EVALUATION OF SLOPING AGRICUL TURAL LAND TECHNOLOGY (SALT) AS A MEANS OF ENSURING S.USU'.INABILITY OF TEA YIELDS IN THE UP-COUNTRY WET ZONE (WU2) OF SRI LANKA

Abstract

Sloping Agricultural Land Technology (SACT) is a system of land management that hasbeen introduced to arrest the decline of soil fertility and sustain yields of tea plantations 0[1sloping terrain in the central highlands of Sri Lanka. SALT involves the incorporation offast-grov.ing, mostly leguminous tree species as hedgerows along contours atpre-determined distances among tea rows. The hedgerows are expected to increase soilfertility by reducing erosion and providing organic matter through frequent addition ofprunings. However, SALT hedges could compete with tea for essential growth resourcessuch as water, nutrient and light and consequently reduce tea yields. Therefore, the mainobjective of this study was to quantify the positive ana negative effects of SALT hedges andto determine their net impact on tea yields and parameters of soil fertility.

Two long-term, on-farm field experiments were conducted at Helbodde Estate, Pussellawain the Up-Country Wet Zone (WU2) The effects of six tree species (Calliandracalothyrsus, Cassia spectabilis, Euphatoriun: innulifolium, Flemingia congesta, Gliricidiaseptum aid Tithonia diversifolia) growing as contour hedgerows on the long-term yields ofmature tea (ie. in the second pruning cycle) and young tea (i.e. first pruning cycle) werequantified in Experiments 1 and 2 respectively. These experiments also measured the yieldresponse to the addition of mulch material from different tree species. Continuous yieldmeasurements were done at weekly intervals since November 1998.

Continuous tea yield measurements that were done at weekly intervals were compiled andanalyzed over a three-year pruning cycle from November 1998 to October, 200 1. InExperirne nt I, yield of mature tea growing with Euphatorium hedgerows was significantlygreater than the yield of tea growing without hedgerows (i.e, control plots). However,yields of .nature tea growing with all other hedgerow species were significantly lower than111 the cor.trol. Mature tea yields of all hedgerow plots increased significantly in response tothe addition of the respective hedgerow prunings as mulch. These results show thatalthough all hedgerow species contribute to the improvement of soil fertility, all hedgerowspecies except Euphatorium exert significant resource competition, whieh exceeds theirrespective positive fertility effects. In Experiment 2, yields of young tea growing with allhedgerow species, including Euphatorium showed significant reductions as compared tothe yield of sole cropped young tea. This shows that young tea is less able to withstandresource competition from hedgerows than mature tea. However, in Experiment 2, the leastyield rediction was shown in tea growing with Euphatorium. Among the differenthedgerow tree species tested, Euphatorium showed the highest yield increase due to theaddition cf prunings as mulch in both' experiments.

There was significant variation in the biomass production between different hedgerow treespecies in both experiments. Calliandra and Cassia produced greater biomass than the restwhile Glir'cidia and Euphatorium produced lower biomass levels. In both experiments,there were moderately strong negative relationships between tea yield and hedgerowbiomass. This is a confirmation that higher biomass production by the hedgerows increasestheir resource u~e and decreases tea yields.

Detailed analysis of soil chemical and physical properties showed significant variationbetween S/,L T systems with different hedgerow species and between mulching treatments.In mature lea, the soil N, P and K contents were lower in SALT plots than in sole leacrops. In young tea, while most of the SALT plots had higher soil N than the control, bothP and K in SALT plots were lower than in the control. In both mature and young tea, soilCa was lower in SALT systems than in the control- In contrast, soil Mg in the majority ofSALT plots was lower than the control in mature tea while the opposite was observed inyoung tea. !n both mature and young tea, the majority of SALT systems had a lower soilpH than the control plots. However, the SALT systems of both mature and young tea had ahigher soil cation exchange capacity (C~C) and organic matter (OM) content than therespective sole tea crops. In SALT plots with both mature and young tea, mulchingsignificantly increased soil N, P, K, Ca, Mg, CEC and OM. However, soil pH did notchange sigr ificantIy due to mulching. Multiple regression' analysis showed that 87% of theobserved yield variation of mature tea in SALT systems could be explained by the variationof the above soil properties. In SALT systems with young tea, 98% of the yield variationcould be explained by the variation of soil properties.

Based on the above results of these two long-term experiments, it is concluded thatincorporatic n of tree hedges in existing tea fields have to be done with caution as it coulddecrease tea yields due to excessive resource competition. However, SALT systems showedsome positive indicators such as greater soil organic matter and cation exchange capacity,which may contribute to long-term increase of soil fertility and sustainability of tea yieldson sloping terrain in the central highlands of Sri Lanka.