Saline Drain Water Reuse in Agroforestry Systems

On the west side of California's San Joaquin Valley, researchers are experimenting with agroforestry systems to help solve the agricultural drainage problem. Eucalyptus tree plantations are used to consume the shallow ground water and saline drainage waters from croplands. The long‐term efficacy of this practice is being evaluated. This paper presents a growing body of data on soil water and salt fluxes in a tile‐drained 9.43 ha eucalyptus plantation. The irrigation water used in this study has an electrical conductivity of 10 dS/m, 12 ppm boron, 400 ppb selenium, and a sodium adsorption ratio of 11. The tree plantation was successful in lowering the water table from 0.6 m to 2.3 m and consumptively using the saline irrigation water. But after several years of drain‐water reuse, a substantial buildup of salinity and boron has occurred throughout the soil profile to the extent that the trees are unable to fully extract the available soil water. The estimated leaching fraction of 16% in the 1990 irrigation season will need to be increased so that the trees can survive and continue to consume saline drainage water from croplands.