| In order to further understand the action of auxinic herbicide of phenoxyalkanoic acids, and residue dynamics of 2, 4-D butyl ester in oats, covered oat( Longyan No. 3) and naked oat( Baiyan No. 2) were used as materials, treated with 2, 4-D butyl ester(450, 750 and 1050 mL·hm-2) at 3-4 leaf stage. Dissipation and residue dynamics of 2, 4-DB and its decomposition product in oats were studied after 1d, 7d, 14, 21 d and 28 d of treatment, as well as flowering, grain filling and maturity stages. pH of oat plants were also determined. Chlorophyll content, photosynthesis and chlorophyll fluorescence parameters were analyzed 7 days after treatment. Weed control effect, safety, yield and shell rate of naked oat were investigated. The main results were as follows:(1) The degradation dynamics of 2, 4-D butyl ester in covered and naked oats were significantly different. The average half- life was 3.90 d and 8.81 d for covered and naked oats respectively. In addition, residues of 2, 4-D butyl ester in naked oats were significantly(P<0.05) higher than in the covered. 28 days after 2, 4-d butyl ester treatment, residues in covered oat were 0.055, 0.082, and 0.168 mg·kg-1 under low, medium and high concentration, respectively, which were 54.5%, 39.0% and 41.7% less than the naked. Residues of 2, 4-D butyl ester were not detected in oat seeds.(2) The degradation dynamics of 2, 4-D in covered and naked oats were significantly different. Average half- life were 2.45 d and 2.05 d respectively. The residues of 2, 4-D in naked oat were significantly(P< 0.05) higher than in the covered. 21 days after spraying three concentrations(450, 750 and 1050 mL·hm-2) of 2, 4-d butyl ester, residues of 2, 4-D in naked oat were 66.7, 50.0 and 32.1% higher than the covered. pH in covered and naked oats were also significantly(P< 0.05) different( 6.09 vs. 5.90). 2, 4-D is a product of acid hydrolysis of 2, 4-D butyl ester, its production was correlated with p H, low p H could promote hydrolysis process.(3) 2, 4-D butyl ester had significant effects on photosynthetic physiology of oats, and the reaponses to 2, 4-D butyl ester were different between covered and naked oats. 2, 4-d butyl ester caused the decline of SPAD, Tr, Gs, Pn and C i, and increase of Ls in covered oat. All these indexes showed a does-response relationship to 2, 4-d butyl ester. Nevertheless, low dosage(450 mL·hm-2) of 2, 4-d butyl ester could promote photosynthesis in naked oat, increased SPAD, Tr, Gs, Pn, C i, and reduced Ls. Higher concentrations restrained its photosynthesis.(4) The results of chlorophyll fluorescence were consistent with photosynthetic characteristics. The photoinhibition occurred under 2, 4-d butyl ester treatment, it reduced F0, Fm, Fv, Fv/Fm, Fv/F0, Φ PSII, qP and ETR, and increased NPQ in covered oat. While naked oat had different response, 450 mL·hm-2 2, 4-d butyl ester increased its chlorophyll fluorescence, and higher dosages caused photoinhibition.(5) 2, 4-D butyl ester had significant effects on the safety and weed control efficacy in oat fields. High dosage caused damage on oats, such as top sagging, leaf redness, medicine spots etc. During filling stage to maturity, naked oat showed leaves and spikelets deformity, and shell rate increase(5.61%, significantly higher than control). Weed control efficacy improved with the increasing concentration of 2, 4-D butyl ester. 1050 mL·hm-2 treamtent gave the highest control effect, as much as 90% control efficacy was obtained 45 days after treatment. 2, 4-D butyl ester declined plant height in both covered and naked oat, 10.49% and 12.90% reduction were observed respectively.(6) 2, 4-D butyl ester significantly affected oat hay and grain yield. 450 mL·hm-2 concentration improved oat yield, as much as 40.57% grain increase was obtained in covered oat. 1050 mL·hm-2 dosage reduced naked oat hay yield by 28.45% and grain yield by 26.28%. High concentration 2, 4-D butyl ester was very effective in weed control, but not good for oat production. |
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