Interactions between Leguminous Hedgerows and a Sweet Potato Intercrop in Papua New Guinea

Robert M. Brook


Sweet potato is a staple crop in many areas of the South Pacific. but little has been reported on its potential in multistrata systems. In this experiment it was grown as an intercrop between nine different specifics of leguminous hedgerows, plus a control with no hedge. The aim was to determine whether addition of foliar mulch to sweet potato could compensate for the competitive effects of shrubs, whether such mulch applications could halt the decline in yields successive crops, and to test the performance of a range of lesser utilized shrubs alongside better known species. Hedge species varied greatly in performance, Acacia angustissima, Calliandra calothyrsus and Calliandra houstoniana producing greatest quantities of foliage when pruned, which was then applied to the sweet potato intercrop. Sweet potato biomass did not differ between the two seasons described, but in the second crop tuber yields declined while vine production increased. Regression analysis showed that tuber and vine mass decreased as hedge foliage offtake increased, but also that quantity of potassium applied in mulch increased tuber mass, and quantity of nitrogen applied increased vine mass. In the second cropping cycle, tuber mass in rows closest to hedges increased relative to outer rows. It is hypothesised that this effect was due to the fertilizing effect fine root and nodule dieback following pruning in rows closest to the hedges, in combination with a shortened hedge pruning cycle.

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