Spray Irrigation Of Manure Through Center Pivot Systems

As livestock operations increase in size, they are pursuing new technologies to better manage manure in all phases from the point of production to application in fields.

For example, farmers have made significant investment in technologies to separate the solid fraction of manure from the liquid for purposes of reducing handling and application costs, increasing management options, and minimizing environmental and other risks. Following the lead of about 6 CAFOs in the state of Wisconsin, farmers are considering spray irrigation of manure as a tool to improve manure management. With the focus on center pivot irrigation systems, this approach promises improved nutrient management among its benefits.

Compared to the use of a traveling gun, another tool for spray irrigation, center pivots deliver a more controlled distribution of manure. Currently there remain unresolved issues related to the use of this technology, but best management practices may have the potential to address these issues.

Benefits

Regarding nutrient management, irrigating manure liquids can provide greater uniformity in the distribution of nutrients, enable better timing of applications to meet crop needs throughout the growing season, and allow more frequent applications of small volumes of manure. While spraying manure on growing crops should improve uptake of nitrogen, ammonia is volatized during spraying.

In contrast to application by using tankers or other vehicles, spray irrigation greatly minimizes soil compaction during applications. In addition, piping manure from storage to irrigation systems reduces tanker traffic on local roads, preserving roads from damage, and minimizing vehicle conflicts.

Challenges

Spray irrigation has the potential for increased odors. There is also research that suggests a risk of offsite delivery of airborne pathogens. These factors contribute to a negative public perception that has manifested itself in new local regulations such as bans on spray irrigation of manure. While NR 243 imposes setbacks and other requirements on CAFOS with permanent spray irrigation systems such as center pivots, it is not clear if these are adequate. The livestock facility siting rules do not regulate spray irrigation of manure.

Best Technologies And Management Practices

The following actions may reduce risks and address the challenges related to spray irrigation:

• Install systems in appropriate locations to minimize potential for offsite impacts such as odors and drift, and consider windbreaks to further limit impacts.
• Develop management plans and other strategies that account for variations in weather and other high risk conditions, and identify methods to reduce risk.
• Reduce airborne transmission of pathogens and odors through technologies that treat wastewater to kill pathogens before field applications, and minimize aerosolization of manure during spraying.
• Maintain irrigation equipment to deliver consistent applications, and then monitor applications made with automated spray equipment.