Downward Mobility of C 14 -labeled Simazine in Dormant and Actively Growing Bermudagrass and Fallow Soil H.D. Cummings, J.B. Weber, F.H. Yelverton, R.B. Leidy, NCSU

Introduction Previous studies have characterized the downward movement of pesticides in conventional till systems. If regulatory issues of pesticides are based on downward movement of pesticides in traditional agricultural systems, they may not be appropriate for turf systems.

Introduction In turf, pesticides are rarely applied to bare soil, and compared to agriculture, knowledge is generally lacking on pesticide fate in actively growing and dormant turf. In turf, a lower fraction of pesticides reaches soil. In turf, some pesticides are absorbed and metabolized by plants (biological degradation).

Introduction Managed bermudagrass systems are stratified by pH. Thatch layers have high levels of organic matter. Organic matter and pH can influence some movement of pesticides. Thatch layers contain diverse microorganism populations. Nutrients and irrigation are applied at regular intervals to turf.

Objective To compare the downward movement of simazine in a bermudagrass system to movement in a fallow system.

Materials and Methods ‘Tifway’ hybrid bermudagrass maintained at 1.9 cm at the Sandhills Research Station near Pinehurst, NC Native soil (Candor sand) (sandy siliceous, thermic, Arenic Paleudult) (92% sand, 4% silt, 2% clay, 2% OM) (High potential for leaching)

Materials and Methods  Lysimeters (30 cm long x 15 cm in diameter) were driven into fallow soil and dormant bermudagrass in February  Three bermudagrass and three fallow soil lysimeters were placed either in a greenhouse or a cold growth chamber (5 o C).

Materials and Methods  In April, lysimeters were saturated and drained to achieve field capacity.  C 14 -labeled simazine was added at 2.2 kg ai/ha on April 8, 2004.

Materials and Methods  Immediately after application 1 cm of irrigation was applied and leachate was collected.  Every three or four days, 5 cm of irrigation was applied to each lysimeter and leachate was collected 4 hours later.  The quantity of C 14 in the leachate was determined using a scintillation counter.

Materials and Methods  After 25 days and the addition of 31 cm of irrigation, the lysimeters were harvested.  Lysimeters were divided into the following 9 increments: 0-2, 2-4, 4-6, 6-8, 8-10, 10-15, 15-20, 20-25, and cm.  Four subsamples from each increment were combusted in a Harvey ® biological oxidizer, and 14 C0 2 was captured and placed in the scintillation counter.

Combusting sample in Harvey to collected labeled CO 2 in scintillation cocktail Click pictures to see video

B A A B C NS B B A A A A B B A A A The Effect of Treatment on Leachate Volume when 5 cm of Water Applied Every 3 to 4 Days B B B B A A

Hourly Photosynthetic Active Radiation (PAR) in Greenhouse and Growth Chamber

Effect of Treatment on Amount of 14 C-Labeled Simazine in Leachate (sq. root DPM / mL) over Time

Amount of 14 C-Labeled Simazine in Roots 25 Days after Treatment (DAT) at each Soil Depth as Affected by Treatment

Amount of 14 C-Labeled Simazine in Clippings over Time

Total 14 C Simazine at Each Depth and in Verdure 25 DAT

Conclusion More water is available to move pesticides downward in winter. Capillary action may bring moisture and pesticides toward dryer soil near the surface in summer. Downward movement is more likely in fallow soil in winter than summer. Channels may form in dormant bermudagrass which may lead to rapid pesticide movement. There may be a reduction in the bioavailability of simazine with time. Simazine should be applied in Sept. rather than Nov. when bermudagrass is actively growing.