  |
 |
 |
 |
NWMC Home
About Us
News
Technical Resources
Partnerships
Contact Us
|
   |
|
|
|
Composted Manure Used Along Roadways Controls Erosion
By David C.
Moffitt It's difficult to go for long without hearing of a local, regional, or even national manure "problem." Livestock production across the country has been concentrated in ever larger operating units and these units concentrated geographically. In some parts of the country manure availability exceeds the amount of agricultural land available to properly recycle manure nutrients (1). Clearly, alternative uses of manure are needed. The use of manure-based compost along the nation's roadways to establish and nurture vegetation is one of those alternatives. The use of compost along roadways is not a new concept. A 1997 document (2) listed some seventeen states that had demonstrated the use of compost and had developed specifications for its use to establish vegetation or otherwise beautify roadways and right-of-ways. However, not all states allow the use of compost from manure. Some limit the use of compost to that made from composting yard debris and other organic material believing that it generally contains less pathogens than manure compost. Composting is a natural microbial process taking place in an aerobic environment. When done correctly, composting results in elevated temperatures within the mix sufficient to kill pathogenic organisms of concern. Connecticut and Texas ExperienceMost notable among the state compost studies are those in Connecticut and Texas (3). Not only has the use of compost reduced erosion along roadways in these states, the compost has supplied nutrients, retained moisture, and helped establish vegetation on sites with harsh growing environments. The two-year Connecticut study was a cooperative effort between two state agencies, the Department of Environmental Protection and the Department of Transportation (DOT) and ended in 1998. The study was intended to promote the use of compost creating a demand for the product and creating jobs as well. The study was also viewed as a means of demonstrating to local municipalities and to other groups that compost was a valuable product for their use in roadside development and other soil-related uses. The compost was made primarily from yard debris. The study took place near Chaplin, Connecticut on a 2:1 slope situated on silty sand. Eight cells were treated with variations of compost, mulch, hay, and straw, and one cell left bare for a control. The treated sites showed erosion reductions of more than 90 percent in comparison to the control cell. The cells treated with compost performed as well or better than those receiving the traditional hay and seed mixture. Surprisingly, the depth of application of treatment made little difference; the results with one and one half-inch of mix were the same as that with three inches of mix. The Connecticut trial also included an evaluation of the use of compost to establish turf at the edge of pavements, particularly in drainage swales at the bottom of slopes. Compost was applied at varying rates to different sections and compared to a control section that received no compost. Compost was applied at a rate of one half inch, one inch, and two inches and the sections were tilled. Each site also received a two-inch layer of compost on the tilled surface. All sections, including the control section were seeded with the standard seed mix. Another section only received compost on the soil surface at the time it was seeded. The area receiving compost, even in small amounts exhibited lush vegetation growth as compared to fewer and smaller plants in the non-treated sites. There seemed to be little difference between the sites receiving various rates of compost, indicating the addition of any compost improved the site conditions. The results of the Connecticut study has encouraged Connecticut Department of Environmental Protection (DOE) to develop a materials specification and a construction detail for the use of compost as a substitute for peat in planting backfill. The material specification does allow the use of composted manure as well as many other organic residues based on successful studies in other states. A partnership between Texas Department of Transportation (TxDOT), Texas Natural Resources Conservation Commission (TNRCC), and the Texas State Soil and Water Conservation Board has resulted in compost being applied to roadways in Texas as a part of TxDOT's emphasis of the use of recycled products. Unlike the Connecticut trials, the Texas demonstrations were conducted with compost from cow manure. Officials cite the two-fold benefit of using composted manure - the compost protects the often-fragile soils along the roadways and the use of compost helps manage the surplus of manure in some locations. TxDOT recognizes the value of composted chicken litter as well as cow manure and notes the finished product meets strict Environmental Protection Agency (EPA) standards for Class A biosolids (4)(6). The use of compost along roadways has been demonstrated in the Dallas, Abilene, Tyler, and Amarillo districts of TxDOT, often with remarkable results. In one case TxDOT had tried unsuccessfully five times to establish vegetation on a steep, severely eroded overpass near Big Springs, Texas. The site had been barren since 1968 and is in a low rainfall area. Compost was applied to the site and one month later grass was thriving on the site. Wood chips and compost were blended at a ratio of three parts compost to one part wood chips. The wood chips reduce the potential water and wind erosion of the compost and topsoil. Near Austin and Dallas, Texas, compost has been used side by side with conventional vegetative establishment techniques. These trials have resulted in dramatic visual evidence of the benefits of composting. Photo #1 taken at the site near Dallas shows the compost treated site in the foreground with the conventionally treated site in the background. Note the color of the vegetation. The photograph was taken during a period of drought in north Texas and the grass established with conventional treatment is showing the effects of limited moisture. The compost treated site has retained moisture and the vegetation is still green. Photo #2 shows the moist compost beneath the courser wood chips used for erosion control at the Dallas site. Photo #3 taken in south Fort Worth, TX, shows the use of compost to aid in the establishment of landscaping near an interchange. The site in photo #3 is to be irrigated, and the compost is viewed as an aid to retain moisture and reduce the amount of irrigation needed. The successes with the use of compost in vegetation establishment along Texas roadways have shown the utility of the product for erosion control and moisture retention as expected. The Texas demonstrations have also shown the benefit of compost for vegetation establishment in the harshest of climatic and soil conditions. Probably it is the latter benefit of compost that makes it the most attractive to Texas contractors. Current practice is for the state to withhold five percent of the payment for highway projects until vegetation is established on 70 percent of the disturbed area. Using compost to accelerate the establishment of vegetation is a real incentive (3). Compost is being applied to the soil surface as a top dressing as well as being applied and tilled into the soil in the Texas demonstrations. Applications range from ½ inch to two inches deep, with most all studies show the maximum benefit of compost is limited to one inch in depth. Additional depth adds cost without increasing benefits as noted in the Connecticut study as well. Tilling in the compost increases the soil microbe activity with positive benefits to soil tilth, but also decreases the longevity of the effectiveness of the compost application, as the carbon in the compost is converted to carbon dioxide (5). Application of the compost to the soil surface will prolong the longevity of treatment, but without the dramatic soil changes in the first years after application. The soil treatments shown in Photos #2 and #3 are surface applied. The success of the Texas demonstration projects has lead to the development of a statewide TxDOT Special Specification Item 1027; "Furnishing and Placing Compost" (6). The Texas specification, like its counterpart in other states, sets minimum requirements for the quality of material and construction methods. With the specification in place, it will be easier for the statewide use of compost to develop. The Texas specification identifies three grades or classes of compost; compost for manufactured topsoil, erosion control compost, and general use compost. Erosion control compost and general use compost are required to have 40 – 60 percent organic matter, while compost for manufactured top soil can have as little as 30 percent organic matter. Particle sizes for the erosion control compost are two to three times that of the other two compost classes. The compost shown in Photo #2 meets the erosion control compost specification, while the area pictured in Photo #3 is most likely general purpose compost. EconomicsAs previously mentioned, current TxDOT policy provides an economic incentive for the rapid establishment of vegetation in disturbed areas. Compost has been demonstrated as a viable option for successfully completing the vegetation process. But how about the economics of compost versus other technology? One demonstration reported in Texas showed the cost of a compost based treatment as $17,000 as compared to an estimated $30,000 for the traditional topsoil, seeding, and the erosion control blanket (3). The report did go on to note the cost savings would be reduced where additional thickness of compost was used, but the thickness used to compute the $17,000 cost was not given. From a livestock producer view, the composting process makes sense. A study at Texas A&M – Commerce for a 400 cow dairy showed composting the manure could yield an annual net income of approximately $20,000. Composting was done in an in-vessel composter at a cost of approximately $11 per cubic yard at the site. Texas A&M – Commerce estimated the finished compost value at $20 per cubic yard. One of the weakest links in the manure composting effort has been the development of markets where the value of the compost can be realized, so the above mentioned profits must be considered to be potential. The use of the compost for highway vegetation establishment and beautification would create markets in areas where the market does not now exist. EPA's Region 6 is further encouraging the use of composted cow manure through funding of a section 319 grant. Contractors using compost made from cow manure from the Bosque Watershed (Erath County, Texas) will receive a payment per cubic yard of compost used. The 319 grant is provided as an incentive to use manure from an area where manure is in excess and thus develop the market potential. For more information about the use of compost along roadways, contact NWMC
Environmental Engineer at (501) 210-8900. Additional contacts include Scott McCoy, TNRCC Program Specialist IV at (512) 239-6774 or
smccoy@tnrcc.state.tx.us. and Barrie Cogburn, TxDOT Landscape
Architect at (512) 416-3086 or
bcogburn@dot.state.tx.us. You might also want
to check out compost web-sites at: References1. Lander, Charles, David C. Moffitt, and Klaus Alt, "Nutrients Available from Livestock Manure Relative to Crop Growth Requirements", Resource Assessment and Strategic Planning Working Paper 98-1, USDA - Natural Resources Conservation Service, February 1998 2. Mitchell, Donna, "Compost Utilization by Departments of Transportation in the United States," Soil and Water Science Department, University of Florida. March 1997 3. Block, Dave, "Controlling Erosion from Highway Projects," Pages 59-62, BIOCYCLE, January 2000 4. Bishop, Chris, "TxDOT Tests Compost Mixture as ROW Erosion Control Option," ENVision, Texas Department of Transportation, Austin, TX Summer/Fall 1999 5. Smith, Darrell, "You Can Build Organic Matter," Farm Journal, December 1995 6. Texas Department of Transportation, Statewide Special Specification Item 1027, "Furnishing and Placing Compost," Revised May 1999 7. Texas A&M University-Commerce, "Economics of Composting and Marketing of Dairy Cattle Solid Waste Using In-Vessel Techniques," Department of Agricultural Sciences, Texas A&M University-Commerce, Commerce, Texas March 1999 |
|
|
|
Back to Top