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.
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.
|Animals||7,796||14,175||Crop Acres||Animal Units||Ratio|
|Protein/Minerals||39,607||0||Excess P (lb.)||Crop Acres||Ratio|
|Manure||0||0||Excess P (lb.)||Animal Units||Ratio|
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:
- Conserve more nitrogen in the manure by incorporation immediately after application
- 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.
- Apply only fertilizer N to the other half of the corn acres, taking the N credit for the previous year manure application.
- 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:
- Recommended N application rate for high-productive soils for corn following corn is 180 lb. nitrogen/acre1.
- Actual manure analysis from this farm:
- N 19.6 lb./ton or 0.98%
- P2O5 15.0 lb./ton or 0.75%
- K2O 12.0 lb./ton or 0.6%
- N available from beef manure 1st year if not incorporated: 25%.
- N available from beef manure 1st year if incorporated within 12 hours: 60%.
- N available from beef manure in second year: 25%.
- Amount of manure created/finish steer fed 153 days: 9800 lb.
- Number of animals finished per year: 1537.
- Manure produced per year: 15,062,600 lb. (7531 tons).
Manure can be applied on half the available crop acres at crop P replacement rates for two years:
- P2O5 for 250 acres at two-year P replacement for corn = 68 lb. P2O5 x 250 acres x 2 years = 34,000 lb.
- Because soil test P is not limiting on this farm, we do not consider first year P availability in the manure, just total P applied to the soil.
- Manure required on 250 acres at two-year P replacement rate = 34,000 lb. P2O5 ÷ 0.75% P2O5 in manure = 4,533,333 lb. manure (2267 tons).
- Manure applied per acre = 4,533,333 lb. manure ÷ 250 acres = 18,133 lb./acre (9.07 tons/acre).
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|
P2O5/acre to apply (lb./acre)
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
|None||< 4 days||< 12 hours||Sweep||Knife|
% Total N
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.
N application rate when manure is not incorporated
- 4,533,333 lb. manure applied x 0.98% N = 44,427 lb. total N
- 44,427 lb. N x 25% available when manure not incorporated = 11,107 lb. available N
- 11,107 lb. ÷ 250 acres = 44.4 lb./acre available N
- Supplemental fertilizer N needed = 180 lb./acre - 44.4 lb./acre from manure = 135.6 lb./acre
N application rate when manure is incorporated within 12 hours
- 44,427 lb. N x 60% available when incorporated within 12 hours = 26,656 lb. available N
- 26,656 lb. ÷ 250 acres = 106.6 lb./acre available N
- Supplemental fertilizer N needed = 180 lb./acre - 106.6 lb./acre from manure = 73.4 lb./acre
N fertilizer needed on non-manured acres
- N available from previous year manure application (second year N credit) = 44,427 lb. N x 25% = 11,107 lb.
- 11,107 lb. ÷ 250 acres = 44.43 lb./acre
- Fertilizer N required = 180 lb./acre - 44.43 lb./acre = 135.57 lb./acre
Total fertilizer N if follow new manure application strategy
- 73.4 lb./acre supplemental N required on manured acres x 250 acres = 18,344 lb.
- 135.57 lb./acre fertilizer N required on non-manured acres x 250 acres = 33,893 lb.
- Total supplemental N required: 52,237 lb.
- Current fertilizer N purchased: 36 tons anhydrous ammonia = 72,000 lb. x 82% N in anhydrous ammonia = 59,040 lb. N
- As reference, the total current fertilizer N cost = 36 tons x $775/ton = $27,900
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.
- Manure can provide significant nutrient contributions for crop production.
- The ratio of nitrogen/phosphorus in manure does not usually match the relative needs of crops.
- Incorporating manure within 12 hours after application enables maximum potential availability of nitrogen in manure, reducing the need for purchased fertilizer N.
- 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.
- 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.
- Hernandez, J.A. and Schmitt, M.A. 2012. "Manure Management in Minnesota". University of Minnesota Extension.
- Kaiser D.E., Lamb J.A., and Eliason R. 2011. "Fertilizer Guidelines for Agronomic Crops in Minnesota". University of Minnesota Extension.
- USDA-NRCS. Agriculture Waste Management Field Handbook. "Agriculture Waste Characteristics". 651 pp 16.