Effects Of Herbicides On Alfalfa Growth,Physicochemical Indexes And Biological Characteristics In Alfalfa Soil

Heilongjiang Province is animal by-products base of China,especially where dairy and beef cattle production hold a dominant position of livestock husbandry in China.The feed source is one of the most important problems which limit the development of livestock husbandry in Heilongjiang Province.As the main feed,the production area of lucerne is approximately 82,368 acres,and annual yield of hay is around 250,000 tons,which are far from the needs of livestock husbandry in Heilongjiang Province.Therefore,to expand the planting of lucerne is an urgent need,especially production area of alfalfa.Heilongjiang province is the demonstration base of modernized agriculture in China,and applying mechanized methods to product herbage.Therefore,herbicide as the core method of weeding control is to apply necessarily in the pasture production,especially in the alfalfa industry.However,compared with legume crop,no specificity and effective herbicides of alfalfa were applied to production,limiting the yield and quality of large-scale production.In order to solve this problem,this study chose six pre-emergence herbicides as test objects:acetolor-clomazone,thifensulfuron,imazethapyr,metolachlor,acetolor and chlorimuron-ethyl,which had been applied to production of alfalfa.The field experiment was conducted to test the effects of different chemical herbicides to the growth,yield and stem-leaf ratio of alfalfa,soil physicochemical properties and soil biological characteristics(soil enzymes and soil microbial diversity).The results of herbicides applications were evaluated to provide technical supports for the further development of alfalfa herbicides.Results as follows:The effects of weeding showed:to main weeds of alfalfa field,the prevention and elimination effects of acetolor-clomazone and acetochlor were better than others,and acetolor-clomazone was the best weeding effects to monocotyledonous weeds.The changes of afalfa yield showed:in branching period,acetochlor had the least effect on the yield of alfalfa;acetolor-clomazone and thifensulfuron obviously reduced the yield of alfalfa,production of which were in 35 percent and 34 percent of production with acetochlor treating respectively.In budding period and flowering period,acetochlor and chlorimuron-ethyl least affected the yield of alfalfa respectively;acetolor-clomazone and thifensulfuron obviously reduced the yield of alfalfa.The changes of soil physicochemical properties showed:six herbicides reduced soil pH to make soil acidification.The contents of soil available nitrogen,soil available phosphorus,soil available potassium and organic matter were changed because of different chemical herbicides treating,and metolachlor had the greatest influence on soil physicochemical properties.All of six herbicides inhibited the activity of soil urease.The changes of soil microbial diversity showed:to six herbicides,the most significant inhibition to bacterial was thifensulfuron;the most significant inhibition to actinomycetes was acetochlor;the most significant inhibition to fungi was acetolor-clomazone.Metolachlor,acetochlor and chlorimuron-ethyl changed the structure of soil microbial community,and improved the diversity of soil microbial community.Herbicides maked utilization ability and types of soil microbes to carbon source changed.