Responses of Two Sweet Potato Varieties to Four Green Manure Sources and Inorganic Fertilizer in a Humid Tropical Ultisol

Abstract

ABSTRACT Field experiments conducted from 1998 to 2000 are reported in which three legume green manure crops were studied for biomass production. The legume green manure crops and grass cover (control) were then turned into the soil as green manures and compared with inorganic fertilizer for production of two sweet potato varieties (Ipomea batatas (L.) Lam). Treatments comprised green manure legumes (Mucuna pruriens, Centrosema pubescens, Pueraria phaseoloides), natural grass cover (control) and inorganic fertilizer NPK. Sweet potato varieties were TIS 87/0087 and TIS 8164. All possible combinations of sweet potato varieties and the manure treatments were laid out in a randomized complete block design with three replications. Mucuna pruriens produced significantly higher biomass than Centrosema pubescens and Pueraria phaseoloides at 2 months after planting (MAP) in May-established green manure plots but not in August plantings. At 10 MAP in August establishment, however, Centrosema pubescens and Pueraria phaseoloides gave higher dry matter than Mucuna pruriens. Biomass production increased up to 3 MAP, with the dry matter obtained with Mucuna and natural grass cover being over 4 t ha−1 at 3 MAP in August establishment. Soil nitrogen was significantly higher with Mucuna than with other legumes and natural grass fallows. Sweet potato tuber yields obtained from Mucuna improved fallow were similar to those obtained with NPK fertilizer treatment, which was better than the yield with Pueraria and natural grass fallow. Sweet potato variety TIS 8164 produced significantly higher tuber yield than TIS 87/0087 in 1999 but not in 2000. Sweet potato tuber yields were higher with the two-year fallow than with one-year fallow by 176%.