Determining manure application rates
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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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