Microbial Communities And Nutrient Cycling In The Soil Growing Spring With Plastistic Film Mulching In Semi-arid Loess Plateau

There are some problems about unstable yield and soil quality under plastic film mulching in semi-arid loess plateau. To reach their causes, four treatments of different mulching period of the main provision, spring wheat, were arranged: for 0 day, for 30 days, for 60 days, and for whole growth period. Biomasses of spring wheat, population numbers and biomasses of total soil microorganisms, soil nutrient, organic matter, nitrogen, phosphorus during different wheat growth period were measured, and corrlelative coefficients between them were analysized. Some results and conclusions were gotton. They are as follows.1. Good effects of soil moisture and temperature were caused by plastic film mulch. The effects showed: soil moisture effect rose higher by decreasing moisture evaporation of top soil layer and regulating the distribution of soil moisture from space to time;development of the crop during early stage was advanced because of low temperature hurt in spring reduced. In different rainfall year, the roles of soil moisture and temperature were different, too, for examples, the higher promotion of soil temperature by film in the rich rainfall year than in the poor;and the conservation of soil moisture by film more important to the crop growth in dry year.2. Soil microorganism population quantities and microbial biomasses were increased by plastic film mulch. There were different correlations between the promotions increased and the changes of soil moisture and temperature in rich and poor rainfall year. The cooperation between soil moisture and soil temperature was changed, and it correlated significantly with soil microorganism population quantities and microbial biomass in two years. In rich rainfall year, the peaks of the quantities and biomasses appeared in the middle growth stage of spring wheat earlier, and lasted to the end, for a long time;the peaks appeared in the end in the poor rainfall year, resulting in the stages that soil could provide a lot of effective nutrients didn't coincide with the stages that spring wheat needed nutrients. The mulch for whole growth period would cause high temperature and decrease the rate of the quantities in rich rainfall year, butwould conserve more soil water and increase the quantities in poor rainfall year.3. Different microorganism populations showed different behavior to the changes of soil moisture and temperature in rich and poor rainfall year. In brief, they were negative significant correlative between microorganism population quantities and soil moisture, and significant relative between microorganism population quantities and soil temperature in rich rainfall year. In dry year, the quantities of nitrite bacteria, cellulose decomposing bacteria, actinomycetes and fungi were not relative to soil water, and the coefficients of the quantities of ammonibacteria, nitrite bacteria, denitrobacteria, and phosphorus bacteria were decreased;to soil temperature, the quantities of ammonibacteria, phosphorus bacteria and heat-resistant actinomycetes, which quantities were absolute most of total quantities, were significant relative, the others' coefficients were lessened a little, to low relative, even not relative. The quantities of fungi was relative neither soil moisture nor temperature.4. hi poor rainfall year, soil microbial biochemical activities were significant corelative with their microbial populations. Ammonification and phosphorus transformation were increased continuously before 60 days, and the changes of nitrification were not regular affected by nitrate nitrogen.5. Soil organic matter decomposition was increased under mulch. Organic matter was decomposing more in rich rainfall year than dry year;the quantities were close with organic matter in rich rainfall year, and separate in dry year;and organic matter decomposition was lessened during late stage under mulching for whole period in rich rainfall year, increased in dry year.6. Efficiency of soil nitrogen was affected differently by mulch under different precipitation, mulch made nitrate nitrogen decrease. Biological efficient of nitrogen was increased, rate of absorption by the crop was more, but loss by rainfall was more in rich rainfall, so total nitrogen was down more. They were opposite in dry year, nitrate nitrogen was accumulated in soil.7. Efficiency of soil phosphorus was increased, because of the quantity of phosphorus bacteria and phosphorus transformation increased by mulch.8. Efficiency of soil nutrients was increased by mulch. In the rich rainfall year, although the peaks of the biological activities showed in the middle of the spring wheat growth period, the quantities of ammonibacteria, nitrate bacteria and nitrite bacteria increased were restrained under the whole growth mulch treatment during the late days, so, the efficiency of soil nitrogen of the whole growth mulch was not the highest. In poor rainfall year, under whole growthmulch treatments, efficiencies of nutrients were highest, resulting in yield increased.