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.

Bermudagrass Reseeding Intervals for Rimsulfuron, Simazine, and Sulfosulfuron

“…It was concluded that perennial ryegrass may be safely reseeded two weeks after sulfosulfuron applications at 34 or 67 g a.i./ha, but creeping bentgrass and Kentucky bluegrass may require up to four weeks to safely reestablish in treated areas. Simazine is generally safe for actively growing bermudagrass, but soil residual activity may influence turf establishment (Lawson et al, 2002;Syngenta, 2008;Cummings et al, 2009). In Georgia, simazine applied at 1.1, 2.2, or 4.4 kg a.i./ha the day of centipedegrass seeding [Eremochloa ophiuroides (Munro) Hack.]…”

“…Simazine is a photosynthesis inhibitor used for controlling numerous grassy and broadleaf weeds and may be safely applied to established bermudagrass during spring greenup (Johnson, 1982;Tworkoski et al, 2000;Syngenta, 2008). Simazine is efficacious for postemergence weed control, but treatments may also have significant soil residual activity that may affect turfgrass seedling establishment (Tworkoski et al, 2000;Cummings et al, 2009;Hixson et al, 2009). Reseeding bermudagrass over areas once occupied by patches of weeds may be desirable following rimsulfuron, simazine, or sulfosulfuron treatments.…”

Characterization, Development, and Management of Organic Matter in Turfgrass Systems

“…The percentage of bound 14 C increased with the age of the turf, which had soil carbon contents of 16.6 mg kg −1 soil for 4-yr-old turf (52% bound), 24.5 mg kg −1 for 21-yr-old turf (70% bound), and 39.0 mg kg −1 for 99-yr-old turf (71% bound). In other work with 14 C-simazine, Cummings et al (2009) indicated that applied herbicide may have adsorbed to the rhizoplane of dormant bermudagrass roots. Grass roots are reported to have a CEC of 10 to 30 cmol c kg −1 and OM has 120 to 250 or more, with most (90-100%) being pH dependent (Carrow et al, 2001).…”

“…Organic ma er binds metals (Jeong et al, 2007), inorganic nutrients (Danneberger et al, 1984;Kaiser et al, 2008;Kang et al, 2009), pesticides (Hurto and Turgeon, 1979;Balogh and Anderson, 1992;Dell et al, 1994;Lickfeldt and Branham, 1995;Cisar and Snyder, 1996;Raturi et al, 1997Raturi et al, , 2003Wu et al, 2002;Cummings et al, 2009;Hixson et al, 2009;Magri and Haith, 2009), organic compounds (Shih, 2007), and compounds such as tetracycline (Gu and Karthikeyan, 2008). In turn, OM can also be bound to soil minerals such as clays (Zhang et al, 2008;Kothawala et al, 2009).…”

“…Both low-and high-energy bonds are involved in OM adsorption processes (Balogh and Anderson, 1992;McCarty et al, 2003). Sorption of s-triazine herbicides to OM is governed by hydrogen bonding and hydrogen ion transfer between the s-triazines and the acid groups of humic substances (Cummings et al, 2009), while sorption of humic acid to clay minerals involves a combination of ionic bonds, van der Waal's interactions, and hydrogen bonds (Paul and Clark, 1996;Wang and Xing, 2005;Horwath, 2007). Addition of 14 C-simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) to sterile turfgrass soils, where microbial activity was suppressed, resulted in high levels of 14 C bound to OM, with binding directly related to the amount of OM (Hixson et al, 2009).…”