Sweet potato production in hedgerow intercropping systems in the lowlands of Papua New Guinea.

Abstract

In an experiment in the Morobe Province of Papua New Guinea, sweet potato (Ipomoea batatas) was grown between Leucaena diversifolia and Acacia auriculiformis hedgerows (1650 trees ha1), and as a sole crop. The experiment was conducted at three locations on Entisols and Inceptisols at altitudes below 550 m a.s.l. Sweet potato yields, above ground biomass of the trees, and nutrient contents of the leaf mulch were measured from 1992 to 1994. The hedgerows were copped annually. There were no significant differences in sweet potato yields between the inter cropped hedgerows and when grown as a sole crop. Average marketable tuber yields were very low and varied from 2.1 to 6.6 t ha-1 yr1 (CV%: 27- 51%). Biomass (i.e. wood and mulch) production of Leucaena and Acacia was also low but varied widely between years. Leucaena produced significantly more biomass (7.6 t ha1) than Acacia (1.8 t ha1) only in 1994. The nitrogen concentration of the Leucaena leaves (mean 29.5 g kg1) was higher than of Acacia (mean 21.1 g kg1) but phosphorus concentrations were similar. Potassium and sulphur concentrations were higher in Leucaena than in Acacia in 1993 and 1994. Due to higher biomass production and higher nutrient concentrations, there were more nutrients returned to the soil with Leucaena than with Acacia mulch. After three seasons of sweet potato cropping, no statistical differences in soil chemical properties were found. It was concluded that annually coppiced Leucaena and Acacia hedgerows is attractive for subsistence farmers in areas where wood or fodder is scarce since it is not affecting sweet potato yields.