EFFECT OF CONTINUOUS APPLICATION OF GLYPOSATE AND PARAQUAT ON WEED CONTROLLING EFFICACY, PHYTOTOXICITY AND YIELD OF WET SEEDED RICE

摘要

A long-term experiment was carried out to evaluate perennial weed controlling ability, phytotoxicity and yield of rice by continuous application of Glyphosate and Paraquat as pre-plant herbicides in wet seeded rice cultivation. Five treatment viz. l)Glyphosate, one ploughing, one harrowing and leveling (Gly+P+H+L); 2)paraquat, one ploughing, one harrowing and leveling (Para, P+H+L), 3)no chemical, two ploughing, one harrowing and leveling (NoC2P+H+L); 4)no chemical, one ploughing, one harrowing and leveling (NCP+H+L), 5) no chemical, no ploughing, one harrowing and leveling (Noc+NoP+H+L) were used in randomized complete block design with 3 replicates. Chemical application, one ploughing, one harrowing and leveling is the common farmers practice of controlling weeds in Sri Lanka. Experiment was conducted for three major seasons and three minor seasons starting from 1996 major season in the rice fields. Soil is sandy clay loam classified as low humic gley soil of pH 6.2 with 2.8% organic matter content. Dominant weeds were Ischane globosa, Panicum repens, Cyperus species, Commelina diffusa and Murdania nudiflora. Results showed that Glyphosate treatment has significantly highest weed controlling ability followed by NoC NoP+H+L and NoC 2P+H+L, Para P+H+L, NoC P+H+L treatments in decreasing in sequence, but Gly+P+H+L and NoC 2P+H+L treatments were not significantly different in weed control. Glyphosate treatment reduced the perennial weed biomas by 30% in 1996 minor season, by 40% and 45% in 1997 major and minor seasons and by 70% and 80% in 1998 major and minor seasons respectively. Paraquat treatment reduced the weed biomass but this reduction was significantly lower than the glyphosate treated plot and higher than the plots with out chemicals. No phytotoxicity damage was observed in paraquat and Glyphosate applied treatments. Highest grain yield of rice was given by 2P+H+L treatment but this yield was not significantly different from the yield given by Gly+P+H+L and Para +P+H+L treatments. Rice yield by NoC P+H+L treatments was the lowest. Therefore this experiment revealed that Glyposate and paraquat can be used continuously as preplant herbicides for wet seeded rice without damaging the rice plant.