Evaluation Of Soil Water Resources Under Organic Dry Farming In Shanxi Province

Shanxi Province is located in an arid and semi-arid area and is one of the provinces with the most serious water shortages in our country.Water resources are unevenly distributed in time and space and drought occurs frequently.This kind of provincial and agricultural conditions determines that Shanxi Province must take the road of organic dry farming,and use soil to store water to meet the water resources needed for agricultural production.The evaluation of soil water resources in Shanxi Province can adjust the irrigation system and planting structure of organic dry farming from the perspective of water cycle,effectively improve the utilization efficiency of precipitation resources,thereby optimizing the allocation of water resources and reducing agricultural water consumption will help alleviate the current water shortage in Shanxi Province.This research combines the actual situation of organic dry farming in Shanxi Province,based on the theoretical research of soil water resources and the principle of water balance,to determine the calculation methods and evaluation indicators of soil water resources.Use the Tyson polygon to calculate the surface precipitation value of Shanxi Province from 1999 to 2018,and select the hydrological years of different frequencies in Shanxi Province from the theoretical frequency curve.Use the moving average method,the cumulative anomaly method and the linear tendency method,combined with the Mann-Kendall trend test method to analyze the trend of annual precipitation in Shanxi Province.Finally use the daily precipitation data of Shanxi Province in typical years,under the condition of no irrigation and no coverage,calculate the soil water resources in Shanxi Province in typical years based on the SIMDual Kc model and the principle of water balance.The temporal and spatial distribution of soil water resources and the water demand during the growth period of main crops in Shanxi Province have been systematically studied.The main findings are as follows:(1)Determine 2010,2012,and 2014 as the dry year,normal water year,and wet year in the hydrological year of Shanxi Province.The precipitation in 1999-2018 has a large inter-annual variation.The difference between the minimum annual precipitation and the maximum annual precipitation is 1.7 times,showing an overall upward trend,and the upward trend is significant.The monthly precipitation in Shanxi Province is unevenly distributed throughout the year.There is more precipitation in summer,and the precipitation is highly concentrated,with the least precipitation in winter.The precipitation in spring and autumn is in the transitional period of summer and winter.(2)The typical hydrological representative year’s precipitation flood season is July,August,and September,and the average precipitation in the flood season accounts for 63.85% of the annual precipitation.The peak monthly precipitation in a wet year is smaller than the peak monthly precipitation in a dry year and a normal year,but the total precipitation in a wet year is higher than that in a dry year and a normal year.There was no heavy rain >50 mm/d during the year.The precipitation days with precipitation <5 mm accounted for 85.9% of the total precipitation days on average,while the precipitation with >25 mm was less than 20% of the annual precipitation.The rainfall intensity is too small to meet the growth needs of plants,which is the main reason for the drought and water shortage in Shanxi Province.(3)The changes in the temporal and spatial distribution of soil water resources in Shanxi Province are basically consistent with the changes in the temporal and spatial distribution of precipitation.In areas with a lot of precipitation,soil water resources are relatively large.In terms of time,the amount of soil water resources is the largest in the wet year,followed by the normal water year,and the least in the dry year.The months with the larger amount of soil water appear from July to September,which is consistent with the distribution of monthly precipitation during the year.In terms of space,the spatial distribution of soil water resources in Shanxi Province is obviously uneven,showing that the eastern part is lower than the western part.Among them,Taiyuan City and Yangquan City have the least amount of soil water resources,while Xinzhou City has the most,which is related to the area of arable land and the distribution of precipitation in each city.(4)The evaluation coefficient of soil water resources in Shanxi Province is 80.69% in wet years,followed by dry years and the minimum in normal year is 72.35%.Soil water resources provide a certain degree of crop water demand for crop growth and development,and the contribution rate is high,but there is still room for utilization of precipitation in dry years and flat water years.The coefficient of soil water resources in Shanxi Province is less than 0.30 in dry years,normal years and wet years.The soil water resources coefficient of each city is less than 0.50,and there is still a lot of room for the use of precipitation,which can increase the use of precipitation resources.(5)The amount of soil water resources during the growth period of winter wheat is significantly lower than that of summer corn.The evaluation coefficient of soil water resources during the growth period of winter wheat is lower than that of summer maize,and the water loss is relatively large.The evaluation coefficient of soil water resources in wet years is 55.35%,indicating that even in wet years,about 50% of crop water requirements are needed to supplement the shortage of soil water resources.The jointing-filling period of winter wheat is the key stage of water demand,and the moisture loss during the overwinteringjoining period is serious,so it is necessary to pay attention to timely replenishment of farmland irrigation water during the growth period of winter wheat.The evaluation coefficient of soil water resources for summer maize is 90.81% on average.In the jointing period when more water is needed,there is even a water surplus.It shows that the water conditions are better,and the soil water resources can basically meet the water requirements for the growth of summer corn.