The Ohio State University Land application of wastes (such as manure, sludge, septage and food processing wastes) takes advantage of the nutrients and organic matter in wastes for crop production. Properly applied waste can provide plant nutrients and act as a soil conditioner. Land application of waste is often a very affordable waste disposal alternative for the waste generator. The objectives in land application are to maximize nutrient use while minimizing pollution hazards.
Surface spreading and subsurface injection are the
two most commonly used land application methods. To meet the
objectives of maximum nutrient use with minimum environmental hazard,
several guidelines for spreading and injection should be followed:
Tractor-pulled or truck-mounted box spreaders are used to spread wastes that contain 20% or more solids. The box must be watertight for road transport. Spreaders are equipped with paddles, flails, or augers to spread the waste evenly over the land area. Feed aprons, moving front-end gates, augers or conveyors are used to move the waste to the spreader. Large spreaders can reduce the number of trips to the field, but may increase soil compaction.
To calibrate a spreader and determine its application rate, use a bucket, sheet of plastic and a scale. Place the plastic sheet in the bucket and note the weight. Lay the sheet in the field and start applying waste down-range of the sheet. Drive the spreader over the sheet at the normal speed for applying waste. Gather up the plastic sheet with the manure, place in bucket, weigh, and subtract the weight of the bucket and plastic sheet. Repeat this procedure three times and average the weights. The manure application rate in tons per acre is equal to:
Weight of manure on sheet (lbs)/ (1 ton / Area of the sheet
ft2) X 43,560 ft2/ appl. rate acre
X 2000 lb (tons/acre)
|Table 1. Application rates in tons per acre for four common sheet sizes.|
Tank wagons or tank trucks are used to haul and spread liquid waste. The waste is either loaded or pumped into the tank through a top hatch, or drawn into the tank with a vacuum. Liquid wastes (up to 4% solids) can be pumped into spreading equipment. Waste with a higher percentage of solids (up to 15% solids) can also be pumped with special equipment. Bedding, hair and feed must be chopped up or separated out of the waste material to avoid clogging pumps, pipes and nozzles. Large tanks should be baffled to avoid inertia problems with starting, stopping and cornering. Once in the tank, the waste should be agitated to prevent settling.
Waste is discharged from a tank using a pump, flail, spinner or deflector plate. Most systems rely on gravity to empty the load, which results in a decrease in the discharge rate as the tank empties. Pump systems provide more uniform discharge.
When spreading liquid manure it is important to limit each
application to bring the soil moisture just up to field capacity. If
too much liquid is applied at one time it can run off or move
directly into drainage tile, which may result in stream pollution.
The available soil moisture capacity for different soils can be found
in the Ohio Irrigation Guide. Limit the application of liquid waste
to the water-holding capacity in the top 24 inches of the soil
profile. The proportion of the water-holding capacity available for
waste application can be estimated using the observations listed in
|Table 2. Practical interpretation chart of soil moisture for various soil textures and conditions*|
|Available moisture in soil||Coarse-textured soils||Moderately coarse textured soils||Medium-textured soils||Fine and very fine textured soils|
|0 percent||Dry, loose and single-grained; flows through fingers.||Dry and loose; flows through fingers.||Powdery dry; in some places slightly crusted but breaks down easily into powder.||Hard, baked and cracked; has loose crumbs on surface in some places.|
|50 percent or less||Appears to be dry; does not form a ball under pressure.||Appears to be dry; does not form a ball under pressure.||Somewhat crumbly but holds together under pressure.||Somewhat pliable; balls under pressure.|
|50 to 75 percent||Appears to be dry; does not form a ball under pressure.||Balls under pressure but seldom holds together.||Forms a ball under pressure; somewhat plastic; slicks slightly under pressure.||Forms a ball; ribbons out between thumb and forefinger.|
|75 percent of field capacity||Sticks together slightly; may form a very weak ball under pressure.||Forms weak ball that breaks easily; does not slick.||Forms ball; very plastic; slicks readily if relactively high in clay.||Ribbons out between fingers easily; has a slick feeling.|
|At field capacity (100 percent)||On squeezing, no free water appears on soil wet outline of ball is left on hand.||Same as coarse textured soils at field capacity.||Same as coarse textured soils at field capacity.||Same as coarse textured soils at field capacity.|
|Above field capacity||Free water appears when soil is bounced in hand.||Free water is released with kneading.||Free water can bes queezed out.||Puddles; free water forms on surface.|
|From the USDA, Soil Conservation Service, National Engineering Handbook (Section 15, Irrigation).|
The application rate for a liquid waste spreader can be determined by knowing: 1) the capacity of the tank in gallons; 2) the distance the spreader travels to empty the tank; and 3) the path width over which the waste is spread. The path width can be paced off or measured with a tape. Determining the travel distance can be more difficult. One method is to measure and count the number of wheel rotations. Measure the tire from one side to the other-this is the tire's diameter. Multiply the diameter by 3.14 to determine the distance the spreader will travel in one tire rotation. Tie a piece of rope at the top of the tire, and as the spreader moves through the field, count the the number of times the rope comes to the top of the tire until the tank is empty.
Multiply this number by the length of one revolution to determine the total travel distance. The waste application rate is equal to:
Tank capacity (gallons)/Travel distance (ft) 43,560 ft2 = Application rate x acre (gallons/acre) Spreading width (ft)
Transporting waste to distant fields can be time-consuming and costly, but may be necessary if adequate acreage is not close to the waste source. Using large "nurse" tanks to transport wastes to distant fields is one way to save time and reduce costs. Large, baffled tankers can be filled and transported to the field using a farm-tractor or semi-truck. The spreader tank wagons or trucks can remain in the field, traveling to the large tankers to be refilled two to four times. This technique also allows for the use of appropriate equipment to travel on roads and work in fields. This use of nurse tanks appears to be most effective for haul distances greater than 6 miles.
Application of waste may also be limited by soil conditions. Hauling waste in a tank through a wet field may cause soil compaction. One method of limiting compaction is to eliminating the weight of the tank completely by using a flexible hose to deliver waste to the spreader in the field. Figure 1 illustrates the layout for one field. In addition to limiting compaction, the flexible hose system can reduce application time by eliminating return and fill time.
Figure 1. Flexible hose waste application system.
Raw waste should be incorporated immediately to prevent odors and reduce nitrogen loss. Table 3 lists the nitrogen losses for different application methods. Surface-applied waste can be plowed under or waste can be injected just below the surface about 6 to 14 inches. Injection deposits the waste beneath the soil surface without turning the soil over. This minimizes disturbance of sod and other vegetation. The injectors are mounted on the tank, followed by discharge pipes, and are commonly chisel-shovels or sweep-shovels (also called winged injectors), which create a cavity in the soil that is filled by the liquid waste. As shown in Figure 2, sweeps create larger and shallower channels than chisels for waste injection.
Figure 2. Channel shapes created by chisel and sweep injectors.
|Table 3. Nitrogen losses during land application of wastes.|
|Percent of nitrogen applied that is lost within 4 days of application.|
|Application Method||Waste type||% Nitrogen lost|
|Surface spreading with immediate incorporation||Solid||1-5|
|From the Midwest Plan Service. 1985. Livestock Waste Facilities Handbook. MWPS-18.|
Spreading or injecting waste is usually the most affordable and appropriate method for use and disposal of manure, sludge, septage, and food processing waste. When undertaken with care through testing, calibration and timing of application, land application of waste can add plant nutrients and organic matter to the soil while limiting odors and protecting surface and ground water quality.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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