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|
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.
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).