Studies On Characteristics Of Soil Water And Salt Movement

The increasing severity of soil contamination, salinization and alkalization make soil solute transport one of the key issues in soil science study. With the increasing demands of growing population for food and water, saline water utilization and saline-alkaline soil amelioration are of great importance. Based on the review of national and international research results of soil solute transport, saline water utilization and improvement of alkaline soil with drip irrigation under film, both theoretical analysis and indoor and field experiments were conducted to determine the parameters of soil solute movement models, and safe utilization of slightly saline water and amelioration of alkaline soil with drip irrigation under film. Major findings are as follows:1. Under special conditions, the two-flow domain model can be transformed into a two-domain model. Under continuous input, the parameters of the two models are in good agreement. The immobile water content of tube bundle model can be considered the same as that of the two-region model. A simple relationship was established between dispersivity and the exponential term of the Brooks-Corey model, and then the hydrodynamic dispersion coefficient of the two-region model can easily be obtained from the soil water retention curve.2. When saline water infiltrated, cumulative infiltration, wetting front advance andinfiltration rate increased with the concentration of infiltration solution and initial water content. When the concentration was greater than 3g/l, infiltration decreased with increasing salinity of infiltration water. Infiltrated saline water can also desalt soil with high initial salt content, the desalting depth increased exponentially with cumulative infiltration, and decreased with increasing salinity of infiltration water and initial soil water content. The desalting efficiency of saline water decreased with increasing amount of leaching water and the concentration of saline water, but was independent of initial soil water content.3. Irrigation experiments with both fresh and saline water showed that winter wheat yield reduced by 20-30% with saline water irrigation, the number of ears per mu decreased by 30%, the average water consumption intensity and water use efficiency were lower under saline water irrigation. With fresh water irrigation, water use efficiency was enhanced when no irrigation was conducted during elongation and milking periods, and reduced during earring period. So the priority of irrigation should be given to earring period when there is not enough water. Under saline water irrigation, lacking of water during milking period reduced wheat yield obviously, so the priority of irrigation should be given to milking period when water supply is scarce.4. Irrigation experiments with different saline water showed that wheat yield decreased with the increasing salinity of the irrigation water, 3g/l was the upper limit of concentration that causes no yield loss. High salinity of irrigation water resulted in lower average water consumption intensity of wheat during the whole growing season, but higher water use efficiency. The field experiments with alternating saline and fresh water irrigation showed that winter wheat yield was higher than that with saline water irrigation only and lower than that with fresh water.5. The field experiments of drip irrigation under film showed a remarkable distribution feature of soil water and salt radially. Soil water content decreased gradually along radial distance. The average soil salt content tended to cumulate at thewetting front. The variation of soil salt concentration was lower at greater depth, the maximum value occurred on the top 0-10 cm. The water conservation and salt control effect of drip irrigation under film is related to irrigation scheduling. In alkaline regions with strong evaporation, the salt control effect of film was more remarkable than water conservation. The impact of irrigation duration on average soil water content was connected with quota of irrigation. Soil salt res...