Soil Water And Nitrogen Transport Characteristic Experiment And Numerical Simulation Of Film Hole Irrigation Under Facilities

Aimed to the characteristic of film covering cultivation and irrigation and fertilization under facilities and combined with the National Natural Science Foundation of Hebei, this paper uses the technical route including indoor and shed experiment, computer simulation and theoretical analysis, and studies the characteristics of soil water and nitrogen transport and distribution and the factors to the characteristics. The main research results are as follows:1. Analysis the relationship between mean water infiltration depth and film hole diameter and percentage of open area. The mean water infiltration depth increases with film hole diameter and percentage of open area. The function relationship between wetting front and film hole diameter, percentage of open area and time is set up, which has an clear physical meaning and a little relative error.2. Studies the change of wetting front with time. From the early irrigation time to irrigation end, the wetting body looks like a semi-ellipsoid and increases with time, the wetting center of which is near top soil of film hole center; form irrigation end to wetting front intersect, the wetting body is still semi-ellipsoid, but the wetting center of which moves down along the film hole center; from wetting front intersect to the third day, the wetting front still looks like a semi-ellipsoid; after the third day, the wetting front assumes horizontal lines from top to bottom.3. Discusses the effect of film hole diameter, irrigation amount and film hole spacing on soil water content.In the stage of irrigation, the film hole spacing has effect on soil water content and has no effect during soil water redistribution.Irrigation amount has a direct effect on soil water content. With the increase of irrigation amount, the wetting body is bigger, the wetting center is deeper and the time of wetting front interact is shorter; among the relationship between irrigation quota and even coefficient, the most value appears when irrigation quota is16mm, so irrigation quota has an effect on water even coefficient.Film hole spacing has an effect on soil water content. With the decrease of film hole spacing, the gradient of soil water in horizontal direction is little and soil water content changes more evenly; soil water happens to intersect in the horizontal direction under different film hole spacing, so film hole spacing has an effect on water even coefficient. The effect is obvious in the early irrigation time and up to90%after soil water redistribution. The film hole space can be determined according to planting requirements.4. Studies the effect of film hole diameter and irrigation amount on wetting front transport under applying nitric nitrogen solution.Film hole diameter has an effect on soil nitric nitrogen front in the horizontal and vertical direction. The horizontal front transport distance of soil nitric nitrogen increases with film hole diameter and the function relationship between horizontal wetting front and film hole diameter is set up; the effect of film hole diameter on soil nitric nitrogen front in the vertical direction is reverse and there is no obvious function relationship between them.Irrigation amount has a direct effect on soil nitric nitrogen front in the horizontal and vertical direction. The horizontal front transport distance of soil nitric nitrogen increases with irrigation quota, but there is no obvious function relationship between them; the vertical front transport distance of soil nitric nitrogen increases with irrigation quota, there is power function between them.Most of soil nitric nitrogen is in the range of12cm away from film hole center and can be easily absorbed by plant.5. Reveal the distribution rule of soil nitric nitrogen concentration under applying nitric nitrogen solution.The distribution of soil nitric nitrogen concentration can be divided into three parts:①the part can be named high concentration area which change gently with little concentration gradient;②the part can be named high gradient which change sharply with big concentration gradient;③the part can be named low concentration area which change gently with little concentration gradient. So the soil nitric nitrogen transports by high concentration gradient. The three parts above can also be named salt accumulation area, pushing area and gradually effected area.6. Reveal the relationship between soil water and soil nitric nitrogen under applying nitric nitrogen solution. The soil water wetting front does not synchronize with soil nitric nitrogen front, but there is a good line relationship between them and the effect of solution concentration on them is also obvious.These results provide theoretic proof for developing water and fertilizer application with film hole irrigation under facilities.