Optimization Of Winter Wheat Irrigation Schedule In Guangzhong Region Shaanxi Province By Crop Models

In order to study the law of water requirement, and water effect on dry matter accumulation and yield of winter wheat,a 2-year water-controlled experiment of winter wheat was conducted to calibrate and validate SIMDualKc model and CERES-Wheat model. SIMDualKc model was used to estimate evapotranspiration and soil evaporation of winter wheat. On the basis of the simulation, we investigated the relationship between soil evaporation ratio and meteorological factors(minimum temperature, maximum temperature, average relative humidity, wind speed at 2 m above ground surface, solar radiation), and crop factor(ground surface coverage) by using the path analysis method. Dry matter accumulation, as well as yield formation and transportation was studied by using dry matter and yield data of different water treatments. After that, the water prodution of winter wheat was solved. Simulated irrigation experiment of different higher and lower limit was conducted by using CERES-Wheat model. For the purpose of yield improving and water saving, we evaluated different irrigation schedules. This study can be a guidance to water saving and irrigation decision making of winter wheat in Guanzhong region. Main conclusions of this study are showed as follows.(1) SIMDualKc model could accurately simulate evapotranspiration and soil evaporation of winter wheat under different irrigation schedules. Modeling result showed that the key water requirement period of winter wheat was from jointing to grain filling stage, and the soil evaporation ratio in the whole winter wheat growth stage was highest in the mid season stage, followed by the late season stage, crop development stage, and initial stage. On the basis of the simulation, we investigated the relationship between soil evaporation ratio and meteorological factors(minimum temperature, maximum temperature, average relative humidity, wind speed at 2 m above ground surface, solar radiation), and crop factor(ground surface coverage) by using the path analysis method. The result showed that the irrigation only affected soil evaporation in a short period, while ground surface coverage affected it most in a long period. A regression model of soil evaporation ratio and ground surface coverage was developed by using the soil evaporation ratio simulated by SIMDualKc model and the ground surface observed in the field experiment. The regression model could accurately calculate soil evaporation of winter wheat under different water conditions with determination coefficients 0.721-0.902 and it could be used as a simplified method to calculate soil evaporation.(2) Continuous drought during green and jointing stage will inhibit the process of dry matter accumulation of winter wheat. Irrigation at wintering stage will directly inlunence soil water conditon at the beginning of green stage because of a long period of wintering stage. Therefore, irrigation at wintering stage is significant to dry matter accumulation of winter wheat. Continuous drought before anthesis will inhibit transportation of dry matter to grain. Drought during heading and grain filing stage will reduce dry matter accumulation after anthesis. Effective spike number affects yield most with a decision-making coefficient of 0.348. Water supplication during green and jointing stage should be ensured for the purpose of ensuring effective spike number. Water sensitivity indexes of jointing to heading, green to jointing, and grain filling to mature come first to third in each growth stage, and soil water conditon during green to jointing affects dry matter accumulation and formation of effective spike number, while soil water conditon during grain filling stage affects formation and weight of grain.(3) The key growth period of winter wheat(flowering and maturity), dry matter, and grain yield can be simulated well by CERES-Wheat model with a absolute value of the relative error of less than 15%. P1 V should be re-estimated for different water treatments. Dynamic process of soil moisture, dry matter accumulation, and soil moisture changing can be be simulated well by CERES-Wheat model. Water stress factors have a big influence on dynamic simulation of wheat growth, and water stress factor still need to re-estimated for different water treatments.(4) The lower limit of irrigation have a significant influence on irrigation frequency, irrigation amount, grain yield, and irrigation water use efficiency of winter wheat. A high lower limit of irrigation can help to obtain high grain yield, while can lead to frequent irrigation and a large irrigation amount. For the purpose of avoiding a serious cut of grain yield, the lower limit of irrigation should be 60%~65% of field capacity. The influence of higher limit of irrigation on irrigation frequency, irrigation amount, grain yield, and irrigation water use efficiency of winter wheat is corresponding to the relevant lower limit. A high lower limit of irrigation can lead to a water-sufficient condition, which will lead make the effect of higher limit not significant. The higher limit of irrigation in wintering to green, jointingheading and heading-grain filling should be more than 90% of field capacity, for the purpose of improving grain yield and irrigation water use efficiency. In water-controllde conditon, the higger limit of irrigaiton in seedling-wintering, wintering-greening, greening-jointing, jointing-heading, heading-grain filling, grain filling-mature should be 90%, 95%, 85%, 100%, 90%, and 80% of field capacity, respectively.