ABSTRACT
"Conservation" and "efficiency" are relative terms, employed for their positive political valences by a host of competing perspectives and interests. Irrigation efficiency can be considered in both a physical and economic sense. The economic efficiency may be measured by comparing the productivity of water used for irrigation to that of its alternative uses. Water is consumed in irrigation by evaporation from wet soil and water surfaces and by transpiration from plant surfaces, a necessary function of plant growth. Water can be lost to the air nonrecoverably by open water or soil evaporation and by transpiration from plants. It can be "lost" recoverably by seepage, leakage, spillage, runoff, and deep percolation. Scheduling water delivery under a "water budget" through irrigation management programming can increase water use efficiency. The advantages of most drip irrigation installations in California and elsewhere have been the potential to solve specific problems such as water shortage, water cost, poor or excessive soil permeability, steep slope of land.
