Improved Water and Nutrient Management Through HighFrequency Irrigation

High frequency irrigation implies the uniform, frequent application of water to crops. The fequency may range from several irrigations per week to daily irrigation to even several irrigations per day in greenhouse and nursery settings. Most of the high frequency irrigation in the United States is through necessity; i.e., the limited water holding capacity of the soils or a limited water supply make irrigation application of more than a few centimeters impractical.

Irrigation of field crops in sandy soils (such as in the Nebraska Sand Hills) with traveling or outer pivot sprinkler systems is a classic example of high frequency irrigation dictated by a limited water holding capacity. Another widespread use of high frequency irrigation is found in the various low pressure systems such as drip, trickle, bi-well, and bubbler. These systems deliver relatively small amounts of water to the root zone as a consequence of factors such as limited water, shallow soils, limited water holding capacity, and high erosion potential.

The increased frequency of irrigation is not commonly a goal in itself, but several advantages of high frequency irrigation have been identified (Rawlins and Raats, 1975; Howell, et. al., 1976). These include:

1. Improved plant internal water balance,
2. Decreased drainage from the root zone,
3. Decreased runoff from the crop,
4. Decreased importance of soil hydraulic characteristics,
5. Improved salinity control,
6. Increased enhancement of rainfall utilization,
7. Reduction of high temperature stress, and
8. Reduction of nutrient leaching

The results of these advantages are usually increased crop yield or quality, decreased water use, and decreased pollution from drainage and runoff. The yield expected under high frequency irrigation may not be signsficantly increased over well-managed conventional irrigation, but increased efficiency of water, energy, fertilizer, and labor make even modest yield increases important.

Nutrient management is critical with high frequency irrigation. Nitrogen in particular is susceptible to loss from the root zone by leaching, so high frequency irrigation systems require frequent, light nitrogen applications. This is facilitated by distribution of nutrients through the irrigation system. Other chemicals such as soil fumigents for nematode control, systemic insecticides, and herbicides can also be injected into the irrigation system and applied very uniformly to the crop.

This research was directed toward defining the best management practices for irrigation timing and fertilizer applications under high frequency irrigation. The specific objectives were to:

1. quantitatively determine plant nutrient requirements for specific crops grown under high frequency irrigation, under optimum soil-water metric potential, and
2. evaluate the impact of high frequency irrigation on water quality and water and energy consumption.