Nitrogen from urine (ammonium N) is quickly available for crop uptake, while N from feces (organic N) is more slowly released. Manure represents a mix of both urine and feces, so estimations of the amount of plant available N from manure should be based on both.
The total manure N calculator, below, will help in estimating the combined contributions of organic N and ammonium N to the total pool of plant available N from manure. The scenario, below, is provided as a place to start.
A dairy farm had its manure analyzed and found that its cow manure has 8% dry matter, 5 lbs organic-N/ton (assume it's the same as in the past), and 4 lbs NH4+-N/ton. They also calibrated their manure spreader and realized that they will continue, as they have in the past 2 years, to apply manure to a corn field at 15 tons/acre. They plan to surface apply manure this spring and till it in 2 days later. How much total N from manure will be available to this year's corn crop?
If the same amount of manure was applied during the fall, how much total manure N would be available? What happened to the N? The calculator can be used to assess N credits from a full range of manure management approaches, by changing application rates, manure analyses, timings, methods, etc.