Energy Impact on Manure Nutrient Management
by David B. Fischer
TAKE HOME MESSAGES
- Manure is a cost of production to the dairy enterprise that can be reduced by its proper use and credit as a plant nutrient on cropland.
- Select fields for manure application based on the cropping program in order to achieve the most efficient utilization of manure nutrients.
- Calculate manure nutrients available for plant growth and calibrate spreader application rates needed per acre.
- A well planned manure nutrient management plan will reduce energy costs associated with livestock waste and help maintain a quality environment.
A major concern or need for a manure nutrient management plan is to get the most possible plant nutrient value from the manure applied on cropland. As we see an increasing concentration of dairy animals per farm, an added concern dairy producers must deal with is the impact of excess nutrients on environmental quality. Excess nitrogen in the soil can leach down to the groundwater thus raising the nitrate levels in drinking water. Surface movement of nitrogen (N), phosphorus (P) and potash (K) in runoff increases the potential for surface water pollution. With these two concerns in mind, a well planned nutrient management program will reduce the energy costs associated with livestock waste handling and the maintaining of a quality environment.
REDUCING ENERGY INPUTS
Manure is a cost of production. The cost will vary from farm to farm depending on the type of manure storage and handling system. Emphasis needs to be placed on maximizing the value of livestock manure and/or decreasing the cost of storing and handling. As energy costs continue to increase so will the cost of commercial fertilizers used for crop production. It is important to credit manure applications as a prime source of N, P and K for the growing crops. By using commercial fertilizer as a supplement, costs of crop production can be reduced and the increased value of these manure nutrients can be credited to the dairy enterprise. In addition, with less purchased fertilizer energy costs associated with its manufacture can be reduced.
In order to set up a nutrient management plan, producers need to:
- Know what nutrients are available from the dairy herd.
- Prioritize the fields available for manure placement.
- Calculate amount of manure N P K actually available for crops.
- Determine manure application rates per acre.
MANURE NUTRIENTS AVAILABLE
The average dairy cow will produce 82 pounds of manure per day per 1000 pounds liveweight (Table 1). Thus, a Holstein (1400 pounds) cow produces 115 pounds of manure per day or about 21 tons per year. Replacement heifers will average about 7 tons per year. The nutrient content values listed in the table are approximate and do not include the bedding or added water. Manure nutrient characteristics can vary considerably from farm to farm depending on the ration fed and the manure handling system. Therefore, it is important to have representative manure samples tested as it comes out of storage. Storage and field application systems will have an impact on nutrients available for plant growth. Significant nitrogen loss can occur through various storing and handling methods (Table 2). Phosphorus and potassium losses are negligible due to their stable nature. The exception would be losses caused by lot/storage runoff and soil erosion.
Selecting which fields to apply manure needs more thought than merely the closest field to the barn. Granted this will create added cost for time and equipment. Producers who have a limited land base will need to seek out other land owners on which cropland is available for manure application. Where manure is spread should depend on the cropping system and rotation plans for the future crops. Manure needs to be applied on the crops which will use the nutrients most efficiently. Manure nutrients, especially nitrogen, are used more efficiently by corn and cereal grains than by legumes. Following is a priority order of fields for manure placement: 1) corn acres from which corn silage was harvested last season; 2) corn acres from which corn was harvested for grain last season; 3) small grain acres which were in corn last season; 4) corn acres which were in legumes last season; 5) soybean acres which were in corn last season; 6) older alfalfa stands or other legumes.
If manure is applied to meet the crop nitrogen needs, phosphorus and potassium will be likely applied in excess and will eventually create a build up of excessive levels in the soil. However, by using the legume hay crops in the rotation the P and K soil levels can be drawn down, thus providing a closer balance of the three soil nutrients over the years. Producers who must use existing alfalfa fields to dispose of manure should spread on the oldest stands with the most grass. A rate of less than 3,000 gallons of liquid or 10 tons of solid manure per acre is suggested to avoid salt burn and damage to the plants. Again, this will depend on the nutrient concentration of the manure coming out of storage. Spreading the manure should be done immediately after removing the hay crop to avoid crop damage and palatability problems from the next cutting. Applying manure to legumes tends to stimulate broadleaf weeds and grass growth, thus shortening the length of stand. If manure is to be applied to the forage crops in the rotation it should be applied at a rate based on the phosphorus needs of the forage crop.
NUTRIENTS AVAILABLE TO CROP
The manure nutrient management program is one part of the overall crop nutrient management program. Determining the total nutrients available for plant growth includes accounting for residues from previous crops, livestock manure, legume credits, commercial fertilizers and nutrients currently available in the soil. Routine soil testing every four years will provide a basis for calculating amounts of added nutrients needed for optimum economic crop production. While the nitrate nitrogen test is not routinely recommended, recent research has shown that it may be beneficial in helping determine whether additional N will be needed for fields that have received manure for the current crop or that have a long term history of manure application. Nitrogen availability is more difficult to manage than the other nutrients due to its chemical nature of stable and unstable forms. In addition to the nitrogen losses occurring during storage, 25 to 50 percent of the ammonium N surface applied on the field can be lost within a few days after application. Approximately 35 percent of the organic N will be available the first year, with the remaining being available in the second and later crop years. Manure is a good source for P and K. Caution must be taken when balancing for the N content on manured fields as it pertains to the excess application of P and K as discussed earlier.
Estimating or crediting the amount of available crop nutrients from the manure can be done through worksheets or computer programs. With that information in hand and having the fields prioritized by nutrient needs, the next step is to calculate the manure supply needed per acre.
DETERMINING APPLICATION RATES
The success of a manure nutrient management plan depends on controlling the amount of manure applied per acre based on crop nutrient needs. The goal is to spread the calculated amount evenly over the entire field. This can be accomplished by determining the manure spreader capacity and the rate of application on the field. Most manure spreader manufacturers will list the spreader capacity in cubic feet, bushels or gallons. This information needs to be interpreted into pounds or tons in order to know how much manure is being taken to the field with each load. The following approximate weights can be used; one cubic foot of manure equals sixty pounds, one bushel weighs seventy-five pounds and one gallon weighs eight pounds. The conversion chart (Table 3) can be used as a guide to calculate the spreader capacity. These capacities are for spreaders filled even with the top. If the peak of manure in the center is higher than the sides by half the depth, add an additional twenty-five percent to the volume. Allow an extra fifteen percent for loads filled a third higher in the center.
Spreader application rates will vary depending on field conditions, manure consistency, and tractor speed. It is important to calibrate the amount applied on the field. The simplest is to divide the spreader volume by the acreage covered. If scales are available weigh before and after for more accurate results. When making passes through the field, a small amount of overlap is required for even coverage. However, if there is too much or too little, application rates will be off from those calibrated. Some field studies have been conducted called "sampled weight method" by using a plastic sheet in the path of the spreader and collecting the solid manure to calculate the amount applied on a per acre basis. The results of these field test have surprised many participating producers by demonstrating the true application rates in the field.
Table 1. Manure Production and Characteristics as Produced by Dairy Cattle.
Total manure production
Nutrient content, lb/day
|| ft3 day
Table 2. Nitrogen Losses During Handling and Storage.
||Nitrogen Lost (%)
||Daily scrape and haul
Table 3. Manure Spreader Capacity.
|200 cubic feet3
11 gallon liquid manure weighs 8 pounds
21 bushel of manure weighs 75 pounds
31 cubic foot of manure weighs 60 pounds
This topic is sponsored by the Illinois Department of Commerce and Community Affairs, Bureau of Energy and Recycling.