EFFECT OF SUBIRRIGATION ON THE MOBILITY OF ATRAZINE

Abstract

A three-year field lysimeter study was conducted to investigate the effect of water table management on themobility of applied atrazine in a sandy soil. The mobility of herbicide atrazine was examined under three water tablemanagement schemes: shallow subirrigation, deep subirrigation, and free drainage. Nine PVC lysimeters, 1.0 m long and0.45 m in diameter, were packed with sandy soil to a bulk density of 1350 kg/m3 and atrazine was applied to the soilsurface each summer at the rate of 2.4 kg/ha of active ingredient. Only water samples were collected in 1993 and 1994,but both water and soil were sampled and analyzed in 1995 at different time intervals. Atrazine was found to have leacheddown the soil profile, and its concentration level reduced with depth. The mass balance study showed a significantdifference in the dissipation of atrazine levels in the 0.4-m subirrigation treatment (shallow subirrigation treatment). Itdissipated more quickly under shallow subirrigation, and dissipation loss of around 96.5% were observed during thegrowing season of 1995. The contrast between the atrazine residues in the 0.4-m subirrigation versus 0.8-m subirrigationand free drainage treatment was statistically significant at the 95% level. Although relatively lower atrazine residues werefound in the 0.8 m subirrigation compared to the free drainage treatment, the contrast between them was not statisticallysignificant. This indicates that the most atrazine dissipation occurs at the soil root zone depths, and that only shallowsubirrigation could significantly reduce atrazine residues in this sandy soil by maintaining higher moisture content in thecrop root zone.