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Chemigation: the Benefits and Pitfalls

Chemigation is the process of injecting a chemical into irrigation water, which is then applied to a crop or field. The term includes the application of herbicides (herbigation), fertilisers (fertigation), insecticides (insectigation) and fungicides (fungigation).

Chemigation is a method that has been used successfully for many years in certain types of agriculture and is mostly used in conjunction with drip or sprinkler irrigation systems. It has a number of advantages over other types of spray applications, but also some disadvantages.

Advantages include:

  • It is generally much cheaper than other forms of application
  • It provides more uniform coverage
  • Less labour is required

  • The chemical is applied more accurately
  • The chemical can be applied in conditions unfavourable for other forms of application (i.e. when the soil is wet)
  • There is limited soil compaction and crop damage
  • There is less human exposure to chemicals.

Disadvantages include:

  • Initial cost of equipment can be high
  • It requires more knowledge and management
  • Extra equipment is needed for safety and storage
  • It presents hazards through potential run-off and groundwater contamination
  • Application times are generally longer
  • There is a possibility of equipment malfunction while unattended
  • There is a potential to over-water crops in periods when chemicals are needed, but not water.

The biggest hazard by far of chemigation is that it has the potential to contaminate irrigation water sources if safety measures are not implemented and maintained. Risks include the chemical flowing back into the water source when the system shuts off, the chemical continuing to be injected after the irrigation water is shut off, causing flow back or spillage, or the chemigation system shutting down while the irrigation system continues to run, causing overflow and spillage.

Safety devices that need to be installed to prevent this from happening include:

  • A main pipeline check valve between the point of chemical injection and the irrigation pump, to prevent flow back into the water source
  • Interlocked chemigation and irrigation power and water supplies, so that if one shuts down, the other does too
  • A solenoid valve installed in the chemical injection line as an added precaution
  • A check valve in the chemical injection line between the meter and the point of injection
  • A shutdown switch that activates at lower pressure installed in the main pipeline.

In addition to these devices, other safety measures include using double-skinned chemical supply tanks, not locating them too close to the water source, ensuring that all components in contact with chemicals are chemical-resistant, and posting clear warning signs on the field’s perimeters during chemigation treatment.

Chemigation can be a safe and effective means of applying chemicals to crops and it has a number of advantages over other application methods. However, the very real potential for contamination of the water source through spillage and flow back means the process must be rigorously managed at all times.

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