Yield and Nutritive Quality of Five Sweet Potato Varieties in Response to Nitrogen Levels

Abstract

Sweet potato (Ipomoea batatas (L) Lam) that able to thrive in the tropical harsh condition is one of the vital commodities to small scale farmers. With more than 6,500 wild, traditional and improved varieties globally and the importance of nitrogen (N) fertilization in producing high yield of quality tuber in the tropical region, further research on selected sweet potato varieties and optimum N fertilization was conducted in Field 2 of University Putra Malaysia (UPM) that specifically determining tuber yield and its nutritive quality (carbohydrate, total sugar, and β-carotene) and its selected plant parameters. Five varieties (labeled as A, B, C, D, and E for accessions E10073, E10236, E10136, E10173, and E10051, respectively) at four N application rates (0, 17, 34, and 68 kg ha -1 ) were used in the 2-factorial experiment with a split plot design. With generally of no N*varieties interaction effect on all parameters, the N rate for optimum yield determined by regression method was 45 kg N ha -1 . At this N rate, the resulted high yielder varieties were E and D with estimated yields of 15.1 and 14.5 t ha -1 respectively. The medium yielders were A (13.1 t ha -1 ) and C (12.7 t ha -1 ), while the low yielder was B (11.6 t ha -1 ). The LAI and photosynthetic rate for obtaining higher yield at the N rate were > 1.6 units and > 37 u moles m -2 s -1 respectively. Much higher leaves relative to stem did not cause the Peru originated variety (C) had higher yield than those of the high yielder Malaysian varieties. The high yielder E (E 10051) had carbohydrate, total sugar and β-carotene of 22.4%, 8.3%, 9248 ug g -1 , respectively, while the respective values for the medium yielder B (E 10236 ) were 24.1%, 8.0% and 7448 ug g -1 . Other varieties had minimal β-carotene of < 16 ug g -1