Study On Water Supply-demand Equilibrium And Ecological Adaptability Of Dryland Farming Systems In Hot And Summer Drought Areas

Precipitation is the major water resource in dryland farming systems of hot and summer drought areas. To use agricultural water resources rationally, meliorate contradiction of water supply and demand, propose optimization scheme of adjusting agricultural water use, get the ultimate goal to efficiently use of precipitation, the study of precipitation supply-demand state, evaluation of water ecological adaptability in dryland farming systems are terribly necessary.In this study, with the basic objective to optimize species of crops and reuse precipitation, according to survey data and field test results, taking representatives of hot and summer drought areas, Fengjie, Wanzhou, Shapingba as study areas, water demand was calculated for several major crops as wheat, corn, sweet potato, potato, horsebean, soybean, rape and the main planting patterns as wheat-corn-sweet potato, horsebean-corn-sweet potato, wheat-corn-soybean, potato-corn-sweet potato, horsebean-corn-soybean, rape-corn-sweet potato, analysed systematically the temporal relationship between crop growth and rainfall distribution, water supply-demand equilibrium and dislocation characteristics of the main crops and planting patterns in farmland with the slope 0°,5°, 10°,15°,20°,25°, on different years of rainfall types, and evaluated by mathematical model of water ecological adaptability, in order to provide scientific guidance for optimizing planting system and improving production techniques. The main results were as follows:(1) Distribution characteristic of precipitation in time and space and effective rainfall:There was large change in Chongqing annual rainfall, and since 1994, this wave was being great. The average rainfall centralized mainly in four months period from May to September, accounting 68.62% of total annual rainfall, of which the maximum rainfall appeared in July. Three rainfall types year of Fengjie were mainly decided by actual rainfall in the months from May to September. Precipitation from May to September accounted 76.48% of the total rainfall in wet year, the percent in average year was 67.34%, and dry year was 64.39%. The month rainfall differences of three rainfall types year in Wanzhou was mainly centralized in the months from July to September, precipitation from July to September accounted 51.46% of the total rainfall in wet year, the percent in average year was 51.46%, and dry year was 50.49%. The most obvious rainfall difference of three rainfall type year in Shapingba appeared in July, in the wet year, the rainfall of July accounted 38.45% of the total rainfall, and just 9.97% in average year,3.25% in the dry year. In the same region and the same rainfall type, the effective rainfall was less and less as the slope increasing. Compared with 0°farmland, the effective rainfall in the farmland with slope of 5°,10°,15°,20°, 25°was decreased by 4%,12%,20%,27 and 35% respectively.(2) Crop water demand and crop coefficient in dry land: the order of average annual reference evapotranspiration of three study regions and Beibei was Fengjie>Beibei>Wanzhou>Shapingba. The monthly distribution of daily average reference evapotranspiration was similar with temperature distribution, of which higher values appeared in the months from May to August. The order of major single crops coefficient with whole growth period was sweet potato potato>soybean>horsebean >rape>maize>wheat. As the same crop or the same planting pattern, the order of water demand in different regions was Fengjie>Beibei>Wanzhou>Shapingba. As the same region, the order of different complex planting pattern water demand was: rape-corn-sweet potato >horsebean-corn-soybean>potato-corn-sweet potato>wheat-corn-soybean>horsebean-corn-sweet potato>wheat-corn-sweet potato.(3) Water supply-demand equilibrium characteristic of the main dryland crops and cropping patterns in hot and summer drought areas: In the same rainfall type year, water satisfaction rate of monoculture crops and complex cropping patterns in different study regions was less and less as the as the slope increasing. The growth period of complex planting pattern was the whole production year, in the same study region, the water satisfaction rate of complex planting patterns was related to rainfall type, and the order was wet year>average year>dry year. In the flat farmland, sweet potatoes, corn and soybeans were appropriate to plant in wet and average year, wheat and rape could be chosen in dry year as a few suitable crops in Fengjie. The monoculture crops suitable for Wanzhou in three rainfall types were more, such as corn, potatoes, horsebean and rape. The water satisfaction rate of monoculture crops in Shapingba were greater than or equal to 1, on which could choose the crop varieties according to actual needs. As Fengjie there was just wheat-corn-sweet potato, horsebean-corn-sweet potato and wheat-corn-soybean could be planted on smaller slope land in wet year. But for Wanzhou, all of the complex planting patterns were suitable in wet year, and wheat-corn-sweet potato could be chosen in average year. As Shapingba, wheat-corn-sweet potato, horsebean-corn-sweet potato and wheat-corn-soybean were suitable in average year.(4) The rule of water ecological adaptability of dryland farming systems in hot and summer drought areas: According to water ecological adaptability index size and stability of growth period in three study regions, the order was Shapingba>Wanzhou>Fengjie. The whole growth period was disparted into four parts asⅠ,Ⅱ,ⅢandⅣ. Then analysed the water ecological adaptability index of four growth periods separately. Monoculture crops with low water ecological adaptability index (less than 0.9) in Fengjie were wheat which ecological adaptability index in whole and II growth period was 0.85 and 0.84, potato which ecological adaptability index in whole growth period was 0.85, maize which ecological adaptability index in whole and III growth period was 0.89, horsebean which ecological adaptability index in whole,ⅡandⅢgrowth period was 0.79,0.8 and 0.73 respectively, rape which ecological adaptability index in whole andⅡgrowth period was 0.77 and 0.75. As the Wanzhou, wheat in II was 0.85, horsebean in the whole,ⅡandⅢwas 0.81,0.8 and 0.89 respectively, rape in II was 0.77. As Shapingba, horsebean in II was 0.89. The water ecological adaptability index order of complex planting patterns in three study regions was Shapingba>Wanzhou>Fengjie. Patterns with low water ecological adaptability index (less than 0.8) in Fengjie were potato-corn-sweet potato which was 0.78, rape-corn-sweet potato which was 0.73, and horsebean-corn-soybean which was 0.75.(5) Agricultural water-saving and drought-resistance countermeasures of dryland:As the characteristics of high frequency and long duration of summer hot and drought, uneven spatial and temporal distribution of rainfall in hot and summer drought areas, some measures should be taken to meliorate water resources utilization and improve dryland agricultural sustainable development ability, such as planting structure and planting time adjustment, using conservation tillage, cultivating drought-resistant varieties, taking biological drought-resistance technology, building water-storage project and developing building agriculture.