What’s my farm’s manure worth?

Manure can be a very rich nutrient that can account for a substantial amount of nitrogen (N), phosphorus (P), potassium (K) and micronutrients. In feeds fed to livestock, approximately 70% to 80% of nitrogen, 60% to 85% of phosphorus, and 80% to 90% of potassium are excreted in manure. Plants can’t distinguish between manure and commercial fertilizer, so taking advantage of these nutrients can help you manage fertilizer costs for crop production.

In addition to these nutrients, manure is an excellent source of organic carbon. Organic carbon can positively impact the soil’s cation exchange capacity, tilth, water-holding capacity and overall soil health.

Numerous factors can affect the nutrient composition of manure, including animal species, bedding type, ration, storage/handling, environmental conditions, field application and age of manure. These factors impact nutrient availability for growing plants. In addition, soil and climactic conditions can affect plant nutrient utilization as microbial activity within the soil is the main driver in the decomposition of the manure and organic matter.

Because the nutrient composition is so variable, it is best to test your manure. A manure sample will reveal how much of each nutrient – specifically nitrogen, phosphorus and potassium – is present in the manure. It is very important to follow proper manure sampling techniques to give you the most accurate results. Here are the guidelines for taking a manure sample from University of Wisconsin-Madison Department of Soil Science.

Availability of manure nitrogen depends on several uncontrollable factors whereas the availability of the phosphorus and potassium does not. Most of the fertilizer value in manure comes from phosphorus and potassium not nitrogen. When applying manure to meet the crop nitrogen needs, phosphorus and potassium will likely be applied in excess of the crop’s requirements. If applying manure to meet the crop’s phosphorus requirements, potassium and nitrogen will likely be short of crop requirements.

Nutrient credits
Not all nutrients in the manure are 100% available the first year after application. As such, nitrogen and sulfur nutrient credits should be taken the second and third year after manure application.

The nitrogen in manure is present in inorganic and organic forms.

• Inorganic nitrogen availability varies with animal species, how the manure was applied, if it was incorporated, and how much time between application and incorporation. Inorganic nitrogen in the manure is present as ammonium. Ammonium is easily volatized and lost if the manure lies on the soil surface. Thus, nitrogen credits for surface application, unincorporated manure are less than when manure is incorporated or injected.
• Organic nitrogen availability is dependent on animal species, management and environment (moisture and temperature).

Sulfur (S) is also present in manure in both inorganic and organic forms. The availability of sulfur from manure is estimated at 55% in the first year. There is some inherent variability in spreading manure evenly across the field. Thus, nutrient content of each load of manure can be variable.

Manure phosphorus is also present in both inorganic and organic forms, but inorganic phosphorus is the most dominant. Potassium is present in manure in an inorganic form is readily available to plants.
Second- or third-year manure credits can be available for all nutrients except phosphorus and potassium. Second- and third-year credits will be less than the first-year credits. Some losses will occur, especially with nitrogen, and manure is not always applied uniformly.

Calculating the dollar value
The example below shows how to calculate the value of injected manure using first-year application credits.

Image 1. Example of manure sample results (source:  UW-Madison Department of Soil Science).

Table 1. Example calculations of manure’s dollar value.

More in-depth manure calculators can be found online. Here is a link to one.

Getting the most from your farm’s manure
Manure certainly carries a high value with this year’s high input costs. When utilizing manure as fertilizer, consider timing and method of application to get the most out of it as these factors impact nutrient utilization. Spread the manure as uniformly as possible for consistent results. Calibrate equipment to ensure the correct application rate and uniform application.