yr bahiagrass (Paspalum notatum Flugge.) and 1 yr sweet potato, and, (vi) soybean, sweet corn and sweet potato. Two complete cycles (1988–1990 and 1991–1993) of the rotations were analyzed. The crop rotation producing the largest annual yield (4.70 tons/acre) and one of the largest cumulative (11.35 tons/acre) sweet potato yields was 2 yr of bahiagrass followed by sweet potato. Continuous sweet potatoes produced the lowest annual (2.12 tons/acre) and one of the highest total marketable cumulative yields (11.39 tons/acre) during the 6 yr. In general, a rotation containing a grass (bahiagrass, sweet corn) produced higher annual sweet potato yields than those without. ProblemSustainable methods of crop production have long included the use of rotations. Many rotations are field-crop based, and the use of vegetables in the rotation is not common. Sweet potatoes may fit well into field-crop rotations because they are usually managed like a field crop. The objective of this study was to examine annual and cumulative sweet potato yields as affected by rotation with sweet corn, soybean, and bahiagrass. BackgroundThere is ample long-term research which examines the effect of rotations on crop yield and quality, yet the majority of this work uses field crops such as corn, soybeans, and wheat. The effect of crop rotations on soil characteristics such as pH, organic matter, organic N and extractable P and K has been studied in many field crop rotations. Rotations have also been shown to alter populations of weeds, insects, and nematodes, and to affect disease severity. Study DescriptionThe experiment was initiated in 1985 in central Alabama on a Ruston fine sandy loam. The experiment consisted of 6 replications of 6 different rotations: (i) continuous sweet potatoes; (ii) 2 yr rotation of sweet potatoes and sweet corn; (iii) 3 yr rotation of 1 yr sweet potato and 2 yr sweet corn, (iv) 2 yr rotation of sweet potato and soybean, (v) 3 yr rotation of sweet potato, soybean, and sweet corn, and, (vi) 3 yr rotation of 1 yr sweet potato and 2 yr bahiagrass. Every cropping sequence (ex., sweet corn first year, sweet potato second, and sweet potato first, sweet corn second year) of each rotation was considered, so that each replication of the experiment contained 14 treatments. Both annual and cumulative sweet potato yields from 1988 to 1993 were analyzed. Applied QuestionsWhat rotation produced the largest annual sweet potato yields? The rotation consisting of 2 yr of bahiagrass and 1 yr of sweet potatoes produced a higher annual yield than any other rotation. This rotation had a sweet potato yield of 4.79 tons/acre,, just above the 5-yr state average of 4.5 tons/acre. Continuous sweet potatoes produced the lowest annual yield (2.12 tons/acre). What rotation produced the highest cumulative sweet potato yields? Over the 6 yr, the rotation of 2 yr of bahiagrass and 1 yr of sweet potatoes produced as high a cumulative yield as when sweet potatoes were grown continuously. The lowest cumulative yields occurred when soybeans were included in the rotation. The rotation of continuous sweet potatoes had more diseased or damaged sweet potatoes (cull) than any other rotation, when cumulative yield was considered. RecommendationsA rotation of sweet potatoes and bahiagrass is an effective alternative to continuous sweet potatoes, as it produces annual yields well in excess of continuous cropping. This study suggests that rotation with a grass crop will produce greater annual sweet potato yields and cumulative yields comparable to continuous sweet potato production, without the increased incidence of cull sweet potatoes.