This article is Part 1 of a two-part discussion on the value of manure. Part 2 focuses on soil quality benefits provided by manure and appeared in the March 6, 2017 CropWatch.

Manure has the potential to be both an economic “Win” – due to its fertility value – and a soil quality/health “Win” – due to the organic matter that fuels the activity of soil-dwelling organisms. In the right situations, soil quality benefits can improve drought resilience and water quality, but the impacts of manure will vary from field to field. Identifying those fields with the greatest potential for a Win/Win opportunity is the challenge of every farmer using manure.

These Win/Win opportunities result from manure’s:

• Nutrient substitution for commercial fertilizer;
• Organic matter contributing to soil quality improvements; and
• Potential to achieve a possible yield boost.

Part 1 of this two-part discussion focuses on manure nutrient substitution for commercial fertilizer. Part 2 will address the soil quality benefits provided by manure.

Manure Fertility Benefit

Manure contains nutrients important to crop growth. Manure nitrogen (N) is typically 50 to 90% organic N, which is slowly released as soils warm in the spring and summer. Credits for a single-year application of organic N occur over multiple years. Typically, 25 to 40% of the organic N is available in the crop year manure is applied with roughly half that amount becoming available with each succeeding year (roughly 15% in year 2, 7% in year 3, etc.). Most manures also contain ammonium nitrogen, a fast-release form of nitrogen, which must be incorporated or irrigated into the soil for its value to be realized. More information about manure nitrogen availability can be found in the NebGuide, Determining Crop Available Nutrients from Manure.

Manure also contains phosphorus (P) and potassium (K), although not always in the right ratio to match crop needs. Applying manure to meet most of the crop nitrogen needs generally exceeds the phosphorus needs of the crop three to five, or more, times what the crop needs. Manure P generally does not move through the soil but it can runoff with soil runoff and erosion. Additional micronutrients such as sulfur and zinc are also found in manure. These nutrients are largely in their organic form in manure, making them readily available in the crop year following application.

Based upon the assumptions that are relevant to an individual field situation and whether or not manure is incorporated to conserve the ammonium-N, manure may have a value in the range shown in table 1. For a 20 ton/acre application of beef manure solids, the value per acre might range from $240 to $660 per acre. Note the critical importance for feedlot manure is to place it on fields requiring P if you want to achieve an economic “Win” (Figure 1). For other manures, the organic and ammonium-N can be equally critical to the value of manure. Fields that also have low soil potassium levels will gain significantly greater value from manure. Selecting fields/crops carefully will produce a benefit closer to the $660/acre benefit for a 20 ton/ac beef manure application.

Because manure nutrient content varies greatly among species and the manure storage and handling methods employed, it is best to determine a value for the specific manure to which your farm has access. With a manure sample specific to your manure source and a worksheet for estimating manure value (e.g. Calculating the Value of Manure for Crop Production) or an on-line or spreadsheet tool (e.g. Nebraska Manure Value Calculator), farm specific estimates of manure value can be made. 

To achieve a higher economic “Win” from manure’s fertility value:

• Prioritize application to fields with soil P concentrations of 20 ppm or less.
• Avoid annual manure applications on the same field. Wait for soil P concentrations to return to a 20 ppm target before reapplying manure, often delaying manure application for three to eight years.
• Apply manure ahead of non-legume crops benefitting from supplemental N.
• Conserve the ammonium N value of manure by incorporating the manure into the soil immediately. This is especially important for swine and dairy slurry manures while of little value for open lot beef manure.
• Credit the manure’s organic nitrogen for the second and third cropping years after a manure application.  A soil test will not give credit to residual organic nitrogen in the soil. For estimating these credits, see Determining Crop Available Nutrients from Manure.
• Target fields requiring potassium, sulfur, or micronutrients. Fields requiring potassium experience a much greater economic return from manure application (see Figure 1).
• Apply manure at a rate less than the N requirement of the intended crop, and then side-dress the crop with commercial fertilizer based upon in-season soil or crop N measures. 

Suggested References:

• Nebguide G1335. Determining Crop Available Nutrients from Manure.  http://extensionpublications.unl.edu/assets/pdf/g1335.pdf
• NebGuide G1519. Calculating the Value of Manure for Crop Production.  http://extensionpublications.unl.edu/assets/pdf/g1519.pdf
• Nebraska Manure Value Calculator. http://water.unl.edu/manure/software#manurevalue

Reviewers: Leslie Johnson, Extension Animal Manure Management Coordinator; Amy Schmidt, Extension Animal Manure Management Specialist; Jim Jansen, Extension Educator