| Slope farmland accounts for about 1/3 of the total cultivated land in China,which is of great significance to ensure China’s food production.As one of the advanced and commonly used agricultural water-saving irrigation technologies,sprinkler irrigation has many advantages,such as water saving,labor saving,yield increasing,strong terrain adaptability,easy to promote irrigation mechanization,automation and so on.It is widely used in slope irrigation.Affected by the terrain slope,sprinkler irrigation on sloping land is more likely to accumulate water than the flat land,and produce surface runoff,which resulting in surface runoff,low water uses efficiency and poor irrigation quality.In addition,the uniformity of water distribution on the surface is low,and the uneven distribution of water will reduce the uniformity of soil moisture,which will bring adverse effects on crop growth.Therefore,in order to solve the above problems,this paper established the mathematical model of soil water movement by combining experiment and simulation,explored the characteristics of soil water infiltration,put forward the calculation model of the allowable sprinkler irrigation rate,and gave the measures to increase soil moisture uniformity.So as to increase the water uses efficiency of sprinkler irrigation,improve the soil moisture uniformity,and provide a certain basis for the optimization of technical parameters of sprinkler irrigation system.The main research contents and results are summarized as follows"(1)A mathematical model of soil water movement was established based on unsaturated soil hydrodynamics theory,and its accuracy was verified by experiments.The model was applied to analyze the effects of terrain slope,sprinkler working pressure and sprinkler spacing on soil water infiltration.The results show that the smaller the slope,and the greater the sprinkler working pressure,led to the more uniform the soil water infiltration,the deeper the soil water infiltration depth,and the higher the average water content.When the sprinkler spacing is less than a certain value,the soil water infiltration depth is deeper and the average water content is higher,and when the sprinkler spacing increases to a certain extent,the effect of sprinkler spacing on soil water infiltration increases,and the soil water infiltration depth and average water content decrease rapidly with the increase of sprinkler spacing.Therefore,when the Rainbird R5000 sprinkler is used for slope irrigation,it is suggested that the sprinkler system should be arranged on the gentle slope,within the working pressure range recommended by the manufacturer,the working pressure of the sprinkler should be greater than 300 k Pa,and the suitable sprinkler spacing is 8m-10 m.(2)A calculation model of maximum allowable water application rate on sloping land was established,which was based on the principle of hydrological,and the accuracy of the model was verified by experiments.The model was applied to analyze the effects of soil texture,terrain slope and irrigation quota on the maximum allowable water application rate.The results showed that the heavier the soil clay ratio,the steeper the terrain slope,and the more irrigation quota,led to the smaller the maximum allowable water application rate,and the longer the irrigation time.Considering the operation efficiency and energy consumption of sprinkler system,when the Rainbird R5000 sprinkler is used for sprinkler irrigation on sloping land,it is suggested that the maximum allowable water application rate of clay soil should be controlled within 0.118 mm/min and that of sand soil should be controlled within0.461 mm/min.The maximum allowable water application rate can be reduced according to the terrain slope.It is suggested that the maximum allowable water application rate should be reduced by 11.69% when the slope increases by 5%.When the irrigation quota is greater than 30 mm,the allowable sprinkling irrigation intensity should be reduced by 50%.(3)The optimization method of sprinkler irrigation technical parameters based on soil moisture uniformity was put forward,and the soil water movement model of sprinkler irrigation was applied to analyze the influence of terrain slope,sprinkler working pressure and sprinkler spacing on soil moisture uniformity,the optimization method of technical parameters of sprinkler irrigation was established based on the antagonistic cross evaluation.The results show that the larger the slope,the more uneven the surface water distribution and soil water distribution.The average CU of surface water distribution is about 10.3% lower than that of CU of water distribution,and decrease of the soil water distribution of downhill is more obvious than that of uphill area;In a certain range,the aboveground and underground CU increase rapidly with the increase of the working pressure of the sprinkler.When the working pressure of the sprinkler exceeds a certain range,the effect of increasing the working pressure of the sprinkler on promoting the uniformity of surface water distribution and the uniformity of underground soil moisture is small.The results show that the best irrigation quality and the highest economic input efficiency can be obtained when the sprinkler working pressure is 300 k Pa and the sprinkler spacing is 10 m.(4)Intermittent irrigation was introduced into sprinkler irrigation on sloping land.The soil water infiltration characteristics of continuous sprinkler irrigation and intermittent sprinkler irrigation were compared and analyzed,and the effects of terrain slope,intermittent time and nozzle working pressure on soil water infiltration of intermittent sprinkler irrigation were studied.The results showed that intermittent sprinkler irrigation could effectively improve the effect of soil water infiltration.Compared with continuous sprinkler irrigation,it could increase the cumulative infiltration amount of soil water by 16.70%,increase the infiltration depth by 15.99%,make the distribution of soil water more uniform,and reduce the coefficient of variation of soil water content by 12.06%.The smaller the slope,the longer the intermittent time,the more conducive to soil water infiltration.However,when the intermittent time increases to a certain extent,the effect of promoting soil water infiltration is weakened.The higher the working pressure of sprinkler,the more the cumulative soil water infiltration.However,when the working pressure exceeds a certain value,the ratio of cumulative soil water infiltration to irrigation water decreases,and the efficiency of transforming irrigation water into soil water decreases.Considering the operation cost of the system and the efficiency of irrigation water conversion,when the Rainbird R5000 sprinkler is used for intermittent irrigation on slope land,it is suggested that the suitable working pressure of the sprinkler is 300 k Pa,and the suitable intermittent time is 9h-12 h for the terrain slope less than 15%. |
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