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:
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Step 1: Find the nutrient needs of the crop
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Step 2: Calculate the actual nutrient availability in the manure
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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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Tips:
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For Total N needed:
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Use University of Minnesota’s recommendations for non-legume crops.
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For non-legume crops, calculate crop N removal (see Table 1).
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N credits include N from previous legumes or manure application
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Other N sources include starter fertilizer, irrigation water, etc.
Tips:
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Total N Content: Make sure to use the reported test value, not the “first year available” numbers
Tips:
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Liquid vs. solid manure:
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Since liquid manure nutrients are described on a “per 1000 gallon” basis, multiply the Manure Application Rate by 1000.
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If using solid manure, you do not need to do anything further.
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Manure application rate calculations - phosphorus-based
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Tips:
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For Total P needs, you’ll need to know your soil P test levels:
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For very low or low P testing soils, use University of Minnesota fertilizer guidelines
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For medium or higher P testing soils, calculate crop P removal (see Table 1).
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Other P sources include starter fertilizer, etc.
Tips:
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Total P Content:
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Make sure to use the reported test value, not the “first year available” numbers
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Make sure the Total P is reported as Total P2O5 content on your manure analysis. If not, multiply Total P by 2.29 to get Total P2O5.
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P Availability Factor: 80% of manure P is available the first year, so multiply the total P content by 0.8.
Tips:
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Liquid vs solid manure:
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Since liquid manure nutrients are described on a “per 1000 gallon” basis, multiply the Manure Application Rate by 1000.
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If using solid manure, you do not need to do anything further.
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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 |
Reviewed in 2018
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