Forestry and Environment Sympoisum 2002, Sri Lanka

Monday, September 18, 2006

EVALUATION OF SLOPING AGRICULTURAL LAND TECHNOLOGY (SALT) AS A MEANS OF ENSURING SUSTAINABILITY OF TEA YIELDS IN THE UP- COUNTRY WET ZONE (WU2) OF SRI

W.A.J.M. De Costa & P. Surenthran
Department of Crop Science, Faculty of Agriculture, University of Peradeniya


Sloping Agricultural Land Technology (SALT) is a system of land management that has been introduced to arrest the decline of soil fertility and sustain yields of tea plantations on sloping terrain in the central highlands of Sri Lanka. SALT involves the incorporation of fast-growing, mostly leguminous tree species as hedgerows along contours at pre-determined distances among tea rows. 'The hedgerows are expected to increase soil fertility by reducing erosion and providing organic matter through frequent addition of prunings. However, SALT hedges could compete with tea for essential growth resources such as water, nutrient and light and consequently reduce tea yields. Therefore, the main objective of this study was to quantify the positive and negative effects of SALT hedges and to determine their net impact on tea yields and parameters of soil fertility.

Two long-term, on-farm field experiments were conducted at Helbodde Estate, Pussellawa in the Up-Country Wet Zone (WU2). The effects of six tree species (Calliandra calothyrsus, Cassia spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) growing as contour hedgerows on the long-term yields of mature tea (i.e. in the second pruning cycle) and young tea (i.e. first pruning cycle) were quantified in Experiments 1 and 2 respectively. These experiments also measured the yield response to the addition of mulch material. from different tree species. Continuous yield measurements were done at weekly intervals since November 1998.

Continuous tea yield measurements that were done at weekly intervals were compiled and analyzed over a three-year pruning cycle from November 1998 to October, 2001. In Experiment 1, yield of mature tea growing with Euphatorium hedgerows was significantly greater titan the yield of tea growing without hedgerows (i.e. control plots). However, yields of nature tea growing with all other laadgerow species were significantly lower than in the cor.trol. Mature tea yields of all hedgerow plots increased significantly in response to the addition of the respective hedgerow prunings as mulch. These results show that although all hedgerow species contribute to the improvement of soil fertility, all hedgerow species except Euphatorium exert significant resource competition, which exceeds their respective positive fertility effects. In Experiment 2, yields of young tea growing with all hedgerow species, including Euphatorium showed significant reductions as compared to the yield of sole cropped young tea. This shows that young tea is less able to withstand resource competition from hedgerows than mature tea. However, in Experiment 2, the least yield red action was shown in tea growiag with Euphatorium. Among the different hedgerow tree species tested, Euphatorium showed the highest yield increase due to the addition of prunings as mulch in both'experiments.

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