The response of three sweet potato cultivars to inorganic fertilizers on an Andisol in the highlands of Papua New Guinea.

Abstract

A experiment is reported in which the response of three sweet potato varieties under farmers field conditions to inorganic fertilizer were examined in Gumine, Simbu Province. Fertilizer treatments were 0, 75 and 150 kg N ha applied as urea; 0, 50, 100 kg P ha1 applied as triple super phosphate, and 0, 75 and 150 kg K ha1 applied as muriate of potash. Marketable sweet potato yields were substantially increased due to a significant P x K interaction, indicating that these nutrients were limiting sweet potato production. There was greater P-effect than K but the pattern of interactions was related to a significant inter-varietal difference in their response to added nutrients. The magnitude of response by variety Ongi and to an extent, Tripalangi, to added P and K was greater than variety Spagi. Variety adaptation mechanisms developed to offset pest and disease attack and other environmental stress, could reduce variety vigour and responsiveness to fertilizers. The occurrence of such interaction has implications for future on-farm trial work and proper management of fertilizer in subsistence gardens.