Organic N in manure

Organic N in manure becomes plant available over time, some during the year of application and some in the years to follow. Thinking back to the N Cycle, organic N must be mineralized by soil microorganisms before it can be taken up by plants. The major factors that influence organic N mineralization from manure are:

Mineralization of organic N in manure varies from season to season and field to field, because of the range in the conditions, above. To estimate the amount of organic N in manure that becomes available for crop production, research-based, average mineralization rates across a range of conditions have been developed, shown in the table, below.

Release rate for organic N in manure (%)
Source Dry Matter Content (%) Applied in current year Applied last Year Two Years Ago
Cows <18 35 12 5
Cows 18 25 12 5
Poultry <18 55 12 5
Poultry 18 55 12 5
Swine <18 35 12 5
Swine 18 25 12 5
Horses <18 30 12 5
Horses 18 25 12 5
Sheep <18 35 12 5
Sheep 18 25 12 5

For instance, if 10 tons/acre of 6% dry matter cow manure is applied in the spring, 35% of manure's organic N would, on average, be used by the crop during this growing season. If the same application was made in each of the previous two years, then 12% of the organic manure N would be available this season from last year's application and 5% from the application made two years prior.

The calculator, below, is designed to determine the N available to crops from organic N in manure. To do this, assume that 10 tons/acre of cow manure with 5 lbs organic-N/ton and 6% dry matter is applied to a field.

  1. Enter Cows in the "Animal Species" drop down menu and <18% in the "% dry matter" menu.
  2. Enter 10 into the "Application Rate" cell for "This Year".
  3. Enter 5 into the "Organic N from Manure Analysis" cell.
  4. Hit "calculate it!".
  5. Track the differences in N availability.
  6. Enter the same manure rate and analysis for "Last Year" and "Two Years Ago" and hit "calculate it" to see the N contribution from past manure applications.

The calculator can also be used to assess organic N availability from manure for other manure types as well as different rates and histories of application.

To read more on this subject: Nitrogen Guidelines for Field Crops in New York (section 3.3).

Manure N Worksheet

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