The Characteristics Of Carbon And Nitrogen Of Alfalfa Grassland In The Loess Plateau

With human beings on the environment effect of grassland ecosystem knowledgeincreasing attention and utilization of grassland, carbon, nitrogen change characteristic and itscirculation mechanism becomes more significant. Based on the four different years of alfalfagrassland and six different production capacity of alfalfa varieties as the research object, toleisure as control, analysis of alfalfa grassland soil carbon, nitrogen and changing features ofalfalfa production performance and carbon component relations, the main results are asfollows:1. Alfalfa grassland in Loess Plateau in soil carbon sequestration, and concentrated in the0-80cm soil, the years of alfalfa grassland0-80cm soil carbon sequestration respectivelyaccounted for the total amount of carbon41.02%,39.43%,41.56%,39.59%; soil biomasscarbon sequestration occurs mainly in0-20cm soil layer, respectively, accounted for the totalamount of carbon biomass of underground45.74%,55.68%,53.12%and43.28%. Alfalfagrassland in the entire life cycle of the total amount of carbon sequestration with growth yearsincreased year by year, but the rate of growth is not obvious, the life of unit area total annualfixed carbon content were12.69kg/m²,13.49kg/m²,13.31kg/m²and14.83kg/m².2. Fixed carbon content1a,3a,5a and10a in alfalfa grassland region were13.32Tg,49.58Tg,48.92Tg and31.15Tg.3a and5a alfalfa grassland area of fixed carbon content ishigher, respectively, than the1a and10a increased by73.13%,37.17%and72.77%,36.32%.The Loess Plateau alfalfa grassland carbon sequestration total approximately142.97Tg.3. There is a big difference between the different growth years of Alfalfa Grassland onsoil nitrogen pool increased,5a and10a of Alfalfa increased0-300cm soil total nitrogencontent, more leisure were increased by66.87%and56.44%. In the0-60cm soil layer, soiltotal nitrogen contents increase with the growing years increasing; in the60-180cm soillayer, higher5a,3a alfalfa grassland soil nitrogen content in a vigorous growth period; soilbelow180cm, increase soil nitrogen content of alfalfa grassland than in the control of leisuredecreases, and the difference of soil total nitrogen content of different growth of grasslanddecreased,5a and10a in the high grass.1a alfalfa grassland had little effect on soil totalnitrogen.5a,10a,3a alfalfa grassland was significantly increased by0-300cm soil nitrogen content, were significantly higher than that of1a and fallow （P<0.05）.5a alfalfa grasslandsoil nitrogen average content was the highest (27.08mg·kg^-1),1a,3a,10a and fallow were61.4%,6.1%,9.5%and59.5%, and over140cm soil layer increased soil nitrogen availabilityeffects are strong.4. In the0-300cm soil layer,≥3a alfalfa grassland soil nitrate nitrogen content with thedeepening of soil layer has a trend of decline.1a alfalfa grass and fallow land appeared in the160-240cm soil nitrate nitrogen accumulation, other years of alfalfa grassland nitrateaccumulation disappear. The biggest difference in0-20cm soil layer among the years ofalfalfa grassland soil nitrate nitrogen content in5a alfalfa grassland, soil nitrate nitrogencontent was the highest (11.36mg·kg^-1), a leisure61.9%. This shows that the use of morethan3a of Alfalfa on soil nitrate nitrogen rate is higher, can reduce soil nitrate nitrogenaccumulation in formation. More than3a of alfalfa grassland significantly increasedammonium nitrogen in the soil below60cm, Especially in5a.5. In the0-200cm layer,10years old of six different varieties of alfalfa grasslandproductivity were increased soil carbon storage, there are differences between the differentproduction performance of varieties, with sustained higher productivity and pastoral giantwas the most significant, sustained low productivity of Xinjiang big leaf are not obvious.Alfalfa grassland in0-40cm soil layer on soil carbon mineralization and soil microbialbiomass carbon has a significant increase in productivity, higher pastoral and giant alfalfagrassland increase maximum, minimum amount of Xinjiang big leaf increased. Alfalfagrassland in0-60cm soil water soluble carbon and carbon dioxide have increased to varyingdegrees, and there exist differences in the production of high performance of pastoral andgiant was the most significant, Xinjiang Daye and super13R is not obvious.6. Changes in soil carbon, nitrogen content in alfalfa grassland comprehensive analysis,when alfalfa growth5a, should be rotation to maintain the balance of soil carbon and nitrogen.Sustained high production capacity of Alfalfa Varieties （giant and pastoral） not only outputenergy and high economic benefit, but also increase on soil carbon and nitrogen storageenvironment effect is better, more useful in Medicago sativa artificial grassland constructionin Loess plateau.