Downward Mobility of CDownward Mobility of C1414-labeled -labeled

Simazine in Dormant and Actively Simazine in Dormant and Actively

Growing Bermudagrass and Growing Bermudagrass and

Fallow SoilFallow 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.

ObjectiveObjective

• 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 2004.

Three bermudagrass and three fallow soil lysimeters were placed either in a greenhouse or a cold growth chamber (5oC).

Materials and Methods

In April, lysimeters were saturated and drained to achieve field capacity.

C14-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 C14 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 25-30 cm.

Four subsamples from each increment were combusted in a Harvey® biological oxidizer, and 14C02 was captured and placed in the scintillation counter.

Combusting sample in Harvey to collected labeled CO2 in scintillation cocktail

Click pictures to see video

0100200300400500600700800900

1000

4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29

Date (month/day)

Vol

ume

(mL

)

Acrively Growing

Dormant

Warm-Fallow

Cold-Fallow

Volume AppliedB

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

AA

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

0

200

400

600

800

1000

1200

1400

1600

1800

2000

4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5

Time (month/day)

PA

R (

µm

ol /

s / m

2 )

GreenhouseGrowth Chamber

Effect of Treatment on Amount of 14C-Labeled Simazine in Leachate

(sq. root DPM / mL) over Time

0

50

100

150

200

250

300

4/5 4/7 4/9 4/11 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1

Time (month / day)

14C

-Sim

azin

e in

Lea

chat

e (S

q. R

oot

DP

M /

mL

)

Acrively GrowingDormantWarm-FallowCold-Fallow

AA

ANS

NS

B

B

B

AB

B

B

AB

BC

C

NS

NS

NS NS

NS

NSNS

NS

NS

NS

NS

NS

NS

NS

Amount of 14C-Labeled Simazine in Roots 25 Days after Treatment (DAT) at each

Soil Depth as Affected by Treatment

-14

-12

-10

-8

-6

-4

-2

0

0 1 2 3 4 5 6Log DPM g-1

Soil

Dept

h (c

m)

Actively Growing

Dormant

AB

NS

NS

NS

NS

NSNS

NS

NS

NS

NS

Amount of 14C-Labeled Simazine in Clippings over Time

Translocated Simazine in Clippings = -429.8x2 + 13738x - 57144

R2 = 0.6427

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4/10 4/12 4/14 4/16 4/18 4/20 4/22 4/24 4/26 4/28 4/30 5/2 5/4 5/6Date

14C

in C

lippi

ngs (

Log

DPM

/ g)

)

Translocated Simazine

Residual Simazine

Translocated Simazine (quadratic)

A

AB

B

C

D

E

F

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

-30

-25

-20

-15

-10

-5

0

-1 -0.5 0 0.5 1 1.5 2

Log Normalized Percent of Applied

Soil

Dep

th (c

m)

Actively Growing

Dormant

Warm Fallow

Cold Fallow

ABBCC

A

NS

NS

NS

NS

B

NS

NS

NS

BB

NS

ConclusionConclusion• 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.