University of California Water Resources Center

This recently-completed 3-year field study evaluated the effectiveness of winter cover crop incorporation and surface gypsum applications relative to conventional fallows for maintaining/improving soil physical properties, stand establishment and crop productivity in a cropping system relying on saline drainage water for irrigation. Six amendment/soil cover treatments were imposed on a rotation of tomato-tomato-cotton as summer crops. Drainage water accounted for about 70% of the total water applied over the course of the experiment. Yields of toamtoes irrigated with saline water were maintained relative to non-saline irrigation in year 1, but were decreased by 33% in year 2. Estimated cotton lint yields of plants irrigated with saline drainage water in 1994, following two seasons of drainage water irrigation, were similar to yields of plants irrigated exclusively with non-saline water. Soil surface crust strength, measured by micro penetrometer was lower in gypsum and cover-crop amended plots relative to saline water irrigated fallow plots during the period of cotton seedling emergence in 1994 in the third year of the experiment. Water stable aggregation was increased following cover crop incorporation relative to saline fallows. Following two seasons of saline drainage water reuse, emergence of cotton seedlings was highest in gypsum-amended plots, but considerably lower in cover crop incorporated plots. Mechanisms accounting for poor establishment following cover crop incorporation may include higher incidences of seed and seedling pathogens in plots where cover crop residues had been incorporated into the soil, and stubble-reinforced surface crusts that resulted in interconnected slabs that impeded timely seedling emergence. These findings and increasing soil surface ECe and SAR values during the course of this study point to the need for special management practices for sustained crop production if drainage water is routinely used.