The Respond Of Alfalfa Yield And Soil Quality To Nitrogen And Phosphorus Fertilizer Applied In The Loess Plateau Semi-arid Areas

Alfalfa (Medicago sativa L.) is one of the main forage grass species in returning farmland and grassland in the loess plateau region, it plays an important role in reducing soil erosion and improve soil ecology condition. To explore the land management of artificial alfalfa in the loess plateau semi-arid areas, we designed two years of.field trials in the Lanzhou University Experiment Station, Yuzhong county, Gansu province, two sites of different alfalfa land was designed to completely randomized block, set up six processing, namely NOPO (no nitrogen and phosphorus), N0P17 (no nitrogen and low phosphorus), N0P34 (no nitrogen and high phosphorus), N70P0 (nitrogen without phosphorus), N70P17 (nitrogen and low phosphorus), N70P34 (nitrogen and high phosphorus).3 replications, so there are 18 blocks in each site. Experimental study on the yield, yield components of alfalfa, soil moisture and soil microorganism, enzyme activity under typical loess plateau climate, and the differences between the nutrient change under different fertilization conditions, we also discussed the differences performance between different stand years of alfalfa. The conclusions are as follows:Yield and yield components:Phosphorus can significantly increase the production of alfalfa in 4-year and 9-year grassland, nitrogen only plays a significant role in long term years of alfalfa production, nitrogen and phosphorus fertilizer have no interaction.4-year alfalfa site cumulative yield of 2013-2014:N0P17、N0P34、N70P17、N70P34 treatments significantly increased by 36.5%,52%,42.9%,64.8% when compared with NOPO treatment in alfalfa aboveground biomass dry weight.9-year alfalfa site cumulative yield of 2013-2014:N0P17、N0P34、N70P17、 N70P34 treatments significantly increased by 34.1%、47.7%、65.4%、105.3% when compared with NOPO treatment in alfalfa aboveground biomass dry weight. Phosphate significantly improved single stem weight both in 4-year and 9-year of alfalfa grassland.Soil water consumption and water use efficiency:In the 4-year alfalfa site and 9-year alfalfa site, soil water consumption of each layer have no significant difference with the increase of fertilizer rate, shows that fertilization can not intensify soil water consumption. In the 4-year alfalfa site, two years of accumulated water use efficiency shows that phosphorus can significantly improve the efficiency of water use, nitrogen had no significant effect, nitrogen and phosphate have no interaction. In the 9-year alfalfa site, two years of accumulated water use efficiency shows that phosphorus can significantly improve the efficiency of water use, water use efficiency of high phosphorus with nitrogen treatment was significantly higher than that of low phosphorus treatment, nitrogen and phosphorus fertilizer have no interactionAfter fertilizing for four years, soil quality changes:The total nitrogen (N):In the 4-year alfalfa site, the total nitrogen is more stable than that at the 9-year alfalfa site. Soil available phosphorus (P):available phosphorus increased dramatically in 4-year alfalfa site, while increased slowly in 9-year alfalfa site. Microbial phosphorus: Microbial biomass and soil available p content have significant positive correlation in both sites.Soil phosphatase activity:In 4-year alfalfa site, acid phosphatase activity has significantly negative correlation with soil available P, as the available P in the 9-year alfalfa site has a downward trend, but no correlation. Alkaline phosphatase activity have no correlation with soil available P in two sites, Two acid phosphatase activity have no correlation with the mineralized nitrogen content in both sites, whereas, alkaline phosphatase activity have significant correlation with the mineralized nitrogen content in both sites.Soil C/P ratio:In the 4-year alfalfa site, as the phosphorus C/P ratio are significantly reduced, and change over time, the C/P ratio of NOP17、N0P34 and N70P34 decreased significantly, in the 9-year alfalfa site, C/P ratio are decreased significantly in treatments N70P0、N70P17 and N70P34.Soil phosphorus surplus:In 4-year alfalfa site, output of phosphorus do not increase significantly with the increase of phosphorus fertilizer gradient, the 9-year alfalfa site, output of phosphorus increased significantly with the increase of phosphorus fertilizer gradient, Both of P residue with gradient and application rate of phosphoric fertilizer increased significantly, in 2013, in the 4-year alfalfa site, add nitrogen fertilizer can significantly reduce removal capacity surplus when apply high phosphorus, in the 9-year alfalfa site, add nitrogen fertilizer can significantly reduce removal capacity surplus when apply low phosphorus.To conclusion, N0P17 is the most suitable fertilization scheme in 4-year alfalfa site. N70P34 is the most suitable fertilization scheme in 9-year alfalfa site.