LONG-TERM TILLAGE EFFECTS ON ATRAZINE AND FLUOMETURON SORPTION IN COASTAL-PLAIN SOILS

Conservation tillage (CnT) management practices are known to increase levels of soil organic matter (SOM) in southeastern Coastal Plain soil s. Plant residues in CnT systems accumulate at the surface and, with t ime, will form a layer enriched in SOM, The authors hypothesize that h erbicide sorption will be highest in this SOM-enriched zone of CnT sys tems when compared to sorption at a similar depth in conventional till age (CT) systems. The objective was to characterize the impact of two different tillage systems, CnT and CT, on sorption of atrazine hyl-N'- (1-methylethyl)-1,3,6-triazine-2,4-diamine] and fluometuron [N,N-dimet hyl-N'-3-(trifluoromethyl)phenyl urea] in plots of Norfolk loamy sand (fine-loamy, siliceous thermic Typic Kandiudult). The plots have been under CnT and CT management for 18 yrs. Bulk (0-15 cm) and five equal incremental soil samples to a 15 cm depth were collected from 10 CnT a nd 10 CT plots, and the atrazine (ATR) and fluometuron (FLMT) sorption coefficients (K-d) were measured using batch equilibration. Significa ntly higher herbicide K-d values occurred in the CnT 0-3 cm samples, i ndicating that the highest amount of herbicide sorption occurred in th e top few cm of soil. This corresponded to the stratified soil organic carbon (SOC) contents in topsoil of the CnT plots. In addition, analy ses of covariance using SOC as the covariant to test for tillage effec ts indicated complex interactions among SOC, tillage, and depth. Those results confirm that tillage and soil depth will affect SOC contents of a Norfolk loamy sand, which correspondly will influence the magnitu de of ATR and FLMT sorption.