H. Magdi Selim, Michael R. Lindsey, Brian J. Naquin and Brad Venuto
A major objective of the Clean Water Act and the Coastal Zone Management Act is to evaluate, demonstrate and implement best management practices (BMPs) to improve water quality. Because applied agricultural chemicals and sediment are potential contributors to nonpoint-source pollution, it is essential to quantify each commodity’s contribution to water quality problems and evaluate BMPs that can improve water quality.
The Clean Water Act and the U.S. Environmental Protection Agency’s (EPA) water quality regulations require all states to identify and designate beneficial uses for each water body and adopt standards that protect those beneficial uses. Water quality standards may be either numerical, such as the amount of dissolved oxygen, or narrative, such as no toxic materials. Water bodies that do not meet water quality standards are listed as impaired. Nationally, EPA has concluded that agriculture has contributed nearly 60 percent of the impaired river miles and half of impaired lakes.
The Louisiana Department of Environmental Quality (LDEQ) is developing and implementing a moni-toring and management approach to identify sources of pollutants that place specific water bodies at risk. The management scheme is based on the Total Maximum Daily Load (TMDL) of a pollutant that a stream or water body can tolerate before its use is compromised. The pollutants identified as being of concern in Louisiana surface waters are suspended sediments, nutrients (nitrate and phosphate) and organic matter enrichment.
LDEQ selected the Bayou Plaquemine-Brule sub-basin in South Louisiana for initial implementation of a number of BMPs expected to reduce TMDLs. This region is characterized by somewhat sloping topography and highly erodible soils, which are a potential source of sediment if not managed properly. While pasture, sugarcane, soybeans, corn and rice are the major agricultural activities, pasture acreage exceeds 50 percent of the watershed. Sugarcane has only recently been introduced into the southern region of the drainage basin, whereas soybeans are grown throughout the sub-basin, often in rotation with corn or sugarcane In 2003, LSU AgCenter researchers initiated a study to quantify control measures for implementation of best management practices that reduce nonpoint-source pollution in the Bayou Wikoff watershed region of the Bayou Plaquemine-Brule sub-basin. Sampling and water and soil analysis will continue through 2004 and 2005. Three local farmers agreed to participate in the study.
A 5-acre area adjacent to Bayou Wikoff was selected to serve as a control area. Land-use operations consist of a minimum-input tree farm. The grassed areas are never grazed and only infrequently mowed. This land-use scenario closely mimics the pre-settlement natural prairie ecosystem of the region, and monitoring should yield an estimate of pre-settlement nonpoint-source values before settlement.
Two areas adjacent to Bayou Wikoff were selected for sugarcane BMP comparison. The first area is a 14-acre tract of land where standard sugarcane practices, including burning of standing cane, will be monitored. A mulch and no-burn BMP treatment will be implemented on an adjacent area of a similar size.
For both treatments – burn and no-burn – a combine harvester that cuts the cane stalks into billets, which are direct-ly loaded into wagons for transport to the mill, is used. Extractor fans in the combine separate leaf material from billets. The plant residue or mulch falls to the soil surface averaging 6 to 8 tons per acre.
The selection of the no-burn BMP will have the additional benefit of eliminating air pollutants (smoke and ash) associated with sugarcane harvest in addition to the anticipated benefits of pollution reduction from mulch residue retention, sediments and applied agricultural chemicals.
We identified two areas in which to monitor different forage BMPs and their influence on water quality and sediment runoff. The first site is a 12-acre pasture that borders Bayou Wikoff in the central part of the sub-watershed. The treatment here is minimum input with low main-tenance and involves continuous grazing at recommended stocking rates, supple-mental feeding and minimum tillage. Summer forage consists of perennial grasses, and winter forage is sod-seeded annual ryegrass.
The second site for BMP monitoring is a 10-acre section of pasture adjacent to the first site but separated by a road. In this treatment, the BMP consists of a rotational grazing system wherein duration, intensity and frequency of grazing is managed to enhance nutrient cycling. This requires monitoring manure distribution and fertilizer inputs and minimizing soil compaction and erosion. Forages in these treatment areas consist of perennial summer grasses and
Monitoring and sampling equip-ment have been placed at edge-of-field locations to facilitate evaluation of all treatment options. In addition, there is in-stream monitoring of the changes in the water quality, both upstream and downstream. The upstream location is not influenced by the various treatments, whereas the downstream location captures total runoff from all treatments in Bayou Wikoff.
This study is among the first in Louisiana to quantify the impact on water quality within a watershed from application of recommended BMP’s to specific agricultural cropping systems. These results will help direct future implementation and adoption of BMP’s and lead ultimately to cleaner water for everyone.
(Spring 2004, Louisiana Agriculture)