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TECHNICAL REPORTS
Organic Compounds in the Environment

Preferential Bromide and Pesticide Movement to Tile Drains under Different Cropping Practices

^a Département des sols et de génie agroalimentaire, Pavillon Paul-Comtois, Université Laval, Québec, QC, Canada G1K 7P4
^b Ministère de l'Environnement du Québec, Direction des politiques agricoles, 675, Blvd René-Lévesque Est, Québec, QC, Canada G1R 5V7
^c Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec (MAPAQ), Direction régionale du Bas Saint-Laurent, 335, rue Moreault, Rimouski, QC, Canada G5L 9C8
^d Institut de Recherche et de Développement en Agroenvironnement (IRDA), 2700, rue Einstein, Sainte-Foy, QC, Canada G1P 3W8

* Corresponding author (josee.fortin{at}sga.ulaval.ca)

Received for publication July 16, 2001.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Subsurface drainage systems are useful tools to study chemical leaching in soils. Our objective was to compare the breakthrough behavior of bromide, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamid] to tile drains under two fall tillage practices (conventional tillage [CT] with a moldboard plow, and reduced tillage [RT] with a chisel plow) in field plots cultivated with corn (Zea mays L.). Leachate volume were greater in RT than in CT, with no statistical differences. Soil analysis showed that bromide migrated deeper in the soil profile than both herbicides, with little tillage effect. All chemicals were detected in drainage water at the same time and followed an event-driven behavior. Tillage had no effect on atrazine and metolachlor found in drainage water, while bromide concentration peaks were higher in RT than in CT in 1999. Concentration peaks were recorded earlier for atrazine and metolachlor than for bromide. Plots of cumulative relative chemical mass (cumulative mass divided by total mass measured in drainage) as a function of cumulative drainage were mostly linear for bromide, while they were S-shaped for both herbicides. Drainage that corresponded to 50% of relative cumulative mass ranged from 40 to 55% for bromide and from 5 to 28% for both herbicides. Rapid chemical movement to tile drains suggested that preferential flow was important in both CT and RT, and that these tillage practices had little influence on this phenomena.

Abbreviations: CM, solid cow manure • CT, conventional tillage with a moldboard plow • MF, mineral fertilizer • PM, liquid pig manure • RCM, relative cumulative mass • RT, reduced tillage with a chisel plow

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
IN MANY REGIONS, tile drains discharge directly into surface waters (e.g., streams) and may contaminate them if the water discharged contains significant amounts of inorganic (nitrate, phosphate) and organic (pesticides) contaminants. Factors that control leaching losses of agrochemicals through soil and into tiles are weather patterns, annual precipitation, soil type, and timing and method of agrochemical application (Gentry et al., 2000). Contamination risk of surface water from tile-drained fields increases with the occurrence of preferential flow. Under normal flow conditions, the soil matrix removes a good portion of pesticides present in water by adsorption and degradation. When preferential flow occurs, water containing chemicals bypasses the soil matrix and reaches tile drains. Many researchers have reported rapid movement in tile-drained fields of conservative tracers (Everts and Kanwar, 1990; Bronswijk et al., 1995) and reactive inorganic (Baker and Johnson, 1981; Kladivko et al., 1991; Davis et al., 2000) and organic (Kladivko et al., 1991; Southwick et al., 1992; Traub-Eberhard et al., 1993; Phillips et al., 1999; Elliott et al., 2000) chemicals. Very few experiments studying the movement of pesticides in tile-drained fields have used conservative tracers (either Br^- or Cl^-) as indicators of the water flux (Steenhuis et al., 1990; Czapar et al., 1994; Zehe and Flühler, 2001). According to Flury (1996), it is difficult to interpret transport of adsorbing solutes with respect to preferential flow phenomena without using conservative tracers to characterize water transport. More studies with conservative tracers along with pesticides should be done to evaluate and understand reactive chemical movement to tile drains under different cultural practices.

Many studies on pesticide fate and movement in soils as affected by tillage practices have been conducted throughout the years. The use of different tillage practices can modify many soils properties that can affect fate and movement of pesticides in soils, such as microbial populations (Doran, 1980), organic matter content and composition of surface horizons (Hussain et al., 1999; Needelman et al., 1999; Rhoton, 2000), and chemical properties (Hussain et al., 1999; Rhoton, 2000), as well as soil structure (Eghball et al., 1993; Vyn and Raimbault, 1993; Franzluebbers et al., 1999). The effect of different tillage practices on chemical movement in soils is unclear. Some researchers have demonstrated that reduced tillage practices can decrease downward pesticide movement in the soil profile due to the higher amount of crop residues remaining at the soil surface, which can increase pesticide sorption and microbial degradation (Gish et al., 1995; Sadeghi et al., 1998). Others have postulated that reduced tillage practices can result in an increased movement of pesticides in the soil profile caused by preferential flow (Isensee et al., 1990; Gish et al., 1991; Kanwar et al., 1997). There is a need for a better understanding of the influence of different tillage practices on pesticide fate in soil. In this study, we monitored bromide, atrazine, and metolachlor concentrations in tile drain effluent during corn growing season under natural rainfall in plots where two different tillage practices were applied. Our objective was to compare the outflow behavior to tile drains of conservative (bromide) and reactive (herbicides) chemicals under conventional and reduced tillage practices.

	MATERIAL AND METHODS

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Experimental Site and Treatments
The experimental site was located at the St-Lambert Research Farm of the Institut de Recherche et de Développement en Agroenvironnement (IRDA) near Québec City, Canada (46°05' N, 71°02' W; altitude 110 m). Long-term (1961–1990) mean temperature and cumulative summer rainfall from May to October recorded at the Ministère de l'Environnement du Québec permanent meteorological station (Beauséjour station) (46°40' N, 71°10' W; altitude 107 m) were 13.8°C and 670.6 mm, respectively. Rainfall data recorded on a daily basis from this meteorological station (located at approximately 4 km north of the study site) were used in this study.

Soil at the study site belonged to the Le Bras soil series (frigid Aeric Haplaquept). Selected soil properties evaluated on four soil samples collected in each experimental plot in the fall of 1997 were summarized in Table 1. Soil texture was evaluated with the hydrometer method (Day, 1965). Mean weight diameters (MWD) were measured with the method described by Kemper and Chepil (1965). Soil organic carbon was quantified by wet oxidation with the Walkley and Black method (Nelson and Sommers, 1982), and soil pH was measured in water (1:1 soil to water ratio).

View larger version (30K): [in this window] [in a new window]   Fig. 1. Experiment layout at the Saint-Lambert-de-Lauzon site, showing the plots sizes and treatments, the tile lines, and the access chambers. The drained surface for each plot was 750 m2 (1998) and 600 m2 (1999) for cow manure–reduced tillage (CM–RT), 1500 m2 (1998) and 1200 m2 (1999) for CM–conventional tillage (CT), and 1200 m2 for mineral fertilizer (MF)–CT, MF–RT, pig manure (PM)–CT, and PM–RT. See text for details concerning the changes in the drained surface for CM plots.

Drained surface for each plot was calculated, assuming that the area of influence of a tile line extended to a distance of half the drain spacing (Fig. 1). One problem was encountered with the drainage system for CM plots. We first noticed that calculated drainage in these plots in 1998 was higher than for other plots. We dug a trench at the southwest extremity of the plots in May 1999 and realized that drains extended out of the plots. This problem, which resulted from a mistake in the 1989 original field drainage plan, was corrected immediately by cutting the drains and filling back the trench. As a result, drained surfaces for these plots in 1998 were estimated to be 750 and 1500 m² under reduced tillage (RT) and conventional tillage (CT), respectively. After 25 May 1999, drained surfaces for these plots were 600 and 1200 m², respectively. Drained surfaces for the other plots were 1200 m². Even after this modification, CM plots always behaved differently than the other plots. Chemicals in drainage water were analyzed from 15 May to 15 November of each year. For the rest of the year, drainage volumes were measured, but no chemicals were analyzed. Surface runoff was not controlled and no significant surface runoff was observed during the monitored periods.

Treatments applied to the plots were summarized in Table 2. Two tillage practices (reduced tillage [RT] with a chisel plow and conventional tillage [CT] with a moldboard plow) were applied in the fall (October) as shown in Fig. 1. The following spring, soil surface of both CT and RT plots was disked and harrowed just after manure application to prepare for seeding, as was the normal practice. Mineral fertilizers were applied according to plant needs as evaluated from soil analysis. Soil fertilization in the plots receiving manure was completed with inorganic fertilizer to fulfill plant needs based on soil analysis, amendment analysis, and fertilizer recommendation charts. Experimental plots were under a 4-yr crop rotation with canola (Brassica napus L.) the first year, corn for silage for two consecutive years, and barley (Hordeum vulgare L.) the last year. Plots were in place since 1993 and the second rotation cycle started in 1997. For this experiment, monitoring of two herbicides (atrazine and metolachlor) and a conservative tracer (bromide) in tile drainage system took place in 1998 and 1999, when plots were cultivated with corn.

Soils were sampled in the fall of each year just before tillage to evaluate herbicide and bromide distribution in the soil profile. Prior to the start of the experiment, background levels of herbicides and bromide in the soil profile were evaluated and found to be negligible (data not shown). Soils were sampled at four different sampling locations in each plot, which were selected randomly, but were located at a distance from one another to cover a good portion of the plot surface. At each sampling location, soil sampled at a given depth was a composite of three subsamples. Soils were sampled in depth increments of 20 cm up to 1 m deep with a hand auger. Between each sampling depth, the auger was cleaned to avoid contamination of the next sample. Soil samples were air dried and sieved to 2 mm prior to analysis. For bromide analysis, 5 g of soil was agitated at high speed on a platform shaker (300 cycles per minute) with 25 mL of water for 30 min, then filtered with a Whatman (Maidstone, UK) no. 42 (particle retention 2.5 µm) filter paper. Filtrate was analyzed for bromide content with the bromide ion specific electrode. Bromide detection limit of this method for soil samples was evaluated to be 50 µg kg^-1. The pesticide soil extraction method used was the one described in the Ohmicron Technical Bulletin T00003. Ten grams of soil were extracted with 30 mL of a 25:75 (v/v) mixture of water and methanol. The extraction procedure consisted in an initial agitation of 30 min on a platform shaker (200 cycles per minute), followed by a resting period overnight in the refrigerator and a final agitation of 30 min at the same speed. Supernatant was recovered following centrifugation at 1500 x g, diluted 50 times with water, and analyzed for atrazine and metolachlor content with magnetic particle-based ELISA kits. Percentage recovery for atrazine and metolachlor, evaluated with 10 fortified soil samples, was 84 and 87%, respectively. Detection limit in soils was 15 µg kg^-1 for both atrazine and metolachlor. Bromide and herbicides concentrations in water and soils were reported without correction.

Data Evaluation
Proportion of rainwater leaving the field through the drainage system was obtained by dividing the total amount of water collected in the drainage system for each plot by the total amount of rain. Chemical mass remaining in the soil profile was calculated with minimum and maximum soil concentrations evaluated at each depth and corresponding soil bulk density. Chemical mass in drainage water was obtained by multiplying the chemical concentration analyzed by the corresponding drainage volume recorded during the sampling period. Bromide and herbicide breakthrough behaviors to tile drains were compared by plotting relative cumulative mass (RCM) found in tile drains as a function of cumulative drainage. The RCM was defined as:

[1]

where RCM(I) was the relative cumulative mass at cumulative drainage I, M_i was the chemical mass at drainage i, and M_tot was the total chemical mass recovered in tile drains during the experiment.

Statistical differences between tillage treatments were evaluated with simple t tests for each year, considering the different fertilization treatments together. All statistical analysis were performed with SAS (SAS Institute, 1997) with a significance level of P < 0.05.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Hydrologic Conditions during the Study Period
Typical discharge hydrographs for the two years are presented in Fig. 2 , and show a fast response of the drainage system to rainfall, with major drainage peaks corresponding to large rain events. Drainage of the different treatments overlapped in Fig. 2, with only some variations in intensity of drainage among treatments and no particular trend. Maximum flow rates observed from May to August and from September to November for both years are summarized in Table 3. Because drainage volumes were recorded twice a week, maximum flow rates reported were in fact average values of 3 or 4 d. In 1998, the maximum flow rates were observed in the first part of the growing season (June), while they were observed in July or October in 1999 depending on the plot. Maximum flow rates were slightly greater in 1999 as compared with 1998, probably because a greater amount of rain caused the drainage. Values ranged from 2.1 to 4.9 mm d^-1 in 1998 and from 3.9 to 8.4 mm d^-1 in 1999 (Table 3) and were much less than the ones obtained in other tile drainage studies. In Illinois, Gentry et al. (2000) observed maximum flow rates of 20.2 and 29.3 mm d^-1 for the two tiles studied, which occurred in May after 105 mm of precipitation during a 5-d period (21 mm d^-1 rain). Lennartz et al. (1999) observed maximum flow rates near 16.8 mm d^-1, which occurred in early winter (December) and in early spring (March) under German climate. Both these studies recorded drainage volume continuously, which may explain the differences. In this study, the corresponding cumulative precipitation during the 4-d period prior to the sampling date when the maximum flow rates were observed ranged between 30 and 49 mm and 36 and 81 mm in 1998 and 1999, respectively (Table 3). Mean comparisons showed no statistical differences in the maximum flow rates with tillage treatment, although the values were slightly higher for RT as compared with CT (Table 3).

View larger version (26K): [in this window] [in a new window]   Fig. 2. Rainfall and drain discharge for the different plots during the two years studied. Cow manure conventional (CM–CT) () and reduced (CM–RT) () tillage; pig slurry conventional (PS–CT) () and reduced (PS–RT) () tillage; mineral fertilizer conventional (MF–CT) (•) and reduced (MF–RT) () tillage.

Mean comparisons revealed no statistical differences between tillage treatments for total drain discharge during the monitored period, although values for a given year were always higher for RT (113 and 143 mm in 1998 and 1999, respectively) than for CT (77 and 122 mm in 1998 and 1999, respectively) (Table 3). Singh et al. (1996) observed similar results, with no significant differences in total drainage between RT and CT for two consecutive years, although mean values for RT were higher than for CT. It was possible that the difference between the effect of RT and CT on water movement in soil was not pronounced enough to detect significant effects. This was supported by the results of Seta et al. (1993) for runoff volume and runoff rate, who observed significant differences between no-till and CT, but not between RT and CT. However, mean values obtained by these authors were in the order of no-till < RT < CT. Similarly, Bicki and Guo (1991) observed significantly greater hydraulic conductivity and macropore continuity in soil managed under long-term no-till than when other tillage practices, such as RT and CT, were used.

Chemicals in Soil
Bromide
Bromide was detected up to the maximum sampling depth of 1 m, with differences in the vertical distribution for both years (Fig. 3 and 4) . In 1998, most of the bromide was found in the top 0- to 20-cm layer, with concentrations ranging from 0.81 to 4.50 mg kg^-1 (Fig. 3). In 1999, bromide concentrations in the soil were much less than in 1998 and were not always concentrated in the top 0- to 20-cm layer (Fig. 4). Values found in the top 0- to 20-cm layer in 1999 ranged from not detected to 0.6 mg kg^-1. The highest bromide concentration measured in 1999 (0.78 mg kg^-1) was in the 40- to 60-cm layer of the liquid pig manure (PM)–CT plot (Fig. 4). A simple piston flow calculation, assuming that volumetric water content at field capacity occupied 50% of porosity and using bulk density values reported in Table 1, showed that one pore volume was equal to 195 to 228 mm of water, depending on the plot. Since total drainage from 15 May 1998 to 14 May 1999 ranged between 281 and 396 mm (Table 3), little of the bromide applied in 1998 should be left in the soil as of 17 May 1999. It was thus unlikely that bromide applied in 1998 affected the final bromide distribution profile in 1999. Although soil bromide distribution profiles showed some increase in concentration with depth (Fig. 3 and 4), this was not enough to conclude that preferential flow really occurred because of the small number of soil samples collected (Steenhuis et al., 1990) and the possibility that this observation resulted from different hydraulic conductivities with soil horizons (Fleming and Butters, 1995).

View larger version (34K): [in this window] [in a new window]   Fig. 3. Vertical distribution of bromide and pesticides in the soil profile in 1998 in plots treated with different amendments [cow manure (CM), pig slurry (PS), or mineral fertilizer (MF)] and tillage practices [conventional tillage (CT) and reduced tillage (RT)]. Boxes end at minimum and maximum values measured at each sampling depth from the four sampling locations in each plot. Values below the detection limit were plotted as zero.

View larger version (38K): [in this window] [in a new window]   Fig. 4. Vertical distribution of bromide and pesticides in the soil profile in 1999 in plots treated with different amendments [cow manure (CM), pig slurry (PS), or mineral fertilizer (MF)] and tillage practices [conventional tillage (CT) and reduced tillage (RT)]. Boxes end at minimum and maximum values measured at each sampling depth from the four sampling locations in each plot. Values below the detection limit were plotted as zero.

Herbicides
In contrast to bromide, no herbicides were detected at greater depth than 40 cm. Atrazine and metolachlor were detected in most plots in the 0- to 20-cm layer both years (Table 4), while only metolachlor was detected in the 20- to 40-cm layer in three samples in 1998 (12.6 µg kg^-1 in CM–CT, 24.3 µg kg^-1 in liquid pig manure [PM]–CT, and 21.3 µg kg^-1 in mineral fertilizer [MF]–RT). No herbicides were detected in the 20- to 40-cm soil layer in 1999. Atrazine concentration in the 0- to 20-cm soil layer ranged from not detected to 201.6 µg kg^-1 in 1998 and from not detected to 40.5 µg kg^-1 in 1999 (Table 4). This corresponded to 0 to 47.5% and 0 to 8.6% of the mass applied in 1998 and 1999, respectively (Table 5). Atrazine detection frequency was higher in 1998 than in 1999, with respectively 13 and 6 samples where the herbicide was detected out of 24 (Table 4). Metolachlor concentration in the 0- to 20-cm soil layer ranged from not detected to 107.7 µg kg^-1 in 1998 and from not detected to 147.0 µg kg^-1 in 1999 (Table 4). This corresponded to 0 to 12.6% and 0 to 17.1% of the mass applied in 1998 and 1999, respectively (Table 5). Metolachlor detection frequency was slightly higher in 1999 than in 1998, with respectively 21 and 17 samples where metolachlor was detected out of 24 soil samples (Table 4). Differences between herbicides may be due to a lower soil retention for atrazine (K_oc = 100 cm³ g^-1) than for metolachlor (K_oc = 200 cm³ g^-1) (Wauchope et al., 1992). One possible explanation for the lower atrazine detection frequency and concentrations in 1999 than in 1998 may come from microflore adaptation and subsequent biodegradation increase due to the 1998 atrazine application. This phenomena is well documented for atrazine (Gan et al., 1996; Ostrofsky et al., 1997; Shapir et al., 2000), while it has never been observed for metolachlor.

Chemicals in Tile Drains
Breakthrough curves for bromide and both herbicides to tile drains are displayed in Fig. 5 and 6 for 1998 and 1999, respectively. The breakthrough curves were typical of preferential flow behavior, with all chemicals arriving to the tile drains at the same time, irrespective of their physico–chemical properties (Kladivko et al., 1991; Traub-Eberhard et al., 1995). In fact, even the first drainage after chemical application contained all three compounds, which was a reliable indication of preferential chemical movement in the soil (Kladivko et al., 1991; Flury, 1996).

View larger version (42K): [in this window] [in a new window]   Fig. 5. Breakthrough curves for bromide and herbicides to tile drains under different cultural practices in 1998 [cow manure (CM), pig slurry (PS), mineral fertilizer (MF), conventional tillage (CT), reduced tillage (RT)].

View larger version (37K): [in this window] [in a new window]   Fig. 6. Breakthrough curves for bromide and herbicides to tile drains under different cultural practices in 1999 [cow manure (CM), pig slurry (PS), mineral fertilizer (MF), conventional tillage (CT), reduced tillage (RT)].

In this study, results were different between years, with higher concentration peaks (Table 3, Fig. 5 and 6) and a higher proportion of bromide recovered in tile drains (Table 5) in 1999 as compared with 1998. The different hydrological conditions for both years, with total drain discharge and maximum flow rates higher in 1999 than in 1998 (Table 3), could explain these differences. It was also possible that part of the bromide applied in 1998 was recovered in tile drains in 1999, as was observed by Lennartz et al. (1999). However, piston flow calculations performed in the preceding section showed that this was probably not an important factor. Furthermore, the total bromide mass recovered (sum of drainage and soil) was less in 1999 than in 1998 (Table 5), while the reverse would be expected if bromide applied in 1998 influenced the results observed in 1999.

Mean comparisons revealed no statistical differences between tillage treatments for proportion of the applied bromide recovered in tile drains in 1998 and 1999, and for maximum bromide concentrations found in drainage water in 1998. However, in 1999, mean maximum bromide concentration was significantly higher in RT (19.9 mg L^-1) as compared with CT (10.7 mg L^-1) (P = 0.02). This last result contrasted with other studies where no significant tillage effects on bromide movement to tile drains (Steenhuis et al., 1990) and to lysimeters (Ogden et al., 1999) were found. Possible explanations for the present results include (i) interception by crop residues of the bromide applied in the spring of 1999, with subsequent leaching or (ii) decay of crop residue early in 1999 that released some of the bromide taken up by corn in 1998. Since chisel plowing leaves typically more crop residue at the soil surface than moldboard plowing (data not shown), this could have resulted in more bromide released in RT than in CT.

Plots of RCM against cumulative drainage showed that the bromide loss was relatively constant during the season, except for CM plots (Fig. 7) . Slopes of the bromide curves in Fig. 7 were calculated with linear regressions (R² = 0.81 to 0.99, data not shown) and were used to evaluate cumulative drainage corresponding to 50% of the relative cumulative bromide mass loss to tile drains. Bromide losses to tile drains were similar for both years, with 43 to 55% and 40 to 55% of cumulative drainage corresponding to 50% of relative bromide mass found in drainage water in 1998 and 1999, respectively. Mean comparisons revealed no tillage treatment effects on this parameter for both years.

View larger version (36K): [in this window] [in a new window]   Fig. 7. Relative cumulative mass loss as a function of the cumulative drain discharge for the different treatments in 1998 and 1999. Cow manure conventional (CM–CT) () and reduced (CM–RT) () tillage; pig slurry conventional (PS–CT) () and reduced (PS–RT) () tillage; mineral fertilizer conventional (MF–CT) (•) and reduced (MF-RT) () tillage.

Herbicides
Less than 1% of applied herbicides were recovered in tile drains for both years (Table 5). Values reported in the literature ranged from 0.01 to 3.56% for atrazine (Kladivko et al., 1991; Gaynor et al., 1995; Gentry et al., 2000) and from 0.07 to 2.23% for metolachlor (Gaynor et al., 1995; Gentry et al., 2000). For both atrazine and metolachlor, the percentage recovered in tile drains was greater in 1999 than in 1998, as was the case for bromide (Table 5). The amount of both pesticides remaining in the soil at the end of 1998 was small (Table 4), so this cannot explain the higher chemical loss in drainage in 1999 than in 1998. Total drain discharge and the maximum flow rates were higher in 1999 than in 1998 (Table 3), which may have contributed to more chemical movement to tile drains. Percentage of the mass applied recovered in drainage water was generally less for metolachlor than for atrazine, which may be due to its higher soil retention (Table 4). According to Gaynor et al. (1995), even if metolachlor has a greater water solubility than atrazine (530 and 33 mg L^-1 for metolachlor and atrazine, respectively), the quantity of metolachlor available for transport is reduced because of its greater adsorption to soil organic matter. The present observations confirmed the findings of others that even if herbicides arrived to tile drains at the same time, their physico–chemical properties determined the amount transported (Kladivko et al., 1991; Flury et al., 1995; Elliott et al., 2000).

Total mass loss to tile drains for both herbicides corresponded in most cases to one or two major peaks in the first part of the growing season, especially in 1999 (Fig. 5 and 6). These peaks occurred close to the application date, as was observed by others (Kladivko et al., 1991; Watts and Hall, 1996; Gentry et al., 2000). A smaller amount of reactive chemicals was probably available for transport later in the season due to sorption, degradation, and plant uptake. Atrazine and metolachlor maximum concentration peaks were observed in June for both years (Table 3) and herbicide concentrations in drain discharge decreased with time (Fig. 5 and 6). Atrazine and metolachlor concentration peaks were also recorded earlier than bromide concentration peaks (Table 3), which emphasized the influence of adsorption and degradation on chemical transport even when preferential flow was involved.

Mean comparison revealed no statistical differences in atrazine and metolachlor maximum concentration peaks and percentage of the applied mass recovered in tile drains between tillage treatments for both years. Kanwar et al. (1997) also found no statistical differences between tillage for atrazine losses to tile drains, with a tendency for greater losses for no-till and ridge-till than for moldboard plow and chisel plow. Literature results on the effect of tillage practices on pesticide movement to tile drains or shallow ground water are contradictory. Some studies reported increased movement of pesticides to tile drains (Pivetz and Steenhuis, 1989, Steenhuis et al., 1990; Elliott et al., 2000) and ground water (Pivetz and Steenhuis, 1989; Isensee et al., 1990; Gish et al., 1991) when conservation tillage practices were used as compared with conventional tillage. Other studies on reactive chemical transport to tile drains (Gaynor et al., 1992; Buhler et al., 1993; Logan et al., 1994; Gaynor et al., 1995) failed to detect any tillage treatment effect. Gaynor et al. (1995) conducted a four-year study to evaluate the effect of three tillage practices (conventional, ridge, and zero tillage) on herbicide losses to runoff and tile drains. They observed that variations in the data, mostly related to intensity and duration of rain, masked statistical significance for identifying tillage effects. According to these authors, variation between replicates and differences in loss patterns among years emphasized the large role of environmental conditions on herbicide losses. Furthermore, few studies compared chisel plow and moldboard plow with respect to pesticide movement to tile drains (Kanwar et al., 1997). As stated earlier for drainage, it was possible that these two tillage practices were not contrasting enough with respect to soil disturbance and change in soil properties to result in any significant differences in the behavior of pesticides. In fact, results from Table 1 tended to confirm this hypothesis, with no real tendency in soil bulk density and soil organic carbon content with tillage practice, although particle mean weight diameters were slightly higher in RT than in CT, with no statistically significant differences.

Plots of RCM for each herbicide as a function of cumulative drainage are presented in Fig. 7. In contrast to bromide, the curves for both herbicides were S-shaped, with a distinct change in rate at a cumulative drain discharge that corresponded to the beginning of the fall period. In fact, the change in rate occurred after the period where drainage was very small (Fig. 2). When important drainage resumed, small concentrations of each pesticide were detected. Cumulative drainage at which 50% of each pesticide was found in drains was less than 50 mm in all cases (Fig. 7), and ranged from 10 to 28% of cumulative drainage in 1998 and from 5 to 18% of cumulative drainage in 1999. No tillage effects were observed and both herbicides behaved in a similar manner. The time at which 50% of the chemical found in drainage was recorded corresponded to 21 to 27 d after chemical application (except for the CM–RT plot, which was 100 d) in 1998, and to 57 to 64 d after chemical application in 1999. This was slower than what was observed by Southwick et al. (1992), who reported that 97 to 98% of the atrazine that was found in tile drains occurred within 21 d following application. This was, however, faster than what was found for bromide and emphasized the different behavior of inert and reactive chemicals. For reactive chemicals, processes such as sorption and degradation played an important role in the amount of chemical available for transport. These processes may be affected by many factors, one being the time the chemical remained at a given place in the soil, which can be affected by flowing water (climatic conditions). In this study, there was probably no significant deep displacement of any solute for the period where drainage was very small (Fig. 2). This period was probably favorable for pesticide sorption and degradation in soil, and for pesticide absorption by plants. Notice that there was rain during that period, and that evapotranspiration was probably important. This period was also longer in 1999 as compared with 1998 (Fig. 2), which may explain some of the differences observed between these two years, mainly for atrazine. One other important factor was fertilization, which may have affected soil microbial activity, and subsequently pesticide degradation and sorption, as was previously mentioned.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
This study used a subsurface drainage system to compare bromide, atrazine, and metolachlor leaching in soil under two tillage practices. All chemicals were detected in drainage water at the same time, irrespective of their physico–chemical properties, which was attributed to preferential flow. Different rain intensities and distribution of rain in 1998 and 1999 resulted in different total drainage and chemical leaching with years. Evaluation of different soil treatments effects on chemical movement to tile drains under natural rainfall probably requires long-term experiments to take into account climatic variability.

Reduced tillage and CT had little significant influence on total drainage and chemical leaching to tile drains, although there was a tendency toward greater drain discharge in RT as compared with CT. These two tillage practices were probably not contrasting enough, with respect of their effects on key soil properties that affect water and chemical movement in soils, to see any significant effect. One other important factor to consider was that plots received different amendments, which may have affected chemical fate and transport in the studied plots, and masked in a certain way tillage treatment effects. This point would need to be investigated in detail.

Soil analysis gave little information on chemical leaching and did not show evidence of preferential flow. As expected, bromide was found deeper in the soil profile than both herbicides, with no consistent tillage effect. Comparison of tile drain breakthrough behavior of the three chemicals gave some interesting results. Concentration peaks were recorded earlier for herbicides than for bromide both years, which resulted from lower herbicide availability due to interaction with soil. Fifty percent of bromide found in drainage water occurred after 40 to 55% of cumulative drainage, while it was much faster for herbicides (5 to 28% depending on the plot and year). Proportion of applied mass recovered in tile drains was lower for metolachlor than for atrazine, even if metolachlor was applied at a dose almost twice the one of atrazine. Thus, even if they arrived to tile drains at the same time, physico–chemical properties of herbicides affected the total mass found in drainage.

	ACKNOWLEDGMENTS

 
The authors are grateful to the Conseil des recherches en pêche et en agro-alimentaire du Québec (CORPAQ) for financial support, and to Raynald Royer for his assistance.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIAL AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Alvey, S., and D.E. Crowley. 1995. Influence of organic amendments on biodegradation of atrazine as nitrogen source. J. Environ. Qual. 24:1156–1162.[Abstract/Free Full Text]
• Baker, J.L., and H.P. Johnson. 1981. Nitrate-nitrogen in tile drainage as affected by fertilization. J. Environ. Qual. 10:519–522.[Abstract/Free Full Text]
• Barriuso, E., S. Houot, and C. Serra-Wittling. 1997. Influence of compost addition to soil on the behaviour of herbicides. Pestic. Sci. 49:65–75.
• Bicki, T.J., and L. Guo. 1991. Tillage and simulated rainfall intensity effect on bromide movement in an Argiudoll. Soil Sci. Soc. Am. J. 55:794–799.[Abstract/Free Full Text]
• Bronswijk, J.J.B., W. Hamminga, and L. Oostindie. 1995. Field-scale solute transport in a heavy clay soil. Water Resour. Res. 31:517–526.
• Buhler, D.D., G.W. Randall, W.C. Koskinen, and D.L. Wyse. 1993. Atrazine and alachlor losses from subsurface tile drainage of a clay loam soil. J. Environ. Qual. 22:583–588.[Abstract/Free Full Text]
• Businelli, D. 1997. Pig slurry amendment and herbicide coapplication effects on s-triazine mobility in soil: An adsorption–desorption study. J. Environ. Qual. 26:102–108.[Abstract/Free Full Text]
• Butters, G.L., J.G. Benjamin, L.R. Ahuja, and H. Ruan. 2000. Bromide and atrazine leaching in furrow- and sprinkler-irrigated corn. Soil Sci. Soc. Am. J. 64:1723–1732.[Abstract/Free Full Text]
• Caron, J., O. Banton, D.A. Angers, and J.P. Villeneuve. 1996. Preferential bromide transport through a clay loam under alfalfa and corn. Geoderma 69:175–191.
• Chow, T.T. 1976. A low-cost tipping bucket flowmeter for overland and subsurface stormflow studies. Can. J. Soil Sci. 56:197–202.
• Czapar, G.F., R.S. Kanwar, and R.S. Fawcett. 1994. Herbicide and tracer movement to field drainage tiles under simulated rainfall conditions. Soil Tillage Res. 30:19–32.
• Davis, D.M., P.H. Gowda, D.J. Mulla, and G.W. Randall. 2000. Modeling nitrate leaching in response to nitrogen fertilizer rate and tile drain depth or spacing for southern Minnesota, USA. J. Environ. Qual. 29:1568–1581.[Abstract/Free Full Text]
• Day, P.R. 1965. Particle fractionation and particle size analysis. p. 545–567. In C.A. Black (ed.) Methods of soil analysis. Part 1. Agron. Monogr. 9. ASA, Madison, WI.
• Doran, J.W. 1980. Soil microbial and biochemical changes associated with reduced tillage. Soil Sci. Soc. Am. J. 44:765–771.[Abstract/Free Full Text]
• Eghball, B., L.N. Mielke, G.A. Calvo, and W.W. Wilhelon. 1993. Fractal description of soil fragmentation for various tillage methods and crop sequences. Soil Sci. Soc. Am. J. 57:1337–1341.[Abstract/Free Full Text]
• Elliott, J.A., A.J. Cessna, W. Nicholaichuk, and L.C. Tollefson. 2000. Leaching rates and preferential flow of selected herbicides through tilled and untilled soil. J. Environ. Qual. 29:1650–1656.[Abstract/Free Full Text]
• Everts, C.S., and R.S. Kanwar. 1990. Estimating preferential flow to a subsurface drain with tracers. Trans. ASAE 33:451–457.
• Fleming, J.B., and G.L. Butters. 1995. Bromide transport detection in tilled and nontilled soils: Solution samplers vs. soil cores. Soil Sci. Soc. Am. J. 59:1207–1216.[Abstract/Free Full Text]
• Flury, M. 1996. Experimental evidence of transport of pesticides through field soil—A review. J. Environ. Qual. 25:25–45.
• Flury, M., J. Leuenberger, B. Studer, and H. Flüler. 1995. Transport of anions and herbicides in a loamy and sandy field soil. Water Resour. Res. 31:823–835.
• Franzluebbers, A.J., G.W. Langdale, and H.H. Schomberg. 1999. Soil carbon, nitrogen, and aggregation in response to type and frequency of tillage. Soil Sci. Soc. Am. J. 63:349–355.[Abstract/Free Full Text]
• Gan, J., R.L. Becker, W.C. Koskinen, and D.D. Buhler. 1996. Degradation of atrazine in two soils as a function of concentration. J. Environ. Qual. 25:1064–1072.[Abstract/Free Full Text]
• Gaynor, J.D., D.C. MacTavish, and W.I. Findlay. 1992. Surface and subsurface transport of atrazine and alachlor from a Brookston clay loam under continuous corn production. Arch. Environ. Contam. Toxicol. 23:240–245.
• Gaynor, J.D., D.C. MacTavish, and W.I. Findlay. 1995. Atrazine and metolachlor loss in surface and subsurface runoff from three tillage treatments under corn. J. Environ. Qual. 24:246–256.[Abstract/Free Full Text]
• Gaynor, J.D., D.C. MacTavish, and A.B. Labaj. 1998. Atrazine and metolachlor residues in Brookston CL following conventional and conservation tillage culture. Chemosphere 36:3199–3210.[Medline]
• Gaynor, J.D., C.S. Tan, H.Y.F. Ng, C.F. Drury, T.W. Welacky, and I.J. Van Wesenbeeck. 2000. Tillage and controlled drainage–subirrigation management effects on soil persistence of atrazine, metolachlor, and metribuzin in corn. J. Environ. Qual. 29:936–947.[Abstract/Free Full Text]
• Gentry, L.E., M.B. David, K.M. Smith-Straks, and D.A. Kovacic. 2000. Nitrogen fertilizer and herbicide transport from tile drained fields. J. Environ. Qual. 29:232–240.[Abstract/Free Full Text]
• Gish, T.J., A.R. Isensee, R.G. Nash, and C.S. Helling. 1991. Impact of pesticides on shallow groundwater quality. Trans. ASAE 34:1745–1753.
• Gish, T.J., A. Shirmohammadi, R. Vyravipillai, and B.J. Wienhold. 1995. Herbicide leaching under tilled and no-tilled fields. Soil Sci. Soc. Am. J. 59:895–901.[Abstract/Free Full Text]
• Gruessner, B., N.C. Shambaugh, and M.C. Watzin. 1995. Comparison on an enzyme immunoassay and gas chromatography/mass spectrometry for the detection of atrazine in surface waters. Environ. Sci. Technol. 29:251–254.
• Hall, J.C., T.D. Van Deynze, J. Struger, and C.H. Chan. 1993. Enzyme immunoassay based survey of precipitation and surface water for the presence of atrazine, metolachlor and 2,4-D. J. Environ. Sci. Health Part B 28:577–598.
• Hussain, I., K.R. Olson, and S.A. Ebelkhar. 1999. Long-term tillage effects on soil chemical properties and organic matter fractions. Soil Sci. Soc. Am. J. 63:1335–1341.[Abstract/Free Full Text]
• Isensee, A.R., R.G. Nash, and C.S. Helling. 1990. Effect of conventional vs. no-tillage on pesticide leaching to shallow groundwater. J. Environ. Qual. 19:434–440.[Abstract/Free Full Text]
• Jemison, J.M., and R.H. Fox. 1991. Corn uptake of bromide under greenhouse and field conditions. Commun. Soil Sci. Plant Anal. 22:283–297.
• Kanwar, R.S., T.S. Colvin, and D. Karlen. 1997. Ridge, moldboard, chisel and no-till effects on tile water quality beneath two cropping systems. J. Prod. Agric. 10:227–234.
• Kemper, W.D., and W.C. Chepil. 1965. Size distribution of aggregates. p. 499–510. In C.A. Black (ed.) Methods of soil analysis. Part 1. Agron. Monogr. 9. ASA, Madison, WI.
• Kladivko, E.J., L.C. Brown, and J.L. Baker. 2001. Pesticide transport to subsurface tile drains in humid regions of North America. Crit. Rev. Environ. Sci. Technol. 31:1–62.
• Kladivko, E.J., G.E. Van Scoyoc, E.J. Monke, K.M. Oates, and W. Pask. 1991. Pesticide and nutrient movement into subsurface tile drains on a silt loam soil in Indiana. J. Environ. Qual. 20:264–270.[Abstract/Free Full Text]
• Lawruk, T.S., C.E. Lachman, S.W. Jourdan, J.R. Fleeker, D.P. Herzog, and F.M. Rubio. 1993. Determination of metolachlor in water and soil by a rapid magnetic particle-based ELISA. J. Agric. Food Chem. 41:1426–1431.
• Lennartz, B., J. Michaelsen, W. Wichtmann, and P. Widmoser. 1999. Time variance analysis of preferential solute movement at a tile-drained field site. Soil Sci. Soc. Am. J. 63:39–47.[Abstract/Free Full Text]
• Logan, T.J., D.J. Eckert, and D.G. Beak. 1994. Tillage, crop, and climatic effects on runoff and tile drainage losses of nitrate and four herbicides. Soil Tillage Res. 30:75–103.
• Maraux, F., and F. Lafolie. 1998. Modeling soil water balance of a maize–sorghum sequence. Soil Sci. Soc. Am. J. 62:75–82.[Abstract/Free Full Text]
• Needelman, B.A., M.M. Wander, G.A. Bollero, C.W. Boast, G.K. Sims, and D.G. Bullock. 1999. Interaction of tillage and soil texture: Biologically active soil organic matter in Illinois. Soil Sci. Soc. Am. J. 63:1326–1334.[Abstract/Free Full Text]
• Nelson, D.W., and L.E. Sommers. 1982. Total carbon, organic carbon, and organic matter. p. 539–579. In A.L. Page et al. (ed.) Methods of soil analysis. Part 2. 2nd ed. Agron. Monogr. 9. ASA, Madison, WI.
• Ogden, C.B., H.M. van Es, R.J. Wagenet, and T.S. Steenhuis. 1999. Spatial–temporal variability of preferential flow in a clay soil under no-till and plow-till. J. Environ. Qual. 28:1264–1273.[Abstract/Free Full Text]
• Ostrofsky, E.B., S.B. Traina, and O.H. Tuovinen. 1997. Variation in atrazine mineralization rates in relation to agricultural management practice. J. Environ. Qual. 26:647–657.[Abstract/Free Full Text]
• Phillips, P.J., G.R. Wall, E.M. Thurman, D.A. Eckhardt, and J. Vanhoesen. 1999. Metolachlor and its metabolites in tile drain and stream runoff in the Canajoharie Creek watershed. Environ. Sci. Technol. 33:3531–3537.
• Pivetz, B., and T.S. Steenhuis. 1989. Pesticide, nitrate, and tracer loss in agricultural tile lines and to groundwater under conventional and conservation tillage. ASAE Paper 89-2579. Am. Soc. Agric. Eng., St. Joseph, MI.
• Rhoton, F.E. 2000. Influence of time and soil response to no-till practices. Soil Sci. Soc. Am. J. 64:700–709.[Abstract/Free Full Text]
• Rouchaud, J., F. Gustin, O. Cappelen, and D. Moraux. 1994. Pig slurry and cow manure effect on atrazine and metolachlor soil biodegradation in maize. Bull. Environ. Contam. Toxicol. 52:568–573.[Medline]
• Rubio, F.M., J.A. Itak, A.M. Scutellaro, M.Y. Selisker, and D.P. Herzog. 1991. Performance characteristics of a novel magnetic-particle-based enzyme-linked immunosorbent assay for the quantitative analysis of atrazine and related triazines in water samples. Food Agric. Immunol. 3:113–125.
• Sadeghi, A.M., and A.R. Isensee. 1992. Effect of tillage system and rainfall patterns on atrazine distribution in soil. J. Environ. Qual. 21:464–469.[Abstract/Free Full Text]
• Sadeghi, A.M., A.R. Isensee, and D.R. Shelton. 1998. Effect of tillage age on herbicide dissipation: A side-by-side comparison using microplots. Soil Sci. 163:883–890.
• SAS Institute. 1997. SAS/STAT software: Changes and enhancements through release 6.12. SAS Inst., Cary, NC.
• Seta, A.K., R.L. Blevins, W.W. Frye, and B.J. Barfield. 1993. Reducing soil erosion and agricultural chemical losses with conservation tillage. J. Environ. Qual. 22:661–665.[Abstract/Free Full Text]
• Shapir, N., S. Goux, R.T. Mandelbaum, and L. Pussemier. 2000. The potential of soil micro-organisms to mineralise atrazine as predicted by MCH-PCR followed by nested PCR. Can. J. Microbiol. 46:425–432.[Medline]
• Singh, P., R.S. Kanwar, K.E. Johnsen, and L.R. Ahuja. 1996. Calibration and evaluation of subsurface drainage component of RZWQM V.2.5. J. Environ. Qual. 25:56–63.[Abstract/Free Full Text]
• Southwick, L.M., G.H. Willis, and H.M. Sewlim. 1992. Leaching of atrazine from sugarcane in southern Louisiana. J. Agric. Food Chem. 40:1264–1268.
• Steenhuis, T. S., W. Staubitz, M.S. Andreini, J. Surface, T.L. Richard, R. Paulsen, N.B. Pickering, J.R. Hagerman, and L.D. Goehring. 1990. Preferential movement of pesticides and tracers in agricultural soils. J. Irrig. Drain. Eng. 116:50–66.
• Topp, E., L. Tessier, and E.G. Gregorich. 1996. Dairy manure incorporation stimulates rapid atrazine mineralization in an agricultural soil. Can. J. Soil Sci. 76:403–409.
• Traub-Eberhard, U., K.-P. Henschel, W. Kördel, and W. Klein. 1995. Influence of different field sites on pesticide movement into subsurface drains. Pestic. Sci. 43:121–129.
• Traub-Eberhard, U., W. Kördel, and W. Klein. 1993. Pesticide movement into subsurface drains on a loamy silt soil. Chemosphere 28:273–284.
• Turco, R.F., and E.J. Kladivko. 1994. Studies on pesticide mobility: Laboratory vs. field. p. 63–80. In R.C. Honeycutt and D.J. Schabacker (ed.) Mechanisms of pesticide movement into ground water. Lewis Publ., Boca Raton, FL.
• Vyn, T.J., and B.A. Raimbault. 1993. Long-term effect of five tillage systems on corn response and soil structure. Agron. J. 85:1074–1079.[Abstract/Free Full Text]
• Watts, D.W., and J.K. Hall. 1996. Tillage and application effects on herbicide leaching and runoff. Soil Tillage Res. 39:241–257.
• Wauchope, R.D., T.M. Buttler, A.G. Hornsby, P.M. Augustin-Beckers, and J.P. Burt. 1992. The SCS/ARS/CES pesticide properties database for environmental decision making. Rev. Environ. Contam. Toxicol. 123:1–155.[ISI][Medline]
• Zehe, E., and H. Flühler. 2001. Preferential transport of isoproturon at a plot scale and a field-scale tile-drained site. J. Hydrol. (Amsterdam) 247:100–115.

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