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Most read articles
|0406 ANM: Feedlot manure management|
|Archives - Past Articles|
|Friday, 23 June 2006 06:27|
Many concerns at feedlot operations are directly linked to pen maintenance and manure management. Odors and dust problems, animal health and performance, water runoff and protection of groundwater and surface water are all interconnected within confined feeding operations.
Studies have shown animal performance to be reduced by as much as 25 percent under prolonged muddy conditions. Respiratory problems occur, and treatment costs dramatically increase, if pens are constantly dusty. Improper pen cleaning can result in low areas that collect water or a rough surface that impedes effective and efficient runoff control. Aggressive pen cleaning can damage the underlying compacted “hard pan” and contribute to groundwater contamination.
Therefore, it is necessary to take an integrated approach to feedlot pen maintenance and manure management. Encompassing so many variables will, however, result in compromises between opposing performance objectives. For example, low initial construction costs might equate to higher maintenance costs. Another common compromise is between dust and odor control. If the feedlot surface is too dry, dust will become a problem. If it remains too wet, odor is a great concern. Compromises often are needed in an integrated approach if the overall feedlot goals are to be met.
Typically, there are about 1,000,000 cattle on feed at any one time in Colorado. Each 1,000-pound animal produces between 50 and 60 pounds of manure and urine per day, with a moisture content of about 90 percent. By the time the manure is removed from the feedlot, its moisture content has dropped to less than 40 percent. The nutrients excreted in the manure from these cattle have a fertilizer value of $34.2 million every year. How these nutrients are managed determines whether they are an economic benefit or an environmental liability to the feedlot operator.
Nitrates from manure can be leached to groundwater, and excessive nutrients in surface water can lead to overgrowth of aquatic plants, which use up dissolved oxygen, causing fish to suffocate. Nutrients can be lost or conserved for future crop use at every stage: in the production units, in storage and after the manure is applied back to the land.
The best way to control dust is through proper pen design and maintenance of surface moisture levels. Routine cleaning of pen surfaces also helps to minimize dust problems. One survey suggests most feedlots use a mechanical scraper as the main tool in their dust control strategies. Keep the loose manure layer less than 1 inch deep and pen moisture between 25 and 35 percent. Too much moisture will increase odor and fly problems; too little moisture will promote difficulties with dust.
Pen size and shape dictate the type of water distribution system to use. For example, large, deep pens probably require fenceline sprinkling systems, while shallow pens may favor mobile equipment. Selecting a sprinkling system assumes the feedlot has adequate amounts of water beyond drinking water needs.
Windbreaks also may be used to control or capture fugitive dust. Fast-growing trees planted along the perimeter of the feedlot will provide shelter from the wind and may largely contain any fugitive dust.
There are numerous surface amendments and chemical agents being evaluated for dust control. Fly ash looks promising. Other compounds that have been considered include sawdust, apple pumice, lignosulfate and gypsum.
Fenceline versus mobile sprinklers
Mobile equipment is expensive. A used 8,000-gallon tanker may exceed $60,000 initial cost, plus it will require a driver and operating expenses. For a medium- to large-size feedlot, there may not be enough time to haul water to raise the pen moisture.
One area commonly overlooked in pen maintenance is manure buildup directly under fencerows and adjacent to structures like waterers and feedbunks. These areas are not readily accessible with heavy equipment and require small equipment or manual labor. However, they are significant breeding areas for insects.
Keeping pens clean and dry will reduce insect populations, enhance performance and minimize a feedlot’s reliance on chemicals and other costly insect-control methods.
Manipulating stocking rate of feedlot pens to control the amount of feces and urine produced per pen is an economical dust-control strategy. Know the area and weight per animal. For example, a 1,000-pound steer allocated to 125 square feet of pen space produces about 28 inches of moisture per year or 0.08 inches per day. Stocking density has a significant influence on the animal and environmental performance of a feedlot.
Stocking density partly determines the average moisture content of the pen surface. Each day, cattle add moisture to the pens through feces and urine. Determining how much moisture is desirable requires careful observation. This decision varies with management style and experience with the specific site and climatic conditions.
Cattle size and rations will also influence moisture balance and the corresponding appropriate stocking rate. Typical pen stocking densities are between 150 to 300 square feet per animal. Increase stocking density during warmer, dry periods; reduce density during wet or cool seasons.
For both odor and dust control, the choice of stocking density should achieve a balance between a pen surface that is too dry versus one that is too wet. If this management goal is not achieved, more elaborate and expensive methods (such as sprinkling systems for dust control or frequent manure removal for odor control) will be necessary.
A combination of cattle density, sprinkling, spraying and precipitation may be needed. Cattle density alone may not be enough to control dust, especially in areas with high evaporation rates. Pens with lightweight feeder cattle, high winds (high evaporation) and low precipitation are at greatest risk for dust problems.
There are numerous options to consider when attacking dust problems. Each has advantages and disadvantages. It is important to have a plan in place and start prior to the time dust is a serious problem. Remember, water application is minimized by removing loose manure and dust from pens in a timely manner.
Frequency of manure removal also varies widely, depending on size of lot and pen stocking rate. However, a thorough pen cleaning once per year is an absolute minimum. Most feedlots clean and prepare a pen prior to receiving new or “fresh” cattle. A feedlot operated year-round typically replaces cattle or “turns a pen” 2.5 times per year and conducts pen maintenance as frequently, weather permitting.
Dairies are also concerned with animal health, comfort and cleanliness. Some dairies harrow their pens daily, with good results in both environmental and animal health benefits. While this is labor intensive for feedlots, it does indicate pen cleaning as frequently as feasible shows good management.
Front-end loaders versus box scrapers
1) providing a smooth pen surface that facilitates proper drainage
A wheeled front-end loader requires an experienced operator. For each bucket of manure accumulated with a wheel loader, the operator must shift gears four times while manipulating the bucket. This is most likely to result in an irregular pen surface at best, or damage to the protective “hard pan.” A combination of a wheeled front-end loader for major manure removal and a scraper for final cleaning and grading would be an effective compromise.
Stockpile location and management
The more control a feedlot manager has over the facility’s manure handling, the more likely nutrients will be conserved and beneficially used. Composting manure requires additional land and equipment, but may be advantageous where markets are available.
First, a feedlot operator must know how much manure nitrogen (N) is produced. Multiply the number of head by the tons produced (Table 1*) to determine how much manure is produced. Multiply the tonnage by the pounds of N per ton in that manure to calculate how many pounds of N are available for land application.
Next, calculate how much crop removal there will be per acre. Multiply the expected yield by the average N content of the harvested crop to determine N removal by the crop.
Finally, divide the pounds of N produced in the manure by the pounds of N used by the crop per acre. The result is the acreage required as a land base for your feedlot.
Runoff management and collection
One of the primary principles of runoff management is to keep clean water clean. In other words, direct clean water away from manure, whether manure is already stockpiled or still in the feedlot. Decreasing the volume of water used reduces the potential for runoff, so minimizing water waste from inefficient waterers and sprinklers not only saves money, but reduces runoff hazard.
Collect and store all wastewater and storm water runoff from pens. It can be evaporated, treated and discharged, or applied to cropland as a source of water and nutrients. If it is applied to cropland, the irrigation application rate must be less than the infiltration rate so runoff does not occur from the cropland.
Fence animals out of watercourses to eliminate direct deposition of manure into water. Runoff solids can be removed by directing the runoff through filter strips or grassed waterways or by using a sediment basin to settle the solids out. Removing solids from the runoff will reduce odors and prevent the pond from filling up with solids.
Management of runoff holding ponds
Seepage can be reduced by several methods, and manure itself has an ability to seal soil surfaces with time. Compact soil to a minimum 12-inch thickness. Take soil type into consideration during site selection. Locate ponds in the most impervious soil available. Soils must be loams or clays to compact well. Low permeability materials may be required in sandier soils.
Installing synthetic plastic or geosynthetic impermeable liners or adding clay (bentonite) are a few of the ways to reduce seepage from runoff holding ponds. Keep livestock away from pond banks in order to maintain the seal. Wastewater holding ponds must be sited a safe distance from wells, a minimum of 150 feet downstream. ANM
References omitted due to space but are available upon request.
Table omitted but is available upon request to
—From Colorado State University Extension website Copywrite 2006 Progressive Dairy Publishing. All Rights Reserved.
J.G. Davis, Extension Soil Specialist, Colorado State University; T.L. Stanton, Extension Feedlot Specialist, Colorado State University; and T. Haren, AgPro, Environmental Services