Water Quality and Soybeans in the Mermentau River Basin

Linda Benedict  |  4/5/2005 1:15:02 AM

The equipment includes an automated runoff collection sampler, bubble flow meter and solar panel and battery for equipment power.

Chuck Lindau, principal investigator, is trying to determine which soybean tillage practices are most effective in reducing pollution. Reducing the amount of runoff from soybean fields means less sediment, fertilizer and pesticide entering local waterways.

The instrumentation is placed around the test plots. At left is Chuck Lindau. At right is Gerry Romero.

Chuck Lindau, Pat Bollich, John J. Clark, Gerry Romero, James Leonards, Ronald Regan and Doug Walker

LSU AgCenter scientists have joined with scientists from the LSU Wetland Biogeochemistry Institute and the Louisiana Department of Environmental Quality (LDEQ) to conduct a research project to determine and demonstrate which soybean tillage practices are most effective in reducing pollution. Reducing the amount of runoff from soybean fields means less sediment, fertilizer and pesticide entering local waterways.

The project is part of LDEQ’s plan to restore waterways in the Mermentau River Basin designated impaired because of poor water quality. In 1999, the U.S. Environmental Protection Agency (EPA) designated all 20 watersheds in the basin impaired.

For every impaired water body, the Federal Clean Water Act requires development of a total maximum daily load (TMDL). A TMDL for a waterway is the maximum amount of pollutant that a waterway can receive on a daily basis and not violate its water quality standards. TMDLs have been developed for 11 of the Mermentau River Basin watersheds with pollutant load reduc-tions ranging from 30 percent to 95 percent.

Water pollution can result from point sources (primarily industrial) and nonpoint sources (primarily agricultural) located within a watershed. Sediment has been identified as one of the major pollutants of Louisiana surface water. Most sediment originates from agricul-tural practices that leave bare soil exposed to rain and wind. Runoff of sediment increases turbidity of surface water, which limits light penetration and restricts photosynthesis. Excess sediment alters oxygen production and consumption and limits the food supply for certain aquatic organisms, including fish. Increased sediment also fills streams and lakes affecting drainage capacity. Surface runoff of sediment can carry dissolved nutrients and pesticides into bayous, rivers and lakes, which may significantly affect local ecosystems.

The major crops grown in the Mermentau River Basin are soybeans and rice. The goal of this project is to determine and demonstrate which soybean tillage practices reduce surface runoff, sediment amount and nutrient levels to surface waters.

Soybean plots were established at the South Farm of the LSU AgCenter’s Rice Research Station in Crowley. The demonstration site was designed to compare three different soybean tillage practices: conventional tillage, stale seedbed and no tillage. Conventional tillage consists of six to eight trips across the field with various implements in the fall and spring to prepare a smooth, bare and weed-free seedbed. Stale seedbed tillage consists of the same general tillage practices, but after fall preparation there are no more soil-disturbing activities. No tillage is the direct seeding of a crop into previous crop residue or native vegetation. In this study the no-tillage practice consisted of soybeans planted into wheat residue.

The field site was designed to have each tillage practice separated into individual plots (0.71 acres) and replicated three times for statistical analysis. Each of the nine plots was isolated from remaining plots with earthen levees. Roundup Ready soy-beans were planted in the spring, and weeds were controlled with Roundup applied at approximately three and six weeks after planting. Other pest control was practiced according to LSU AgCenter recommendations.

Runoff from experimental plots was collected six times during the 2003 soybean season, and data is being evaluated. The project is scheduled to be completed in December 2004. Scientists hope to determine whether stale seedbed and no-tillage soybean practices are more effective than conventional tillage based on the nonpoint-source loading (sediment and nutrients) and runoff flow. Project information will then be disseminated to Mermentau River Basin soybean producers to encourage imple-mentation of best management practices.


(This article appeared in the spring 2004 issue of Louisiana Agriculture.)

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