Role of organic matter, soil microorganisms, and downward mobility in determining fate of pesticides in managed turfgrass systems

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1 Role of organic matter, soil microorganisms, and downward mobility in determining fate of pesticides in managed turfgrass systems Fred H. Yelverton North Carolina State University

2 Introduction 74 agricultural chemicals have been found in groundwater of 38 states (Williams, 1988). Public concern exists over multiple pesticide applications in management of turfgrass systems. Simazine is a high-use herbicide found in groundwater (Barbash et al., 1999).

3 Downward mobility of selected herbicides applied to bermudagrass and bareground soil systems. Determine downward movement of five herbicides Golf course fairway versus bareground Actively growing versus dormant turf

4 Background Past research suggests greater downward movement occurs in bareground systems compared to turfgrass systems. Additionally, greater downward movement occurs when applied to dormant compared to actively growing turf.

5 Downward Mobility Herbicides include: atrazine mesotrione MSMA pendimethalin sulfentrazone

6 Downward Mobility Physicochemical Properties Herbicide property atrazine mesotrione MSMA pendimethalin sulfentrazon e Chemical family triazine triketone org. arsenical dinitroanaline aryl triazinone Water sol. (mg L -1 ) x 10 2 µg/g Field half life (d) 60 5 to to 302 PLP 56 (med) 39 (low) 35 (low) 20 (very low) 54 (med)

7 Downward Mobility Currently, trials have been initiated; however, no analysis have been completed.

8 Factors contributing to leaching Pesticide properties: High water solubility Low soil adsorption Long environmental persistence Soil/Site characteristics: Sand and/or gravel with low OM Shallow depth to groundwater Wet climate or extensive irrigation Management practices: Poor timing with respect to climate Overapplication!! Herbicide S w (ppm) Simazine 3-6 Atrazine 33 Metolachlo r 488 K oc DT 50 (days)

9 Schlesinger, 1977

10 Hypothesis As turfgrass soil systems age and levels of organic carbon increase, larger, more diverse soil microbial populations can be supported, causing simazine to behave differently.

11 Objectives Quantify degrees of sorption of simazine to surface soil and subsoil from a chronosequence of turfgrass systems. Characterize the role of soil inhabiting microorganisms and soil organic carbon in simazine degradation as turfgrass systems age.

12 Bulk Soil Collection and Preparation Soils were collected from four golf courses near Wilmington, NC and the NCSU turfgrass facility near Pinehurst, NC. Intact soil cores were removed from bermudagrass turf and separated into surface soil (0-5 cm) and subsoil (5-15 cm). Soil was allowed to air dry and passed through a 2 mm sieve for separation from plant material.

13 Bermudagrass Soil Profiles 4 yr. 21 yr. 99 yr.

14 Soil Properties Age Soil Depth (cm) % Carbon % OM % Clay p H Soil Texture 99 yr Sand Sand 21 yr Sand Sand 10 yr Sand Sand 4 yr Sand Sand 1 yr Sand Sand

15 Atmosphere Volatilization Photodegradation Runoff Plant uptake Surface water Sorption Leaching Degradation Soil particles Microbial and chemical Groundwater

16 Experimental Design Factorial Experimental Design = 40 total treatments 5 turfgrass system ages (1, 5, 10, 21, and 95) 4 concentrations (1, 2, 3, and 4 ppm) 2 soil depths (0-5 and 5-15 cm) Experiment was repeated Data was pooled for analysis

17 Batch-equilibrium technique Sorption was determined using 14 C- labeled/technical grade simazine. 10 ml of each solution was added to 2 g of soil in a 30 ml teflon lined centrifuge tube. Samples were shaken for 24 hrs. at 22 C. Samples were centrifuged at 6708 g for 10 minutes.

18 Measurements and Statistical Analysis Radioactivity in two 1-ml aliquots of supernatant was quantified using liquid scintillation counting (Packard 2000CA). Simazine distribution between sorbed and solution phases was described by the Freundlich equation: S = K f C 1/n S = amount of simazine sorbed (nmole/g) C = solution concentration (nmole/ml) K f and 1/n are empirical constants derived by nonlinear regression techniques.

19 Surface Soil Simazine Sorbed ( mol kg -1 ) 60 1 yr. 4 yrs. (7.2) yrs. (5.3) 21 yrs yrs. (4.3) pine (3.8) 30 bare r 2 > 0.95 (2.0) (1.9) (0.7) Equilibrium Concentration ( mol L -1 )

20 Simazine Sorbed ( mol kg -1 ) r 2 > 0.95 Subsoil (9.1) (8.3) (2.8) (2.3) (2.4) 1 yr. 4 yrs. 10 yrs. 21 yrs. 99 yrs. pine bare (0.8) (0.3) Equilibrium Concentration ( mol L -1 )

21 Simazine Sorbed ( mol kg -1 ) Surface vs. Subsoil r 2 > yrs (0-5 cm) 95 yrs (5-15 cm) 10 yrs (0-5 cm) 10 yrs (5-15 cm) Equilibrium Concentration ( mol L -1 )

22 Atmosphere Volatilization Photodegradation Runoff Plant uptake Surface water Sorption Leaching Degradation Soil particles Microbial and chemical Groundwater

23 Experimental Design Factorial Experimental Design = 16 total treatments 3 turfgrass ages (5, 21, and 95) + 1 pine area 2 soil treatments (non-sterile and sterile) 2 soil depths (0-5 and 5-15 cm) Experiment was repeated Data was pooled for analysis

24 Microcosm Design Incubation periods (0, 1, 2, 4, 6, 9, 12, 16 wks) Sodium Hydroxide (CO 2 Sink) 14 CO 2 14 CO 2 Extractable Pesticide Bound Pesticide 1 WAT 2 WAT 4 WAT 6 WAT } 10 g dry wt. soil

25 Extraction Procedure Simazine was extracted (shaken) from soil for 4 hours using methanol Extractions were concentrated to 10 ml using a rotary evaporator

26 Analysis of CO 2 & Bound Residues Bound residues Extracted soil was air dried and finely ground. Duplicate 1 g subsamples were oxidized. CO 2 Evolution 14 CO 2 was measured from 1 ml aliquots of NaOH trapping solution. Total CO was measured

27 Nonsterile % of 14 C Applied [ 14 C-Simazine] yrs. 21 yrs yrs. pine yrs. 21 yrs yrs. pine cm 5-15 cm 0-5 cm 5-15 cm 4 yrs. 21 yrs. 99 yrs. pine 4 yrs. 21 yrs. 99 yrs. pine Incubation Time (weeks)

28 Sterile % of 14 C Applied [ 14 C-Simazine] yrs. 21 yrs yrs. pine yrs. 21 yrs yrs. pine cm 5-15 cm 0-5 cm 5-15 cm 4 yrs. 21 yrs. 99 yrs. pine 4 yrs. 21 yrs. 99 yrs. pine Incubation Time (weeks)

29 Cumulative 14 CO 2 % [ 14 C] CO 2 of Applied [ 14 C-Simazine] yrs. 21 yrs yrs. pine yrs. 21 yrs yrs. pine % 14 CO 2 week yrs. 21 yrs. 99 yrs. pine 4 yrs. 21 yrs. 99 yrs. pine Incubation Time (weeks) Incubation Time (weeks)

30 Soil Half-Life (weeks) 0-5 cm 5-15 cm Location Nonsterile Sterile Nonsterile Sterile 4-yr turf yr turf 99-yr turf Pine

31 Summary As turfgrass systems age, simazine sorbed readily to increasing levels of organic matter. Simazine sorption decreased with depth in all soil systems except the 95 year-old bermudagrass system. While 14 CO 2 evolution was similar at both soil depths in the oldest turfgrass system, disparity occurred between soil depths in the two younger systems. Half-lives were very low in nonsterile surface soil due to high microbial degradation and sorption.

32 Conclusions As turfgrass systems age, simazine binds readily to increasing levels of organic matter and may be less available to microorganisms for breakdown. If simazine is able to move below the 5 cm depth in the soil profile, sorption may be delayed and opportunity for leaching could occur. Newly constructed turfgrass systems on coarse textured soil could be more susceptible to downward movement of simazine.

33 Acknowledgements Center for Turfgrass Environmental Research and Education (CENTERE) at North Carolina State University