Downward Mobility of 14C‐Labeled Simazine in a Bermudagrass System vs. a Fallow Soil System

Abstract

Pesticides applied to bermudagrass (Cynodon dactylon L.) can be captured by the canopy, absorbed by the roots, or bound in the thatch layer, which reduces the amount available to leach compared with a fallow soil system where pesticides may be applied directly to soil. 14C‐Simazine was applied to dormant bermudagrass and fallow soil in lysimeters in a cold growth chamber (5°C) (cold‐fallow soil) and to actively growing bermudagrass and fallow soil in lysimeters in a greenhouse (25°C) (warm‐fallow soil) in April. Following clipping collection, lysimeters were irrigated with 5 cm of water every 3–4 d, and leachate was collected. After 25 d, lysimeters were divided into 2‐cm increments from 0 to 10 cm, then 5‐cm increments from 10 to 30 cm. Because of evapotranspiration, actively growing bermudagrass and warm‐fallow soil yielded significantly less leachate than dormant bermudagrass and cold‐fallow soil indicating less moisture is available for downward movement during summer. After the addition of 31 cm of irrigation, the greatest quantities of 14C‐simazine were in the 0‐ to 2‐cm increment for all treatments and decreased with depth. Although the greatest quantities of 14C‐simazine in leachate occurred in dormant bermudagrass, the reached factor was greatest for cold‐fallow soil (0.20), followed by dormant bermudagrass (0.17), warm‐fallow soil (0.16), and actively growing bermudagrass (0.14). Therefore, simazine is least mobile in bermudagrass during summer and most mobile in fallow soil in winter.