| The Hetao Irrigation District(HID)is the largest irrigated region in China,a major grain and oilseeds base,and an important ecological barrier in the north.Due to the unique climatic conditions and the agricultural production is almost completely dependent on irrigation in HID.A special irrigation system,autumn irrigation,has been gradually found out in the production practice year by year,which has the advantages of water and salt to preserve soil moisture,ensure timely sowing of crops in the next year,and meet the water and salt conditions needed for seed germination and seedling growth.In recent years,with the shortage of water resources in the Yellow River and the increase of non-agricultural water consumption,the ecological protection and high-quality development of the Yellow River Basin have been realized.It is particularly important to explore the suitable autumn irrigation mode to ensure the normal growth of crops under the condition of the decreasing agricultural adjustable water index.This study first on the site first to Soil-Water-Atmosphere-Plant WOrld FOod STudies(SWAP-WOFOST)model parameters sensitivity analysis and calibration,and then construct the regional scale distributed SWAP-WOFOST model and verification,and then from the preliminary discussion on the different time and space scale autumn water the mode of soil water salt and crop growth process of quantitative evaluation of spring wheat yield and water productivity(WP).In order to improve the WP of spring wheat,a relatively suitable autumn irrigation mode was proposed.It provides some reference for the future research on the efficient utilization of soil and water resources in cultivated land and the evolution of agricultural soil and water environment.The results as follows:(1)The simulation values of SWAP-WOFOST model well reflect the variation trend of the measured results,and the simulation accuracy is all within the acceptable range.The model verified and calibration can well simulate the distribution of soil water and salt and crop growth under different autumn irrigation modes.(2)Under different autumn irrigation modes,compared with before autumn irrigation,the soil moisture of 0～20 cm in each county of the HID increased significantly after autumn irrigation,and the soil salt concentration decreased significantly,averaging 31.09%and61.88%,respectively.The soil moisture increased from 8.47～13.04%before sowing to before autumn irrigation.Soil salt concentration decreased from 12.07～21.49%.The soil moisture before sowing and after autumn irrigation decreased by 12.60～17.67%.The soil salt concentration increased by 47.23～51.41%,and the soil resalting was more serious through the soil freeze-thaw period after autumn irrigation.The results showed that the effect of autumn irrigation on the salt washing of soil ploughing layer was obvious and could play the role of water storage and soil moisture conservation in the next spring sowing.According to the different patterns of precipitation year,the soil moisture in wet year was higher than that in normal year and lower than that in dry year,and the soil salt concentration in wet year was lower than that in normal year and lower than that in dry year.With the increase of autumn watering quota or the postponement of autumn watering time,the increase of soil moisture was larger,and the decrease of soil salt concentration was larger.(3)Under different autumn irrigation modes,the average annual groundwater depth was 102～147 cm in HID,and the average annual groundwater depth in Hangjinhouqi and Linhe was larger,136 and 133 cm,respectively.The average groundwater depth in Wuyuan and Dengkou is smaller,which is 122 and 111 cm,respectively.The average annual groundwater depth of Wulateqianqi is the smallest,which is 103 cm.According to the different patterns of precipitation years,the groundwater depth in dry years is greater than that in normal years and higher than that in wet years.With the increase of autumn irrigation quota,or with the postponement of autumn irrigation time,the groundwater buried depth is smaller.(4)Under different autumn irrigation modes,the spatial distribution of spring wheat yield and WP were similar,which were higher in Hangjinhouqi and Linhe,followed by Wuyuan,and lower in Dengkou and Wulateqianqi.Compared with the basic scenario,the average annual yield and WP of spring wheat in the scenario four were the highest and increased by 4.80%and 4.39%,respectively,while the average annual yield and WP of spring wheat in the scenario two were the lowest and decreased by 0.83%and 0.14%,respectively.The yield and WP of spring wheat were higher in wet year than in normal year than in dry year under different precipitation year patterns.Compared with the basic scenario,under the other autumn irrigation modes,the average yield and average WP of spring wheat increased by 1.11%and 3.42%in the dry year,and the average yield and average WP of spring wheat increased by 1.03%and 0.62%in the wet year,respectively.(5)With the goal of maximizing spring wheat WP,compared with the basic scenario,the annual average spring wheat yield and WP increased by 6.13%and 6.94%under the autumn irrigation mode recommended by each county in HID,while the irrigation water from Yellow River increased by 41 million m~3.On the spatial scale,the spring wheat WP in the HID was the highest in most years under the scenarios four.The annual average yield and WP were 4986 kg/ha and 1.17 kg/m~3,respectively,which were 4.80%and 4.39%higher than that under the basic scenario.However,the amount of irrigation water from Yellow River was reduced by 204 million m~3.Therefore,in order to improve the WP of spring wheat and save the water amount from the Yellow River,the relatively appropriate autumn irrigation mode is recommended to irrigate 125 mm on September 30 in HID.The specific autumn irrigation mode of different precipitation years in each county can be referred to the recommended autumn irrigation modes. |
