This field study investigated the buildup of soil salinity and distribution of salts as influenced by gypsum-saturated water (34.5 mol SO4(-) m-3) applied through a drip-irrigation system and leaching that occurs by winter rains. Amounts of water applied were 50 and 60 L/plant per week in the first and second irrigation seasons, respectively. The soil was a Pellic Vertisol that contained no gypsum. Soil salinity by time, vertical depth, and lateral distance from the emitter was affected by moisture distribution during the irrigation season and leaching by winter rains. The results obtained indicated that, with frequent drip irrigation and sufficient leaching during the irrigation season, the highly soluble salts beneath the emitter are maintained at levels comparable to those of the irrigation water. Although highly soluble salts accumulated during the irrigation season, particularly in the soil surface at a lateral distance of 20 to 40 cm from the emitter, they decreased to their initial values after leaching by winter rains. Precipitation of Ca with SO4 as gypsum during the irrigation season was greater than dissolution of gypsum and leaching of these ions deeper in the soil by the 390 mm of winter rains. This resulted in a soil profile saturated with gypsum with a uniform EC. of 3 dS m-1 and Ca and SO4 concentration levels of about 30 mol (+/-) m-3 throughout the soil profile in the 0- to 120-cm depth. An increase in soil EC. occurred throughout the wetting front, which must be considered the lowest starting salinity for the beginning of each irrigation season. The increase in sodium adsorption ratio (SAR) was not at a level to adversely affect the infiltration capacity of the soil.
(C) Williams & Wilkins 1988. All Rights Reserved.