| Sweet potato (Ipomoea batatas L.) root yield increases were obtained from P and lime application in a preliminary fertility response study in the Imugan, Santa Fe, Nueva Vizcaya area. The N + K and N-only treatment effects were not significantly different from each other, and were significantly lower-yielding than the N + P + K + Lime, N + P, and N + Lime treatments.;Fertility response surface studies with a sweet potato monocrop showed a significant root yield increase from N during the first season. Optimum yields were predicted at 30N + 150P + 45K and 60N + 0P + 0K. The interaction of N and P was significant, causing root yield decreases at high N + P rates. Sweet potato top yields were increased at high N + P rates. The response surfaces supported the hypothesis that high rates of N relative to P and K enhance vine growth at the expense of root yield. Initial applications of N had less carryover effect on root yield than did P and K. Maximum root yield response to residual fertilizer was obtained at 10N +120P + 130K initial application. Root yield was positively linearly correlated with leaf P concentration.;Fertility response studies with a sweet potato x cowpea intercrop indicated that the yield of both crops was significantly increased by P application. Nitrogen increased cowpea yield but had no effect on intercropped sweet potatoes. Neither crop responded to K.;Research needs, sources of unexplained variation, and experimental design criteria were evaluated. It was concluded that research toward improving shifting cultivation of sweet potatoes in the Imugan area should concentrate on providing P inputs from organic sources.;Cowpea (Vigna unguiculata (L.) Walp.) strains were found different in nodulation and fresh pod yield potential. The strain 'Ces 41-6' was highest yielding, followed by 'ACC 113', 'CES 42-2', 'TVX 289', and 'UPL CP1'. Inoculation with rhizobial strain 'C8' significantly increased nodule mass but did not increase fresh pod yield. |
PDF Full Text Request