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Effects of Application of Farmyard Manure and Inorganic Phosphorus on Tuberous Root Yield and Yield Related Traits of Sweet Potato [Ipomoea batatas (L.) Lam] at Assosa, Western Ethiopia

Merga Boru, Kebede Tsadik W and Tamado Tana

Sweet potato is one the most important root crops produced in western Ethiopia. However, the yield is far below its genetic potential. Lack of recommendation on appropriate rates of fertilizers is one of the problems limiting yield. A study was conducted to determine the effect of application of farm yard manure and inorganic phosphorus on tuberous root yield and yield related traits of sweet potato at Assosa from July to December 2016. The treatment consisted of four levels of farm yard manure (0, 5, 10 and 15 t ha^-1) and four levels of P (0, 23, 46 and 69 kg P₂O₅ ha^-1). The experiment was laid out as a Randomized Complete Block Design in a factorial arrangement and replicated three times. Analysis of the results showed that the main effect of farm yard manure significantly (P<0.05) affected most of the traits studied. The interaction effects of the two also affected most of the growth as well as yield parameters considered. Application of combinations of 15 t ha^-1 farm yard manure and the highest rate of P₂O₅ resulted in 39.3% faster in bud sprouting. The main effects of farm yard manure affects tuber diameter (20.63 cm), unmarketable tuber yield (1.3 t ha^-1), weight of tuber/plant (143 g), weight of marketable tuber/plant (140 g), dry matter content (27.04), specific gravity (1.12), length of tubers(15.68 cm). The highest vine length (139.67 cm), total tuber number per plant (8.0), total tuber yield (24.6 t ha^-1), marketable tuber yield (23.65 t ha^-1) was recorded at 15 t ha^-1 farm yard manure+69 kg P₂O₅ ha^-1 whereas the lowest vine length (45.3 cm), tuber number per plant (2.0), total tuber yield (5.52 t ha^-1), marketable tuber yield (3.61 t ha^-1) was recoreded at un amended control. The main effects of farm yard manure delayed maturity of the crop where the 15 t ha^-1 farm yard manure showed delay by about 18 days. Moreover, tuber diameter, length of roots, and weight of tuberous roots exhibited improvement with increment in the amount of applied farm yard manure while none of these parameters were affected by the application of P₂O₅ fertilizer. From this study, the highest net benefit for tuber yield of sweet potato was recorded from the application of manure and P₂O₅ at the combination level of 15 t ha^-1 farm yard manure+69 kg P₂O₅ ha^-1 which was 57873 Birr ha^-1. Therefore, the doses of 15 t farm yard manure ha^-1 and 69 kg P₂O₅ ha^-1 could be integrated and applied for sweet potato crops in the study area. However, it warrants further testing to give conclusive recommendation.