Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 1996
Publication Date: N/A
Interpretive Summary: Sustainable conservation tillage practices are needed for the 13 million acres of heavy clay soils located in the Texas Blacklands region. Water quality is a major concern with these soils because surface runoff can be very large from rains when the soils are wet. These wet conditions occur quite often in the spring when farmers are also applying herbicides for weed control. This study examined the effect of two tillage systems, a plow system which retained most of the surface residue, on losses of a herbicide (Atrazine) in surface runoff. Losses of herbicide were lower in the no-till, high-residue areas because of smaller amounts of runoff and soil losses. Herbicide losses were generally less than two percent of the amount applied in conditions which should have resulted in the largest losses possible.
The herbicide concentration and mass load of surface runoff depends, to a large extent, on soil management. This study was conducted to determine how tillage impacts herbicide runoff. Atrazine was applied at a rate of 2 kg ai ha**-1 to a Houston Black Clay soil (a fine montmorillonitic, thermic Udic Pellusterts) at the Blackland Research Center in Temple, TX. For four years, the test plot area was under continuous management using a wide-bed system with a wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum (Sorghum bicolor L.) rotation. Tillage treatments consisted of no-till or chisel-tillage. All experiments were repeated four times. A rainfall simulator with an intensity of 12.5 cm ha**-1 was used to apply rainfall events 24 hours after the atrazine applications. Sediment and runoff samples were collected during five time periods (from runoff initiation to 5, 5 to 10, 10 to 20, 20 to 30, and 30 to 40 minutes). No differences were found between treatments with respect to pesticide concentrations in the runoff water or sediment during any of the five time periods. However, crop residues prevented surface seal development and erosion resulting in reduced runoff water and sediment losses. No-tillage treatments significantly reduced the quantity of runoff, rather than the concentration of atrazine in the runoff, resulting in reduced pesticide loads in the runoff water (42 percent decrease) and sediment (77 percent decrease). As a percentage of the total amount applied, runoff water accounted for less than 2 percent of the atrazine. Sediment transported atrazine was much less important and represented only 0.03 percent of the amount applied.