Effect of herbicide application on tea camellia sinensis L o kuntze

Abstract

The thesis consists of four chapters and a bibliography. The first chapter INTRODUCTION describes the objectives of the work, mainly (i) identification and documentation of the toxicity symptoms of commonly used herbicides in tea, record their distinction from deficiency symptoms and to study the physiological effect of the this toxicity, (ii) evaluation of the impact of long term use of various herbicides on (a) yield, (b) soil, pH, organic matter, CEC, NPK, (c) NPK, chlorophyll and carotenoid content of matured tea leaf, (d) quality components and colour of tea liquor, (e) weed spectrum and composition, (iii) investigation of antagonistic/synergistic/additive effects of a few important herbicides in mixtures, (iv) introduction and bioefficacy study of a few new herbicides and (v) residue study in made tea. The chapter then reviews use of herbicides in tea industry describing the mode of action of the herbicides and their environmental implications. The existing relevent literature on the topic has been thouroughly reviewed. The second chapter quotHERBICIDAL TOXICITY SYMPTOMS ON YOUNG TEA PLANTSquot gives a description of the experimental set up used to study the toxicity symptoms on young tea plants and the methodology for estimation of chlorophyll, carotenoids and fatty acids in tea leaf. The investigation revealed that (i) with deliberate soil treatment Paraquat and Oxyluourfen did not induce any phytotoxicity while Dalapon, Diuron, Simazine, 2, 4-D and Glyphosate induced phytotoxicity at different concentrations. In many cases, these crop safety limits (minimum concentrations) were less than the recommended doses, (ii) considering both deliberate soil and foliar treatments, Glyphosate was found to be the safest herbicide so far used in tea, (iii) significant differences exist to distinguish between herbicide toxicity and nutrient deficiency symptoms and (iv) the herbicides inhibit the leaf pigments i.e. chlorophyll a and b, and also carotenoids and fatty acids to different extents. The work has suggested different