The short answer is yes. The "organic-N" value is the same whether or not the manure is incorporated. Organic-N availability to the crop is controlled more by soil temperature and moisture conditions, not by incorporation. However, the "ammonium-N" and the total "Crop Available N" values may increase with incorporation. The ammonium-N availability is controlled primarily by the speed at which manure is mixed with the soil and the weather conditions under which it is applied. The crop available N, sum of organic and ammonium N, is also influenced by speed of incorporation. This last value is what is needed for determining recommended manure application rates. If you want to understand the basis for this answer, a longer answer follows.
To estimate the nitrogen value of manure, you need to start with a manure analysis representative of manure from your farm. Many weather- and management-related factors will influence the concentration of nitrogen and other nutrients. For purpose of illustration, we will assume that a slurry dairy manure is collected with approximately 25 lb of total nitrogen per 1,000 gallons.
Next, you need to know the relative fraction of this nitrogen that is in an organic form versus an ammonium form, also available from most manure analysis reports. For this example, let's assume there is 15 lb of organic-N and 10 lb of ammonium-N per 1,000 gallons.
Now you need to know the availability factors for nitrogen. You should try to find values specific to your state as availability is influenced by weather. In addition, state regulatory processes may require or recommend specific values. Values for many states can be found at State Specific Manure Nutrient Management Information. For this example, we selected "Ohio" on the map in the middle of the page and found the "Ohio Manure Management Guide" that might contain those values. In Chapter 6, "Land Application Guides," we copied some of the values used in Ohio. Now we have all of the data needed to estimate the nitrogen value.
Table 16. Estimated N Availability of Manure Based on Time and Application Method.
Available Nitrogen Percent Time of Application Days Until Incorporated
NH4 Organic N Date Days
50% 33% Nov-Feb < 5
25% 33% Nov-Feb > 5
25% 33% Sept-Oct < 1
15% 33% Sept-Oct > 1
Use this formula to now calculate the crop-available N for individual situations:
Crop Available N = (NH4-N x Available N% / 100) + (Org-N x Available N% / 100)
Dairy manure applied in the fall (assumed November) and not incorporated:
Crop Available N = (10 lb x 25 / 100) + (15 lb x 33 / 100) per 1,000 gallons
Crop Available N = 2.5 + 5 lb = 7.5 lb of crop available N per 1,000 gallons
Dairy manure applied in the fall (assumed November) and incorporated:
Crop Available N = (10 lb x 50 / 100) + (15 lb x 33 / 100) per 1,000 gallons
Crop Available N = 5 + 5 lb = 10 lb of crop available N per 1,000 gallons
In Nebraska, we would assume 95% ammonium-N availability if manure is directly incorporated into the soil and 50% if allowed to remain on the surface for 24 hours before incorporation. Our organic-N availability factors are very similar to Ohio factors. Because our environmental regulatory agency would expect one to use Nebraska numbers for a nutrient plan developed for a Nebraska dairy, it is wise to find your state-specific values and confirm those with your state's environmental regulatory agency. Your states recommendation's may be found at State Specific Manure Nutrient Information
Author: Rick Koelsch, University of Nebraska
