Nutrient Composition of Selected Sweet Potato [Ipomea batatas (L) Lam] Varieties as Influenced by Different Levels of Nitrogen Fertilizer Application

Abstract

Total ß-carotene content of four varieties of Sweet potatoes [Ipomoea batatas (L) Lam] as influenced by different levels of nitrogen fertilizer were determined by High Performance Liquid Chromatography (HPLC) The proximate composition and mineral contents were also determined. The nitrogen fertilizer treatments were combinations of four levels of 0kgN/ha(control), 40 kgN/ha, 80 kg/Nha, 120 kgN/ha on the four varieties of Sweet potato; white-fleshed TIS87/0087 and TIS8164, orange-fleshed Ex-Igbariam and CIP Tanzania. Nitrogen fertilizer significantly (p<0.05) increased the total ß-carotene and crude protein with increase in nitrogen fertilizer application up to 120 kgN/ha. Generally there was a trend in the total ß-carotene increase from 0-80 kgN/ha for all the varieties except CIP Tanzania which showed no such trend. On the average, TIS87/0087 and Ex-Igbariam varieties gave the highest total ß-carotene content at 40-80 kgN/ha when compared with the control. The highest yield for the crude fiber was observed at the control (0 kgN/ha) for all the varieties except TIS8164 which highest value was observed at 40 kgN/ha. Application of nitrogen above 80 kgN/ha did not increase the yield of most nutrient (namely, ß-carotene and protein). Generally, application of nitrogen fertilizer increased the mineral contents of most Sweet potato varieties significantly (p<0.05) from 0-120 kgN/ha with the exception of phosphorus which showed significant decrease. The overall results indicate increased bioavailability of ß-carotene (Provitamin A) and crude protein for good nutrition and health particularly at 40-80 kgN/ha.