Variation in Soil Fertility and Capacity for Supplying Soil Nutrients in a Hedgerow Intercropping System with Different Tree Species in the Upcountry Wet Zone of Sri Lanka

Sloping agricultural land technology (SALT), a form of hedgerow intercropping (HI) system, has been accepted as an appropriate land management practice to overcome some soil related constraints faced by farmers in marginal lands in the wet zone of Sri Lanka. Despite its effectiveness in soil conservation and soil fertility improvement, farmers are reluctant to adopt this practice due to the lack of immediate monetary returns. The lack of expected nutrient inputs through hedgerow mulch and possible tree-crop competition for essential resources seems to be the main drawbacks. In order to test some of these aspects, a study was carried out to assess the soil fertility status after 4 years of HI on the slopes of the wet zone of Sri Lanka, with a special emphasis on the nutrient redistribution in alleyways due to the establishment of contour hedgerows. After 4 years of HI, some soil chemical parameters such as concentrations of organic C, total N, mineralizable N, and organic P were higher in the SALT-HI plot than that of farmer-managed vegetable plot and the abandoned tea land. However, 4 years of HI on the slopes at Doragalla, some chemical parameters showed a significant position effect down the slope compared to the control sites, with a tendency for accumulating nutrients immediately under the hedges compared to open alleyways, yielding a distinct ‘saw-tooth’ pattern down the slope. The organic C and total N concentrations were significantly higher under hedges than in the open alleyways, where the crops were grown. This nutrient patchiness was not present in the two control sites without hedgerows. This nutrient patchiness seems to be a direct consequence of establishing hedgerows along contours and hence will be a crucial factor determining the fate of this agroforestry system in Sri Lanka.