Yield and nitrogen use efficiency of sweet potato in response to cover crop and nitrogen management

Selected cover crops can provide N to sweet potato (Ipomoea batatas [L.] Lam) crops cultivated in succession and reduce the need for mineral N application. This study was conducted to determine the growth, leaf N concentration, N uptake, N removal, storage root yield, and N-use efficiency of sweet potato crop in response to different cover crop sources and mineral N fertilizer rates. A field experiment was performed over 2 agricultural yr using a randomized complete block design with split-plots and four replications. Whole plots consisted of four cover crops: One control (spontaneous weeds), two legumes (Crotalaria spectabilis and Mucuna aterrima), and one cereal (Pennisetum glaucum). Subplots consisted of four N rates (0, 50, 100, and 200 kg ha–1) applied to the sweet potato. When no N was applied, M. aterrima supplied more N to sweet potato grown in succession but had the same effect as C. spectabilis on root yield. P. glaucum and spontaneous weeds had the same effect on the N supply and performance of sweet potato. The N rates for the optimum root yield of sweet potato were 49.6 and 76.6 kg N ha–1 when grown after legume and non-legume species. In tropical conditions, the use of legumes as cover crops reduced the need for mineral N fertilizers by up to 35.2% for sweet potato. The cultivation history of a field should be an important consideration when determining the N fertilization for sweet potato because a high N supply favored the growth of vegetative plant parts.