| Barnyardgrass(Echinochloa crusgalli) is a troublesome weed in paddy fields of China South, and butachlor and quinclorac are commonly two used herbicides on barnyardgrass. The influence of barnyardgrass on the growth of paddy rice in Jiangxi province and economic threshold of butachlor and quinclorac on barnyardgrass were conducted by adding series experiment under different density of barnyardgrass as the research object to barnyardgrass in this paper. The germination and dormancy characteristics of barnyardgrass seed and its resistance to butachlor and quinclorac were assaied by indoor culturing method. The degradation dynamics of butachlor and quinclorac in paddy soil and rice plant were investigated by HPLC. The results are as follows:(1) Results showed that plant height, tillers, effective spikes, filled grains per panicle,1000-grain weight and grain yield of early, mid-season and late rice decreased gradually with the increase of barnyardgrass density. The exponential regression model “y = be ax”was relatively better for describing the relationship between barnyardgrass density and tillers, effective spikes and yield of double-cropping early rice, while quadratic regression model “y =ax2 + bx + c” was the best for plant height, filled grains per panicle, 1000-grain weight and yield loss. The exponential regression model “y = be ax” was relatively better for describing the relationship between barnyardgrass density and effective spikes and yield of mid-season rice, while quadratic regression model “y =ax2 + bx + c” was the best for plant height, 1000-grain weight and yield loss. Meanwhile, quadratic regression model “y =ax2 +bx + c” was relatively better for describing the relationship between barnyardgrass density and plant height, tillers, effective spikes, filled grains per panicle, 1000-grain weight, grain yield and yield loss of double-cropping late rice. When chemical herbicide such as butachlor and quinclorac was used to control barnyardgrass in paddy fields, the economic infestation levels for barnyardgrass were 1.64%-2.91% and 1.11%-9.09% and 1.28%-2.28% in early, mid-season and late paddy fields, respectively, and the economic thresholds were 0.63-1.23 plant/m2, 0.09-5.58 plant/m2 and 1.30-1.85 plant/m2,respectively.(2) Results by indoor culturing test showed that barnyard grass seed would get into dormancy after maturity, and germination rate was only 3.33% before dormancy. The dormancy of barnyard grass seed could be broken by gibberellin and Na OH, but there was greater effect of storage time on breaking dormancy. The rate of seed germination could be increased by about 10 times after one year stored in the refrigerator. The rate of seed germination was promoted by chemical reagent, and as high as 70% with 10000 mg/L of Na OH solution. Soil thickness and temperature had greater effect on the rate of seedgermination, and the most suitable soil thickness and temperature for seed germination were 0.5-2 cm and 30-35℃, respectively.(3) The resistance of eight barnyardgrass biotypes from paddy fields in Jiangxi Province to butachlor and quinclorac was determined using pot planting method. Results showed that different resistance levels of barnyardgrass to butachlor were observed in paddy fields of Jiangxi Province. The biotype from Henghu farm had the highest resistance index to butachlor and its relative resistance index ranged from 11 in 2012 to 13 in 2013, in the middle resistance level. The resistance indexes of the biotypes from Nanchang Guangfu town and Hongkong farm ranged from 6 to 9, in a low resistance level. The resistance indexes of the biotypes from Jinxian Wenzhen town, Ningdu Qingtang town and Fengxin Chian town ranged from 3 to 4, in the decline phase of the sensitivity. The resistance indexes of the biotypes from agricultural science institutes of Ganzhou and Jian were less than 3, corresponding to a sensitive stage. The resistance indexes of the biotypes from eight regions of Jiangxi Province to quinclorac were less than 2, corresponding to a the sensitive stage.(4) The high performance liquid chromatography methods for the determination of butachlor and quinclorac residues in paddy soil and rice plant were developed. The results showed that the recoveries of butachlor in paddy soil and rice plant were 82.43% ~ 91.29%and 84.17% ~ 92.45% with relative standard deviation(RSD) of 4.34% ~ 5.83% and4.92% ~ 5.44% at fortified level of 0.01-0.5 mg·kg-1, respectively. The recoveries of quinclorac in paddy soil and rice plant were 81.75%-90.01% and 83.05%-92.11% with the relative standard deviation(RSD) of 4.53%-6.24% and 3.94%-5.53%, respectively.Degradation dynamics of butachlor and quinclorac in paddy soil and rice plants accorded with the first-order kinetics model, its half-lives were 1.22-4.49 d and 1.39-1.72 d in paddy soil, respectively, 2.17-2.22 d and 2.22-2.23 d in rice plant, respectively. |
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