Study On The Effects Of Alfalfa Yield To Soil Water Content And Mineral N In Profiles Of Alfalfa Grassland

Alfalfa is an excellent perennial leguminous grass, which is widely planted in the world. As the principle legume in Legume-cereal rotations, Alfalfa plays an important role in the ecology and economics of such farming systems in western China. To provide a scientific foundation for reasonable managing and using alfalfa, this paper studied the spatiotemporal variations of soil water content and mineral N (NO3--N and NH4+-N )content as affected by different level yield of alfalfa.Calculated the apparent budget of soil nitrogen at rapid growth stages of alfalfa.The main results showed:1. The plant height, yield of alfalfa increased"slowly-fast-slowly"in lst harvest. The growth speed and yield of 5-year alfalfa were higher than 3-year alfalfa (P<0.01). From branch to early bloom period is the rapid growth stage. During this stage, 3-year,5-year alfalfa have maximum growth speed and AGR. Aboveground biomass increased 8362.42 kg/hm2, 14218.8 kg/hm2 during this stage which made up 59.29%, 71.35% to lst harvest.2. From branch to early bloom period, soil water content decreased in 0-200 cm profiles. The decrease of soil water storage in100-200 cm profiles of 3-year alfalfa grassland is bigger than other layers. In 5-year alfalfa grassland, the decrease happened in 0-200 cm which is bigger than 3-year alfalfa grassland. During this stage, WUE of 3-year,5-year alfalfa is 11.23 g·mm-1,28.31 g·mm-1。3. During early bloom period, comparing with fallow field, soil NO3--N storage decreased in 0-200 cm of alfalfa grassland. The decrease in 0-100 is bigger than other soil layers, in 3-year alfalfa grassland is bigger than 5-year alfalfa grassland, soil NH4+-N storage increased in 0-200 cm of 3-year alfalfa grassland which is bigger than fallow field.No variation of soil NH4+-N storage in 5-year alfalfa grassland during this period.4. Early bloom period,Comparing with free land, positive effect showed by 3-year alfalfa in accumulation of Nmin in 0-100 cm soil, negative effect showed by 5-year alfalfa in 0-200 cm soil during branch to early bloom period, the lose of Nmin in 100-200 cm soil is bigger than other soil layers, the lose of NO3--N in 3-year alfalfa soil is bigger than 5-year alfalfa grassland; Variation of NH4+-N content in different profiles was not significant (P>0.05). During the rapid-growth stage, 3-year alfalfa increased the soil NH4+-N content, the soil NH4+-N content had no significant differene with initial period in 5-year alfalfa grassland.4,Calculated the apparent budget of soil nitrogen at rapid-growth stage of alfalfa.3-year and 5-year alfalfa decreased the apparent surplus of soil nitrogen 745.80 kg/hm2, 1515.31 kg/hm2 during branch to early bloom period.