Response of Sweetpotato [ Ipomoea batatas (L.) Lam.] to Five Rates Each of Nitrogen and Phosphorus under Guinea and Sudan Savannah Agroecological Zones of Ghana

Abstract

A multi-locational field experiment was conducted to evaluate the effects of increasing rates of nitrogen and phosphorus on sweetpotato growth and yield at Bawku and Nyankpala. Shoot yield increased by 31%, 63%, 94% and 125% in Bawku and 49%, 98%, 148% and 197% in Nyankpala, when nitrogen was applied at 30, 60, 90 and 120 kg∙ha − 1 , respectively. When nitrogen was applied at 30, 60, 90 and 120 kg∙ha − 1 , storage root yield increased by 30, 46, 48, and 37% in Bawku and by 13, 17, 14 and 3% in Nyankpala, respectively. The optimum nitrogen required to maximize storage root yield were 80 and 62.5 kg∙ha − 1 for Bawku and Nyankpala, respectively, in a split application at 2 and 6 weeks after planting. Storage root yield increased by 4%, 5%, 2% and −4% in Nyankpala and by 54%, 81%, 82%, 56% in Bawku, when 40, 80, 120 and 160 kg P were applied. Optimum phosphorus required to produce the highest storage root yield in this study are 67.5 and 101.3 t∙ha − 1 for Nyankpala and Bawku, respectively. The maximum net return to investment occurred when 60 kg N∙ha − 1 and 40 kg P∙ha − 1 were applied at Bawku and Nyankpala, respectively.