| In order to know weed species and their distribution in alfalfa production areas in Gansu provine, an investigation was conducted in Jiuquan, Zhangye, Wuwei and Jinchang from June to August 2014 and July to September 2015. To screen safe and effective herbicides in alfalfa field, the influence of herbicides on photosynthetic characteristics and physiological index was studied; the safety and dosages of herbicides were evaluated at Yuzhong Seed Farm from April to October 2015. The results were as follows:(1) A total of 37 weed species, belonging to 33 generas,11 families, was investigated though weed survey in alfalfa field. The main weeds were broadleaf which accouted for 78.38% of the total; annual weeds belonging to 20 species accouted for 54.05%, much greater than perennial weeds. The dominant families were Chenopodiaceae, Gramineae, Compositae, accouted for 54.05% of the total, their FDI value were 117.25%, 60.88% and 52.83%, respectively. It was found that 4 dominant species had > 5 important value, including Chenopodium glaucum L., Amaranthus spinosus L., Echinochloa crusgali(L.) and Beauv., Ixeris polycephala Cass., Chenopodium glaucum L. was the most important control objective because of its highest IV value(34.96).(2) The influences of 10 kinds of herbicides on safety of alfalfa were different. Four soil treatment pesticides inhibited alfalfa germination to some extents. Among stems and leaves treatment herbicides, the phytotoxicity of 2,4-DB and lactofen were serious, dosage higher than 1500 m L·hm-2 of bentazone showed phytotoxicity.(3) Herbicides significantly reduced the SPAD, Pn, Gs, Tr and Ls, and the value furrher decreased with the increasing concentration. Ci rised significantly with the concentration increasing. The WUE was increased under the herbicides stress. 4 kinds of herbicides caused variation of protective enzyme activity, MDA, Pro content. 35-42 days after treatments, all the index recovered to the level of the control.(4) Herbicides were significantly differ in their efficacy to control weeds. The weed control efficiency of soil treatment herbicides on Gramineous weeds was better than broadleaf weeds; Among stems and leaves herbicides, haloxyfop-r-methyl and sethoxydim were more effective in controling Gramineous weeds, while imazethapyr could control both Gramineous and broadleaf weeds. For soil treatment before seeding, 2250 m L·hm-2 trifluralin was the best; 1300 m L·hm-2 dual was the best choice for soil treatment before emergence; the best stems and leaves treatment herbicides were Haloxyfop-R-Methyl, Sethoxydim and Imazethapyr, with concentrations of 450 m L·hm-2, 1400 m L·hm-2, 1800 m L·hm-2, respectively.(5) Herbicides had a significant impact on hay yield of alfalfa. Among stem and leaves treatments, bentazone caused severe reduction while Haloxyfop-R-Methyl had no significant effect. The concentrations of herbicides also affected hay yield significantly, 1500 m L·hm-2 and 3200 m L·hm-2 bentazone caused 35.31% and 42.80% decrease. 2250 m L·hm-2 trifluralin increased alfalfa yield by 49.48%; low dual concentration and medium imazethapyr dosage led to 45.66% and 44.51%.hay yield increase.(6) Considering the influences of 10 herbicides on field weed control efficiency, alfalfa safety, hay yield, photosynthetic characteristics and physiological indexes, the most appropriate herbicides treatment were: 2250 m L·hm-2 trifluralin for soil treatment before seeding; 1300 m L·hm-2 dual for soil treatment before emergence after sowing; and the best stems and leaves herbicides were 1400 m L·hm-2 Sethoxydim and 1800 m L·hm-2 Imazethapyr. |
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