Investigation of compost × fertilizer interactions in sweet potato grown on volcanic ash soils in the highlands of Papua New Guinea

Abstract

Large quantities of organic matter are traditionally used in sweet potato mulch mounds on volcanic ash soils in the highlands of Papua New Guinea. Two trials investigated compost x fertilizer interactions using a 24 factorial combination of compost (C), urea (N), triple superphosphate (P) and potassium chloride (K). At Taluma (altitude 2570 m) there was a highly significant (P < 0.01) positive C x K interaction in addition to positive effects of C, N and Pon tuber yield. At Kandep (2350 m) there was a significant (P = 0.05) negative C × N × K interaction, in addition to positive effects of C and P and a negative effect of N on yield. The occurrence of consistent compost × fertilizer interactions, whether positive or negative, would have implications for the development of subsistence agriculture in PNG.