Study On Effects Of Planting Years On Alfalfa Soil Physical-chemical Characteristics And Microorganisms

Using one-year, two-year, three-year, four-year and six-year alfalfa as experimental materials, effects of different planting years on alfalfa physical-chemical characteritics and microorganisms were studied from 2006 to 2007 on experimental farm of the Inner Mongolia University for Nationalities by methods of investigation and sampling in field and laboratory analysis. The results showed as follows:1,Roots biomass are different from different planting years alfalfa. The roots volume, dry weight of roots and the number of minor roots of three-year alfalfa was highest, the last was one-year alfalfa and the lowest was six-year alfalfa. With the increasing of growing years, the rate of rot roots increased and the rate of rot roots was 73.21%. Comparing with one-year, two-year, three-year and four-year alfalfa, density in field of six-year alfalfa was the lowest and was 11.91%, 21.28%,40.00% and 43.40% of one-year, two-year, three-year andfour-year alfalfa.2,Effects of alfalfa planting times on physical-chemical characteritics was that: with the increasing of planting years, soil bulk density decreased but a few differences in different soil layers and soil porosity, content of soil saturated water and soil field capacity all decreased; with the increasing of planting years, content of soil organic matter, soil total nitrogen, soil available nitrogen and soil available phosphorus increased; content of soil total phosphorus showed tendency of increasing first and decreasing second; with the increasing of planting years, soil available potassium, soil total potassium and soil PH decreased; with the increasing of planting years, content of humic acid and furies acid in soil humus increased and so did HA/FA; with the increasing of planting years, soil nitrogen fixing power showed tendency of increasing first and decreasing second and soil nitrogen fixing power of three-year and four-year alfalfa were high and their differences was little. In 0-40cm soil layer, with the depth increasing, all kinds of soil nutrients decreased and the soil nutrients in 40-50cm soil layer were higher than that in 30-40cm soil layer.3,In 0-40cm soil layer, the number of bacterial and actinomycetes of five-yearalfalfa field were higher than that of two-year alfalfa field, but their difference in the number of fungi was not obvious; the number of cellulose decomposition microbes, ammonifers and soil nitifying bacterica of five-year alfalfa field were higher than that of two-year alfalfa field; the number of nitrogen-fixing bacteria, denitrifying bacterica and phosphate-solving microorganisms of five-year alfalfa field were higher than that of two-year alfalfa field;the number, volume and dry weight of rhizobia of five-year alfalfa field were higher than that of two-year alfalfa field, respectively 1.85, 2.81 and 1.43 times.4,In 0-40cm soil layer, activities of urease, catalase and invertase of two-year alfalfa field were higher than that of five-year alfalfa field and with the depth increasing of soil layer, their activities decreased; activity of amylase of two-year alfalfa field was higher than that of five-year alfalfa field and with the depth increasing of soil layer, its activity increased; activity of cellulase of five-year alfalfa field was higher than that of two-year alfalfa field.