Irrigation Systems for Idaho Agriculture

daho has approximately 4 million acres of irrigated agricultural land. Most of it is in pasture and hay crops, grain crops, potatoes, and sugar beets, in hierarchical order. Table 1 shows the number of irrigated acres in the state by crop for 1994. Nearly all of this land is irrigated by either sprinklers (59 percent) or surface irrigation systems (40 percent), with only a very small amount (less than 1 percent) in micro-irrigation systems (trickle or drip) (table 2). The selection of an irrigation system, or the decision to continue with a gravity system rather than convert to a sprinkler system, is a matter of tradeoffs among the following factors: initial investment costs, operating costs, site factors, and management skills. A relative comparison of these factors is given on pages 4-5. In general, the higher-investment, higher-water-applicationefficiency systems are found in areas where large fields of high-value, water-sensitive crops are grown, or where water supply may be limited or pumping lift is high. Lower-initial-investment surface systems are generally used in short-growing season areas or areas where soil depth or texture limits production. Lack of available threephase electric power and seed production requirements for dry foliage (for disease control) may also dictate the continued use of surface irrigation. In a ideal irrigation system, on a field with uniform soil properties, water is supplied uniformly over the entire area of a field at a rate not to exceed the rate at which water will enter the soil (infiltration rate), and with a frequency and amount to meet the crop need. Since crop water use varies during the year, water application should also vary to just meet this need. Water in excess of crop need should be applied only on Irrigation Systems for Idaho Agriculture