Reducing the amount of drainage water that contains salts, nutrients, and trace elements may reduce environmental contamination to groundwater by reducing the dissolution of trace-element-containing minerals, maximizing chemical precipitation of salts, and improving nutrient uptake efficiency. If salt accumulates, transpiration and yield will decrease and some fraction of the irrigation water will not be extracted by roots, subsequently becoming drainage. We modeled yield and salt and water budgets under conditions of extended irrigation with poor quality water in amounts ranging from 0.6 to 1.6 times the ratio of irrigation (I) to reference evaporation (E0). The surface boundary conditions were taken from a field experiment where melon (Cucumis melo ssp. melo cv. Galia) was irrigated with waters of electrical conductivities of 1.2, 3, 6, and 9 dS/m at I/E0 = 1.0 for a growing season (1152 h). The model contained one-dimensional solutions to Richards' equation with a root-sink term and the equation of continuity for salt transport. Solutes were treated conservatively. For any given salinity value, the leaching fraction had a minimum value corresponding to the irrigation level where a minimum amount of water was used to control salinity and those minimum values were 0.11, 0.24, 0.44, and 0.54 for salinity levels 1.2, 3, 6, and 9 dS/m. Yield reduction for these irrigation levels were 80, 70, 60, and 40% of maximum possible yields, suggesting an economic price to minimizing drainage and further suggesting that plant–irrigation–drainage relationships are highly self-regulating.

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