Determining 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.

Manure application rate calculations - nitrogen-based

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Manure application rate calculations - phosphorus-based

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Table 1: Amount of nutrients removed in harvested portion of the crop

Crop Yield units Crop nutrient removal: N Crop nutrient removal: P2O5 Crop nutrient removal: K2O
Alfalfa Tons (air dry) 50.4 lbs per unit 10.8 lbs per unit 46.2 lbs per unit
Barley (grain) Tons (air dry) -- 0.41 lbs per unit 0.28 lbs per unit
Barley (grain and straw) Bushels -- 0.55 lbs per unit 1.67 lbs per unit
Canola Cwt. -- 1.3 lbs per unit 1.1 lbs per unit
Corn (grain) Bushels -- 0.34 lbs per unit 0.19 lbs per unit
Corn (silage) Tons (as fed) -- 3.8 lbs per unit 7.4 lbs per unit
Edible beans Pounds -- 0.01 lbs per unit 0.03 lbs per unit
Grass or hay pasture Tons (air dry) 27.1 lbs per unit 8.9 lbs per unit 31.3 lbs per unit
Grass/legume Tons (air dry) 43.5 lbs per unit 11.2 lbs per unit 41.3 lbs per unit
Oats (grain) Bushels -- 0.25 lbs per unit 0.16 lbs per unit
Oats (grain and straw) Bushels -- 0.32 lbs per unit 1.31 lbs per unit
Peas Pounds -- 0.01 lbs per unit 0.01 lbs per unit
Potatoes Cwt. -- 0.14 lbs per unit 0.56 lbs per unit
Red Clover Tons (air dry) 45.1 lbs per unit 10.8 lbs per unit 41.1 lbs per unit
Rye (grain) Bushels -- 0.44 lbs per unit 0.31 lbs per unit
Rye (grain and straw) Bushels -- 0.59 lbs per unit 1.25 lbs per unit
Soybeans Bushels 3.5 lbs per unit 0.82 lbs per unit 1.0 lbs per unit
Sugarbeets Tons -- 2.2 lbs per unit 7.3 lbs per unit
Sunflower Pounds -- 0.01 lbs per unit 0.01 lbs per unit
Sweet corn Tons -- 11.0 lbs per unit 13.9 lbs per unit
Wheat (grain) Bushels -- 0.53 lbs per unit 0.3 lbs per unit
Wheat (grain and straw) Bushels -- 0.64 lbs per unit 1.5 lbs per unit

Table 2: 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 2018

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