Influence of soil texture and tillage on herbicide transport

Two long-term no-till corn production studies, representing different soil texture, consistently showed higher leaching of atrazine [2-chloro-4-(ethyl amino)-6-(isopropylamino)-s-triazine] to groundwater in a silt loam soil th an in a sandy loam soil. A laboratory leaching study was initiated using in tact soil cores from the two sites to determine whether the soil texture co uld account for the observed differences. Six intact soil cores (16 cm dia by 20 cm high) were collected from a four-year old no-till corn plots at ea ch of the two locations (ca. 25 km apart). All cores were mounted in funnel s and the saturated hydraulic conductivity (K-sat) was measured. Three core s (from each soil texture) with the lowest K-sat were mixed and repacked. A ll cores were surface treated with 1.7 kg ai ha(-1) [ring-C-14] atrazine, s ubjected to simulated rainfall at a constant 12 mm h(-1) intensity until ne arly 3 pore volume of leachate was collected and analyzed for a total of C- 14. On an average, nearly 40% more of atrazine was leached through the inta ct silt loam than the sandy loam soil cores. For both the intact and repack ed cores, the initial atrazine leaching rates were higher in the silt loam than the sandy loam soils, indicating that macropore flow was a more promin ent mechanism for atrazine leaching in the silt loam soil. A predominance o f macropore flow in the silt loam soil, possibly due to greater aggregate s tability, may account for the observed leaching patterns for both field and laboratory studies. (C) 2000 Elsevier Science Ltd. All rights reserved.