| تبليغات | X |
This definition is from the Soil Science Glossary (Soil Science Society of America).
| soil - (i) The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. (ii) The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics. |  |
This definition is from Soil Taxonomy, second edition.
soil - Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.
The upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants.
The lower boundary that separates soil from the nonsoil underneath is most difficult to define. Soil consists of horizons near the earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm.
See also AGRICULTURE; DIRT; GEOLOGY.
Bioengineering techniques for hillslope, streambank and lakeshore erosion control are described, as are tips for a successful bioengineering installation and demonstration project.
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Figure 1. Preparation of wattling and installation procedure. Installation starts at the bottom of the cut or fill and proceeds upslope. Numbered sequence of operations is shown schematically. (From Gray and Leiser, 1982) |
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Figure 2. Installation of brush layering. Numbered sequence of operations is shown. Vertical spacing depends on slope angle. (From Gray and Leiser, 1982) |
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Figure 3. Coir fascines stabilize banks and help establishment of wetland plants. The coconut fiber accumulates sediment and biodegrades as plant roots develop and become a stabilizing system. (From Bestmann-Green Systems) |
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Figure 4. Slope treatment using wattles and live plants or stakes. Use for loose surface soils with sheet, rill or small gully erosion. (From A.T. Leiser) |
Soil erosion occurs whenever water meets land with enough force to move soil. Often this occurs along streambanks and lakeshores or where excess water flows over hillslopes. Streambank and hillslope erosion can be dramatic, especially after large rainfalls or floods. However, normal streamflows, excess runoff from urbanized areas and wave action along lakeshores continually erode soil. Erosion can be severe, as is the case in many man-made lakes, where shorelines are composed of easily erodible soil. Traditional methods of controlling streamflow and wave-induced erosion have relied on structural practices like rip rap, retaining walls and sheet piles. In many cases these methods are expensive, ineffective or socially unacceptable. An alternative approach is bioengineering, a method of construction using live plants alone or combined with dead or inorganic materials, to produce living, functioning systems to prevent erosion, control sediment and provide habitat. Bioengineering uses combinations of structural practices and live vegetation to provide erosion protection for hillslopes, streambanks and lakeshores. Bioengineering is a diverse and multidisciplinary field, requiring the knowledge of engineers, botanists, horticulturalists, hydrologists, soil scientists and construction contractors. It is a rapidly growing field, subject to innovations and changing design specifications. Terms such as biotechnical erosion control, biostabilization or soil-bioengineering often are used synonymously with bioengineering.
The use of bioengineering methods dates back to 12th century China, when brush bundles were used to stabilize slopes. In the early 20th century, similar techniques were used in China to control flooding and erosion along the Yellow River. In Europe, especially Germany, bioengineering methods have been used for over 150 years. Documented use of bioengineering in the United States dates to the 1920s and ’30s. Streambank stabilization, timber access road stabilization and slope restoration were common applications. After World War II, with increased access to earth-moving equipment and the development of new structural slope stabilization and erosion control methods, bioengineering practices all but disappeared. In the last 20 years bioengineering has been recognized as a re-emerging technique to provide erosion control, environmentally sound design and aesthetically pleasing structures. Gray and Leiser (1982) published the first U.S. textbook on bioengineering: Biotechnical Slope Protection and Erosion Control.
Bioengineering solutions can be adopted in many soil stabilization and erosion control situations, from streambank and lakeshore protection to upland gully restoration and slope stabilization. Bioengineered restoration of flood or high water damage to streams and lakes provides a more natural-looking solution than traditional rip rap or concrete structures.
Advantages of bioengineering solutions are: 1) low cost and lower long-term maintenance cost than traditional methods; 2) low maintenance of live plants after they are established; 3) environmental benefits of wildlife habitat, water quality improvement and aesthetics; 4) improved strength over time as root systems develop and increase structural stability; and 5) compatibility with environmentally sensitive sites or sites with limited access.
Limitations to bioengineering methods include: 1) installation season often is limited to plant dormant seasons, when site access may be limited; 2) availability of locally adapted plants may be limited; 3) labor needs are intensive and skilled, and experienced labor may be unavailable; 4) installers may be unfamiliar with bioengineering principles and designs, so upfront training may be required; and 5) alternative practices are aggressively marketed and often more widely accepted by society and contractors.
Homeowners who have streamside or lakeside property, contractors required to work in difficult environmental circumstances, or professionals interested in natural restoration of landscapes will find bioengineering techniques useful. New methods of application and materials being developed will result in new and improved bioengineering design.
Contour Wattling—This method is used to control surface erosion by breaking long slopes into shorter slopes. Bundles of branches, called wattles or fascines, are placed in shallow trenches along the slope or streambank contour (Figure 1). Trenches are excavated by hand to half the diameter of the bundles. Wattles are typically 8 to 10 inches in diameter and branches secured with twine. After the wattle is staked in place, the trench is backfilled until only the top of the bundle is exposed. Wattles can be used for hillslope restoration, road embankments, wide gullies or slump areas.
Brush Layering—This method is used to restore slopes by constructing a fill-slope consisting of alternating layers of live branches and soil, creating a series of reinforced benches (Figure 2). Large quantities of dormant willow branches often are used. While about 75 percent to 80 percent of the branch is buried, the tips are left exposed. The layers of branches help reinforce the fill, which improves as the branches develop roots throughout the fill area. Brush layering can be used to place new fill or repair old fill areas, restore shallow slumps, repair narrow gullies and stabilize loose soil slopes.
Trench Packing—This method is used to slow or spread water by placing live plants in a trench perpendicular to the flow. To reduce wave impact, live plants are placed in trenches running parallel to the shoreline. Several trenches may be used with different plants in each, depending on the distance to water. Generally, a wide planting area is needed to dissipate wave energy. In upland areas, trench packing serves to slow water and spread it over the soil surface, reducing its erosion potential. Trench packing also can be used to control shallow seeps, protect wetland construction and renovation, and protect abandoned roads.
Brush Matting—This method protects streambanks by placing a mattress-like layer of branches over it to protect soil and slow water velocity. The mat is composed of interwoven, usually dead, branches secured to the soil by live stakes, wire, twine or live branches. Live stakes often are cut from dormant willow. Brush matting helps collect sediment and enables establishment of vegetation on banks. Like brush layering, this method requires large quantities of branches.
Live Cuttings—Live cuttings can be used to secure materials in place and to increase plantings on a slope. Live cuttings can be from 18 inches to 4 feet in length. Longer cuttings are used for live staking of wattles, while shorter cuttings are used for plantings.
Coir Fascines—Coir fascines are wattles made from the fibrous outer husk of coconuts. Coir is denser than water so it won’t float and is very slow to decay. Coir fascines are a readily available manufactured product and are popular for streambank and wetland restoration where a natural look is desired (Figure 3). Coir fascines are placed with their tops at the water surface. Live plants can be placed into coir fascines to create a natural look.
Prevegetated Mats—Prevegetated mats are live plants grown on a movable mat of organic material. They come in many sizes and materials and are moved and installed in one piece. They are generally 4- by 8-feet in size for easy handling. Mats are grown in nurseries for up to a year or more to provide a good plant stand. Thin mats can be rolled up and shipped without special packing. Thick mats are handled with heavy equipment because of their weight. Prevegetated mats are made of coir or other slowly degradable material and can use many types of plants. Mats usually are used in wetland or lakeshore environments so wetland plants are the most common. Currently, most prevegetated mats are custom ordered one to two years in advance.
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Figure 5. Lakeshore erosion control using a combination design of coir fascine and wetland plantings, prevegetated mat and live plantings. (From A.T. Leiser) |
Interplanting Rip Rap—Rip rap often is used to protect streambanks and lakeshores. Rip rap is composed of various size large stones placed on the soil surface where the water contacts the soil. Live cuttings can be interplanted in rip rap to provide additional slope stability. Root growth below the rip rap will improve soil strength and live vegetation will hide the rocks, presenting a more natural look.
Staking—Staking is used extensively in bioengineering practice. Stakes can be live or dead. Live staking often is done with willows to stabilize soil or to stake other materials in place. Manufactured timber stakes, 2 to 3 feet long, are used to secure wattles and coir fascines. Timber stakes for upland application need to have a bias, or angle, cut making them easier to install. For wetland or streamside applications, stakes need straight parallel sides to prevent heaving from water pressure.
Combinations—Combinations of the above practices are usually used for most bioengineering designs. For example, brush wattles and live staking is a common combination used to stabilize slopes (Figure 4). A coir fascine can be used with live plantings, brush matting and trench packing to restore wetlands or stream channels (Figure 5). New combinations of existing methods, and the use of new materials, will provide creative applications of bioengineering techniques.
Bioengineering involves the use of live plants to add structural strength to soil. Many different plant materials are used. Live cuttings should be soaked in cold water for at least 24 hours before they are used. This not only provides the cuttings with needed moisture but also improves rooting. Live potted plants often are used. Care of live plants before and during planting is critical for success. Live plants raised indoors need to be acclimatized to the outdoor environment before planting.
Plants can be planted directly into coir fascines, coir pots or mats. Prevegetated mats, as described earlier, are another method used to transplant live plants. A plant roll can be developed by wrapping several live plants in a roll of degradable material and placing the roll in the ground like a wattle. This method also can be used for trench packing.
Seeding can be used where appropriate. Seeding and mulching are not appropriate in areas of flooding, high water flow or rapid changes in water depth, as the mulch and seed will be washed away. Proper seedbed preparation, fertilization and irrigation may be needed to assure seedling survival.
Expect some failure of plantings in all bioengineering application. A 75 percent to 80 percent survival rate is considered very good. Replanting generally is inexpensive and often the plants will reestablish themselves in time. Some loss of vegetation does not seriously impact a project as long as most of the soil stays in place and the structural features of the design are sound.
Protect Plantings—Protect live plantings from animals, especially ducks and geese along lakeshores and streamsides. Deer, muskrats, beaver, dogs and humans also can pose a threat. Signs may keep people away, but fencing may be needed if animals are a problem. For lakeshore or streamsides, an enclosed fencing layout is best to keep waterfowl away. One fence should be placed 1 to 2 feet into the water away from the shoreline plantings with a parallel fence 2 to 3 feet upslope from the plantings. Also, protection from flooding or excess water flowing across the planting is important to establish all bioengineering plantings. Be sure surface drainage and water flow is directed away from the new plantings or protected slope.
Vegetation Type—Selection, procurement and installation of the proper plant material is essential for a successful design. In the case of lakeshore and streambank protection, both herbaceous and woody plants are needed. Herbaceous plants, or wetland plants, will be needed at and near the water’s edge. These plants can grow with their roots underwater. This root growth adds considerable strength to the soil. Generally, using several different wetland plant species increases the chance of a successful planting. However, woody plants placed too near the water or water table will not provide good structural strength and may not survive. Woody plants should be used on the upper slope and upland areas where their roots can grow in soil above the water table.
Native vegetation existing at or near the site will give good guidance concerning plant selection. As mentioned, willow cuttings often are used for wattles and live cuttings. Proper species selection is important. Willows need not be native, but should be well adapted to the region. The use of introduced species allows the potential for increasing the number of different species available.
The availability of plant species, in the appropriate size and quantity, often is a limiting factor in the final selection process. Local nurseries may not carry the types of wetland plants needed. They may be able to propagate the species needed, but this will take 12 to 18 months. A compromise between use of native species and what may be locally or regionally available will be needed to develop a successful design. Consult horticulturalists and botanists for plant selection assistance. The International Erosion Control Association (IECA) publishes a products and services directory listing sources of plant material and professional assistance (see resource listing).
Bioengineering can be effective in many streambank, lakeshore and hillslope erosion situations, but it will not solve all soil erosion or slope failure problems. The success of a project hinges on many factors including proper design, plant selection, proper installation, weather conditions and outside factors like animal damage. Site evaluation is important to determine whether there is adequate sunlight, soil type and water quality to support vigorous plant growth. Do not expect bioengineering solutions to stop slope failure caused by high water tables or landslides. Nor are they ideal for high stress areas with severe wave action, rapid or long-term water level fluctuations or fast water flows. The following list includes tips that may help ensure a successful bioengineering project. 1. Do not attempt bioengineering solutions in situations where: 1) there is severe soil or water contamination; 2) the stream bottom is degrading; 3) human or animal traffic cannot be controlled at the site; or 4) there is too much shade for selected plant species to thrive. 2. Check with local, state and federal regulatory agencies before beginning the project. Do not alter a wetland area without proper permits. In Nebraska, check with the local Natural Resources District or the Natural Resources Conservation Service to inquire about permits. 3. Water elevation is the most critical element in a successful installation. Be sure to know the normal, high and low water elevations for the site. Know the seasonal changes in water elevation and how rapidly these changes occur. 4. Be sure to fence out animals and people, if needed. If damage occurs, supplemental planting may be necessary. 5. Be aware of flood or drought conditions that could impact installation. Severe weather will reduce seedling survival. Supplemental planting may be needed. 6. Provide regular monitoring and maintenance, especially in the first year, to assure adequate plant survival. 7. Plan ahead. Involve the proper design professionals and experts to provide information on hydrology, plantings and structural design. A multidisciplinary approach will assure success.
Bioengineering consultants are available to help with all aspects of site assessment, design and installation. Their input could make the difference between success or failure. Use the IECA Products & Services Directory to seek out professional assistance (see resource listing). Many bioengineering techniques can be used successfully without input from consultants, however it is best to consider expert help if characteristics of your site are such that: 1) stream velocities are greater than 3 to 5 feet per second; 2) streambank heights are greater than 3 feet; or 3) wave impacts are from waves greater than 1 foot high.
Demonstration projects can help show the advantages and benefits of bioengineering solutions. Keep demonstration projects small, from 100 to 500 feet in length for most situations. A smaller project puts less property and dollars at risk. A demonstration helps evaluate what methods or plant species perform best under similar conditions. Incorporate some variety into the project so you can compare differences. To start, choose a simple project, in a low impact area, with a low profile or incorporate some bioengineering methods into larger projects and collect data to evaluate their success. Provide adequate maintenance and keep good monitoring records. Schedule agency personnel and public visits to the site to maximize public relations. Plan to hold these visits during installation and again after one growing season.
Gray, D.H. and A.T. Leiser. 1982. Biotechnical slope protection and erosion control. Van Nostrand Reinhold Company Inc., New York, 271 pp.
International Erosion Control Association, www.ieca.org
Index: Soil Resource Management
Conservation
1996, Revised September 2006
This NebGuide will help you understand how natural processes and management practices can reduce existing soil compaction and minimize its further development.
Charles S. Wortmann, Nutrient Management Specialist
Paul J. Jasa, Extension Engineer
Nature has built-in processes that reduce soil compaction, including cycles of wetting and drying, freezing and thawing, as well as plant growth and microbial activity. In the last 30 to 40 years, farming practices have changed drastically, creating situations where natural rejuvenation of the soil environment by wet-dry and freeze-thaw cycles is inadequate to maintain optimum conditions for crops. Performing field operations on wet soils, using multiple field operations for crop production, eliminating perennial crops from crop rotations, and using heavy equipment contribute to more extensive and deeper compaction.
Soil compaction problems can be reduced or eliminated through use of proper management practices.
Stay Off Wet Soils
Soil is most susceptible to compaction when soil water in the three- to six-inch soil depth is near field capacity or wetter. Under such moisture conditions, the potential for compaction increases as soil clay content increases and soil organic matter decreases.
The water content of a soil can be determined using the feel-and-appearance method, or by molding soil from the three to six-inch depth and dropping the soil ball onto a hard surface; if it does not break or crack on impact, it is too wet for field operations.
Perform field operations in your driest fields first to allow more drying time for wetter fields. If field operations need to be conducted when the soil is near field capacity to remain timely, minimize the axle load and increase tire size to reduce deep compaction. Larger tires will compact more of the soil surface, but with less pressure on the soil and less penetration of compactive forces.
Reduce Tillage
Tilled soils are more susceptible to compaction than no-till soils. Tillage contributes to the breakdown of soil structure by compressing and breaking soil aggregates, which are necessary for good air and water movement and good root growth. Tillage also results in the loss of soil organic matter which is important to soil aggregate stability. Reduced tillage systems leave greater amounts of plant residue on the soil surface which helps prevent surface sealing, a form of compaction, by intercepting raindrops before they hit the soil surface.
Tillage affects microbial activity in the soil. Reduced tillage causes fungal decomposers of organic matter to increase relative to bacterial decomposers. Fungal, as compared to bacterial, decomposers aid aggregate formation and stability on fine-textured soils.
Build Soil Organic Matter
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Organic matter promotes the development of good soil structure and decreases soil bulk density. It helps bind soil particles together as aggregates so they are not as easily cracked, split, or compressed by tillage or wheel traffic. Root derived organic matter is especially effective in aggregate formation. Building soil organic matter also increases soil nutrient mineralization and availability for crop growth, especially for nitrogen, phosphorus, sulfur and trace elements.
Organic matter can be added to the soil in the form of animal manure, municipal biosolids, or green manure crops, and by leaving crop residues in the field. Tillage generally accelerates the decomposition of soil organic matter.
Rotations with Perennial Crops
When crop rotations include alfalfa, clover, or grass, soils usually are less compact than soils in fields without these rotations. This is true as 1) there generally is no tillage for several years after seeding, 2) trips across the field tend to be associated with hay harvesting when the soil is dry and less susceptible to compaction, 3) the deeper rooting depth and large taproot of alfalfa and clover keeps the soil more porous (Figure 1) and 4) these crops remove large amounts of water which helps dry the soil and increase cracking in some soil types.
Alter the Tillage Depth
If you till the soil, vary tillage depth to minimize the development of a “tillage pan” or compacted zone where the tillage implement shears the soil. Till deeper in dry years when soil fracturing is greatest. Keep tillage shallow in wet years to avoid formation of a deep tillage pan. Shallow pans can be easily fractured with tillage when the soil is dry.
Control Wheel Traffic
Compaction will be intense but localized if all equipment wheel traffic is restricted to “tracks” or traffic lanes in the field, while the nontraffic areas are protected from compaction (Figure 2). The area in traffic lanes is minimized when the operating widths and wheel bases of various implements are well matched. Farm implements have different wheel widths making it difficult to confine traffic. Traffic control is easier with fewer operations such as with ridge plant and no-till systems. Planning is required in equipment purchase or hire to reduce the variability in wheel track requirements. Table I gives suggested wheel spacings and estimates of wheel traffic compaction for various equipment sets. Infield operation on moist soils, such as with grain carts, may be reduced to minimize compaction.
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| Figure 2. Traffic lane patterns to minimize field area affected by compacting forces. |
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Deep Tillage
Compaction causes reduced yields and may worsen other problems that reduce yields, such as disease and low nutrient supply because of reduced root distribution. Assessment of the severity of compaction problems is best done by inspection of crop roots. If root growth is restricted due to compaction, deep tillage such as subsoiling may be warranted.
The depth of yield-limiting soil compaction will determine the required depth of tillage and tillage tool selection. If compaction occurs in the top six to eight inches of the soil, tillage tools such as a chisel plow or moldboard plow can be used to shatter the compacted layer (Figure 3). However, if compaction is below eight to 10 inches, tillage tools such as a subsoiler, ripper, or paraplow may be needed (Figure 4).
Many types of subsoilers are available. Most are chisel-like tools having curved or straight shanks. Each shank will require at least 20 to 30 PTO horsepower for deep tillage. Subsoiling depth should be 50% deeper than the compacted layer with shank spacing equal to the tillage depth for greatest shattering; however, tillage at this depth has a high power requirement which quadruples as tillage depth is doubled. An alternative is to operate the subsoiler one to two inches below the compaction layer with shanks spacing equal to the row spacing (Figure 5). The compacted zone will be most shattered, in a V-Shaped pattern, when the soil is dry to the tillage depth. Subsoiling tillage is often best performed in the late summer or fall, but can be done whenever the soil is dry enough. The relative success of subsoiling will vary with soil type, soil water content, soil texture and bulk density, and the shape of the subsoiler shank. To ensure that the compacted zone has been shattered properly, dig a hole and look for the V-Shaped wedge of loosened soil.
“Slot ripping” allows roots and water to penetrate into the soil, especially if the rows of the next crop follow the slots (Figures 5 and 6). Parabolic shanked subsoilers heave the soil surface too much to allow slot planting of the next crop. Secondary tillage may be used in the spring to level the field prior to seeding but subsoiled fields can redevelop a compacted layer if the loosened soil is worked when wet or if wheel traffic is not controlled. Soil heaving and the need for secondary tillage to smooth the field can be reduced by using a coulter in front of a straight legged subsoiler shank.
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| Figure 3. A chisel shank shatters a V-Shaped section of soil from the base of the shank upward toward the soil surface. | Figure 4. Deep tillage can be performed with a subsoiler (shown) or other implement depending upon the depth of compaction. |
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| Figure 5. An example of the V-Shaped fracture from a ripper shank operating in dry soil. The field was slot ripped the fall before and the current crop was no-till planted above the slots. Portions of the tillage pan remain between the rows. | Figure 6. The corn roots grew in the loose soil above the tillage pan and down through the slot cut in a severely compacted tillage pan. This soil was wet when slot ripping and the shattering of the pan was much less than desired. |
Most important is to manage land to minimize soil compaction and avoid problems with deep compaction. Most cropland in Nebraska should never require deep tillage if well managed. When it is necessary to subsoil, rip, or slot rip due to deep compaction, deep till when the soil is dry to shatter the compacted layer.
Visit the University of Nebraska–Lincoln Extension Publications Web site for more publications.
Index: Soil Resource Management
Compaction
1989, Revised December 2003
How injector/applicator spacing, tire spacing, field speed, and other factors influence the amount of residue cover reduction after manure incorporation.
Previous Category | Catalog | Order Info
Manure incorporation represents a conflict between best management practices for soil erosion control and manure management. Manure should be incorporated into the soil for odor control, maximum availability of nutrients, and control of potential manure runoff. However, for maximum soil erosion control, the soil and crop residue should remain undisturbed. These two best management practices must be balanced since disturbing the soil and residue for manure incorporation, either with conventional tillage implements or equipment specifically designed for manure application, reduces the residue cover remaining for erosion control.
The companion NebGuide, Manure Incorporation and Crop Residue Cover - Part I: Reduction of Cover, presents results from a field study conducted at the University of Nebraska Haskell Agricultural Laboratory at Concord to evaluate the degree of residue cover reduction caused by soil-engaging components typically used with tank spreaders and towed hose systems to apply liquid or slurry manure. Ranges of values are given for the percentage of the initial residue cover that could be expected to remain after the operation of chisel and sweep manure injectors, disk and coulter applicators and a tandem disk.
This NebGuide discusses how injector/applicator spacing, tire spacing, field speed, and other factors influence the amount of residue cover reduction. Much of this information is based on experience and field observations and is intended to help livestock producers select and operate manure application/incorporation equipment to maximize residue cover and erosion control.
The type of soil-engaging component (chisel or sweep injector, disk-type applicator, coulter-type applicator, etc.) is the predominant factor affecting residue cover reduction during manure incorporation. Adjustments, operating conditions, and many other factors also can influence the amount of reduction that occurs. Following is a discussion of some of these factors.
To evaluate the degree of disturbance caused by individual injectors/applicators, passes in soybean residue were made with single injector or applicator units. The width of the disturbance (defined as loose soil on the surface) was measured perpendicular to the direction of travel in 50 places over a distance of 200 feet. The average disturbed width ranged from 7 inches for the coulter-type applicator to 57 inches for a disk-type applicator (Table I). In general, as the width of the soil-engaging component increased, the width of disturbance also increased. For example, the coulter applicator consists of a 25-inch diameter coulter that is angled approximately 5 degrees relative to both the direction of travel and to vertical.
The maximum profile width of this component perpendicular to the direction of travel is approximately 2 inches. At the soil surface, however, this width is 1 inch or less, depending on the operating depth. Since the soil is opened with a cutting action, rather than a lifting or inverting action, the disturbed width would be expected to be the least. Much of the disturbance that did occur resulted from soil that adhered to the coulter blade and then fell or was thrown to the side as the implement moved through the field.
For the other components, the width at the soil surface perpendicular to the direction of travel was approximately 0.5 inch for the knife-type anhydrous ammonia applicator, 2 inches for both the Calumet chisel and sweep (width of shank), 15 inches for the Calumet disk applicator, and 30 inches for the Vittetoe disk applicator. Also, with the exception of the coulter-type applicator and knife-type ammonia applicator, the soil-engaging components evaluated are designed to loosen and lift or throw the soil and mix the manure with it. As such, a wider area of disturbance would be expected as the width of the soil-engaging component increased.
Results from the Vittetoe disk applicators (22-inch diameter disks with 31-inch spacing between disks) also illustrate the influence of applicator spacing. Because of the wide spacing between the two disks, these applicators were spaced 60 inches apart on the tank toolbar, rather than 30 inches as was used for all other injectors/applicators. This configuration resulted in strips of disturbed soil and residue between the disks, alternated with strips of essentially undisturbed soil and residue between adjacent applicators. Both strips were approximately 30 inches wide. Residue cover was measured in both areas. Average residue cover reductions are shown in Table II.
Table I. Average width of soil disturbance for single manure injectors or applicators.
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Description of Injector or Applicatora |
Disturbed Width (inches) |
| Sukup Coulter Applicator (25-inch diameter blade, 5 mph) |
7 |
| Knife-type Fertilizer Applicator (0.5-inch wide knife with smooth coulter, 5 mph) |
17 |
| Calumet Chisel Injector (2-inch wide straight chisel, 5 mph) |
36 |
| Calumet Disk Applicator (16-inch disks, 16 inches apart, 7 mph) |
36 |
| Calumet Sweep Injector (14-inch wide sweep, 5 mph) |
42 |
| Calumet Disk Applicator (16-inch disks, 16 inches apart, 10.5 mph) |
45 |
| Vittetoe Disk Applicator (22-inch disks, 31 inches apart, 7 mph) |
57 |
aMention of brand names is for descriptive purposes only. Endorsement or exclusion of others is not intended or implied.
Table II. Average residue cover reduction for disk applica-tors with 22-inch diameter disks, 31-inch spacing between disks, and 60-inch spacing of applicators on tank toolbar.
| Area |
Residue Cover Reduction (percent) | |
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Soybean Residue |
Corn Residue | |
| Between individual disks |
89 |
57 |
| Between adjacent applicators |
47 |
29 |
| Overall |
68 |
43 |
As expected, significantly more reduction occurred between the individual disks than between adjacent applicator units. The reduction between adjacent applicators was due primarily to soil that was thrown by the disks and fell in the area between the applicators. If the applicators were spaced closer together on the toolbar, proportionately more of the total area would be disturbed directly by the individual disks, and the overall reduction would be greater. Conversely, for a given applicator unit spacing, if the individual disks were spaced closer together, less of the total area would be disturbed directly by the disks, and overall residue cover reduction would be less. Thus, to minimize residue cover reduction, the width of the applicator unit should be as narrow as possible and applicator spacing on the toolbar should be as wide as possible.
For both disk-type applicators used in this study, the spacing between the disks of each unit was approximately 50 percent of the applicator unit spacing on the tank toolbar. The values presented in Part I (G05-1563) to estimate residue cover reduction by disk-type applicators are based on this spacing; however, field observations and manufacturer's sales literature indicate that disk-type applicators are sometimes mounted on the tank toolbar so that the spacing between disks of adjacent applicator units is minimal (i.e. the disks are nearly hub-to-hub). In these cases, the overall reduction would likely be close to the values in Table II for the area between individual disks, or similar to the reductions that would be expected from chisel and sweep injectors.
Disk-type applicators might fit well in a ridge-plant system. When operated on a flat field (no ridges), disk applicators leave a ridge about four to eight inches high that is a mixture of soil, residue, and manure. These ridges could be used as the start of a ridge-plant system. If manure application was done in the fall, the loose soil/residue/manure mixture would have time to settle and consolidate prior to planting on the ridge top the following spring. Similarly, if the applicators were centered on an existing ridge, some rebuilding of the ridge would occur, and manure would be applied in the area where the next year's crop would be planted. In either case, manure application rates should be carefully controlled to avoid potential seedling injury; however, this may concentrate weed seeds in the manure or on the soil surface directly in the crop row.
It appears that coulter-type applicators might offer the opportunity to apply manure into a growing crop or pasture, a practice that has been used for some time in the United Kingdom. There, one researcher concluded that shallow injection of manure slurry into a growing cereal grain crop 1) allowed manure application when crop nutrient requirements were at their maximum, 2) provided a much longer period for manure application, and 3) had no detrimental influence on crop yield.
Manure application rate (volume per unit area) is primarily controlled by field speed for some manure tanks, with faster speeds required to achieve lower application rates. Also, a speed on the order of 10 mph was recommended by the factory representative for the Calumet disk applicator to achieve thorough mixing of the loosened soil, residue, and manure being applied. Thus, in certain cases, the operator may have only limited ability to reduce field speed in an effort to leave more residue cover. This suggests that the ability to control flow rates from the manure tank, and hence control application rates independent of field speed, may be beneficial for lessening residue cover reduction and improving manure nutrient utilization. Some manufacturers are now offering this option.
Manure application rates also may be controlled by component design. For example, manure supply tubes on the chisels, sweeps, and disk applicators used in this study were all 3 inches in diameter, whereas the coulter applicators were equipped with 2 inch supply tubes. This should not be a factor, however, if manure is applied at agronomic rates to meet crop nutrient needs.
If tire spacing does not match row spacing, injectors/applicators mounted on the front of the tank (as opposed to the rear) may leave somewhat greater amounts of residue cover. With this configuration, standing residue that was knocked down by the tank tires would be knocked down onto the area that had already been disturbed, rather than in front of the injectors/applicators. Situations similar to this have been observed when no-till planting into corn residue. Standing corn stalks were knocked down by the planter components, slightly increasing the amount of residue cover compared to the cover prior to the planting operation. However, judging from sales literature, only a very limited number of manure equipment manufacturers offer a front-mount option. Also, front-mounting may substantially limit the use of different types of injectors/applicators since clearance below the tank is usually quite limited.
If possible, apply and incorporate manure in the spring, rather than the fall, to maximize the amount of residue cover remaining. This also more closely matches crop nutrient needs, and may provide less opportunity for nutrient leaching. Also, more residue would remain on the soil surface during the winter and early spring for increased erosion protection. Applying manure only in spring, however, may not be feasible due to limited manure storage capacity. Also, field access and compaction may be more of a concern since the soil is usually wetter in spring than in fall. As mentioned previously, manure application into a growing crop or pasture may be a manure management alternative that could overcome some of these issues.
Results of this research project indicate that adequate residue cover can be maintained for effective erosion control with some configurations of manure injectors/applicators, particularly in corn or other non-fragile residue; however, to achieve this the equipment must be selected, adjusted, and operated with the dual objectives of manure and residue management, rather than the objective of simply disposing of the manure. With careful planning, livestock producers should be able to select a manure management system that is compatible with their objectives for controlling soil erosion.
Acknowledgments: Financial support for this project was provided by the Nebraska Pork Producers Association. Manure equipment was provided by Balzer Manufacturing Corp., Mountain Lake, Minnesota; Calumet Division of Imperial Industries Inc., Wausau, Wisconsin; Sukup Manufacturing Co., Sheffield, Iowa; and Vittetoe, Inc., Keota, Iowa.
Residue cover reduction caused by soil-engaging components typically used with tank spreaders and towed hose systems to apply liquid or slurry manure.
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Manure incorporation represents a compromise between best management practices for soil erosion control and manure management. Manure should be incorporated into the soil for odor control, increased availability of nutrients, and control of potential manure runoff; however, disturbing the soil and crop residue may increase soil erosion and water runoff. This NebGuide summarizes the results of a field study to determine the influences on crop residue cover of common equipment used to simultaneously apply and incorporate manure.
Manure management has become a focal point for many livestock producers because of environmental concerns such as water quality and odor control and an interest in capitalizing on its fertilizer value. A best management practice is to incorporate manure into the soil to maximize nutrient availability, especially nitrogen, and to minimize odors and potential degradation of surface water quality through manure runoff.
Maintaining crop residue on the soil surface is one of the most cost-effective soil erosion control practices. Compared to a cleanly tilled field, erosion can be reduced by 50 percent when just 20 percent of the soil surface is covered with residue. A best management practice for soil erosion control is to minimize soil and crop residue disturbance, thus leaving more crop residue on the soil surface. Today's livestock producer must balance these two best management practices.
Three general configurations of soil-engaging components are typically used with tank spreaders and towed hose systems to simultaneously apply and incorporate either liquid or slurry manure.
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Chisels and sweeps (Figure 1-a) are the most common and generally consist of a C-shaped shank, 2-3 inches wide, with either a chisel or sweep point attached. Shank spacing on the toolbar usually ranges from 20 to 60 inches. Chisel points are typically 2-3 inches wide and can be either straight or twisted. Sweeps are typically 7-24 inches wide. At least one manufacturer offers a combination chisel point and sweep as a single unit. Most manufacturers also offer coulters that can be mounted in front of the shanks to help cut the crop residue, allowing it to pass between and around the shanks. Operating depth of chisels and sweeps is usually 4-8 inches. Manure exits the supply tube below the soil surface, making these units true manure injectors.
Disk-type applicators (Figure 1-b) consist of two opposed concave disks, typically 14-22 inches in diameter, mounted on an angled shaft. Spacing between the centers of the individual disks is generally 12-32 inches. Because of the angled shaft, the disks are skewed relative to the direction of travel, giving a wider spacing between the disks at the front edges than at the rear. Manure exits slightly above the soil surface through the supply tube between the disks. Operating depth is generally 3-6 inches. As the applicator moves through the field, the disks throw loosened soil and crop residue inward and upward, mixing the soil and residue with the manure flowing from the supply tubes. Following application, the field often appears as strips of essentially undisturbed residue and soil alternated with strips of mixed soil, residue, and manure. The width of the undisturbed strip depends on the spacing between the two opposing disks and the spacing of the disk units along the toolbar (typically 15-60 inches).
Coulter-type applicators (Figure 1-c) consist of a large rolling coulter, typically 22-25 inches in diameter, a manure supply tube, and a closing or press wheel. The coulter is angled approximately 5 degrees compared to both the direction of travel and to vertical. As the applicator moves through the field, the soil and residue is cut by the coulter and a slot is wedged open. Manure is applied in this slot, which is closed by the press wheel. Operating depth is usually 4-8 inches. Coulter applicators are operated in pairs, with one skewed to the right and one skewed to the left, to eliminate implement side-draft.
Trials were conducted at the University of Nebraska Haskell Agricultural Laboratory near Concord in the spring and fall of 1996 and 1997 to study residue cover reduction by various components. Seven configurations of manure application/incorporation components were used in this study. A tandem disk also was included for comparison. Equipment descriptions are given in Table I. Evaluations were made in both irrigated and dryland corn residue (non-fragile) and in soybean and oat residue (fragile).
Chisel and Sweep Injectors
Balzer 20.5-inch wide sweeps with integral 2.25-inch wide straight chisel points and 17.5-inch diameter ripple coulter in front of each injector; 30-inch spacing on toolbar Calumet 2-inch wide straight chisel points; 30-inch spacing on toolbar Calumet 14-inch wide sweeps; 30-inch spacing on toolbar |
Disk-type Applicators
Vittetoe disk applicator with 22-inch diameter disks spaced 31 inches at the center; 60-inch spacing on toolbar |
Coulter-type Applicator
|
Tandem Disk
|
aMention of brand names is for description only. Endorsement or exclusion of others is not intended or implied. |
Residue cover reduction averaged 92 percent when chisel and sweep injectors were used in soybean and oat residue. In some instances, residue was reduced by as much as 98 percent. In corn residue, the average reduction was 52 percent with chisel and sweep injectors, with reductions ranging from 25 to 87 percent. Average residue cover reductions with the tandem disk were about the same as those from the chisel and sweep injectors in all four residues.
Average residue cover reduction by the disk-type applicator was 72 percent for soybean and oat residues and 45 percent for corn residue. Residue cover reduction by the disk applicators was not significantly different compared with the tandem disk in either irrigated or non-irrigated corn residue, but was significantly less in soybean and oat residues.
Residue cover reductions by the coulter-type applicator were significantly less than the reductions caused by all other components. When taken across year and season, mean residue cover reduction for the coulter applicator was 37 percent for soybean and oat residues and 11 percent for corn residue.
One objective of this study was to determine values for the amount of residue cover that could be expected to remain after using manure application/incorporation equipment. (Similar values are already available for many tillage and residue-disturbing operations.) Suggested ranges of values for both fragile and non-fragile residues are presented in Table II. These data can be used for planning if site and equipment-specific values are not available. [Note: The values in Table II are percentage of initial residue cover remaining, not percent residue reduction as previously discussed. Percentage cover remaining = (100 - percent reduction).]
| Table II. Percentage of initial residue cover remaining after manure application/incorporation. | |||
| Application/ Incorporation Component |
Percentage of Initial Residue Cover Retained | ||
| |||
| Chisel and Sweep Injector | 5-15 | 30-65 | |
| Disk-Type Applicator | 15-40 | 40-65 | |
| Coulter-Type Applicator | 65-80 | 80-95 | |
| Tandem Disk | 5-25 | 35-60 | |
The values in Table II can be multiplied by the percent residue cover present before manure application/incorporation to estimate the amount of cover that will remain after manure incorporation. For example, assume that a coulter-type applicator is used to apply manure in a recently combined soybean field having an average residue cover of 70 percent. Multiply 70 percent (after harvest cover) by 0.7 (estimated percentage of cover remaining for a coulter-type applicator used in soybean residue, expressed as a decimal) which gives about 50 percent residue cover following manure application. In contrast, if a chisel or sweep injector was used in the same soybean field, less than 10 percent cover would likely remain (70% x 0.1 = 7%). Likewise, in an irrigated corn field having an average residue cover of 95 percent, the expected percent cover following manure application/incorporation would be approximately 40 percent (95% x 0.45) if a chisel or sweep injector is used; slightly over 50 percent (95% x 0.55) if a disk-type applicator is used; and about 80 percent (95% x 0.85) if a coulter-type applicator is used.
As with tillage operations, the amount of residue cover remaining after manure incorporation is influenced by many factors, including component design, shank spacing on the toolbar, adjustments, field speed, depth of soil disturbance, previous residue disturbance, and soil and residue condition. Thus, the best procedure is to operate the manure incorporation equipment in a small, representative area of the field and then measure the amount of residue cover remaining (see University of Nebraska Extension NebGuide G93-1133, Estimating Percent Residue Cover Using the Line-Transect Method). Also, manure incorporation is only one operation within a series or system of operations performed in a field between harvest of one crop and planting of the next crop. Each soil and residue-disturbing operation must be considered when evaluating the amount of residue that will remain for erosion control. (For a more complete list of implements and the residue amounts remaining after their use, as well as more information about the influence of other factors, refer to University of Nebraska Extension NebGuide G93-1135, Estimating Percent Residue Cover Using the Calculation Method.)
Results of this study indicate that adequate residue cover can remain for effective erosion control with some configurations of manure injectors and applicators, particularly in corn or other non-fragile residue. Equipment must be selected, adjusted, and operated with the dual objectives of manure and residue management, rather than the objective of simply disposing of the manure. The companion NebGuide, Manure Incorporation and Crop Residue Cover - Part II: Fine-Tuning the System (G05-1564), discusses some of these considerations. With this information, livestock producers should be better able to select a manure management system that is also compatible with their soil erosion control objectives.
Acknowledgments: Financial support for this work was provided by the Nebraska Pork Producers Association. Manure equipment was provided by Balzer Manufacturing Corp., Mountain Lake, Minnesota; Calumet Division of Imperial Industries Inc., Wausau, Wisconsin; Sukup Manufacturing Co., Sheffield, Iowa; and Vittetoe, Inc., Keota, Iowa.
This NebGuide discusses how wind erosion occurs and presents methods for reducing wind erosion on land devoted to crop production.
Wind erosion is widespread on agricultural land in the Great Plains, particularly in the semi-arid regions. Wind erosion physically removes the most fertile part of the soil (organic matter, clay, and silt) and lowers soil productivity. This loss in productivity increases the costs of producing crops. Blowing soil can reduce seedling survival and growth, depress crop yields, and increase the susceptibility of plants to certain types of stress, including diseases.
Some soil from eroded land enters suspension and becomes part of the atmospheric dust load. Dust obscures visibility and pollutes the air, fills road ditches and impacts water quality, causes automobile accidents, fouls machinery, and imperils animal and human health. Wind erosion is a threat to the sustainability of the land as well as the viability and quality of life for rural and urban communities. A strong, turbulent wind, coupled with highly erodible field conditions, causes wind erosion. A wind speed as low as 6 mph one foot above the soil surface is capable of starting soil movement under highly erodible field conditions. Erodible field conditions consist of an unprotected soil surface that is smooth, bare, loose, dry, and finely granulated (Figure 1). If a 20 mph wind increases to 30 mph, the rate of erosion will triple. Any erosion control system that increases the minimum wind speed at which soil erosion begins or reduces wind speed at the soil surface will effectively reduce soil erosion. |
| Figure 1. Blowing soil fills seed furrows and partially buries small wheat plants in the spring, resulting in increased plant stress that weakens the plants and makes them more susceptible to further damage by disease and other environmental stresses. |
| Table I. Effect of nonerodible soil cover on relative soil loss reduction compared to bare soil. | |
|
Soil cover (%) |
Relative soil loss reduction (%) |
|
0 |
0 |
|
10 |
35 |
|
20 |
60 |
|
30 |
70 |
|
40 |
80 |
|
50 |
85 |
|
60 |
90 |
|
70 |
93 |
|
80 |
96 |
|
90 |
98 |
|
100 |
99 |
 |
| Figure 2. Relationship between silhouette area and soil loss ratio. The silhouette area is calculated by multiplying stalk height in inches by stalk diameter in inches by the number of stalks per 1600 square inches (approximately equivalent to 1 square meter or 11.1 square feet) of soil surface area. The smaller the soil loss ratio, the smaller the calculated soil loss will be. |
| Table II. Examples of silhouette areas for several dryland crops grown in western Nebraska. | |||||
|
Crop |
Stalk height |
Stalk diameter |
Stalk no.a |
Silhouette area |
Soil loss ratio |
|
---- inches ---- |
no./1600 in.2 |
in.2/1600 in.2 | |||
| Winter wheat | 10 | 0.12 | 300 | 360 | 0.01 |
| Winter wheat | 10 | 0.12 | 200 | 240 | 0.02 |
| Proso millet | 6 | 0.16 | 100 | 96 | 0.11 |
| Corn | 24 | 0.75 | 3.5 | 63 | 0.19 |
| Sunflower (short) | 12 | 0.85 | 3.7 | 38 | 0.30 |
| Sunflower (tall) | 24 | 0.85 | 3.7 | 75 | 0.15 |
| aNumber of stalks in 1600 square inches, which is approximately equivalent to 1 square meter or 11.1 square feet. | |||||
| Table III. Small grain equivalents (SGe) for 1,000 lb/ac of various vegetative covers.a Amended from 1988 Natural Resources Conservation Service National Agronomy Manual. | |
| Vegetative cover 1,000 lb/ac | Small grain equivalents lb/ac |
| Standing winter wheat stubble (10 inches high, in 10-inch rows perpendicular to wind) | 3,500 |
| Flat winter wheat stubble (10 inches long, randomly distributed) | 1,600 |
| Growing small grain, flat surface | 2,000 |
| Flat corn stalks | 200 |
| Standing millet stubble | 1,700 |
| Standing grain sorghum residue | 1,300 |
| Flat grain sorghum stalks | 350 |
| Standing alfalfa residue, stalks only | 2,900 |
| Dry bean and soybean (random flat residue) | 600 |
| Standing sunflower residue (17 inches high, 30-inch rows perpendicular to wind) | 225 |
| Properly grazed western wheatgrass, 4 inches high | 4,800 |
| aNatural Resources Conservation Service may discontinue use of SGe, but SGe is currently the method used to link the amount of residue with a corresponding reduction in wind erosion. | |
| Table IV. Effective (x) ridge heights for various ridge spacings, assuming wind direction is perpendicular to the ridges. | ||||||
|
Ridge spacing, feet | ||||||
| Ridge height, inches | 1 | 2 | 3 | 4 | 5 | 6 |
| 2 | x | |||||
| 4 | x | x | x | x | x | |
| 6 | x | x | x | x | x | |
| 8 | x | x | x | x | ||
| 10 | x | x | ||||
 |
| Figure 3. This wheat field south of Sidney, Nebraska was harvested with a Shelborne Reynolds Combine Stripper Header. The use of a stripper header for wheat harvest can leave a tall wheat stubble that provides excellent protection against wind erosion. Additionally, a taller stubble has been found to decrease soil water loss through evaporation, reduce weed infestations, and catch and retain more wind-driven snow in fields where the extra moisture can significantly increase the yield of the following crop. |
 |
| Figure 4. Carl Mortensen, Jr., has found that stripcropping reduces wind erosion and winterkill problems on his Kimball County farm. Soil type is one factor that determines the width of strips. Strips should be arranged perpendicular to the prevailing wind direction. |
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