Intensification of subsistence agriculture on the Nembi Plateau, Papua New Guinea 3. Sweet potato cultivar trials, crop rotation trials and crop introductions.

Abstract

Three sweet potato (Ipomoea batatas,) cultivar trials were conducted in village gardens on the Nembi Plateau. Local cultivars were compared with selections from Aiyura. The Aiyura selection, Markham l, had the highest yield in all three trials. Its taste is acceptable to the villagers and its use should be promoted on the Plateau. In one of the cultivar trials plots were split for nematicide application as root knot nematode (Meloidogyne sp.) had been previously identified from sweet potato stems. No response to the chemical was obtained.
A second series of trials evaluated a number of species for use as rotation or fallow crops in sweet potato gardens. Five grain legumes were compared. These were cowpea ("Vigna unguiculata unguiculata), peanut (Arachis hypogaea), rice bean (Vigna umbellata), soyabean (Glycine max) and winged bean (Psophocarpus tetragonolobus). Peanuts gave the highest yield and are acceptable as a supplementary
food. Three rotation trials were then conducted to compare a sweet potatojpeanut rotation with continuous planting of sweet potato. No beneficial effect was recorded for sweet potato Crops that followed peanuts. Three food crops that are presently not much used on the Plateau were evaluated. Potatoes (Solanum tuberosum) gave a mean tuber yield, of 8.1 t/ha when grown in a trial that compared three micro environments. No significant difference between environments was found. Potatoes have potential as a food crop. Cassava (Manihot esculenta) plots planted on poor soils in sweet potato gardens yielded 2.2 t/ha. No potential is seen for cassava on these soils. Pigeon pea was grown in mixed garden soils and yielded reasonably well. It may have a role as a vegetable crop grown in mixed vegetable gardens.