runoff losses of atrazine and terbutryn from unlimed and limed soil

4
(4) Guiliani, A. J. “Methane Recovery From a Shallow Landfill: Experience at the Fresh Kills, Staten Island, N.Y.”; Symposium Proceedings, Methane from Landfills: Hazards and Opportuni- ties, Denver, CO, March 21-23, 1979. (5) Lu, A. H.; Kunz, C. “Tranducer Measurement of Landfill Gas Pressure”; Symposium Proceedings, Methane from Landfills: Hazards and Opportunities, Denver, CO, March 21-23,1979. (6) Kunz, C.; Lu, A. H., “Flux-Box Measurement of Methane Ema- nation from Landfills”; Symposium Proceedings, Methane from Landfills: Hazards and Opportunities, Denver, CO, March 21-23, 1979. Received for review December 17,1979. Accepted December I, 2980. This project has been partially funded by the New York State En- ergy Research and Development Authorzty. Runoff Losses of Atrazine and Terbutryn from Unlimed and Limed Soil John D. Gaynor”? and V. V. Volk Department of Soil Science, Oregon State University, Corvallis, Oregon 97331 Atrazine (2-chloro-4-(ethylamino) -6-(isopropylamino) - s -triazine) and terbutryn (2-( tert -butylamine) -4-(ethyl- amino)-6-(methylthio)-s -triazine) leaching and loss by surface runoff waters and sediment were measured under simulated rainfall conditions from unlimed and limed Peavine silt loam soil. Application of 7 cm of water produced 2-14% runoff water from the unlimed soil and little (1-3%) or no runoff from the limed soil. Sediment losses were low, averaging 16 kg/ha. Terbutryn was adsorbed by the soil (98%)to a greater extent than atrazine (60%);hence, the eroded sediments contained higher concentrations of terbutryn than atrazine. The amount of terbutryn and atrazine in the runoff water and sediment from simulated sample applied 12 h after herbicide applica- tion was only 0.3 and 3.7%, respectively, of that applied. Of that amount, soil transport accounted for 1-3% of the s-tria- zine in the runoff. Recoveries of atrazine and terbutryn were similar on unlimed and limed soil except for atrazine on un- limed soil. Atrazine recovered after 12 days was 25 and 74% of that applied to the unlimed and limed soil, respectively. Introduction The s -triazine herbicides applied directly to soil or foliage for broadleaf weed and annual grass control constitute one of the most widely used families of herbicides. With their use under many different soil conditions, s-triazine may move to adjacent fields and waterways by surface runoff and by leaching to ground water. Many environmental and edaphic factors in addition to the chemical and physical properties of the herbicides interrelate to affect runoff losses (1-4). Atrazine loss after a normal and an intensive simulated rainfall averaged 4 and 17%,respec- tively, while delaying rainfall for 96 h after atrazine applica- tion reduced runoff losses 50% (5). Under natural rainfall conditions, annual losses of atrazine by surface runoff and sediment transport averaged 2.6% (6). Most of the loss oc- curred during the first month after herbicide application, with losses in the aqueous phase of runoff exceeding those associ- ated with the sediment phase. When rainfall occurred closer to application date, 5% of the added atrazine was lost in sur- face runoff but only 0.02-0.03% of a methoxy-s-triazine (N- ethyl - 6 -methoxy-N-( 1 - methylpropyl) - 1,3,5-triazine-2,4- diamine) was lost (7). In another study, more prometryn (2,4-bis( isopropylamino) -6-( methylthio) -s -triazine) was lost from moist soil than dry soil presumably because of decreased adsorption sites, but rainfall intensity did not affect losses (8). + Present address: Res. Stn., Agriculture Canada, Harrow, Ontario NOR 1G0, Canada. Similarly, leaching of s -triazine herbicides is related to solubility, formulation and application rate, adsorption, soil moisture content, and infiltration rate of the soil. s-Triazine mobility increases with a decrease in the clay fraction in soils (9), but high adsorption and low solubility of the s-triazine herbicides generally prevents leaching to depths greater than 15 cm (9,10).Leaching in fine textured soils to depths greater than the plow layer has been observed when rainfall averaged 70 cm and high rates (>4 kg/ha) of simazine (2-chloro-4,6- bis(ethy1amino)-s-triazine) or atrazine were applied (9). Leaching up to 20 cm has been reported in coarse textured soils at application rates of <4 kg/ha, but usually the highest concentration of the compound was found in the top 8 cm. Several studies (10-13) suggest that maximum adsorption of the s-triazines occurs at or near the vicinity of their ph, value. Thus, for atrazine (ph, = 1.68) and terbutryn (ph, = 4.10) lime would be expected to decrease both adsorption and sediment phase losses and increase aqueous phase losses. This research was conducted to compare runoff losses for atrazine and terbutryn from unlimed and limed soil after a simulated rainfall and to relate runoff results, leaching, and persistence to the adsorption of these herbicides by the soil. Experimental Section Four plot areas (3 X 9 m) of a well-drained Peavine silt loam soil with a 3-5% north-facing slope were rototilled to a depth of 15 cm. After rototilling, excess plant material was removed and the plot areas were leveled to a uniform slope (-3%). Lime (11.2 metric tons/ha) was rototilled into two of the four areas and allowed to react with the moist soil for 2 weeks prior to herbicide application. Atrazine or terbutryn, 3.6 kg/ha active ingredient in an 80% wettable powder formulation, were applied (425 L of water/ha) to the limed and unlimed plots with a bicycle-plot sprayer. Immediately after the herbicide application, three plot frames (1.16 m square X 20.3 cm high) fitted with holes for runoff collection (14) were equally spaced in each plot area and set to a depth of 10 cm at a radius of 3.8 m from the water source (Figure 1). Rubber hoses were connected to the runoff holes to channel surface water and sediment to a 15-L cali- brated collection container. The three plot frames on each treatment area constituted replications for runoff collection. Only two plot frames were installed on the unlimed plot which was treated with atrazine. Water applications (7 cm) were made 12 h and 8 days after chemical application. Water was applied at a rate of 3.1 cm/h through a 64-mm nozzle at 262 kPa. Because water had to be transported to the site, three 15-min refill periods were re- quired before all water was applied. The actual amount of water applied to each area was calculated from calibrated 440 Environmental Science & Technology 0013-936X/81/0915-0440$01.25/0 @ 1981 American Chemical Society

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(4) Guiliani, A. J. “Methane Recovery From a Shallow Landfill: Experience a t the Fresh Kills, Staten Island, N.Y.”; Symposium Proceedings, Methane from Landfills: Hazards and Opportuni- ties, Denver, CO, March 21-23, 1979.

(5) Lu, A. H.; Kunz, C. “Tranducer Measurement of Landfill Gas Pressure”; Symposium Proceedings, Methane from Landfills: Hazards and Opportunities, Denver, CO, March 21-23,1979.

(6) Kunz, C.; Lu, A. H., “Flux-Box Measurement of Methane Ema- nation from Landfills”; Symposium Proceedings, Methane from Landfills: Hazards and Opportunities, Denver, CO, March 21-23, 1979.

Received for review December 17,1979. Accepted December I , 2980. This project has been partially funded by the New York State En- ergy Research and Development Authorzty.

Runoff Losses of Atrazine and Terbutryn from Unlimed and Limed Soil

John D. Gaynor”? and V. V. Volk Department of Soil Science, Oregon State University, Corvallis, Oregon 97331

Atrazine (2-chloro-4-(ethylamino) -6- (isopropylamino) - s -triazine) and terbutryn (2-( tert -butylamine) -4-(ethyl- amino)-6-(methylthio)-s -triazine) leaching and loss by surface runoff waters and sediment were measured under simulated rainfall conditions from unlimed and limed Peavine silt loam soil. Application of 7 cm of water produced 2-14% runoff water from the unlimed soil and little (1-3%) or no runoff from the limed soil. Sediment losses were low, averaging 16 kg/ha. Terbutryn was adsorbed by the soil (98%) to a greater extent than atrazine (60%); hence, the eroded sediments contained higher concentrations of terbutryn than atrazine. The amount of terbutryn and atrazine in the runoff water and sediment from simulated sample applied 12 h after herbicide applica- tion was only 0.3 and 3.7%, respectively, of that applied. Of that amount, soil transport accounted for 1-3% of the s-tria- zine in the runoff. Recoveries of atrazine and terbutryn were similar on unlimed and limed soil except for atrazine on un- limed soil. Atrazine recovered after 12 days was 25 and 74% of that applied to the unlimed and limed soil, respectively.

Introduction The s -triazine herbicides applied directly to soil or foliage

for broadleaf weed and annual grass control constitute one of the most widely used families of herbicides. With their use under many different soil conditions, s-triazine may move to adjacent fields and waterways by surface runoff and by leaching to ground water.

Many environmental and edaphic factors in addition to the chemical and physical properties of the herbicides interrelate to affect runoff losses (1-4). Atrazine loss after a normal and an intensive simulated rainfall averaged 4 and 17%, respec- tively, while delaying rainfall for 96 h after atrazine applica- tion reduced runoff losses 50% (5). Under natural rainfall conditions, annual losses of atrazine by surface runoff and sediment transport averaged 2.6% (6). Most of the loss oc- curred during the first month after herbicide application, with losses in the aqueous phase of runoff exceeding those associ- ated with the sediment phase. When rainfall occurred closer to application date, 5% of the added atrazine was lost in sur- face runoff but only 0.02-0.03% of a methoxy-s-triazine ( N - ethyl - 6 -methoxy-N-( 1 - methylpropyl) - 1,3,5-triazine-2,4- diamine) was lost (7). In another study, more prometryn (2,4-bis( isopropylamino) -6-( methylthio) -s -triazine) was lost from moist soil than dry soil presumably because of decreased adsorption sites, but rainfall intensity did not affect losses (8).

+ Present address: Res. Stn., Agriculture Canada, Harrow, Ontario NOR 1G0, Canada.

Similarly, leaching of s -triazine herbicides is related to solubility, formulation and application rate, adsorption, soil moisture content, and infiltration rate of the soil. s-Triazine mobility increases with a decrease in the clay fraction in soils (9), but high adsorption and low solubility of the s-triazine herbicides generally prevents leaching to depths greater than 15 cm (9,10). Leaching in fine textured soils to depths greater than the plow layer has been observed when rainfall averaged 70 cm and high rates (>4 kg/ha) of simazine (2-chloro-4,6- bis(ethy1amino)-s-triazine) or atrazine were applied (9). Leaching up to 20 cm has been reported in coarse textured soils a t application rates of <4 kg/ha, but usually the highest concentration of the compound was found in the top 8 cm.

Several studies (10-13) suggest that maximum adsorption of the s-triazines occurs a t or near the vicinity of their ph, value. Thus, for atrazine (ph, = 1.68) and terbutryn (ph, = 4.10) lime would be expected to decrease both adsorption and sediment phase losses and increase aqueous phase losses.

This research was conducted to compare runoff losses for atrazine and terbutryn from unlimed and limed soil after a simulated rainfall and to relate runoff results, leaching, and persistence to the adsorption of these herbicides by the soil.

Experimental Section Four plot areas (3 X 9 m) of a well-drained Peavine silt loam

soil with a 3-5% north-facing slope were rototilled to a depth of 15 cm. After rototilling, excess plant material was removed and the plot areas were leveled to a uniform slope (-3%). Lime (11.2 metric tons/ha) was rototilled into two of the four areas and allowed to react with the moist soil for 2 weeks prior to herbicide application.

Atrazine or terbutryn, 3.6 kg/ha active ingredient in an 80% wettable powder formulation, were applied (425 L of water/ha) to the limed and unlimed plots with a bicycle-plot sprayer.

Immediately after the herbicide application, three plot frames (1.16 m square X 20.3 cm high) fitted with holes for runoff collection (14) were equally spaced in each plot area and set to a depth of 10 cm a t a radius of 3.8 m from the water source (Figure 1). Rubber hoses were connected to the runoff holes to channel surface water and sediment to a 15-L cali- brated collection container. The three plot frames on each treatment area constituted replications for runoff collection. Only two plot frames were installed on the unlimed plot which was treated with atrazine.

Water applications (7 cm) were made 12 h and 8 days after chemical application. Water was applied a t a rate of 3.1 cm/h through a 64-mm nozzle a t 262 kPa. Because water had to be transported to the site, three 15-min refill periods were re- quired before all water was applied. The actual amount of water applied to each area was calculated from calibrated

440 Environmental Science & Technology 0013-936X/81/0915-0440$01.25/0 @ 1981 American Chemical Society

containers placed along arcs (5 c a d a r c ) 3.1, 3.8, and 4.6 m from the sprinkler head.

The amount of runoff water collected after each water ap- plication was volumetrically measured. Eroded sediments were determined gravimetrically after separation from the runoff water by decantation and filtration.

One-liter aliquots of runoff water from the plots which were treated with atrazine were extracted twice with chloroform (1:1, water-chloroform) in a 1-L separatory funnel. Aqueous ammonia (1 mL) was added to the water samples from the terbutryn-treated plots before chloroform extraction (8:1, water-chloroform) (15) . The chloroform extracts were dried, and the residue was transferred with 2 mL of benzene to 180 X 20 mm chromatographic columns containing 12.5 g of basic alumina (Activity V) (16). The columns were leached with 75 mL of n-hexane (85%) followed by elution of the s-triazines with 150 mL of benzene-n-hexane ( l : l , v/v).

Following the alumina cleanup, the benzene-n-hexane el- uate was dried and the residue transferred with acetone to 25-mL glass-stoppered Erlenmeyer flasks. After the samples were dried, 10 mL of HzS04 (1 and 2 N for terbutryn and atrazine, respectively) were added, and the samples hydro- lyzed in a water bath at 90 OC for 3 h. After cooling, the acid hydrolyzate was extracted with 50 mL of reagent-grade chloroform, and the hydroxy-s -triazine in the acid media analyzed on a Cary Model 11 ultraviolet spectrophotometer a t 240,225, and 255 nm. The concentration of s-triazine was calculated by utilizing the base-line technique for background correction (1 7).

Atrazine and terbutryn recovery from the water samples averaged 67 & 10% and 24 f 8%, respectively. Chemical re- covery was calculated from results obtained when 100 pg of compound was added to 1 L of water which was processed the same as all water samples. The detection limit in water was 0.02 ppm for atrazine and 0.06 ppm for terbutryn.

Twenty-four hours after water application, soil samples a t 8-cm increments to a total depth of 45 cm were collected from four locations in each treatment area (Figure 1). The soil moisture content was determined, and the samples were stored moist a t 1 "C to reduce herbicide volatilization ahd degradation losses.

Sufficient moist soil to give 50 g of oven-dry soil was ad- justed to 30% moisture content (w/w) and extracted on a shaker for 24 h with 100 mL of reagent-grade methanol. Aqueous ammonia (1 mL) was added to the soil-methanol mixtures from plots treated with terbutryn. The soil recovered from the water samples was dried a t 70 "C and extracted similarly. After extraction, the samples were suction filtered and leached with an additional 100 mL of methanol. Cleanup with basic alumina and analysis of the hydrolyzate were per- formed as described for water samples. Atrazine and terbutryn recovery percentages were determined by addition of 50 pg of each chemical to a 50-g soil sample from each horizon. The treated samples were processed the same as samples collected from the field. Terbutryn recovery ranged from 69 f 9.9% to 83 f 2.3%, and atrazine recovery ranged from 53 f 0.4% to 56 f 2.2% for horizons of limed and unlimed soil. Hydrolyzed s-triazines extracted from the soil are removed during the cleanup process.

Atrazine and terbutryn adsorption by the soil was deter- mined by treating duplicate 5-g samples of air-dry soil from various depths from the unlimed and limed plots for 12 h with ,5 ppm I4C-ring-labeled atrazine or terbutryn (soil-solution ratio, 1 2 ) a t 25 "C in a shaking water bath.

The supernatant solution was separated by centrifugation for 20 min a t 12.5 X 103 g. A 1 -mL aliquot of the supernatant solution was assayed for s-triazine in a toluene-Triton X-100 (21, v/v) scintillant (18) by liquid scintillation spectropho- tometry. Adsorption was calculated by difference in activity before and after equilibration.

Results and Discussion Runoff Losses. Each of the plot areas received similar

amounts of water except for the first water application to the unlimed plot treated with atrazine (Table I); consequently, less runoff water was collected in comparison to the other unlimed plots. Compared to the amount of water applied, runoff was low, representing 0-14% of that applied. The 15- min intervals in water application, because of refill of the water reservoir, probably reduced the total runoff volume. In effect, each application period represented four 30-min storms of 3.1 cm/h intensity in a period of 2.75 h.

Runoff from unlimed soil was greater than from limed soil presumably because of the beneficial effect of CaC03 on the soil microstructure which increased water infiltration (19). Herbicide treatment would not be expected to affect soil structure. Sediment losses among treatments were significant a t the 5% level ( F = 3.24, degrees of freedom = 7, 14), but means were not separated by the Studentized Range $-Test (Table I). Generally more soil was lost during the second water application and from unlimed soil.

The concentration of terbutryn in the runoff water and sediment from the unlimed plots was higher for the first than for the second water application (8 days apart), whereas atrazine concentration was similar for the two events (Table 11). Considering only the solubilities of the two herbicides, 34 ppm for atrazine and 35 ppm for terbutryn, no concentration difference in the runoff water would be expected. Atrazine, however, is not sorbed as extensively by the soil (Table 111); thus the lower concentration of atrazine in the runoff water suggests more rapid downward movement from the erodible soil surface compared to terbutryn. Atrazine may also convert to the less soluble hydroxyatrazine. Since atrazine is more readily desorbed than terbutryn (20), higher terbutryn con- centrations would be expected to persist in the surface soil. Most water applied to the study areas moved through the soil, thus providing a transport medium for herbicide leaching.

The concentration of the two herbicides in the runoff water after the second simulated rainfall 8 days after the herbicides were applied was similar. The lower terbutryn loss for the

A SOIL PROFILE SAMPLE LOCATIONS

0 CALIBRATED R A I N F A L L COLLECTION CANS

I I

1 1 6 M

\- \ \

RUNOFF CO L LECTl ON

WATER SUPPLY

Figure 1. Location of plot frames within a treatment area

Volume 15, Number 4, April 1981 441

Table 1. Surface Runoff and Sediment Losses from Unlimed and Limed Peavine Soil

parameter

water applied, cm

water runoff, cm

chemical applied

t h e s h e application unllmed soil a limed so11 a

12 h 8 days 12 h 8 days

atrazine 5.5 b terbutryn 7.3 a

6.9 a 7.7 a

7.4 a 7.3 a 8.0 a 7.0 a

atrazine 0.1 c 0.5 abc o c 0.2 bc

terbutryn 0.8 ab 1.1 a o c <0.1 c range 0.02-0.14 0.2-0.8 0 0.01-0.6

range 0.2-1.1 1 .O-1.3 0 0-0.02

sediment loss, kg/ha atrazine 5.6 a 32.1 a Oa 26.3 a

terbutryn 25.5 a 40.8 a Oa 0.4 a range 5.3-5.9 18-46.2 0 0.8-60.9

range 7-36.4 24.3-56 0 0-0.7

a Means followed by same letter within each parameter are not significantly different at 5 % level (Studentized Range Q-Test).

Table II. Atrazine and Terbutryn Losses in Runoff Water atid Sediment from Peavine Soila chemlcal assoclated wlth: chemical recovered in:

tlme after water sedlment sum water sediment sum appiicatlon g/ha ppm g/ha ppm glha Oh Yo Yo

Atrazine unlimed 12 h 6.7 a 0.6 a Oa Oa 6.7 a 0.3 ab Oa 0.3 ab

8 days 15.2 a 0.4 a 0.5 ab 21.0a 15.7 a 1.6 ab 0.05 b 1.7 ab

_ _ L - - -

range 0.4-13 0.3-0.9 0 0 0.4-13 0.2-0.6 0 0.02-0.6

range 10.7-19.7 0.2-0.5 0.3-0.6 6.2-35.7 11.3-20 1.2-2.1 0.03-0.07 1.3-2.1

limed 12 h b 0 0 0 0 0 0 0 0 8 days 1.5 a 0.2 a <0.1 a 0.9 a 1.6 a <0.1 a <0.01 a <0.1 a

range 0.2-3.2 0.02-0.3 0-0.2 0-2.8 0.2-3.2 0.01-0.1 0-0.01 0.01-0.1

Terbutryn unlimed 12 h 116.4 b 1.5 b 1.1 b 44.4 b 117.4 b 3.7 b 0.03ab 3.7 b

8 days 26.7 a 0.3 a 0.4 a 9.0 a 27.1 a 0.9 ab 0.01 ab 1.0 a range 31.6-202 1.3-1.8 0.4-1.7 29.2-52.6 32-203.7 1.0-6.4 0.01-0.05 1.0-6.5

range 14.4-33.4 0.2-0.3 0.2-0.5 7.8-9.6 14.6-33.9 0.5-1.2 0.01-0.02 0.5-1.2

limed 12 h b 0 0 0 0 0 0 0 0 8 days 0.3 a 0.2 a Oa Oa 0.3 a <0.1 a Oa <0.1 a

range 0-0.7 0-0.3 0 0 0-0.7 0-0.02 0 0-0.02

a Values corrected for recovery percentage. Means within columns followed by the same letter are not significantly different at the 5 % level (Studentized Range Q-Test). No runoff from plots. Values not included in statistical analysis.

Table 111. Chemical Properties and s-Triazine Adsorption on Peavine Silt Loam Soil catlon exchange capacity,

depth, cm PH carbon, % mequiv/l00 g

Unlimed Soil 0-8 5.4 2.6 11.9 8-16 5.6 2.5 12.6

16-24 5.6 1.1 15.0

0-8 7.2 8-16 6.9

16-24 6.4

Limed Soil 2.6 25.0 2.5 17.6 1.1 15.9

s-trlarlne adsorbed, % atrazine terbutryn

65 f 0.1 59 f 1.0 57 f 0.2

98 f 0 96 f 0.1 98 f 0

56 f 0.4 56 f 0.7 68 f 0.2

86 f 0.1 91 f 0.1 97 f 0.1

second simulated rainfall implies that terbutryn was leached from the surface-erodible zone in the first water applica- tion.

The amount of s-triazine recovered in the water and sedi- ment fractions was small compared to the total amount re- covered from the soil profile even though conditions were optimum (i.e., high-intensity storm soon after application) for runoff to occur (Table 11). Higher concentrations of atra- zine and terbutryn were found on the sediment than in the water, but more herbicide was removed with the aqueous phase because of the greater volume of runoff water (Table 11). Less than 0.05% of the total s-triazine added was removed with the sediment.

For the study area, the 30-yr average monthly rainfall in the spring when herbicides are likely to be applied is 6.8 cm at an intensity of 0.5 cm/h, well below the conditions used in this study. These results confirm previous studies which show that for these herbicides control of water runoff is most effective to reduce herbicide losses. Lime application to the Peavine soil appears to have improved soil structure, thus reducing runoff and herbicide loss a t the critical period when the po- tential for herbicide loss was highest.

Leaching and Persistence. Atrazine appeared to degrade readily in the unlimed soil (Table IV). Ca. 60% of the applied atrazine was recovered from the soil profile 3 days after ap- plication, whereas only 25% was recovered after 12 days.

442 Environmental Science & Technology

Table IV. Recovery and Distribution (ppm) of Atrazine in Peavine Soila

days since appllcation depth, unllmed llmed

cm 7 - 0-8 2.6 a 1.0 b 2.5 a 2.3 a 8-16 0.1 b 0.2 b 0.6 b 0.6 b

16-24 <0.1 b <0.1 b 0.1 b 0.3 b

recovery, % 60 a 25 b 73 a 74 a

letter are not significantly different at 5% level (Studentized Range Q-test). a Values corrected for recovery percentage. Means followed by the same

Table V. Recovery and Distribution (ppm) of Terbutryn in Peavine Soil a

days after chemlcal appllcatlon depth, unllmed limed

cm - - 0-8 3.2 a 3.1 a 3.3 a 3.6 a 8-16 0.6 b 0.3 b 0.4 b 0.5 b

16-24 <0.1 b 0.1 b 0.1 b 0.2 b recovery, % 85 a 77 a 84 a 96 a

letter are not significantly different at 5 % level (Studentized Range Q-Test). a Values corrected for recovery percentage. Means followed by the same

Atrazine recovery from the limed soil 10 days after application averaged 74%. The low recovery of atrazine from the unlimed soil is probably due to chemical degradation to the nonphy- totoxic hydroxyatrazine ( 1 0 , 2 1 , 2 2 ) .

The atrazine was recovered primarily from the top 8 cm of the unlimed soil profile (Table IV), and no atrazine was found below 15 cm. Upon addition of lime, higher concentrations of atrazine were found below 8 cm, but sample variability pre- cluded significance a t the 5% level.

A higher percentage of terbutryn than atrazine applied to the unlimed and limed soil was recovered, indicating that soil pH had less effect on terbutryn persistence and that terbutryn was more persistent than atrazine (Table V). The adsorbed terbutryn was probably not hydrolyzed in the acid soil as was noted for atrazine. The high recovery of terbutryn from the soil suggests that the reduction in terbutryn runoff losses re- corded after the second water application (Table 11) did not occur because of compound degradation but rather that ter- butryn had moved from the erodible zone of the soil profile (Table V). On the unlimed soil, no terbutryn was recovered below 15 cm after the first water application period, but some terbutryn, 4%, was recovered at this depth after the second water application. Lime had little effect on the distribution and persistence of terbutryn in the soil. Since terbutryn was more persistent than atrazine, the addition of more water could possibly lead to significant slow leaching.

The higher concentrations (>3 ppm) of terbutryn in the surface horizon of the soil profile could be anticipated from the adsorption data (Table 111). Although atrazine and ter-

butryn adsorption by the surface soil was reduced similarly (8 and 12%) by addition of lime, leaching appeared to occur to a greater extent with atrazine because of its lower adsorp- tion (65% and 98%, respectively).

In conclusion, the potential for terbutryn loss on trans- ported soil exceeds that for atrazine under comparable con- ditions (Table 11) because of higher terbutryn adsorption. The relative loss of these two compounds by sediment transport and in runoff water will depend upon the sediment load in the runoff water and the proximity of the rainfall event to herbi- cide application time. Even though the herbicide concentra- tion in runoff water may be lower than on sediments, signifi- cant total herbicide loss in the aqueous fraction may occur with large runoff events.

The results emphasize that solubility and the adsorption capacity of the soil for the herbicide must be considered to- gether to predict herbicide losses in runoff. A lime application appeared to improve the microstructure of the Peavine soil and increase water infiltration which reduced the amount of early surface runoff when herbicide loss usually would be greatest. Lime also appeared to increase the persistence of atrazine, extending its availability for surface loss. Lime ap- plications did not affect terbutryn persistence or redistribu- tion in the soil, whereas atrazine leaching increased with an increase in soil pH.

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(2) Hall, J. K.; Hartwig, N. L. J . Enuiron. Qual. 1978,7,63-8. (3) Triplett, G. B., Jr.; Conner, B. J.; Edwards, W. M. J . Enuiron

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(6) Hall, J. K.; Pawlus, M.; Higgins, E. R. J . Enuiron. Qual. 1972,I ,

(7) Hall, J. K. J . Enuiron. Qual. 1974,3, 174-80. (8 ) Baldwin, F. L.; Santelmann, P. W.; Davidson, J. M. Weed Sci.

(9) Helling, C. S. Residue Reu. 1970,32,175-210. (10) Best, J. A.; Weber, J. B. Weed Sci. 1974,22, 364-73. (11) Weber, J. B. Soil Sci. SOC. Am. J . 1970,34,401-4. (12) Weber, J. B.; Weed, S. B.; Ward, T. M. Weed SCL. 1969, 17,

(13) Nearpass, D. C. Weeds 1965,13,341-6. (14) Dixon, R. M.; Peterson, A. E. Wisconsin Exp. Sta. Research

(15) Abbott, D. C.; Bunting, J. A.; Thomson, J . (London) Analyst

(16) Mattson, A. M.; Kahrs, R. A.; Murphy, R. T. Residue Reo. 1970,

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Received for reuiew April 4, 1980. Accepted November 24, 1980. Oregon Agricultural Experiment Station Technical Paper 5447.

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