Effects Of Water And Nitrogen Coupling On Pasture Establishment In Hulun Buir

The continuous improvement of the quality of life have accelerated the transformation of the demand for livestock products from quantity to quality and safety flavor.It aggravated the pressure of natural pasture and grassland degredation,the area of degraded grassland in China reached 10.52×10⁷hm².To relieve the pressure of animal husbandry and promote the ecological restoration of degraded grassland,pasture establishment has become a necessary management mode of modern grassland agriculture system in China for its high productivity and ecological restoration function.As an important animal husbandry production base of in China,HulunBuir has a vast amount of natural grassland,in recent years,pasture has developed rapidly with an area of 8.84×10⁴ hm² reserved perennial pasture by the end of 2015 in the city,but only 0.1%of the total area of natural grassland.There also face some challenges,including small planting scale,lack of high-quality germplasm resources,low production performance,poor nutritional quality and short utilization years.It is needed developing and optimizing the pasture establishing modle.The experiemental trial is located in HulunBuir area,the study aims to identify the impact of nitrogen application and legumes-grasses mixed planting on the characteristics of pasture productivity,forage nutrition content and soil quality,hoping to provide guidance for pasture optimized model selecting and efficient environmental management measures formulating during pasture establishment in HulunBuir area.The main results were listed following:（1）There was a strong interspecific competition between alfalfa and Leymus chinensis due to resource constraints,which inhibited the development of two herbage populations,significantly reduced the aboveground biomass,detailly decreased by 31.17%and 28.17%,respectively,compared with alfalfa and Leymus chinensis monocropping.The yield of alfalfa+Bromus inermis mixture was significantly higher than that of alfalfa monocropping,but lower than that of Bromus inermis monocropping with a not significant difference.CP content and RFV of alfalfa+Bromus inermis mixture close to alfalfa monocropping and significantly higher than Bromus inermis monocropping.It is suggested that the mixed planting mode of Alfalfa+Bromus inermis should be adopted in the construction of pasture in HulunBuir.（2）The results of One-Way anova analysis showed that water supplement and nitrogen application had no significant influence on pasture production performance,but the water nitrogen coupling significantly increased the aboveground biomass.Under 150 kg N hm^-2a^-1 nitrogen addition with 16%water supplement,pasture aboveground biomass significangtly higher than the control(0 kg N hm^-2a^-1addition and none water supplement).Whereas the effect of water and nitrogen coupling on the productivity of alfalfa and Bromus inermis mixed planting was not significant.（3）Pasture establishment siginificantly improved soil quality and soil microbial activity to a certain extent.For second years,soil organic carbon content in 0-10cm and 10-20cm soil layer increased by25.8%and 22.04%,respectively,and the total nitrogen content of soil increased by 14.12%and 12.33%,respectively.（4）During forage growing period,the dominant form of soil inorganic nitrogen in pasture is NO₃^--N.Under the condition of no nitrogen application,soil NO₃^--N content has reached 3 times of soil NH₄⁺-N.The content of soil NO₃^--N rose to peak on July 21st,then decreased gradually with the grass growth,after in winter onOctober,the content tended to be stable and similar to soil NH₄⁺-N around 5 mg?kg^-1.Nitrogen application significantly increased the content of soil NO₃^--N and NH₄⁺-N,and the higher the samount of nitrogen fertilizer,the higher the content.（5）The net photosynthetic（Pn）rate of the species showed as:Madicago sativa<Bromus inermis<Leymus chinensis,and soil respiration intensity of pasture expressed as:legume-grass mixed planting>gramineous pasture>alfalfa pasture mixed planting with alfalfa significantly improved grasses Pn and soil respiration.The top point of pasture soil respiration intensity always appeared between 10:00-12:00a.m.The CO₂ emission flux in soil-vegetation system fluctuated between July and October,but the change trend basically similar,all pastures showed a multi peak change with two distinct peak appeared at the beginning of August and September 20^th.Regression analysis showed that system CO₂ emission flux was positively correlated with the temperature inside the box,5cm ground temperature,10cm ground temperature and soil volumetric moisture content,but the relationship with soil DOC content and pH value was not significant.In conclusion,the model of alfalfa+B.inermis mixture was recommended in Hulunbuir region which would not only increase the pasture productivity,and also the nutritional quality.During summar drought period,certain irrigation was needed to sustain a full stand of seedlings.Nitrogen application had no significant effect on pasture biomass and quality,accumulated amount NO₃^--N in soil tended to leaching to the bottom of soil layer,reducing the economic benefit of nitrogen application and cause environment pollution,thus,timely and proper application of nitrogen fertilizer is needed.Water and nitrogen coupling improved pasture productivity and quality to a certain extent.