Chemigation & Fertigation

Chemigation — Delivering Chemicals to Crops & Soils Using Irrigation An excerpt adapted from chapter 28 of Irrigation, Sixth Edition, by Ted W. van der Gulik and Robert G. Evans

The use of irrigation systems for purposes other than providing water for plant growth has increased rapidly in recent years. An irrigation system offers the ability to deliver fertilizers and pesticides to the plant and soil, a practice termed chemigation.

Generally, an irrigation system that delivers chemicals to crops and soils must be designed and managed differently than conventional irrigation and must apply water uniformly. Chemigation can take place via a normal irrigation cycle, but additional factors to consider include uniformity, rate of application, timing and the need to flush chemicals from the system. Adding any chemical to irrigation water requires reliable backflow prevention devices to ensure that the chemicals do not drain or siphon back to the water source.

Generally the chemicals applied are fertilizers and pesticides, including fungicides, insecticides, nematocides and herbicides. In addition, soil conditioners and growth regulators can be applied through an irrigation system under certain circumstances.

Fertigation, which is a form of chemigation, is the term given to the application of fertilizers. Many commodities such as tree fruits, citrus, vegetables, small fruits and berries, and greenhouse and nursery crops use drip irrigation systems to apply fertilizers directly to the plant rooting area. Center pivot systems are used to apply certain fertilizers, insecticides, fungicides and herbicides to many types of field crops. Traveling guns and booms are not acceptable chemigation systems because of their typically poor application uniformity.

Benefits & Limitations

Chemigation offers many benefits over conventional application of fertilizers, pesticides and other chemicals:

• Chemicals can be applied to the crop at the most opportune time even if the field is not trafficable by farm equipment. Nutri- ents can be scheduled and applied to the crop throughout the growing season at specified rates and intervals.

• Chemigation can reduce the leaching potential of certain nu- trients such as nitrogen into the groundwater by applying the correct amount of compound throughout the growing season when the plant most needs the nutrient.

While the benefits of chemigation are evident, other considerations and limitations must be evaluated before deciding to use an irrigation system to apply chemicals:

• Some chemicals cannot be used for chemigation because of their chemical properties.

• Many chemicals, especially insecticides, fungicides and herbicides, may be used for chemigation only if the product

Photo credits: Irrigation Training & Research Center, California Polytechnic State University, San Luis Obispo, California

• Crop yields and quality improve if chemigation is done correctly.

• Chemical application costs are lower because of reduced labor, chemical use and power consumption.

• Fertigation may be the only method by which fertilizers can be incorporated into the soil if using microirrigation in dry climates.

• The irrigation system can incorporate the chemical to the desired soil depth by applying the appropriate amount of water based on soil type and soil moisture.

• Chemigation is compatible with no-till farming because chemi- cals can be applied under various tillage situations.

• Mechanical damage to the crop by air blast sprayers is avoided.

• Operator exposure to chemicals is reduced because operators are not required in the field during the application.

• Chemigation of post-emergence, soil-acting herbicides may reduce crop phytotoxicity and increase activity.

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