Salinity management in a closed irrigation system

The present salinity management research project to evaluate the effects of recirculation and reuse of drainage water from a soil profile was initiated in September 1990 by other researchers. Two weighing laboratory lysimeters, 2 m high and 0.35 m diameter, were packed with Millville silt loam soil, a naturally calcareous soil. The water table was fixed at the 140 cm depth. An ornamental plant, China Doll, was established to maintain a constant growth of vegetation, and energy was supplied with a greenhouse lamp. Different instruments were used to measure the soil water content and the salinity of the soil profile (at 20-cm depth increments) as well as irrigation water, and drainage water volumes and qualities. Different irrigation management practices were analyzed, including the effect of different leaching fractions, under-irrigation, and continuous irrigation reusing all the drainage water. The drainage water was blended with tap water and used for irrigation. Soil profile water extracts, irrigation water and drainage water were sampled and analyzed. At the end of the research, the soil in the columns was sampled to assess the effects of the long-term reuse of the drainage water in the soil profile. Through the analyses of the laboratory results and the data collected over a period of 12 years, there were some chemical changes in the soil profile due to dissolution/precipitation processes, but all ion concentrations and ion balances are within a safe level for plant growth.; It was found that the soil profile salt concentration did not progressively increase downward; therefore the electrical conductivity of the soil in the saturated layers and in the drainage water is lower than the electrical conductivities of the soil profile.; The electric conductivity of the drainage water and blended irrigation water (less than 0.7 dS/m) did not exceed the safe limits according to the guidelines for interpretations of water quality for irrigation and the water quality for irrigation (USDA Technical Bulletin No. 448), to cause soil problems (destruction of soil structure, reducing soil permeability and the availability of water to crops, and/or toxicity to crops). For irrigation purposes, the recycling of the drainage water collected still feasible.; The quality of the drainage water did not reflect the salt content and ion distribution within the soil profile, specially the root zone where most of the salt accumulation occurred. (Abstract shortened by UMI.)...