Your livestock’s manure is an excellent source of nutrients for your crops – take a manure sample to estimate the application rate needed. Check out this factsheet explaining how to take a manure test.
Unlike synthetic fertilizers, the availability of N from manure will not be 100%, so consider incorporating the manure immediately to increase available N. You might also consider adding a nitrogen inhibitor to reduce manure-N losses.
Another consideration is modifying your cropping system. Plowing down a legume or grass hay crop can provide the next crop of corn with all or most of its N requirements. Nitrogen that is tied up in roots and above-ground biomass is released over time as soil microorganisms break down the plants and release N in forms that plants can use.
3) Resist the Impulse to Top-off
The plant’s capacity to uptake nutrients does have a limit and going beyond that limit is like flushing money down the toilet. The same rate of actual N should be applied regardless of the fertilizer source.
Source : uvm.edu