The system you use for land application of manure or wastewater can have an impact on several environmental issues, says Rick Koelsch, Livestock Environmental Engineer at the University of Nebraska.
In terms of water quality, Dr. Koelsch says pivot irrigation systems have the least potential environmental impact if properly operated. He lists the following advantages of a pivot from a water quality perspective:
- Uniformity of nutrient application. A well-managed pivot has few equals in uniformity of distribution of manure nutrients. Uniform application of nutrients provides better opportunity for crop uptake of nutrients and less opportunity for nutrient leaching or runoff.
- Timing to limit runoff. If manure or lagoon effluent is applied to assist in meeting crop water needs, application is generally at a time of soil moisture deficit and high crop uptake resulting is a very low runoff potential. Most other application methods are confined to applications outside the crop-growing season thus increasing their potential for runoff.
- Timing to meet crop nutrient needs. Application of nutrients, both manure and commercial nutrients in close proximity to the time of crop nutrient uptake is ideal for minimizing leaching and runoff of nutrients. Pivot application during the growing season limits nutrient losses.
The biggest water quality disadvantage associated with pivot irrigation is the potential for over application of nutrients. Lagoon effluent applied based upon crop water needs will be substantially above crop nutrient needs. Two to five inches of lagoon effluent is often sufficient to meet all crop nutrient needs. To avoid over application through pivots, a nutrient analysis must be completed for the effluent being applied and application rates adjusted to not exceed crop nutrient requirements.
Water quality problems can also be associated with pivot application on wet, frozen or snow covered fields. Timing of pivot application, similar to any other method of application, influences the risk to water quality. Finally, application of manure through a pivot provides the potential for contaminating a fresh water source. Appropriate check valves must be used for irrigation systems plumbed to a manure source and a fresh waster supply, simultaneously.
For more information on methods of applying manure and wastewater to crops, go to http://manure.unl.edu.