Experimental Studies On Saline Water Surface Irrigation

The increasing problem of fresh water shortage influences the development of industry and agriculture severely. Exploitation and utilization of saline water for surface irrigation are of great importance. Based on the review of national and international research results of slightly saline water irrigation, theoretical analysis, laboratory and field experiments were conducted to study soil salt-water transfer under saline water irrigation, and the optimization technique on parameters of saline water surge irrigation. Major findings are as follows:1. Experiments in soils with same SAR and different saline water infiltration showed that soil hydraulic conductivity and water holding capacity increased with the concentration of infiltration solution. When the concentration was greater than 3g/l, the increase rate reduced. The soil salt content increased with the concentration of infiltration solution obviously. When the concentration was greater than 3g/l, salt accumulation appeared on the soil profile, salt concentration increased clearly. When SAR of infiltration solution was 8, 3g/l was the upper limit of concentration for safe irrigation.2. Experiments in soils with same concentration and different SAR showed that soil hydraulic conductivity and water holding capacity decreased with the concentration of infiltration solution. Different SAR affected soil salt content and concentration weakly. Soil solution SAR and ESP increased with the SAR of infiltration solution. SAR=8 was the upper limit for alkalinity of soil when salinity was 3g/l. When SAR of infiltration solution reached 25, the soil did not show moderate alkalinity.3. Experiments with alternating irrigation with saline and fresh water showed that saline-fresh-saline mode resulted the maximum k. In fresh-saline-saline mode the soil water holding capacity increased. The saline-fresh-saline mode was good for soil desalination. Overall, irrigation with saline water and fresh water cycle may provide favorable condition for crop growth.4. Irrigation experiments with both fresh and saline water showed that winter wheat yield reduced by 18%-28% with saline water irrigation. For safe irrigation, the maximum irrigation depth of fresh water was 180m~3/667m~2, and saline water was 140m~3/667m~2. With fresh and saline water irrigation, winter wheat yield and water use efficiency reduced when no irrigation was conducted during the elongation periods. When water supply is scarce, the priority of irrigation should be given to young plants.5. The field experiments showed that the soil salinity occurred when the concentration was greater than 3g/l. The winter wheat yield decreased with the increasing salinity of irrigation water. So the suitable concentration of irrigation water was should be less than 3g/l. The field experiments with saline and fresh water alternating irrigation showed that soil salt content and wheat yield were between that with saline water or fresh water only. The saline and fresh water alternating irrigation may improve wheat yield and water use efficiency.6. The surge irrigation with saline water showed that the maximum stream advance with surge irrigation was 1.06-1.3 times that of the continuous irrigation. The roughness factor reduced as the wheat grown. The soil water content, salt content and concentration were more even under surge irrigation. Simulations using SRFR model for technique parameters and field irrigation parameters with surge irrigation performance showed that the appropriate conditions for surge flow irrigation with saline water are: cycle ratio equals to 1/3, period of 3-4, border length in the range of 200-250 meters, and intake flow rate within 3.0-4.0 L/m·s.