Spreading Manure on a Few Acres

Even if you don’t need a feedlot permit, you still need to understand and employ proper practices when spreading manure. Limit manure application to agronomic rates (rates that are equal to or less than what the existing plants can use in a year), and ensure that the manure does not pollute water. Do not apply manure on shoreline property.

The MPCA prohibits manure spreading

• on soils with a high water table;
• on floodplains;
• on lakes, intermittent streams (streams flowing after certain rainfall events), seasonal streams (streams flowing only during snowmelt), and ditches;
• on grassed waterways;
• on frozen soils with slopes greater than 15 percent; and
• near direct groundwater conduits (e.g., wellheads and quarries).

Check with your local soil and water conservation district or Natural Resources Conservation Service office to help identify these special protection areas on your land and on bordering properties.

Land Application Guidelines

Proper manure application generally requires a series of decisions and some additional information gathering.

If all of the manure will be applied to existing pasture, the horses can do a fairly good job of distributing it themselves. Unfortunately, the droppings from the horses are often quite concentrated and can suffocate or stunt plants underneath them. To maximize pasture production, drag or harrow the pasture to break up the droppings and more evenly spread the manure.

If stockpiled manure is to be spread onto a field, you need to know the nutrient content so the application matches the nutrient needs of the crop. Although each source of horse manure will vary, a standard "N-P-K" value (Table 1) can be used to determine the number of acres needed to properly spread the horse manure.

When using stored manure in place of purchased fertilizer, you may wish to have a more accurate estimate of its nutrient content. Manure can be sampled, packaged, and sent to a soil-testing laboratory for nutrient analysis. Check with the University of Minnesota Extension Service (Extension) office in your county for bulletins with sampling procedures for manure and interpretation guidelines.

Not all of the nutrients in manure are available for plant use. For example, the percentage of the total nitrogen available is a function of the method of manure application and management as well as the chemical composition of the manure. For horse manure, typical nitrogen availabilities range from 35 percent of the total nitrogen if the manure is spread and left on the soil surface, to 60 percent if the manure is spread and worked into the soil within a day. Availabilities of phosphorus from phosphate (P2O5) and potassium from potash (K2O) are commonly set at 80 percent and 90 percent of totals, respectively.

After estimating the manure’s nutrient content, select the field/crop targeted for application. Certain fields and portions of fields must be excluded from manure application based on environmental precautions. Some guidelines are listed in Tables 2 and 3.

The amount of nutrients to be applied to a field depends on the crop to be grown, its expected yield, soil test levels, and other credits. For more information contact your University of Minnesota Extension Service county office.

Calculating manure application rates is a mathematical exercise that aligns the nutrients supplied in the manure and the nutrient demands of the crops. Although it sounds quite simple to take a manure analysis, account for availability, and then match this to crop needs, several decision aids are available upon request.

After you determine application rates, you need to make some decisions about method of application. The primary goal is to uniformly apply manure throughout the field. This takes time and effort on the part of the person driving the applicator. It is also important to know the actual rate of manure application and how to modify the tractor speed to achieve the desired rate. Several bulletins are available for making this calculation.

The timing of the manure application is also important. The ideal scenario is to spread manure in the spring. This supplies nutrients for the upcoming growing season and minimizes the amount of time for potential losses before crop uptake. An alternative is to spread manure in the fall. Avoid applying manure in winter. Manure applied in this fashion is highly susceptible to movement if it rains.

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