FO-03875 Reviewed 1991
Irrigation water management or scheduling involves more than just turning on the machine because it has not rained for a few days or the neighbor is irrigating. Irrigation scheduling is a decision-making process to determine when and how much water to apply to a growing crop to meet specific management objectives (Rogers, 1989). To be successful requires the blending of the latest scientific information, technologies, and personal irrigation experiences into an effective and sound water management program.
A sound irrigation scheduling program can help an operator:
Leaching of chemicals cannot be totally eliminated by proper irrigation scheduling, according to some specialists (Kranz, 1989; Fishbach et al., 1988; Ritter et al., 1988; Hergert, 1986; and Ritter, 1986). For example, if a significant rainfall occurs shortly after an irrigation, the excess water will percolate deep in the soil and may carry some agrichemicals below the root zone. Likewise, large rainfall during the off-season may leach some agrichemicals that remain in the root zone. It is estimated that 70-80 percent of the annual recharge to surficial ground water in central Minnesota occurs after harvest and before planting (personal communication with Nieber, 1989). Figure 2 shows the normal monthly corn crop water use rates and respective precipitation for west central Minnesota. Months where rainfall is significantly larger than crop use indicate highest potential for ground water recharge and possible leaching of agrichemicals.
|Figure 2. Normal Monthly Corn Crop Water Use and Precipitation Rates for West Central Minnesota.|
Effective irrigation is possible only with regular monitoring of soil-water-plant conditions in the field, predicting future crop water needs, and following the best recommended water management strategies. This also requires a basic understanding of soil-water-plant relationships and soil moisture monitoring techniques.
To set up and operate an effective irrigation scheduling program these sequenced procedures need to be followed for each field:
A brief discussion of each of these steps is presented later in this publication. This procedure typically takes 5 to 20 minutes of the operator's time daily to keep updated after determining the initial soil water characteristics. If operator time is not available to regularly monitor the soil moisture, consider finding a crop consultant to assist in achieving the management objectives.
This material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under special project number 89-EWQI-1-9180.
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