Mr. James J. Hoorman, Water Quality Extension Agent, Hardin County Extension
Spring applications of manure can cause livestock producer's problems with the preferential flow of manure to tile lines. If not addressed by proper manure management, preferential flow can negatively impact the environment, particularly water quality. The damage is typically indicated by fish killed in nearby streams. In the past three decades, the number of fish kills related to agriculture has increased by 72%. In the past four years, 560,000 fish covering 430 miles of Ohio streams have been killed. Agriculture is the number one cause of fish kills in Ohio and accounted for 80 fish kill cases (22.5%) of the 356 Ohio fish kills in the last four years. Livestock and manure accounted for 72% of all fish kills related to agriculture during this four-year time period.
Anything that promotes good drainage may increase preferential flow and can lead to an increase of manure flowing to and through subsurface (tile) drainage outlets. Liquid manure acts just like water! Through gravity, water and manure move downward through the soil profile following a path of least resistance. Liquid manure moves through deep cracks in the soil, root channels from old and new plants, and earthworm channels. There are many factors that can contribute to increases in preferential flow occurrences: excess precipitation, saturated soils, excessive manure application rates, poor management decisions due to lack of manure storage, concentrated manure applications, operator error /equipment failure, high pressure/deep injection, and damaged or shallow tile. Producers should be especially aware of weather conditions (rain, excess moisture) and management decisions (application rates, calibration, and equipment limitations) to avoid problems.
To prevent manure in tile lines, livestock farmers should consider adopting and following various management practices. Appropriate application rates must be followed. Basing the application rate upon the moisture holding capacity of the soil and calibrating manure application equipment can accomplish this goal. Producer management decisions on when to apply manure are critical. Often, producers may make bad decisions when manure storage gets too full. By regularly monitoring manure storage and applying manure in a timely manner, livestock producers can avoid applying the manure when conditions may not be optimal.
Manure application equipment should be designed to allow for calibration and spreading of large volumes of manure evenly over or into soil at low rates and low pressure. Keep in mind that each piece of equipment (irrigation, tankers, dragline, and solid spreaders) has distinct advantages and disadvantages. The type of equipment utilized should not only be economical to operate but should also allow for manure to be applied in an environmentally friendly, responsible, and sensitive manner. Ideally, manure application equipment should allow for manure to be applied evenly to the top three to five inches of the soil surface.
Application rates depend upon the available water capacity (AWC) of the top eight inches of the soil. Manure should not be applied above the AWC. Generally, liquid manure should never be applied at rates greater than 1/2 inch or roughly 13,500 gallons per acre. Lower manure application rates decrease the chance for liquid manure to flow to tile lines because the soil has a better chance of absorbing the liquid manure. Multiple applications of 1/4 inch per acre or 7,000 gallons per acre is better than one large manure application to prevent the flow of liquid manure to tile lines.
Different species of livestock produce manure with distinctively different characteristics, and this should be taken into consideration as well. For example, the make-up of swine manure is typically 95 percent water and five percent solids, while dairy manure usually consists of 97 to 98 percent water and two to three percent solids. Waste from eggwash or milk house operations is typically very thin but contains a very high BOD5, which is the five-day biochemical oxygen demand and is deadly to fish. As water content increases, solid content decreases and viscosity (stickiness) of manure decreases so it flows easier. Liquid manure acts just like water because it is basically dirty water with the ability to kill fish and humans if it is untreated. Agitating the manure to increase the solids content can help decrease the potential for manure flowing to tile lines.
The presence of earthworm burrows, which prefer loamy soil types and are typically present within one to four meters of tile lines, may further exasperate preferential flow problems. Tile plugs and control structures may provide some type of relief. Keep in mind, however, that tile plugs are an emergency measure and fail about 50% of the time because of improper use and installation. Tile plugs should not be used if tile lines are flowing with water nor should liquid manure be applied if tile lines are flowing because the soils are too saturated with water. Drainage outlets should be inspected regularly if manure is being applied. Control structures are a great tool but must be installed and managed correctly to be effective. Check with your local Soil and Water Conservation District (SWCD) or United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) office to see if cost-share assistance is available for installing control structures.
As it is with many issues, management is the key to preventing preferential flow of manure. Therefore, you'll need adequate storage (minimum of six months recommended, one year preferred) and well-maintained and calibrated equipment that applies manure evenly. Additionally, you'll need to know the location of all tile lines and outlets, repair broken tile, maintain buffer zones and setback distances (100 feet from waterways), and inspect tile outlets regularly when applying manure. Manure should not be applied above the AWC of the top eight inches of the soil and should never be applied if tile lines are flowing. If possible, the soil should be tilled to a depth of three to five inches to disrupt macropores (cracks), especially during dry seasons. Lower manure application rates should also be given high consideration. An emergency management plan should be a part of your manure management plan, and accurate records should be maintained to document manure applications and, if any problems occurred, how these problems were addressed and resolved. If you utilize custom applicators for manure application, take time to educate them about this issue. Plan on attending the Manure Science Review August 24 to 26, 2004 or Farm Science Review September 21 to 23, 2004 for more information on manure management and application.