ATRAZINE INCORPORATION AND SOIL EROSION: BALANCING COMPETING WATER QUALITY CONCERNS FOR CLAYPAN SOILS.

In the U.S. Corn Belt, claypan soils are vulnerable to both erosion and transport of unincorporated herbicides. Thus, there is a need to identify tillage practices that can achieve a balance between herbicide transport and soil erosion for these soils. The objectives of this research were to compare the effect of three tillage systems on sediment and atrazine transport in surface runoff for a claypan soil and to compare their agronomic utility. The tillage treatments were: (1) rotary harrow with atrazine incorporated to ~5 cm (RH), (2) no-till without incorporation (NT), and (3) minimum till with atrazine incorporated to ~10 cm (MT). Three main tillage plots were established on a Leonard silt loam (2% to 3% slopes), a typical claypan soil series. For each treatment, two sets of runoff subplots, with three replicates each, were established within the main plots. Runoff was generated with a rainfall simulator at an average rate of 27 mm h-1. Runoff samples were collected at unequal time intervals from 1 to 90 min after runoff initiation and analyzed for total suspended sediment (TSS) and dissolved-phase atrazine concentrations. The RH treatment had significantly lower mean TSS concentrations and load (0.25 g L-1 and 67 kg ha-1) than MT (0.58 g L-1 and 155 kg ha-1), but it did not significantly increase erosion compared to NT (0.16 g L-1 and 42 kg ha-1). The RH treatment also significantly decreased atrazine concentrations and relative loads compared to NT, but it did not significantly increase atrazine transport compared to ME. Average atrazine concentrations (in µg L-1) and relative loads (as a percentage of applied) were: 2100 and 22.2%for NT, 850 and 10.6% for RH, and 405 and 6.4%for MZ. The RH treatment also resulted in comparable or better grain yield than the other treatments. Results indicated that the RH treatment successfully managed the trade-off between erosion and atrazine transport and, thus, holds promise as a best management practice for claypan and related restrictive layer soils. [ABSTRACT FROM AUTHOR]