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Calculating manure application rates

Before planning for manure applications, consider how the nutrients will be managed for the upcoming crop. Will all the nitrogen (N) be supplied from manure? This will require a higher application rate and will overapply phosphorus (P) and potassium (K) for the crop year. If done too often, there could be environmental consequences when excess P enters waterways.  A lower rate can be used to supply all the P the crop needs. This will allow the manure to be spread over more acres but will require additional N and possibly K to be applied as a commercial fertilizer.

Once you choose a strategy, use the following steps to determine application rates:

  • Step 1: Find the nutrient needs of the crop

  • Step 2: Calculate the actual nutrient availability in the manure

  • Step 3: Divide the answer from Step 1 by Step 2

While this sounds simple, there are slight differences in calculations depending on whether you are basing your applications on N or P needs of the crop or are using liquid or solid manure. The following sections will walk through the calculations for N- and P-based application rates, respectively.

Nitrogen-based manure application rate calculations

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Manure application rate calculations - phosphorus-based

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Table 1: Nitrogen availability and loss as affected by method of manure application and animal type.

Year available Broadcast + >96 hours incorporation Broadcast + 12-96 hours incorporation Broadcast + <12 hours incorporation Injection: Sweep Injection: Knife
Beef -- -- -- -- --
1 25% N available/year 45% N available/year 60% N available/year 60% N available/year 50% N available/year
2 25% N available/year 25% N available/year 25% N available/year 25% N available/year 25% N available/year
3 10% N available/year 10% N available/year 10% N available/year 10% N available/year 10% N available/year
Lost 40% N available/year 20% N available/year 5% N available/year 5% N available/year 10% N available/year
Dairy -- -- -- -- --
1 20% N available/year 40% N available/year 55% N available/year 55% N available/year 50% N available/year
2 25% N available/year 25% N available/year 25% N available/year 25% N available/year 25% N available/year
3 15% N available/year 15% N available/year 10% N available/year 15% N available/year 15% N available/year
Lost 40% N available/year 20% N available/year 10% N available/year 5% N available/year 10% N available/year
Swine -- -- -- -- --
1 35% N available/year 55% N available/year 75% N available/year 80% N available/year 70% N available/year
2 15% N available/year 15% N available/year 15% N available/year 15% N available/year 15% N available/year
3 0% N available/year 0% N available/year 0% N available/year 0% N available/year 0% N available/year
Lost 50% N available/year 30% N available/year 10% N available/year 5% N available/year 15% N available/year
Poultry -- -- -- -- --
1 45% N available/year 55% N available/year 70% N available/year n/a n/a
2 25% N available/year 25% N available/year 25% N available/year n/a n/a
3 0% N available/year 0% N available/year 0% N available/year n/a n/a
Lsot 30% N available/year 20% N available/year 5% N available/year n/a n/a

Melissa Wilson, Extension manure management specialist

Reviewed in 2019

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