Agriculture, Ecosystems and Environment, 18 (1987) 273-280 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

273

Atrazine and Simazine in Runoff from Conventional and No-till C&n Watersheds

SCOTT GLENN and J. SCOTT ANGLE

Department of Agronomy, University of Maryland, College Park, MD 20742 (U.S.A.)

(Accepted for publication 10 September 1986)

ABSTRACT

Glenn, S. and Angle, J.S., 1987. Atrazine and simazine in runoff from conventional and no-till corn watersheds. Agric. Ecosystems Environ., 18: 273-280.

A study was initiated to compare the surface runoff of atrazine and simazine from adjacent conventional tillage (CT) and no-tillage (NT) corn watersheds that were otherwise identical. Runoff was collected in H-type flumes and Coshocton wheels. Atrazine [ 2-chloro-4- (ethylam- ino) -6- (isopropylamino) -s-triazine] and simazine [ 2-chloro-4,6-bis(ethylamino) -s-triazine] were applied at 2.2 kg a.i. ha-’ to both watersheds annually from 1979 to 1982.

There was less runoff of water, atrazine and simazine from the NT watershed compared to the CT watershed each year that a major runoff event occurred during the growing season. Between 1979 and 1982, total volume of runoff was 27% less from the NT compared to the CT watershed. Most of the herbicide loss in surface runoff occurred during the first runoff event after application. The concentration of simazine in runoff was much less than that of atrazine. The greatest runoff of herbicides occurred in 1979 when 1.6 and 1.1% of the atrazine applied moved from the CT and NT watershed, respectively, and 0.52 and 0.36% of the simazine applied moved from the CT and NT watershed, respectively.

INTRODUCTION

There have been numerous studies to evaluate the runoff of herbicides from agricultural land. Most of the triazine herbicide loss in runoff was found to be in the water phase (Hall, 1974; Ritter et al., 1974; Leonard et al., 1979). Wauchope (1978)) in a review article concerning herbicide runoff, concluded that the most important runoff events are those that occur within approxi- mately 2 weeks of application. Atrazine seasonal losses in runoff ranged from 0.19 to 15.9% ( Wauchope, 1978). Seasonal loss of simazine has been found to be 3.5% (Edwards, 1972).

In Quebec, Muir et al. (1978) found an average loss of 1.7% of the amount of atrazine applied in watersheds with cultivated areas ranging from 22 to 129 km’. Atrazine concentrations in rivers draining these watersheds ranged from

0167-8809/87/$03.50 0 1987 Elsevier Science Publishers B.V.

274

0.01 to 27 pm 1-l. There was no evidence that proximity of corn fields to streams caused higher herbicide levels. In a 3-year study, Glotfelty et al. (1983 ) meas- ured the amount of atrazine and simazine in the Wye River, a tributary of the Chesapeake Bay. They reported that in a year in which significant rainfall occurred within 2 weeks of application 2-3% of the atrazine applied moved to the estuary, but in other years with less runoff in the critical 2 weeks after application, lesser quantities reached the estuary. Simazine loading was one- tenth that of atrazine.

Ritter et al. (1974) greatly reduced runoff volumes by use of ridged corn planting rather than contour-tillage only. Reductions in atrazine losses were proportional to reduced runoff. Runoff of alachlor [ 2-chloro-2’,6’diethyl-N- (methoxymethyl) acetanilide] and cyanazine { 2- [ [ 4-chloro-6- ( ethylamino ,I. S-triazin-2-yl] amino] -2-methylpropionitrile} from small plots exposed to six different cultural practices were not greatly affected by these practices (Baker et al., 1976). Triplett et al. (1978) examined runoff of atrazine and simazine from eight conventional and 14 no-till watersheds for three years in Ohio. They found that losses of atrazine and simazine in runoff was reduced in no-till watersheds and attributed the reductions to increased infiltration and resist- ance to overland flow by the mulch cover.

The Chesapeake Bay has suffered a long-term decline in submerged aquatic vegetation ( SAV) (Stevenson and Confer, 1978). Because of the importance of SAV to the bay ecology, this is a matter of some concern. Since the decline of SAV has corresponded to an increase in no-till and herbicide use in the watersheds associated with the Chesapeake Bay and its tributaries, herbicide movement from no-till watersheds into waterways may contribute to the decline of SAV. The objective of this study was to evaluate the surface runoff of atra- zine and simazine from conventional and no-till corn watersheds in the coastal Piedmont region of Maryland.

MATERIALS AND METHODS

Two adjacent, but separate, watersheds were chosen for study at Howard County, Maryland. Drainage from this area flows into the Middle Patuxent River which is a fresh water tributary to the Chesapeake Bay. The watersheds were cultivated using minimum tillage procedures (discing twice in opposite directions) and planted to corn in 1977. The soil was a Manor loam (coarse loamy, micaceous, mesic, Typic Dystrochrept ) with a pH of 5.9 and 2.7% (w/w ) organic matter.

In the spring of 1978, one watershed was planted in corn using CT proce- dures (contour ploughed with a mouldboard plough, disc-harrowed, and cul- tipacked) and the other watershed was planted to corn using NT procedures. The tillage procedures for these watersheds remained the same throughout the

remaining years of this study. The CT watershed had a slope of 6% and a total of 0.37 ha. The NT watershed was 0.26 ha with a 7% slope.

In the autumn of each year, both watersheds were planted in barley (Hor- deum uulgure L.) as a cover crop. Corn was planted in the watersheds on 8 June 1979; 4 June 1980; 11 May 1981; and 14 May 1982. Atrazine and simazine were applied pre-emergence at 2.2 kg a.i. ha- ’ to both watersheds immediately after planting each year. Paraquat (1,l’ -dimethyl-4,4’ -bipyridinium ion ) was applied at 0.6 kg a.i. ha-’ to the NT watershed as a tank mixture with the atrazine and simazine.

Runoff from each watershed was collected using 0.6-m H-type flumes con- structed of plywood and lined with stainless steel. The flumes had a slope of 14% in the drop box inlet to create a hydraulic jump that ensured mixing of the sediments carried by the runoff. The runoff flowed through the H-flume and across a 0.6-m Coschocton wheel. The Coschocton wheel collected 0.5% of the total volume of the runoff which flowed into 40-l glass carboys.

Runoff samples were collected after each runoff event and immediately returned to the laboratory where they were stored at 4’ C until analyzed. One litre of water sample was filtered through a glass fibre-cellulose paper combi- nation (Whatman 934-AH/Whatman 1) and partitioned twice with 100 ml of chloroform. The combined organic fractions were reduced to dryness with a stream of dry air and gentle heating, and were immediately redissolved in 1 ml of methanol. Herbicide analysis was performed on a Varian 3700 gas chroma- tograph equipped with a thermionic specific detector (a detector specific for nitrogen- and phosphorus-containing compounds ) . The herbicides were sep- arated on a 100 x 0.2 cm ID column containing 3% Carbowax 20 M on 80--100 mesh chromosorb W-HP. Flow rates were: 180 ml min-’ air, 30 ml min’ N, and 4 ml mix--’ H,. Column, injector and detector temperatures were 175,230 and 250” C, respectively. The limit of detection for atrazine and simazine was 0.1 /lug 1-l.

RESULTS AND DISCUSSION

There was no significant difference in volume of runoff or nutrient runoff loss between the two watersheds in 1977 when both watersheds were cultivated using minimum tillage procedures (data not shown). Samples were not ana- lyzed for herbicides in 1977, however, the runoff volume and nutrient runoff data suggested that these waterheds were comparable. No samples were obtained for herbicide analysis in 1978. This allowed a transition period for the soil chemical and physical properties from minimum tillage to no-till or conventional-till cultivation practices. The runoff events presented in Tables I, II and III represent the major runoff events between corn planting and har- vest in 1979,198l and 1982. There were several minor runoff events that did not provide a sample of sufficient quantity for herbicide analysis. The total

TAB

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une

3.81

20

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13

32

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2.44

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20

385

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98

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volume of runoff presented in each table does not represent total yearly runoff volume, rather it represents only those major runoff producing events during the growing season.

In 1979, there were 12 major runoff events from the CT watershed and 8 from the NT watershed between 18 June and 9 October (Table I). Total vol- ume of runoff was lower from the NT watershed than the CT. The four storms between 3 and 26 August initiated runoff from the CT watershed but not t,he NT watershed. All other storms, except the storm on 3 October, initiated equal or greater runoff from the NT watershed compared to the CT watershed. Apparently the plant residue in the NT watershed reduced the likelihood of a runoff event in 1979, but when the rainfall intensity and soil moisture was great enough to produce a runoff’event the volume of runoff from the NT watershed often equalled or exceeded that from the CT watershed. Greater runoff from the NT watershed during single runoff events may be explained by greater soil moisture in the NT watershed compared to the CT watershed.

Approximately 1.6 and 1.1% of the atrazine applied was found in runoff from the CT and NT watershed, respectivelyc Surface runoff of simazine from the CT and NT watershed was 0.52 and 0.36%, respectively, of that applied. Most, of the herbicide runoff occurred in the first runoff event after application (10 days after application) followed by a decline in herbicide concentrations in samples from subsequent events. Wauchope (1978) reported that runoff dur- ing a rainfall of 10 mm or more within two weeks of herbicide application usually contains the greatest total quantity of herbicide. The concentration of atrazine and simazine was smaller in the runoff during the first event from the NT compared to the CT watershed. The filtering of the herbicides through the plant residue on the NT watershed may have increased the binding of herbi- cides to the plant residue and reduced the concentration of herbicides in the runoff reaching the flume.

There was heavy and frequent rainfall in the spring of 1980, delaying corn planting until 4 June. After planting and herbicide application, precipitation was light and infrequent (data not shown). There were no runoff events from either watershed during the growing season from which samples could be obtained for herbicide analysis.

In 1981, there were three runoff events monitored from the CT watershed and none from the NT watershed during the growing season (Table II). A runoff event occurred on 15 June from both watersheds, but the collection devices failed to operate properly, so this event was not monitored. The plant residue left on the surface of the NT watershed apparently prevented runoff during the storms which produced runoff from the CT watershed (Mannering and Meyer, 1963; Meyer et al., 1970). As in 1979, the greatest concentrations of atrazine and simazine were found in the runoff of the first event from the CT watershed. The concentration of simazine was much less than atrazine. However, the amount of atrazine and simazine in runoff was lower in 1981

279

than in 1979. This can be attributed to the absence of a runoff event for 28 days following herbicide applications. By the time of the first runoff event much of the herbicides were probably degraded (Herbicide Handbook of the Weed Science Society of America, 1983 ) .

During the growing season of 1982, there were five major runoff events from the CT watershed and none from the NT watershed (Table III). The plant residue on the surface of the NT watershed prevented runoff during the storms which produced runoff from the CT watershed (Mannering and Meyer, 1963; Meyer et al., 1970). The concentration of atrazine was greatest in samples from the first runoff event after application (20 May) and steadily declined in later runoff events. Similar results were found in 1979 and 1981 (Tables I and II). The concentrations of simazine in the first two runoff events was very low and simazine was not detected in water from the last two events (Table III). Although the first runoff event in 1982 occurred only 7 days following herbicide application, the total amount of atrazine and simazine in runoff from the CT watershed in 1982 was much less than in 1979. This appears to be related to the amount of precipitation which initiated the runoff event. In 1979, the first two runoff events were initiated by a total of 62.5 mm, whereas, in 1982 the first two events were caused by a total of 21.7 mm. Apparently more atrazine and simazine became soluble in the greater volume of water that passed through the watersheds in 1979 compared to 1982.

There was less runoff of water, atrazine and simazine from the NT compared to the CT watershed each year that a major runoff event occurred during the growing season. Between 1979 and 1982, the total volume of measured runoff was 27% less from the NT compared to the CT watershed. Most of the herbi- cide loss in surface runoff occurred during the first runoff event after applica- tion. This agrees with other reports (Wauchope, 1978; Rhode et al., 1981; Glotfelty et al., 1983). The concentration of simazine in runoff was less than the concentration of atrazine. Many factors may have been involved; however, less runoff of simazine compared to atrazine was probably a result of the lower water solubility of simazine (Herbicide Handbook of the Weed Science Society of America, 1983). The greatest runoff of herbicides occurred in 1979 when 1.6 and 1.1% of the atrazine applied moved from the CT and NT watersheds, respectively, and 0.52 and 0.36% of the simazine applied moved from the CT and NT watersheds, respectively. In this study no-till therefore reduced runoff losses of triazine herbicides. Triplett et al. (1978) also found that atrazine and simazine runoff was smaller from no-tillage watersheds compared to conven- tional-tillage watersheds in Ohio. It appears that the practice of no-till in the watersheds associated with the Chesapeake Bay may reduce the potential con- tamination of the Bay with triazines. These data suggest that from the stand- point of herbicide runoff loss, no-tillage should be encouraged as an environmentally sound practice.

280

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