Moisture Transform Rule And Production Mechanism Of Subsurface Non-Pressure Irrigation And Indirect Drip Irrigation

Subsurface non-pressure irrigation is a new water-saving technology. It is similar to subsurface drip irrigation when its pressures approximate to zero. Indirect drip irrigation is a new water-saving technology which has the same pipeline layout with drip irrigation and the same irrigation results with subsurface drip irrigation. The differences between them are about the gravity effect and infiltration boundary during the moisture transform process and about the wetted zone shape and soil moisture distribution after irrigation. Through the laboratory test and theory analysis, this text studied the soil moisture transform rule and irrigation uniformity for subsurface non-pressure irrigation technology, and built the simulation model for soil moisture content and characteristic values using the concept of field. Through the greenhouse experiment of subsurface non-pressure irrigation, we studied the regulation effect of irrigation water amount on tomato growth. The technique parameter model for indirect drip irrigation was built using water balance principle and steady-state principle of constant-head well permeameter. Moisture transform rule of indirect drip irrigation was studied using the parameters designed by technique parameter model. We also studied the measurement methods about field-saturated hydraulic conductivity using steady-state principle and the infiltration character of constant-head well permeameter. The main results are as follows:(1) The soil moisture transform rule mainly depending on soil matric potential was ascertained through the laboratory test on subsurface non-pressure irrigation. Results indicated that when the irrigation pressures fluctuated in a small range (less than or equal to 6 cm, bigger than or equal to -6 cm), the driving force of emitter discharge rate and the moisture transform in soil was soil matric potential, and the gravity could be ignored. Therefore, the wetted soil shape was sphere or spherical cap. The wetted soil volume was the function of irrigation water amount. The soil moisture content was equal in a concentric sphere centered with emitter and decreased with quadric curve along the sphere radius. In the process of irrigation, the rate of soil infiltration and the movement of wetting front decreased with time. The soil moisture content in the same positions of wetted zone changed small, the irrigation water amount was mainly used to increase the wetted soil volume. There was longer irrigation time than other techniques, and the irrigation time had big relationship with soil types.(2) The relationship between tomato production and water was proved up through the field experiment. It studied the influence of irrigation water amount on the tomato stem height, stem diameter, root dry weight, shoot dry weight, yield and quality. Results indicated that the irrigation water amount 85.68 mm~236.91 mm had no significant effect on tomato production, while the irrigation water amount 284.83 mm~337.75 mm could increase the tomato yield significantly. At the same time, the irrigation water amount had different regulation effect on tomato root system, shoot growth and quality. The stem diameter could be the single indicator to evaluate the tomato high yield. Namely we can get the higher yield through the regulation to environment of tomato growth to get big stem diameter.(3) The factors influencing the irrigation uniformity of subsurface non-pressure irrigation and the feasibility of emitters (holes in the pipe) in the field was verified through the study on the emitter flow rate in air and homogenized soil, and on the tomato growth and yield. Results showed that the pipe length, holes space and irrigation pressures had effect on irrigation quality. The irrigation uniformity in the homogenized soil was improved obviously compared with that in the air, and the deviation rate of emitter discharge rate was less than the micro irrigation designing value 0.2. The space variability of soil and the hydraulic character of irrigation system had small influence on tomato growth.(4) The emitter discharge rate and the water-conducting device dimension were determined by using the water balance principle, Philip model and steady-state principle of constant-head well permeameter. The characteristic values of wetted soil volume were ascertained through the studies on the infiltration character of indirect drip irrigation. Results indicated that the models were simple and practical, and had commonality to all soil types. The shape of wetted soil of sand tube irrigation was ellipsoid, and its symcenter moved up gradually with time. The shape of wetted soil of sand furrow irrigation was onion. The movement rate of wetting front decreased with time. The average volumetric soil moisture content was basically invariable with time.(5) The other two methods used to get steady-state were proposed through the studies on the infiltration rule of constant-head well permeameter and on the measurement of field saturated hydraulic conductivity. Namely using the Philip model to get the steady infiltration rate, and using the indirect drip irrigation to get the steady ponded depth. The application of Green-Ampt model and Philip model was enlarged in the three-dimensional infiltration.Above study revealed the moisture transform rule with gravity or not and the regulation of irrigation water amount on tomato growth. These results will provide theoretical and technical guidance to the application of subsurface non-pressure irrigation and indirect drip irrigation.