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Extension > Agriculture > Manure Management and Air Quality > Manure Application > Incorporate manure to prevent nitrogen losses

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Incorporate manure to prevent nitrogen losses

Case study: beef finishing operation

The purpose of this case study is to demonstrate the economic and environmental value of incorporating manure to prevent nitrogen losses, provide an opportunity for sale of manure, and reduce excessive buildup of soil test phosphorus.

Farm description:

This feedlot in Minnesota finishes about 1500 head of cattle per year for an annual average of 594 animal units. The cattle are purchased at 750 pounds and marketed at 1500 pounds. They are housed in a mono-slope barn with corn stalk bedding. Five hundred acres are used for crop production, and the only fertilizer purchased is 36 tons of anhydrous ammonia annually.

Example of a mono-slope barn

Phosphorus import-export analysis:

Purchased feeds on this farm include dry shell corn, grass hay, wet distiller's grains, and a custom protein mix. Some corn stalk bales for bedding are imported. Some soybeans are grown and sold. They apply all manure to the farm's 500 crop acres without incorporation and there is no exporting or importing of manure. Total phosphorus (P) in the feedlot rations range from 0.40 to 0.50%. Most of the soil P of this farm's Silt Clay Loam type soil exceeds 50-ppm Bray 1-P. The crop acre to animal unit ratio is 0.85. As the table below indicates, there is an annual excess of P imports relative to exports of 65.7 lb. P per crop acre, or 55.7 lb. P per animal unit, with a total of 33,099 lb. excess P per year. That is the equivalent of 150 lb. net increase in P2O5 per acre per year, which would be expected to lead to a steady rise in soil test P above the already very high values and increase the risk of P in runoff.

Phosphorus Balance

Phosphorus (lb.)

Ratios

P Source Imports Exports Excess
Animals 7,796 14,175 Crop Acres Animal Units Ratio
Forages 289 0 504 594 0.85
Grains 0 418
Protein/Minerals 39,607 0 Excess P (lb.) Crop Acres Ratio
Bedding 0 0 33,099 504 65.7
Fertilizer 0 0
Manure 0 0 Excess P (lb.) Animal Units Ratio
Total P 47,692 14,593 33,099 33,099 594 55.7

Strategies for reducing excess P application:

Since the soil test P values far exceed 21 ppm Bray P-1, the level above which no additional P application would give a yield response (see table below from Kaiser et al.), we could consider an application rate equivalent to that at which P is removed by the crop each year. That would more closely approach soil test P stabilization than the farm's current application rate. The removal rate of P2O5 for a 200 bu./acre corn crop is 68 lb./acre. Applying the available manure at 68 lb. of P2O5/acre would require application to more than double the current 500 spreadable acres, all in corn. That is, unless some other strategies to alter the import/export imbalance are employed. The strategy illustrated in this case study is to:

  1. Conserve more nitrogen in the manure by incorporation immediately after application
  2. Apply manure on half of the corn acres at a rate that would supply most of the needed N for one year and all of the P for two years. Supplement with fertilizer N. Alternate sites for manure application over a two year cycle.
  3. Apply only fertilizer N to the other half of the corn acres, taking the N credit for the previous year manure application.
  4. Sell or trade the remaining manure to a neighbor for corn if needed. A crop farmer would be able to utilize all of the N, P, and K in the manure, whereas on this farm the excess P and K have no economic value.

Other options to consider would include reducing imports of P, primarily through reduction in purchase of wet distiller's grain and/or other high P feed supplements, since the P content of the ration is well above the NRC recommended range of 0.30 to 0.35 for finishing cattle.

We know the nutrient analysis but not the total weight or volume of manure produced on this farm in a year, so for the following calculations we will use the NRCS Agriculture Waste Management Field Handbook estimates of manure production based on type and size of animals.

Data and assumptions for subsequent calculations:

Manure can be applied on half the available crop acres at crop P replacement rates for two years:

Remaining manure available for sale each year:

15,062,600 lb. total produced - 4,533,333 lb. applied to 250 acres = 10,529,267 lb. (5,265 tons).

Phosphate suggestions for corn production in Minnesota

Soil test P (ppm)

v. low low medium high v. high

Expected Yield

Bray: 0-5 6-10 11-15 16-20 21+
Olsen: 0-3 4-7 8-11 12-15 16+

Bc1 Band Bc Band Bc Band Bc Band Bc Band
bu./acre

P2O5/acre to apply (lb./acre)

< 100 60 30 40 20 25 20 10 10-15 0 10-15
100-124 75 40 50 25 30 20 10 10-15 0 10-15
125-149 85 45 60 30 35 25 10 10-15 0 10-15
150-174 100 50 70 35 40 30 15 10-15 0 10-15
175-199 110 55 75 40 45 30 15 10-15 0 10-15
200-220 130 65 90 45 55 30 20 10-15 0 10-15
220-240 145 75 100 50 60 30 20 10-15 0 10-15
240+ 160 80 115 60 70 35 25 10-15 0 10-15

1Bc = broadcast

*No phosphate fertilizer is recommended if the soil test for P is higher than 25 ppm (Bray) or 20 ppm (Olsen).

Table from Kaiser et al. 2011. "Fertilizer Guidelines for Agronomic Crops in Minnesota". University of Minnesota Extension.

Manure nitrogen losses based on incorporation practices:

The following table presents the N available in the first year from manure with different incorporation practices. Since this is a feedlot we are going to compare first year availability of beef manure with no incorporation (25%) to manure incorporation less than 12 hours after application (60%). This difference is primarily the result of nitrogen volatilization loss from manure left on the soil surface vs. reduced loss from rapid incorporation after application.

Manure nitrogen availability and loss as affected by method of application and animal species

Animal Species and Year of Application2

Surface Broadcast and Incorporation Timing1

Injection

None < 4 days < 12 hours Sweep Knife

% Total N

Beef
Year 1 25 45 60 60 50
Year 2 25 25 25 25 25
Lost3 40 20 5 5 10
Dairy
Year 1 20 40 55 55 50
Year 2 25 25 25 25 25
Lost3 40 20 10 5 10
Swine
Year 1 35 55 75 80 70
Year 2 15 15 15 15 15
Lost3 50 30 10 5 15
Poultry
Year 1 45 55 70 NA NA
Year 2 25 25 25 NA NA
Lost3 30 20 5 NA NA

1The categories refer to the length of time between manure application and incorporation.

2Third-year available N is not listed but can be computed by adding Year 1 and Year 2 and lost percentages and subtracting this sum from 100.

3Lost refers to estimated volatilization and denitrification processes.

Table from Hernandez and Schmitt. 2012. "Manure Management in Minnesota". University of Minnesota Extension.

Nitrogen calculations:

N application rate when manure is not incorporated

N application rate when manure is incorporated within 12 hours

N fertilizer needed on non-manured acres

Total fertilizer N if follow new manure application strategy

Economic considerations:

The strategy of applying manure to half the acres at twice the crop P removal rate and conserving manure N with immediate incorporation would modestly reduce purchased fertilizer N and would make 70% of the manure available for sale to a crop producer who could use all of the manure nutrients. More of the manure could be used on the farm without further increasing the risk of P in runoff if the percent P in the purchased feed were reduced, thereby reducing the amount of P in the manure. Replacing some or all wet distiller's grains with corn when corn prices are economically feasible would reduce the P in the ration and the manure. Alternatively, additional land would need to be rented or purchased to bring the farm into P balance.

Conclusions:

  1. Manure can provide significant nutrient contributions for crop production.
  2. The ratio of nitrogen/phosphorus in manure does not usually match the relative needs of crops.
  3. Incorporating manure within 12 hours after application enables maximum potential availability of nitrogen in manure, reducing the need for purchased fertilizer N.
  4. Incorporating manure within 12 hours after application gets the manure phosphorus in contact with the soil and reduces surface runoff contact with manure, which reduces soluble P loss in runoff.
  5. Multiple strategies may be necessary on a farm to balance P imports with P exports and reduce the buildup of soil test P to levels that create a risk to streams and lakes.

References:

  1. Hernandez, J.A. and Schmitt, M.A. 2012. "Manure Management in Minnesota". University of Minnesota Extension.
  2. Kaiser D.E., Lamb J.A., and Eliason R. 2011. "Fertilizer Guidelines for Agronomic Crops in Minnesota". University of Minnesota Extension.
  3. USDA-NRCS. Agriculture Waste Management Field Handbook. "Agriculture Waste Characteristics". 651 pp 16.
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