Linda F. Benedict, Derouen, Sidney M., Owens, William E.
William E. Owens and Sidney M. DeRouen
The U.S. Clean Water Act of 1972 requires states to have water quality guidelines that protect the condition of water bodies within that state. Nonpoint sources of pollution are a major concern for possible water quality impairment. Agriculture has been targeted as a contributor to nonpoint source pollution.
The Clean Water Act requires states to make a list of impaired water bodies, establish a priority list and develop Total Maximum Daily Loads (TMDLs) for these waters. A TMDL is an indicator of the maximum amount of a pollutant that can be released into a water body from both point and nonpoint sources without impairing the water body. When a TMDL is established, a watershed implementation plan that describes voluntary actions necessary to achieve compliance must be generated. These guidelines are termed Best Management Practices (BMPs).
BMPs provide farmers with guidelines that help minimize the impact of agricultural practices on water quality. BMP guidelines for beef, dairy, forestry and poultry operations all recommend buffer zones, streamside management zones along rivers and bayous or watershed access management of various sizes and types to slow runoff, decrease erosion and protect water quality. Such zones are effective for controlling non point sources of pollution; however, the optimum size of these zones and intensity of access management are unclear. Furthermore, differences in land use, soil type and topography affect runoff and the amount of sediment and nutrients contained in the runoff. Such variations require different applications of these BMPs to help determine the optimum practices that are practical for implementation by farmers to protect water quality.
Animal waste from dairy and poultry operations is an economical and commonly used fertilizer in Louisiana, but it is a potential nonpoint source of water degradation. Animal waste has been shown to be a source of microorganisms potentially pathogenic to humans. Runoff and percolation can transport animal waste-derived organic matter and nutrients to surface water and groundwater. Proper application of animal waste provides nutrients for crop production while minimizing surface runoff. Animal waste also enters water bodies as cattle enter streams and ponds for water.
The AgCenter Hill Farm Research Station is uniquely suited to evaluate BMPs of beef, dairy, forestry and poultry enterprises. Research projects in all commodities are active at this station where a variety of land types exist. This project is a joint effort of beef, dairy and forestry and will evaluate BMPs from each commodity area. Because the station is situated along the crest of the ridge dividing the Ouachita and Red River watersheds, it provides a unique opportunity to study these watershed areas without upstream contamination of samples.
Buffer strips are an integral part of BMPs and are used to reduce sediment, decrease nutrient loss, control erosion and reduce the bacterial load of surface runoff. Comparisons of surface water quality after application of poultry litter from plots with and without buffer strips indicate that such strips appear to improve water quality.
The presence of a 30-foot buffer zone that received no direct application of poultry litter reduced the concentration of phosphorous and reduced the number of total and fecal coliforms in surface runoff water from test plots compared with identical plots with no buffer zones. Plots received the equivalent of eight tons of poultry litter per acre. Surface runoff samples were collected after each rain event exceeding 0.5 inches. Vegetation in both buffer zones was the same. No differences were noted for nitrate, nitrite and ammonia concentrations.
A previous study at the Hill Farm plots with varying amounts of poultry litter showed no differences in phosphorous and in total and fecal coliforms; however, the effect of buffer zones was not examined in that study.
Restricting cattle access to ponds and streams also has been shown to improve water quality. In one study, cattle were allowed varying degrees of access to ponds, and monthly water samples were collected and analyzed for nutrients and for total and fecal coliforms. Ponds in which cattle had no direct access had lower numbers of total and fecal coliforms. No differences were observed for phosphorous, nitrate, nitrite or ammonia.
In general, these results indicate that the BMPs evaluated protect surface water and pond water. Leaving an unfertilized zone or strip of pasture along creeks or ponds is an easy and effective method for helping protect water quality. Care must be taken during application of poultry litter to ensure that an unfertilized buffer is maintained. BMP guidelines recommend 20 feet of buffer for land with a slope of 0-5 percent. As the slope of the land increases, the width of the recommended buffer zone also increases.
Controlling access of cattle to ponds is more difficult and requires a larger investment. Fencing must be maintained to keep cattle out of ponds, and alternate sources of water must be provided to cattle. In this study, the improvement in pond-water quality was not substantial, and further studies are warranted to determine if restricting cattle access to ponds is cost-effective and justified.
William E. Owens, Professor, Hill Farm Research Station, Homer, La., and Sidney M. DeRouen, Professor, Dean Lee Research Station, Alexandria, La., and Rosepine Research Station, Rosepine, La.
(This articles was published in the spring 2010 issue of Louisiana Agriculture.)