Of all the factors that need to be considered for environmentally friendly applications of manure, some of the most important are timing, method and rate of application.

Time of application

Time of application influences nutrient availability and potential movement. The environmental management plan for your operation, including the storage capacity of your handling system, equipment, labor availability, and land availability should determine when manure is applied.

Fall applications, either injected or broadcast, allow more time for organic portions of the manure to break down and be available for plant uptake. However, the increased time for breakdown also allows for more potential nitrogen loss to the environment. Coarse textured soils have the greatest chances for leaching with fall-applied manure. Manure applied in the spring generally has the least amount of time for nitrogen loss to occur. However, saturated soil conditions in spring can cause significant denitrification and leaching loss of nitrogen.

Spring applications create the greatest likelihood for soil compaction. The exact impact of time of application depends on temperature, moisture content, and type. As a general rule, when applying manure, follow the same local guidelines as for anhydrous ammonia application.

Frozen or saturated soils can increase the potential for environmental contamination. In some areas, regulations prevent these applications. Incorporation is not feasible under these conditions, so nitrogen loss can be high. Nitrogen and phosphorus movement into surface water is also potentially high. When manure is applied to frozen ground, it should be applied on relatively flat land. Land with grass, hay or small grain stubble should be used for these applications. In southern climates, grass is an excellent cover crop for nutrient uptake and should be utilized to its fullest extent.

Method of application

Method of application can also impact the environmental fate of manure. Application method influences the amount of odor, degree of volatilization and area to which it is applied. Different crops have varying nutrient needs and rates of nutrient uptake. Injecting or incorporating manure soon after application reduces nitrogen loss and minimizes odor. Producers should use care when injecting manure on highly erodible land. Injection and incorporation may not always be possible because injectors may not leave adequate crop residue on the soil surface. If your USDA Conservation Compliance Plan includes a minimum crop residue requirement, check to be sure you're maintaining adequate levels. In some cases, broadcast application may be needed. However, there are several new incorporation methods (no-til) available that minimize residue disturbance.

When applying or transporting liquid manure through irrigation systems, care needs to be taken to avoid surface and groundwater contamination. Irrigators also need to be concerned about applying effluent at a rate that matches the infiltration rate of the soil to avoid runoff and ponding. Caution must also be exercised when using this method because odor is a significant challenge for irrigation of lagoon effluent. This may require adjusting the timing of application to when the odor may offend the fewest people.

Rate of application