Manure management should be a top priority on dairy 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 thus economic value. Manure also improves biological activity, soil tilth, and soil chemical properties.

According to 1990 Minnesota Agricultural Statistic Service data, the Minnesota dairy industry generates approximately 11 million tons of manure annually. Dairy cattle in Minnesota excrete almost 55,000 tons of nitrogen (N) per year that can be a nutrient source for crops. This manure also contains 22,000 tons of P₂O₅ (phosphorus fertilizer equivalent) and 44,000 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 dairy operations. Knowing the amount of manure produced as well as its nutrient content will help a dairy farmer to 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 content 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, the 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 dairy manure (Livestock waste facilities handbook, Midwest Plan Service, March 1985).

Form	Dry Matter	Total N	P2O5	K2O
Solid:	%	lbs/ton
No bedding	21	9	4	10
With bedding	21	9	4	10
Liquid:		lbs/1000 gal
Anaerobic storage	8	24	18	29

A third alternative, is relatively easy to calculate: Calculate the average amount of manure produced per day by the dairy animal, multiply by the number of cows/calves and assume standard storage and handling losses. Table 2 can be used to calculate the initial amount of manure produced by the cows/calves. 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 dairy manure production (Livestock waste facilities handbook, Midwest Plan Service, March 1985).

Animal Size	Manure Produced*		N	P2O5	K2O
lbs	lbs	gal	lbs
150	12	1.5	0.06	0.02	0.05
250	21	2.4	0.10	0.05	0.08
500	41	5.0	0.20	0.08	0.17
1000	82	9.9	0.41	0.17	0.33
1400	115	13.9	0.57	0.23	0.46
* 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

Aplication 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	20	60	40	55	45
Availability Years 2-3	45	35	40	40	45
Lots	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