Herbicides Screening Test Of Alfalfa Pasture In The Central Area Of Jilin Province

The slow growth of alfalfa(Medicago sativa L.) seedlings in the central area of Jilin provine results in the rapid growth of weeds, which severely affects the quantity and quality of alfalfa products. Six common herbicides with low toxicity that adapted to legume were selected in this screening test. The results are shown as follows :In spite of the slow growth of alfalfa seedlings, the relative weed strain prevention rate reached 93.81% when spraying 90% acetochlor with the dose of 2.0 L·hm-2 in the soil after sowing, which was significantly higher than that of other traments(P<0.05). With the increase of reagent concentration, the relative plant control effect was increaced. However, high concentration of herbicide showed slight phytotoxicity when used in seedling stage. The application of 40% bentazone with the dose of 3.0 L·hm-2 led the relative strain prevention rate of Echinochloa phyllopogon to 97.09%, and showed no damage to alfalfa. Application of 1.0 L·hm-2 15% fluazifop-p-butyl effectively controled Cirsium setosum and Metaplexis japonica. The relative strain control effect reached 93.63% and 100% respectively. It is not recommended to use herbicide, but to take manual methods to control Chenopodium album, Portulaca oleracea, and Abutilon theophrasti.The crude protein content was 21.98% of 50% prometryne in 4.0 L·hm-2, the ratio of stem to leaf 1:1.67, which was significantly higher than that of other traments(P<0.05). Compared with the blank control group, the nutritional quality of alfalfa was increased significantly. The stem leaf ratio and crude protein content decreased obviously when applying herbicides to alfalfa in stem and leaf, showing that the stem and leaf treatment reduced the nutritional quality of alfalfa.The net photosynthetic rate was 28.26μmol·m-2·s-1 when spraying 50% Prometryne with the dose of 6.0 L·hm-2·s-1 in the soil after sowing, which was significantly higher than that of other traments(P<0.05). The slow net photosynthetic rate and low plant height prensented when spraying 90% acetochlor with three concentrations. The net photosynthetic rate was 27.97μmol·m-2 when spraying 40% Bentazon with the dose of 2.0 L·hm-2 in the stem and leaf treatment, which was significantly higher than that of other traments(P<0.05). Therfore, there was an obvious effect of herbicide on photosynthesis of alfalfa.These results can be concluded:1.90% acetochlor with the dose of 2.0 L·hm-2 was adaptable to alfalfa in central area of Jilin province when spraying in the soil after sowing.2.When spraying on the stem and leaf, herbicides should be selected speafically based on weed species and mechanism of action.For the control of grassy and broadleaf weed, bentazone(administration tag and selective type) and fine fluazifop(uptakeype), showed good results. Their recommended doses were 3.0 L·hm-2 and 1.0 L·hm-2 respectively.3.Foliar treatment at high concentrations of herbicide, will reduce the crude protein content of alfalfa.4.Herbicides produced negetative influence on photosynthesis of alfalfa.