link: Extension Home Page
link: Extension Home Pagelink: Workshopslink: County Officeslink: Online Shopping      
img: Left edge of swash img: Right edge of swash
img: center of swash
img: Bottom edge of swash
  FO-05882-GO     Reviewed 1998 To Order   
Clean Water- You Can Make the Difference

Fertilizing Cropland
with Beef Manure

Michael Schmitt and George Rehm

-
Copyright    2002  Regents of the University of Minnesota. All rights reserved.

Manure management should be a top priority on beef farms as we approach the 21st century. Mismanagement of manure can have a substantial impact on our water, soil and air resources. When used appropriately, manure has nutritive and economic value. Manure also improves biological activity, soil tilth, and soil chemical properties.

According to 1990 Minnesota Agricultural Statistic Service data, the Minnesota beef industry generates approximately 10 million tons of manure annually. Beef in Minnesota excrete almost 55,000 tons of nitrogen (N) per year that can be a nutrient source for crops. This manure also contains 41,000 tons of P2O5 (phosphorus fertilizer equivalent) and 47,000 tons of K2O (potassium fertilizer equivalent). Although some nutrient losses are inevitable in handling and storage, manure can replace the need for commercial fertilizer on thousands of Minnesota's cropland acres.

Manure Inventory Assessment

A comprehensive manure management plan is essential for all beef operations. Knowing the amount of manure produced as well as its nutrient will help a beef producer plan for the number of acres that will be manured.

The best method to determine nutrient supply from manure is to analytically test it for nutrient contents and multiply this by the storage volume. This method does not require numerous assumptions-- yet it does require that representative manure samples be collected and storage volume calculations be made. For solid manure, several subsamples should be taken throughout the manure pile/pack. A long, narrow bladed shovel works well. Collecting a representative sample of liquid manure is difficult because of the constant settling of the solid portion of the manure. Because much of the phosphorus and the organic N is in this layer, manure must be agitated enough to suspend the solids that can be resuspended.

An alternative method to determine nutrient quantities is to calculate storage capacities and multiply by the average nutrient content, based on the species and storage and handling methods (Table 1). While Table 1 might be a good reference to begin developing application rates, these tabled values will vary significantly among storage facilities and livestock operations. Research results for manure analyses in Minnesota range from 25-300% of the average values.

Table 1. Nutrient analysis of beef manure.
Livestock waste facilities handbook,
Midwest Plan Service, March 1985.
Form Dry Matter Total N P2O5 K2O
Solid: % lbs/ton
No bedding-dirt 15 11 7 10
No bedding-concrete 52 21 14 23
With bedding 50 21 18 26
Liquid:
lbs/1000 gal
Anaerobic storage 11 40 27 34

A third alternative, relatively easy to calculate, is to calculate: the average amount of manure produced per day by the beef animal, multiply by the number of animals and assume standard storage and handling losses. Table 2 can be used to calculate the initial amount of manure produced by the steers. Table 3 lists some average N losses that affect nutrient content from several storage and handling systems. This method may be a good one for planning cropland needs with proposed increases in livestock numbers.

Table 2. Daily beef manure production.
Livestock waste facilities handbook,
Midwest Plan Service, March 1985.
Animal Size Manure Produced* N P2O5 K2O
lbs lbs gal lbs
500 30 3.8 0.17 0.14 0.14
750 45 5.6 0.26 0.18 0.23
1000 60 7.5 0.34 0.25 0.29
1250 75 9.4 0.43 0.32 0.37
Cow 63 7.9 0.36 0.27 0.31
*Linear interpolations of manure production between weight categories is acceptable.


Table 3. Storage losses of nitrogen.
Livestock waste facilities handbook,
Midwest Plan Service, March 1985.
System % N Lost
Solid
Daily scrape and haul 15-35
Manure pack 20-40
Open lot 40-60
Liquid
Beneath barn pit 15-30
Above-ground storage 10-30
Earthen storage 20-40

Determining Application Rates

Next, manure application rates must be calculated. This requires knowing the nutrient content of the manure, nutrients required by the crop, and availability of nutrients in the applied manure.

The majority (70-90%) of the phosphorus and potassium applied in manure will be available to the crop the first year after application. The availability of N varies considerably. This variation is primarily a function of the method of application. Table 4 provides an estimate of the amount of the total N that will be available in the application year and in the years after application.

Table 4. Nitrogen availability and loss as affected by method of application.

Broadcast-Incorporate * Injection
None <12 hours <4 days Sweep Knife
% Total N
Availability Year 1 25 60 45 55 45
Availability Years 2-3 40 35 35 40 45
Lost 35 5 20 5 10
* The categories refer to the length of time between manure application and incorporation.

Often there is a sense of futility in trying to use manure analysis, application loss coefficients, and crop nutrient requirements to determine manure application rates. Here is a five-step process to get started:

  1. Determine nutrient needs of each field's crop based on soil tests, previous crops, yield expectations, etc.
  2. Make an initial manure rate selection. Use the crop needs and a tabled nutrient composition of the manure, or a previous year's test.
  3. While applying the manure at the predetermined rate, collect a representative manure sample--either when loading the spreader in yard or unloading the spreader in the field. Send it to a laboratory for analysis.
  4. After receiving the laboratory analysis (presumably the manure will have been applied), calculate the actual amount of nutrients applied based on data and the application rate.
  5. In a record keeping system, record any possible overapplications or underapplications. If fewer nutrients were applied than planned and a fall application was made, starter or sidedressed programs can supply the deficiency. If spring manure applications were made and less N was applied than planned, a sidedressed application of N can be made. Overapplications should be credited for the next year.

Field Spreading Priority

Each livestock producer should determine the amount of manure generated on their farm and the nutrient requirements of the crops where the manure is to be applied. If the manure produced on a farm cannot supply all of the farm's crop nutrient needs, it is best to base the manure application rates on the phosphorus requirements. This strategy will use lower rates of manure and necessitate supplemental N fertilizer, which can be easily applied using starter N, weed-and-feed N, or sidedress-applied N.

If there is an excess of manure produced in relation to the crop's needs, manure rates should be based on the crop's N requirements. At no time should rates in excess of agronomic needs be used--this is both illegal (state rules, chapter 7020) and environmentally unsound. Rates will have to be based on P requirements if there is a potential phosphorus/surface water problem because of soil erosion, a very high soil test for phosphorus, and/or there is close proximity to water. Additional strategies such as applying manure onto legumes (see Special Use), hauling the manure off- farm, composting the manure and/or acquiring more cropland must also be considered in situations where excess manure is produced.

A field priority system should be developed to maximize the nutrient value of the manure. Priority should be given, in order, to those fields that: 1) require the greatest amount of N to grow the crop, 2) have the lowest phosphorus and potassium soil tests, and 3) will benefit most from adding the organic material to the soil.

Making a Multi-Year Plan

Thus far we have discussed annual manure management plans. For most planning processes, a three- to five-year forecast is often desirable. This may also be true with manure. In developing a multi-year plan, cropland nutrient needs often change due to crop rotations. The supply of nutrients should not change from year to year unless animal numbers change.

For each year in a rotation, the crop's needs must be determined and appropriate application rates determined. In an operation where cropland needs always exceed the manure's nutrient supply, shifting application rates and fields will occur. If there is a near balance in nutrient supply and needs, strategies that can correct for those "excess" and "deficient" years are needed. The primary strategies would be to apply/allow for multiple year needs.

Also, due to manure's residual properties, second and third year credits need to be accounted for in determining crop needs. Approximately 35-50% of the N in the organic fraction is available each year. Thus, second and third year N credits should be given for manure (Table 4). After applying beef manure, approximately 20% of the total N is available to the crop in the second year; approximately 5-10% is available in the third year.

Calibrating Application Equipment

Correct application of manure to cropland is critical to maximize the value of manure to crop producers. For manure to replace commercial fertilizer and not create environmental problems, farmers must be confident about the application rate. All calculations involving calibration of manure must be done using manure on an "as is" basis. All analysis should be interpreted on an "as is" basis and the application rate should be as well. Do not worry about the moisture content or change to a dry matter basis.

Three conditions must be addressed to achieve this confidence in rates. First, the analysis of the manure loaded into the application equipment must be known and should not change. For liquid systems, good agitation in the storage facility and in the transport tank are important. Loading procedures that do not separate the solids and the semi-solids can assure this for solid manure systems. Second, the rate of manure being applied to the field must be known and kept constant. Calibration must be conducted for all manure applications. And finally, the application or spread pattern of the manure must be uniform throughout the field so that all plants will have equal access to the nutrients. Having a predetermined travel plan for applying manure to a field and noting where loads stop and start will help ensure uniform applications.

Liquid systems

Calibration of liquid manure equipment requires that the manure be measured in gallons/acre (GPA). Getting a weight of the tank before and after spreading the manure and dividing by the density of the liquid manure (8.3 lb per gallon) is the best way to determine the volume. Combining this with the width of the spread pattern and the distance the tank takes to empty will provide the information to determine the application rate. For example, Operator A takes a loaded manure tank across a scale and it reads 29000 lb. Then the operator applies manure to a field with four injector knives (2.5 ft centers); it takes 1200 ft to empty the tank. Driving the emptied tank across the scale gives a reading of 8500 lb. The rate is:

[(29000 lb - 8500 lb) divided by 8.3 lb/gal] divided by {[1200 ft x (2.5 ft/injector x 4 injectors)] divided by 43560 ft2/acre} = 8965 GPA

Or, fill the tank to its predetermined volume to avoid needing a scale. However, the listed capacity is often different from what is hauled to the field with a "full" tank. Counting the number of loads needed on a given size field and assuming a set volume per load will allow calculation of a rate per acre, although this does not ensure uniform application within a field. This example has Operator B filling a 3200-gal tank 90% full for each load, then spreading 29 loads on a 23-acre field. The solution is:

[(3200 gal/load x 0.90) x 29 loads]divided by 23 acres = 3630 GPA

Solid systems

Calibration of solid manure equipment is similar to liquid manure equipment. The weight of manure applied can be determined by any one of several ways. Weigh your manure spreader before and after going to the field and determine the weight of manure spread. Then determine the width the manure is being spread and the distance it took to unload the manure. Using the ratio of weight per portion of an acre, a per-acre application rate can be calculated. It is best not to unload the entire spreader because the spread pattern at the end of a load is not representative. Example: Operator C weighs a loaded spreader; it is 9800 lb. After spreading a 12-ft width of manure a distance of 300 ft, the spreader is reweighed and it now measures 6200 lb. The rate calculation is:

[(9800 lb - 6200 lb) divided by 2000 lb/ton] divided by [(12 ft x 300 ft) divided by 43560 ft2/acre] = 21.8 tons/acre

A practical method is to use a scale to determine the weight per load and then count the number of loads it takes to spread manure on a given field. Calculate the total tons per field and divide by the number of acres in the field to determine rate of application. For example, if Operator D has previously calculated their spreader to hold 8.5 tons of manure when fully loaded, and uniformly applied 16 loads in a 13-acre field. The solution for rate is:

(16 loads x 8.5 tons/load) divided by 13 acres = 10.5 tons/acre

Another method is to lay a tarp or piece of heavy-duty plastic in a field. After the spreader has passed over, collect and weigh the manure from the tarp or plastic. Then determine the area of the plastic, and convert the weight measurement to a per-acre basis. This method generally has a large amount of variability unless several samples are collected and weighed. In an example, Operator E places five 4 ft by 4 ft plastic sheets in their field and spreads manure across these sheets. The combined weight of the sheets is 38.5 lb. The solution for the rate is:

(38.5 lb divided by 2000 lb/ton) divided by {[5 x (4 ft x 4 ft)] divided by 43560 ft2/acre}= 10.5 tons/acre

After determining the manure application rate, it is often necessary to adjust the rate to better match the recommended rate that you need. The most common method to change application rate is by changing the speed you drive across the field. Solid manure equipment may also have an adjustment that changes the chain speed in the box, thereby changing the manure rate. Liquid manure equipment may have valve opening adjustments to alter the rate. A concern with liquid manure systems is the difference in flow from the start to the end of the tank. Pressurized tanks, flow pumps, and new distributor designs are solving some of these problems in variable flows.

Special Concerns and Issues

Solid versus liquid manure

Nutrients voided by beef animals are the same whether the manure is to be handled as a liquid or a solid. It is the handling systems that create losses of nutrients or changes in the manure composition resulting in different nutrient analyses between solid and liquid manure.

The available plant nutrients in manure are often found in different fractions. Nitrogen, for example, is fairly evenly split between the feces portion, which contains the majority of organic N, and the urine, which contains most of the inorganic N. Therefore, it is essential to preserve and adequately mix these fractions before field application.

Phosphorus is found mainly in the feces component. Phosphorus is not lost by any chemical or biological process and the majority of this nutrient is available in the year of application. With a liquid storage system, the bulk of the phosphorus is in the settled solids at the bottom of the pit unless you agitate before spreading. Potassium is almost the opposite of phosphorus; almost all of it is in the urine.

Spring/winter/fall application times

Time of manure application can be extremely important if site-specific conditions create an environmental hazard. Fall applications allow for maximum time for the manure to break down before the crop uses the nutrients. While this is generally beneficial, it can also lead to environmental hazards if N loss from the soil is a concern. Fall applications of N are generally not recommended on coarse-textured soils.

With spring applications, there is less opportunity for N losses from a field. However, spring applications result in less time for organic decomposition of the manure, including the release of some nutrients. Spring applications also generally delay fieldwork and planting and could increase soil compaction.

Many producers use winter applications. While there will be significant losses of available N, the organic N fraction will still contribute to the plant-available N pool. The potential for nutrient runoff is an environmental concern for winter applications on frozen, sloping soil. If manure is applied to frozen soils and there is runoff from snow melt or rain, nutrients in the manure will be lost with the runoff. This situation is not recommended.

Methods of application

Broadcasting is a common way to apply solid or liquid beef manure. Sometimes this is followed by incorporation with a tillage operation. Other times, like with winter applications, the manure is left on the soil surface. Nitrogen loss is a concern with broadcast manure. The amount of loss depends mainly on the time between application and incorporation. Manure that is broadcast but never incorporated can lose about half of its total N. Incorporation within 12 hours is ideal for maximum N efficiency (See Table 4). Local ordinances and neighbors should be considered in determining where and when manure is broadcast due to odors.

With liquid manure systems, several more application options are available to crop producers. Injection methods place liquid manure below the soil surface, thus eliminating the majority of volatilization losses. Traditionally, injection knives placed the manure in a vertical band about 6-8 inches below the soil surface with 30- to 60-inch spacings between knives. New injection systems such as sweep and disc injectors are being marketed that spread the manure in horizontal patterns under the soil surface.

Special uses

When all of the cereal grain and nonleguminous hay crop acres have their N needs met, applying manure to the legumes is in order. Although legumes do not necessarily benefit from the N applied in manure onto cropland, there is a potential benefit from other nutrients contained in the manure. It is best to apply amounts that will meet their phosphorus or potassium needs.

Manure is deposited in nonuniform patterns when beef are on pasture or rangeland. The nutrient value of the manure must be viewed in terms of net nutrient additions or deletions for a field. In many cases, the forage is grown, eaten by the cattle and then excreted as manure. Some of the N will inevitably be lost via volatilization and some of the nutrients will be taken from the field when the cattle are removed from the field. Thus, the manure did not add to the nutrients in the soil--the nutrients in the soil are essentially being recycled. However, if feed is being imported to feed cattle within a field, even with some N loss from the manure, there is a net increase in nutrients from the manure since the feed, containing nutrients, was added to the field.

In pasture and rangeland situations, the volatilization potential from the manure N is inevitable. The maximum amount of N that can be lost, however, is the amount of N that is in the inorganic form. Therefore, about one-half of the manure N will still be available. To facilitate the efficient crop utilization of this manure N, spreading it more uniformly across the field is advantageous. One method of doing this is by dragging the field in order to spread the individual piles of manure.

Conclusion

Manure will continue to be an issue for beef producers. Recycling the manure to the soil through a predetermined manure management plan is efficient and practical. This will optimize the nutrient value of the manure while minimizing potential environmental hazards. Manure is a valuable resource on a farm and should be treated as an asset.

Michael Schmitt and George Rehm
Extension Soil Fertility Specialists
University of Minnesota Extension Service
Department of Soil, Water and Climate
University of Minnesota
-

Community \ Environment \ Family \ Farm \ Garden \ Living
Home \ Search \ Product Catalog \ News \ Workshops \ Online Shopping
About Extension \ County Offices \ Partners
-

This publication was funded from a 319 grant from the Minnesota Pollution Control Agency to further reduce non-point source pollution.

Produced by Communication and Educational Technology Services, University of Minnesota Extension Service.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request.  Please contact the University of Minnesota Extension Service Distribution Center at (800) 876-8636.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.