Residues and degradation dynamics of paclobutrazol in peanut and soil

ObjectiveResidues of paclobutrazol and its degradation dynamics in peanut soil were studied in order to provide references for the rational use of paclobutrazol in peanut cultivation.MethodSamples were extracted with aceto-nitrile,and soil was purified by liquid-liquid separation. Peanut samples were purified by Cleanert Florisil and graphitized carbon black,then determined by gas chromatograph with nitrogen phosphorous detector using external standard method. Through residue experiments during two years in three places,residues and degradation dynamics of paclobutrazol in pea-nut kernel,peanut shell,peanut plant and soil were researched.ResultThe minimum detectable quantity of paclobutra-zol in gas chromatography-nitrogen and phosphorus detection method was 0.15 ng,and the minimum detectable quantity in soil,peanut kernel,peanut shell and peanut plant was 0.03-0.05 mg/kg. When the concentration of paclobutrazol were 0.05,0.50 and 1.00 mg/kg,the average recovery was 72.5%-108.8% from soil,95.9%-108.3% from peanut kernel, 81.8%-109.6%from peanut shell and 75.2%-96.7%from peanut plant. The relative standard deviation were 5.1%-14.3%(soil),5.8%-8.7%(peanut kernel),4.6%-9.3%(peanut shell)and 5.0%-8.9%(peanut plant). The degradation half-life of paclobutrazol was 2.4-14.3 d in soil and 1.0-5.7 d in peanut plant. The final residues of paclobutrazol in peanut from Guangxi,Hunan and Henan were not detected.ConclusionThe sensitivity,accuracy and precision of gas chro-matography-nitrogen and phosphorus detection method in detecting paclobutrazol meet the requirements for pesticide resi-due analysis,which can be applied to the detection of paclobutrazol residue in paclobutrazol and soil. At acicula forming stage,applying recommended dosage(90-120 g a.i./ha)of 15%paclobutrazol SC once is safe for peanut with no residue at harvest.