Much has been written from the research and field demonstrations on manure management. Descriptive terms such as nuisance, resource, liability, asset, pollutant, plant nutrient, etc., have all been used to discuss what is still a problem for many dairy producers. The fact is that the handling of dairy manure is a cost of producing milk. Producers goal should be understanding the energy aspects of manure to minimize the net costs associated with manure management which in turn may increase the profitability of the farming enterprise.

Several issues can be discussed to illustrate the importance of managing the energy aspects of manure in relation to its influence on economic returns and environmental concerns.

These include:

1. Determining the amounts of crop nutrients available from the dairy herd.
2. Assessing the dollar return for manure produced based on management practices.
3. Balancing manure application and crop acreage.

DETERMINING NUTRIENTS AVAILABLE

Using cropland as an acceptable way to dispose of dairy manure requires planning and management. It is important to know the amount of manure produced on the farm, the nutrient content, and the nutrients required for specific crop production. In order to set up a crop nutrient monitoring program, producers first need to calculate the amount of nutrients available from the dairy herd.

On the average, a dairy cow produces 82 pounds of manure per day per 1000 pounds liveweight. Table 1 can be used to calculate the amount of manure produced from the cow and replacement herd. Thus a Holstein (1400 pounds) cow produces 115 pounds of manure per day or approximately 21 tons per year. Heifers will average approximately 7 tons per year. The nutrient content values listed in Table 1 are approximate and do not include bedding material or added water.

Table 1. Dair Cattle Manure Production and Characteristics as Produced Per Year.

Source: Livestock Waste Facilities Handbook, Midwest Plan Service, March 1985.

Manure nutrient characteristics can vary from farm to farm. The recommended practice is to have manure analytically tested to determine the nutrient content. Samples to be tested must be representative of the manure that is coming out of the storage facility. Samples from a solid storage or manure pack should contain several subsamples taken with a long, narrow-bladed shovel. The subsamples then should be mixed together to obtain one sample. Representative sampling from a liquid or slurry facility is more difficult because of the settling of solids which contain much of the nutrients. Subsamples should be taken after thorough agitation. Table 2 can be used as an alternative to individual sampling by estimating the amount of nutrients produced by the cow.

Table 2. Nutrients in Dairy Cattle Manure as Produced Per Year.

Source: Livestock Waste Facilities Handbook, MWPS-18

The mature Holstein cow produces about 210 pounds of total nitrogen, 84 pounds of phosphorous and 166 pounds of potassium per year. However, the type of storage, handling, and field application will determine the amount of nutrients that will be available to the plant for growth. Nitrogen is very volatile and can be lost to the air as ammonia during storage and handling. Lot runoff and leaching into the soil can also account for lower nitrogen availability as well as storage losses from different systems (Table 3). Phosphorus and potassium losses are negligible except for open lots or lagoon waste handling systems. In the lot and lagoon the phosphorus and potassium can be recovered by collecting the lot runoff and by applying the lagoon sludge to the land. The field application method is another source of nitrogen loss (Table 4). The greatest nutrient response will be on land application with immediate incorporation of the manure into the soil or injected. To minimize nitrogen loss and to begin the release of nutrients for plant use, it is recommended to incorporate the broadcasted manure as soon as possible. Most losses occur in the first 24 hours after application. Ammonia loss is generally greater during the spring and summer months due to the warm, windy days. In order to avoid additional nitrogen loss from

leaching or denitrification producers should try to apply the manure as close to the crop planting date as possible.

Table 3. Nitrogen Losses During Handling and Storage. Typical losses between excretion and land application adjusted for dilution in the various systems. These values are in addition to land application losses, Table 4.

Source: Livestock Waste Facilities Handbook, MWPS-18

Table 4. Nitrogen Losses During Land Application. Percent of nitrogen applied that is lost within 4 days of application. For handling and storage losses, see Table 3.

Source: Livestock Waste Facilities Handbook, MWPS-18

ASSESSING DOLLAR RETURN

When looking at the economic return of dairy manure as a fertilizer, it is easy to note how quickly the value can decline due to the nutrient loss factors just mentioned. In assessing a dollar return to the operation for manure applied to cropland it is assumed that commercial fertilizer application has been reduced proportionately. In some cases this does not happen, thus creating an excessive build-up of soil fertility which is costly to the producer and the environment. The dollar value of manure nutrients credited to crop production will vary based on the nutrient losses occurred in handling and storage. Table 5 shows a potential value of $54.57 per cow annually for manure applied on cropland (assuming a 50 percent nitrogen loss and no phosphorus or potassium loss).

Table 5. Annual Manure Value for One 1400 lb. Cow

¹Current Commercial Fertilizer Prices

All of the nutrients from manure are not available in the first year. However, when calculating manure value it includes all the nutrients that will be available for plant use in one or more years after application.

DETERMINING APPLICATION RATES

It is important to monitor the amount of manure applied to each field so that the nutrients added do not greatly exceed the crop needs. The manure nutrients, especially nitrogen, are utilized more efficiently by corn and small grain crops than by legumes. Legumes get most of their nitrogen from the air, so additional nitrogen is not usually needed. Before heavy manure applications are made, soil should be tested for fertility needs. Then the manure applications can be adjusted to fit the crop needs against the soil tests for nitrogen, phosphorus, and potassium. Nitrogen in excess of crop requirements leaches through the soil in the nitrate form. This excessive nitrogen application can cause nitrate pollution in ground water. Phosphorus build-up should also be a concern. Manured fields with high phosphorus levels can runoff and erode the high soluble phosphorus into lakes and streams causing pollution.

Determine spreading rates based on which nutrients are needed for the crop. This is considered the most economical rate of manure application. Any excess nutrients will not be economical because there is no more savings from reduced commercial fertilizer. Nitrogen is usually the nutrient monitored when deciding on application rates. This is acceptable and will allow the higher amounts of manure applied per acre to corn and small grain fields. However, when soil test P levels go above 150 pounds per acre begin decreasing the amount of manure applied and plant crops that are heavy feeders of phosphorus. A more conservative approach is to apply manure at a rate which will meet the crops phosphorus requirement and additional nitrogen and potassium are supplied with commercial fertilizers as needed.

Dairy producers need to consider manure management as an important part of the total management needs for the dairy operation. Managing manure rates applied to cropland should be done by prioritizing fields. There are various total farm manure management programs available to producers. These include worksheets and computer programs to help select fields and manure amounts based on number of cattle, nutrient needs of the soil, crop to be grown next, and the storage and handling system used in the operation.