Study On Simulation Of Water Cycle And Crop Growth Process In Typical Well-irrigation Area

China is one of the most water shortage country in the world, where the water resources amount per person only accounts for 28% of world average. According to the national bureau of statistics, the total crop area, total crop yield, and the yield per unit area in China are keeping increasing, bringing greater challenges as well as better opportunities to agricultural irrigation. Thus, developing agricultural water-saving irrigation has becoming a strategic option in promoting agricultural productivity and alleviating the contradiction between water supply and demand. At present, three main problems exist in agricultural irrigation in China:(1) low effective irrigation rate, the total effective irrigation area in China is 0.937 billion mu, only accounts for 51.5% of the total farm area, where the water-saving irrigation area only accounts for 50% of the effective irrigation area. (2) low effective utilization of irrigation water, the total effective irrigation coefficient in China is only 0.53, which makes a huge potential for the improvement of water utilization efficiency. (3) severely polluted water ecology, the increasing irrigation water has caused a lot of funnels in North China and Northeast China. To solve the three main problems above, study of crop growth and field water cycle regulations is of high necessity. Currently, crop models are used in a great amount of studies in crop growth and yield assessment, but traditional researches only focus on the change of crop characteristics under different conditions, in order to optimize the field management model and increase the outputs, lacking of integration with other subjects. With the increase of pace speed of Chinese ecological civilization construction, the need of water ecology protection is rising. How to combine crop growth with local water ecology to study out a water-saving and yield-rising irrigation plan, is of great significance to the development of crop management rules and the protection of water ecology.Based on the problems and requirements in Chinese agricultural irrigation, we select a typical well-irrigation area (Anda water-saving and yield-rising demonstration area) as the experiment area. Based on the prototype observation, we collected information such as meteorology, hydrology, geology, soils, crops type, and agricultural management in study area, and analyzed the crop moisture and growth patterns of typical crops (corn) in growing season. Supported by the experiment information, DSSAT and MODFLOW were integrated to construct the simulating system of water cycle and crop growth process. Taking experiment area as the study area, through scenario simulation, the effect of different irrigation patterns and irrigation water amount to the growth and development of spring maize and the groundwater in plain area in Northeast China was studied. The main conclusions are as follows:(1) in 2015, the total maize growth period in study area was 172 days; total rainfall during the growing period is 379.5 mm, which is a normal precipitation year, with an average temperature of 19.8 C. Sprinkler irrigation and surface irrigation are two main irrigation ways in study area, in which the total sprinkler irrigation volume is 60m3/mu for once, and the surface irrigation volume are 60m3/mu and 40m3/mu separately for twice. Corn LAI and plant height increased from the end of May, where the maximum LAI is about 5.0, and the maximum height is about 2.5 m; in general, the difference between LAI and plant height under three irrigation patterns is not huge; the yield in transition zone, sprinkler zone and surface irrigation zone were 531.6 kg/mu,559.4 kg/mu, and 555.3 kg/mu separately, showing that the irrigation effect is very significant. Soil moisture fluctuates around 20% in study area, flattening with the increase of depth. The effect of irrigation and rainfall on soil moisture exceeds 80 cm of depth. The groundwater type in study area is phreatic water; groundwater flows from north east to south west, with a depth of about 6 m, showing a trend of drop-rise-drop in 2015, and a great mutation of groundwater level occurred around May 1 caused by irrigation.(2) On the basis of the basic data collected by prototype observation in study area, the DSSAT and MODFLOW model were integrated to construct the simulating system of water cycle and crop growth process, validated with the observation data. The final results of model fitting are as follows:the Compliance Index (D) values of LAI in three irrigation area were 0.986,0.985,0.981 separately; LAI root mean square error (RMSE) were 0.086,0.090,0.078 separately; height D values were 0.986,0.980,0.990 separately; height RMSE were 0.088, 0.046,0.032 separately, showing that the model simulation of LAI and plant height were very accurate. The simulation values and measured values of crop yield located nearly the 1:1 reference line, and the coefficient of determination R2= 0.9894 shows simulated and measured values has reached a high degree of agreement. The 20cm soil moisture D values under three irrigation methods were 0.594,0.638,0.548 separately and the RMSE were 0.003, in which the system error accounts for a larger proportion; the 40cm,60cm,80cm soil moisture D values in sprinkle area were 0.505,0.547,0.351 separately and the RMSE were 0.002,0.001,0.001 separately, where non-systematic errors account for a larger proportion. Field evapotranspiration D value in sprinkle area was 0.844, and RMSE was 0.038, where non-systematic errors account for a larger proportion. Groundwater level simulation D values is up to 0.968, and RMSE is only 0.010, showing a high accuracy in groundwater level simulation. Overall, the model has a high accuracy in LAI, plant height, yield, evapotranspiration and groundwater level simulation, while the accuracy of soil water simulation is relatively low which needs to be further improved.(3) the Anda rainfall frequency in late 50 years from 1964 to 2013 was arrayed using P-Ⅲ curve, and the year of 2011,2006 and 1999 were selected as a typical wet, normal and dry year separately. Referring to the historical irrigation results and rural irrigation application experience, combining water demand of corn at different growth stages, based on different irrigation quota and irrigation time, six kinds of irrigation schemes and one blank control program were made and applied in typical three years. The results show that:the program V is the best irrigation scheme to increase corn LAI and promote height growth; program VI is the best irrigation scheme to increase the yield and improve water productivity; the water table under the program VII has the largest increase, while the program Ⅵ will lead to the fall of water table. Selecting the crop yields, water productivity and the amount of groundwater level change as evaluation indexes, using the analytic hierarchy process to determine the weight of each index, seven kinds of schemes under different typical years were analyzed and evaluated. The results showed that:in dry years and normal years, program VI is the most optimal irrigation scheme; in wet years, program Ⅲ is the optimal irrigation scheme.