Study On The Water Saving Mechanism And The Optimal Irrigation Schedule Of Artificial Grassland In The West Of Jilin Province

The west of Jilin Province is one of the important bases of animal husbandry in our country, as great grazing pasture and mowing pasture with flat grassland and richness plant species. In recent years, extensive operating and mismanagement cause a series problems: grassland seriously degrades; the environment of grassland deteriorates extremely; the amount of livestock increases but the yield of grass reduces. The supply of nature forage grass is inadequate, which is the bottleneck of the animal husbandry development in the west of Jilin Province. The effective solution to solve this problem is developing intensive grassland animal husbandry——establishing artificial grassland and semi-artificial grassland, developing irrigation and fertilizing for grassland and selecting quality herbage. Irrigation system is important for establishing artificial grassland, but the west of Jilin Province is semi-arid area, which is lack of water for irrigating artificial grassland. Therefore, the save-irrigation should be realized and the irrigation system should be established, which is important for artificial grassland in the west of Jilin Province.With shortage of water resources and increase of irrigation expense, we need not only high unit yield, but optimal economic benefits, which are new goals for irrigation science. Limited irrigation accords with the new theory of irrigation science. The limited irrigation quota is allocated optimally in time sequence and amount, which is named optimal irrigation schedule. This thesis studied the water saving mechanism about artificial grassland in the west of Jilin Province and designed the optimal irrigation schedule.This thesis studied the important herbage——alfalfa in Songyuan area of Jilin Province as the breakthrough point. Firstly, based on the data of the experimentation of limited irrigation of alfalfa, we got the proper model of water production function and the parameters of the model for alfalfa of Songyuan area in Jilin Province. Then we established optimization model of irrigation schedule for alfalfa,and presented solution method for the model. At last, we developed software about the optimal design of irrigation schedule, and validated the reliability and practicality of this software through an example. The concrete study contents are as follows:1. Because the water saving mechanism and the optimal irrigation schedule about alfalfa artificial grassland in Songyuan area of Jilin Province is the key study object, we developed the experimentation of limited irrigation of alfalfa in the grassland station of QianGuo County of Songyuan area in Jilin Province. Through the experimentation and observation in 2006 and 2007, we got the firsthand data for the study of water demand and consumption rules of alfalfa.2. Based on the data of the experimentation, we got parameters of the five models of water product function which are Jensen, Minhas, Blank, Stewart, Singh by using multiple regression analysis. Compared the parameters of the five models, we got the conclusions as follow: (1)Jensen model is most suitable for alfalfa in Songyuan area of Jilin Province; (2)The water stress sensitivity indexes of five stages (returning green stage, branching stage, budding stage, flowering stage and ripening stage) are as follows: 0.1015, 0.5146, 0.3728, 0.3516, 0.1786; (3)The most water stress sensitivity period of alfalfa is branching stage, the second sensitivity periods are budding stage and flowering stage, the third sensitivity period is the ripening stage, and the last water sensitivity period is returning green stage.3. At first, this thesis established two dimensional dynamic programming optimization model based on the characteristics of optimization model of irrigation schedule. Through analyses of the process of using dynamic programming successive approximation (DPSA) to solve the model, we found that the model ignored the relation between soil moisture and evapotranspiration to cause results wrong, which didn't accord with the process of soil moisture subsiding. Then we gave the improvement scheme for the model as follow: added soil moisture subsiding model to that model, then it transformed tow dimensional decision making problems into one dimensional. 4. To solve the improved model, this thesis gave two intelligence optimum algorithms——simulated annealing algorithm (SA) and chaos optimization algorithm (CA). SA, which accepts the optimal value by probability, increases agility of its searching process and avoid local optimized solution. CA, which searches optimal solution in the solution space by using chaos variables based on chaotic motion rule, can avoid local optimized solution with high searching efficiency.5. Based on the established optimization model and its solution methods, this thesis developed software about the optimal design of irrigation schedule, and used this software to design the optimal irrigation schedule according to the data of the experimentation in the grassland station of QianGuo County of Songyuan area in Jilin Province in 2007. The result accorded with the practical situation, which validated the reliability and practicality of this software. 6. Through analysis of the design the optimal irrigation schedule of alfalfa in 2007, we got that branching stage, budding stage and flowering stage are key water requirement periods, whose water quota is more than 70% of the total water supply. Therefore, if we want to get the higher yield with limited water, we should meet the three stages'requirement of water need firstly. Precipitation, which is one of the most important parts of water supply for alfalfa, should be reckoned in the total water supply while distributing water.