Some aspects of nutrient uptake by weeds in tea fields following fertiliser application in up-country tea plantation of Sri Lanka

Abstract

Weed competition is one of the most important limiting factors in tea crop cultivation in Sri umka. Nearly 80% of the total tea area is under seedling tea with poor crop-canopies, creating an ideal environment for weed growth as weeds can compete with tea crop for applied and soil borne nutrients soil moisture and sunlight, and can adapt to extreme climatic conditions. There is a scarcity of available information on th~ nutrient removal by weeds in tea fields. The main objective of this thesis f . was therefore to study the removal of applied fertiliser nutrient& and soil-borne nutrients .by weeds grown in both vegetatively propagated and seedling tea fields, following NPl fertiliser application, at different growth stages. In this study, a good canopy VP tea field trial and a poor canopy seedling tea trial, were used, to study the growth of all the available weeds, their N-, P-, K-, Ca-, Mg and Alconcentrations and uptake of these nutrients, 3-, 6-, 9- and 12 weeks after NPK fertiliser application. These results were rationalised with respective tea-crop parameters obtained from these 2-field trials. In addition, a glass house experiment was carried out with Commellina diffusa, Crassocephalus crepidioides, Panicum repens and Conyza floribunda with 2xdifferent levels of Nand K fertiliser, to study the above parameters at similar time intervals. All the available we-ed shoots have removed upto about 6% of N, 13%of P, 10% of K and 25% of Mg of the total N,P,K and Mg removal of both VP tea + weeds in the mature VP tea field, and have r~moved upto about 12% of N, 12%of P &22% of K of the total N,P and K removal of both seedling tea+weeds in the seedling tea field. II This greatest removal of applied fertiliser nutrients observed about 3-6 weeks after NPK fertiliser application. was This study showed the need for controlling weeds in both VP and. seedling tea fields after about 3-6. weeks period from the NPK and Mg fertiliser application, in additio~ to the weed control measures presently being adopted, generally before fertiliser application, due to the removal of considerable amounts of these nutrients by growing weeds, in order to improve the availability of soil nutrients for tea crop which inturn would improve the tea crop yield.