Dec. 9, 2010

With Nebraska being one of the nation’s top livestock producers, the state has a lot of manure that can serve as a valuable resource for crop production.

Benefits of manure include the nutrients supplied, especially the nitrogen and phosphorus needed for most Nebraska soils, and its soil amendment effects. The soil amendment effects often result in increased productivity for several years after application.

Typical yield increases in the first year after application are 7 bu/ac of corn and 2 bu/ac of soybean, but the effect is commonly greater on sandy soil, once-eroded sites, and heavy clay soils. This effect may be due to a combination of:

• effect on soil aggregation and improved water infiltration with runoff and erosion reduced by about 2% for each ton/acre dry matter manure applied;
• increased soil organic matter; and
• neutralization of soil acidity, at least with beef cattle manure. (A ton of manure, dry weight, has the liming effect of about 60 lb of agricultural lime.)

Some manure nutrients are readily available and usually applied in quantities that far exceed what the crop can remove. For example, most manure phosphorus becomes crop available during the year of application, but the quantity applied may be more than the crop can remove for three or more years. Laboratory analysis of manure nutrient content is needed to accurately estimate the manure value.

It’s difficult to estimate the availability of nitrogen, compared with other nutrients. Nearly all manure N is organic N or ammonium N, each of which behaves very differently.

Organic N is tied up in organic material that needs to decompose before the N can be plant available; the mineralization of organic N varies with manure type with 15% to 50% available in the first year. All applied ammonium is expected to be available to the crop if volatilization losses of ammonia do not occur.

Estimation of ammonium N availability is easier if the manure is injected or otherwise incorporated into the soil during application. If manure is surface applied with delayed or no incorporation, much or all of the ammonium N may be lost due to volatilization of ammonia. A UNL webcast on calculating manure N availability considers rate of release of organic N and volatilization loss of ammonium N.

Proper sampling of manure, knowing the rate of application, and uniform application are important to efficient manure use. Manure sampling is usually done by the animal feeding operation. For more information see Sampling Manures For Nutrient Analysis, a UNL Extension NebGuide G02-1450. Calibration of applicators and uniformity of application is addressed in a webcast.

UNL Extension has developed a downloadable spreadsheet and guide related to this topic, Calculating The Value Of Manure For Crop Production: Spreadsheet Instructions (EC192).

Charles Wortmann
Nutrient Management Specialist
Charles Shapiro
Soil Scientist - Crop Nutrition