Simulation Of The Physiological And Ecological Processes And Researchof The High Efficient Water Irrigation Scheduling On Planted Forage Grass

Because of the over-grazing and unreasonable reclamation, the ecological condition of the grassland in Inner Mongolia is worsening, for example, the grass gradually sparsing, desert spreading etc, and agricultural development has been seriously affected. In order to maintaining the ecological balance, protecting the environment and alleviating the pressure of grazing, forage grass is planted that becomes one of important content in agricultural structure adjusting and constructing. Water requirement of forage grass is one of decisive factors in the course of the growth and development. At present, more and more research on crop water requirement are related to the content of plant physiological ecology.In this paper, Elymus, Leymus, Agropyron and Medicago in the Otinday Sandy area are selected as a typical forage grass for irrigation experiment. The research contents include grass physiological and and ecological process simulation,crop water requirement, high efficient water irrigation plan, the soil moisture content threshold in effective root zone and invalid water requirement, etc. The main results are as follows:(1)By correlation analysis, partial correlation analysis, path analysis and decision-making coefficient between the transpiration rate and photosynthetic rate of the planted grass and environmental factors, the relations of the transpiration rate and photosynthetic rate of the planted grass with environmental factors are revealed. The transpiration and photosynthesis of the planted grass is mainly affected by photosynthetic active radiation(PAR), followed by the other environmental factors in different degree.(2)Based on AGA , the non-rectangular hyperbolic model, rectangular hyperbolic model and rectangular hyperbola correction model are established to modelling the light response of the planted grass. The results show that the simulated effects of three models for the photosynthesis rate and transpiration rate on the light response of Elymus, Leymus, Agropyron and Medicago are better. The exponential models are established to describe the transpiration rate of planted grass for air temperature and humidity response.(3)Based on analysing the relationships between stomatal conductance of the planted grass and environmental factors, and considering the applicability and limitations of classical stomatal conductance model (Jarvis class model and the BWB model), the composite S curve model solved by AGA is proposed to simulate the stomatal conductance changes with environmental variables. The studies show that the composite S curve model can reflect the complicated nonlinear relationships between the environmental variables and stomatal conductance of planted grass better.(4)Based on the energy balance principle and the turbulent diffusion theory, and the stomatal conductance model coupled with energy balance model, the two-source model in canopy-scale are established by two kinds identifying methods for model parameters. The simulated effects of the crop latent heat flux and transpiration are better.(5)The revised basal crop coefficients are proposed for local planted grass by AGA with globe convergence in terms of local metrological and hydrological condition. The water requirement of Elymus, Leymus, Agropyron and Medicago are caculated by the dual crop coefficient approach presented in FAO-56 during 2004 and 2005. The results show better for modelling variation of the evapotranspiration of the planted grass.(6)From qualitative and quantitative view , the correlation diagram method, fitting the residuals indicated the estimation error and correlation analysis are used for verifying the validity of the evapotranspiration, soil evaporation between plants and the effective soil moisture content in root zone.(7)The high efficiency water irrigation scheduling of the planted grass are determined. After the implementation of the high efficiency water irrigation plan, water use efficiency of the planted grass are improved in some degree, for example, the water use efficiency of Elymus, Leymus, Agropyron and Medicago are increased 0.19,0.1,0.09 and 0.17 kg·m-3.(8)Taking crop water stress as the starting point to analysis the soil moisture threshold, irrigation plan should be designed to meet Dr less than RAW or DP equal to zero. The soil moisture threshold in effective root zone is the down bound of photosynthetic efficiency. The upper bound should not exceed the threshold too much. From crop transpiration validity view to analysis the soil moisture threshold and from the crop yield and water demand, photosynthesis and soil moisture in root zone view to estimate the moisture content of planted grass threshold. According to the experiment results, the invalid transpiration is less and higher yield when the soil moisture content maintain in 55% -70% of the field water capacity during the growing season.