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Journal of Environmental Quality 30:561-572 (2001)
© 2001 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America

TECHNICAL REPORT
SURFACE WATER QUALITY

Tillage, Intercrop, and Controlled Drainage–Subirrigation Influence Atrazine, Metribuzin, and Metolachlor Loss

J.D. Gaynora, C.S. Tana, C.F. Drurya, H.Y.F. Nga,b, T.W. Welackya and I.J. van Wesenbeeckc

a Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, ON N0R 1G0
b NWRI Environment Canada, Burlington, ON L7R 4A6
c Dow AgroSciences, Environmental Fate, Bldg 306-Az, 9330 Zionsville Rd., Indianapolis, IN 46268

Corresponding author (gaynorj{at}em.agr.ca)

Received for publication April 7, 2000.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] have been found with increasing occurrence in rivers and streams. Their continued use will require changes in agricultural practices. We compared water quality from four crop-tillage treatments: (i) conventional moldboard plow (MB), (ii) MB with ryegrass (Lolium multiflorum Lam.) intercrop (IC), (iii) soil saver (SS), and (iv) SS + IC; and two drainage control treatments, drained (D) and controlled drainage–subirrigation (CDS). Atrazine (1.1 kg a.i. ha-1), metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazine-5(4H)-one] (0.5 kg a.i. ha-1), and metolachlor (1.68 kg a.i. ha-1) were applied preemergence in a band over seeded corn (Zea mays L.) rows. Herbicide concentration and losses were monitored from 1992 to spring 1995. Annual herbicide losses ranged from <0.3 to 2.7% of application. Crop-tillage treatment influenced herbicide loss in 1992 but not in 1993 or 1994, whereas CDS affected partitioning of losses in most years. In 1992, SS + IC reduced herbicide loss in tile drains and surface runoff by 46 to 49% compared with MB. The intercrop reduced surface runoff, which reduced herbicide transport. Controlled drainage–subirrigation increased herbicide loss in surface runoff but decreased loss through tile drainage so that total herbicide loss did not differ between drainage treatments. Des-ethyl atrazine [6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] comprised 7 to 39% of the total triazine loss.

Abbreviations: CDS, controlled drainage–subirrigation • D, drained • DAA, days after application • IMAC, interim maximum acceptable concentration • MB, moldboard plow • MB + IC, moldboard plow with ryegrass intercrop • SS, soil saver • SS + IC, soil saver with ryegrass intercrop


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
MONOCULTURE cash-cropping in the Great Lakes basin has resulted in increased fertilizer, pesticide, and large machinery use that has contributed to a decrease in soil structure (Stone et al., 1985; Stone, 1987) and water quality (Gaynor et al., 1992, 1995a). In southwestern Ontario, soils are extensively surface and/or tile drained to facilitate early planting and harvest. Early studies suggest tile drainage negatively affected water quality (Gaynor et al., 1992; Gaynor and Findlay, 1995; Frank et al., 1990; vonStryk and Bolton, 1977).

Environmental and cultural factors such as duration of runoff and residue management affect herbicide transport. Crop residue reduced surface runoff, sediment, and herbicide loss from no-till plots compared with conventional tillage on a well-drained silt loam soil (Kenimer et al., 1987). Corn residue cover of 1500 kg ha-1 reduced runoff volume 92% compared with that with no crop residue. Although herbicide concentration of the runoff was higher from plots with corn residue, the lower runoff volumes resulted in less herbicide loss. On another silt loam soil, conservation tillage reduced surface runoff volume 20 to 34% compared with conventional tillage, but the higher herbicide concentrations in the runoff resulted in no differences in herbicide loss (Sauer and Daniel, 1987).

The nature of the hydrological event after herbicide application and cultural practices that have an effect on hydrology appear to be important in herbicide transport. Pantone et al. (1992) reported higher herbicide concentrations and loss in surface runoff 1 day after herbicide application (DAA) than 30 DAA. Zhang et al. (1997), in a simulation study, showed that rain intensities that produced runoff within 10 min transported twice as much herbicide as that from a less intense rain. Greater loss occurred from a silty loam than a sandy loam soil but the effect of rain intensity was greatest on the sandy loam.

Surface runoff from plots managed by conservation tillage appears to be more consistently reduced on coarse- than fine-textured soils (Unger, 1990). Infiltration of water is greater on coarse- than fine-textured soils, which results in enhanced leaching of herbicides (Isensee et al., 1990). Herbicides with high water solubility and low affinity for soil move with the water front, increasing the risk of ground water contamination or transport through tile drainage. Although there are many studies that examine herbicide losses through surface runoff, herbicide loss through tile drainage under various tillage systems and for different soil types has not been extensively studied.

Increased crop residue from conservation tillage may not have as great of an effect on water infiltration and hence surface runoff volumes on fine-textured as on coarse-textured soils because of the lower hydraulic conductivity of these soils. On fine-textured soil, tillage had no consistent effect on surface runoff, tile drainage, or combined surface runoff and tile drainage (Gaynor et al., 1992, 1995a; Olson et al., 1998). The time of the runoff-producing event in relation to herbicide application and the nature of the event had a greater effect on herbicide loss than tillage. Thus, it is increasingly recognized that the effect of tillage on surface runoff of water and herbicide loss is interrelated with antecedent soil moisture content, proximity and amount of rain after herbicide application, rain intensity and duration, soil texture, and water infiltration rate into the soil. Therefore, solutions to the water contamination problems caused by herbicide and nutrient use in agriculture are not simple and will require an interdisciplinary and multifaceted approach.

Cultural practices affecting hydrology, such as residue management, intercropping, and controlled drainage, could influence herbicide transport in a positive way. Grassed buffer strips between waterways and agricultural fields effectively reduced herbicide concentration and transport to receiving waters (Hall et al., 1983; Arora et al., 1996). However, grassed buffer strips are not always practical in agricultural areas where land is at a premium. Our objective was to devise an integrated soil, crop, and water management system to reduce herbicide losses in surface runoff and tile drain outflow. Changes in water quality were measured from two drainage scenarios (CDS and D) incorporating four crop-tillage treatments: MB, MB + IC, SS, and SS + IC. Water quality from each treatment was compared with that from the MB + D treatment. Banded herbicide application technology was used to accommodate the IC treatment and to reduce herbicide input (Eadie et al., 1992; Swanton and Weise, 1991; Gaynor and vanWesenbeeck, 1995; Moorman et al., 1999). A reduction in herbicide rate greatly reduced herbicide loss in surface runoff (Hall, 1974).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 
Site Description
In 1991, an integrated management study incorporating CDS and D treatments with four crop-tillage treatments (MB, MB + IC, SS and SS + IC) with herbicide banding was initiated to study the interaction of these cultural practices on water quality (Tan et al., 1993; Drury et al., 1996). The soil was a poorly drained Brookston clay loam (fine-loamy, mixed, superactive, mesic Typic Argiaquoll). The 30-cm-deep Ap horizon is a dark brown, clay loam with 25 g kg-1 organic matter. The B horizon extends to a 1.5-m depth with a clay texture. Each plot contains two 104-mm-diam. tiles at 7.5 m spacing and 0.6 m depth. There were 16 plots, each 15 m wide by 67 m long (0.10 ha), with less than 1% slope. Water table in the subirrigated treatments is controlled by risers fitted to the drain tile outlet (Tan et al., 1993). During the growing season, the risers control the water level at 30 cm below ground level. Subirrigation is initiated when water level drops below 30 cm. Risers are removed before harvest in fall and before planting in spring to facilitate these operations. After harvest, risers were reinstalled to control drainage at 30 cm for the winter and spring periods and no subirrigation was applied. Subirrigation began in June of each year when required and continued until September. Excess water from rain entered an overflow pipe when the water table exceeded the preset level.

Surface runoff was channelled to 0.5-m-diam. catch basins downslope of the treatments. Surface runoff catchment and tile drainage lines are connected to a central monitoring facility to record volume of runoff and automated sample collection (Calypso 2000s, Buhler Gmbh and Co., Geneq, Weston, ON, Canada). Surface runoff and tile drainage from each individual treatment are pumped through water meters to drain outlets. A multichannel datalogger records water volumes on a continuous basis for each rain event (Soultani et al., 1993). Water samples are collected at 500 to 3000 L depending on time of year and expected runoff volumes. The more frequent sampling was done during the growing season when herbicide concentrations are most dynamic. Water samples, with no preservatives, were stored in glass bottles at 4°C prior to analyses.

Agronomy
Atrazine, metribuzin, and metolachlor were applied preemergence as a tank mix at 1.1, 0.5, and 1.68 kg a.i. ha-1, respectively, in the band on 14 May 1992, 17 May 1993, and 13 May 1994. The herbicide was applied in a 38-cm band over the seeded row (76-cm spacing) so that 550 g ha-1 atrazine, 250 g ha-1 metribuzin, and 840 g ha-1 metolachlor were applied, which represents a 50% reduction in the amount of herbicide applied to the area compared with broadcast application. Herbicide was applied in 270 L ha-1 water with a Chelsea sprayer (Turner Ltd., Blenheim, ON, Canada) equipped with 8004 EVS Tee Jet (Sprayer Systems Co., Wheaton, IL) flat fan nozzles. In 1994, herbicide was applied to the entire area in MB and SS and band-applied at the same rate in the band in MB + IC and SS + IC treatments to assess the effect of banded herbicide application on losses.

Corn (`Pioneer 3573') was seeded at a rate of 65000 seeds ha-1 in 75-cm-wide rows with a Kinze (Williamsburg, IA) four-row planter. Fertilizer (8–32–16, N–P–K) was band-applied beside the seed at a rate of 132 kg ha-1. Urea (46–0–0, N–P–K) was applied (167 kg ha-1) with a brush applicator at the six-leaf stage at a rate based on the average nitrate soil test (Drury et al., 1996). After planting, annual ryegrass intercrop was seeded in the interrow with a Brillion seeder (Brillion Iron Works, Brillion, WI).

Herbicide Analyses
Water samples were analyzed for herbicide concentration within 60 d of collection. Reanalysis of selected samples indicated no change in concentration up to 6 mo. A 500-mL aliquot was filtered under suction through a 0.45-µm filter (Gelman Cat GN-6, Gelman Sciences, Rexdale, ON, Canada). Herbicide in the water was concentrated on a preconditioned cyclohexyl Sep Pak cartridge (Baker Catalog no. 7212-03; Mallinckrodt Baker, Phillipsburg, NJ). After herbicide loading, the cartridge was dried and the herbicide eluted with 1.5 mL methanol. Samples were analyzed on a Varian 3400 gas chromatograph (Varian Canada, Mississauga, ON). Analytes were separated on a 15-m DB-5 capillary column (J & W Scientific, Folsom, CA) temperature programmed from 70 to 210°C. A thermionic sensitive detector operated in N mode was used to detect and quantify the herbicides. Herbicide loss was calculated from the product of the herbicide concentration in the water and the volume of runoff or tile drainage. Herbicide recovery from natural surface runoff and tile drainage fortified with 0.1 and 1.0 µg L-1 of the respective herbicides and des-ethyl atrazine was greater than 80%. All values are reported without correction for recovery. Minimum detectable quantity in water samples depended upon volume assayed (100 to 500 mL) and interferences from residue decomposition encountered during the season. Generally our detection limit, defined as three times the standard deviation of early spring samples (Keith et al., 1983), was 0.01 µg L-1 for each of the four test substances. This was the minimum concentration used in calculating the sum for the period losses of each of the herbicides.

Statistics
The study employed a four by two factorial arranged in a randomized complete block design. There were two replicates of four crop-tillage treatments: MB, MB + IC, SS, and SS + IC. Water management treatments were D and CDS, providing a total of 16 plots. The MB treatment with D was considered the standard conventional treatment for comparison. Statistical significance is reported at the 0.05 level.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
SUMMARY
 REFERENCES
 
Sampling and Rainfall Event Profiles
The occurrence of runoff events and number of samples collected in each year reflected the incidence of rainfall events from May 1992 to May 1995. Rain amounts and distribution are depicted in Fig. 1 . From January to December, 995 mm of rain was received in 1992, 688 mm in 1993, and 717 mm in 1994. The average rainfall for a 10-yr period (1989 to 1998) was 763 mm. In 1992, 486 mm was received during the growing season from May to October, while 310 and 294 mm was received in the 1993 and 1994 growing seasons. Potential evaporation for this period was 585 mm in 1992, 594 mm in 1993, and 616 mm in 1994. Thus, 1993 and 1994 had greater water deficits than 1992, which was reflected in lower runoff and drainage during the growing season (Fig. 2 and 3 , top graphs). Total runoff (surface runoff + tile drainage) during the growing season amounted to 119, 21, and 14 mm in 1992, 1993, and 1994, respectively. Total runoff from herbicide application to application the following year accounted for 449, 153, and 237 mm in 1992, 1993, and 1994, respectively (Table 1), most of which occurred during the winter months when herbicide losses were low (Gaynor et al., 1992, 1995a,b; Olson et al., 1998; Moorman et al., 1999; Jaynes et al., 1999).



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  		Fig. 1. Monthly (bars) and 10-yr average (solid line) rainfall from January 1992 to May 1995 at Woodslee, ON, Canada. Arrows denote time of herbicide application

 


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  		Fig. 2. Runoff and herbicide concentration in the runoff from May 1992 to April 1995 with either drainage (D) or controlled drainage–subirrigation (CDS). Arrows denote time of herbicide application. Vertical bars are standard error of treatment means (n = 8). Dashed lines are Canadian interim maximum acceptable concentration (triazine = 5 µg L-1 and metolachlor = 50 µg L-1)

 


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  		Fig. 3. Tile drainage and herbicide concentration in the drainage from May 1992 to April 1995 with either drainage (D) or controlled drainage–subirrigation (CDS). Arrows denote time of herbicide application. Vertical bars are standard error of treatment means (n = 8). Dashed lines are Canadian interim maximum acceptable concentration (triazine = 5 µg L-1 and metolachlor = 50 µg L-1)

 

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  		Table 1. Annual depth of surface runoff, tile drainage, and total runoff from mold board plow (MB), soil saver (SS), mold board plow with annual ryegrass intercrop (MB + IC), and soil saver with annual ryegrass intercrop (SS + IC) treatments with drained (D) or controlled drainage–subirrigation (CDS) from 1992 to 1993, 1993 to 1994, and 1994 to 1995. F statistics and probability levels for tillage cropping treatments (TMT), water management (WT), and their interaction are included

 
Surface runoff and tile drainage profiles varied from year to year depending upon soil moisture conditions, preceding rainfall, and amount and intensity of rain (Fig. 1 and top graphs in Fig. 2 and 3). Larger runoff and drainage amounts were recorded in the study period from 1992 to 1993 (422 to 469 mm) compared with that from 1993 to 1994 (119 to 188 mm) and 1994 to 1995 (212 to 252 mm) (Table 1). Averaged over management treatments, controlled drainage–subirrigation increased surface runoff 107% compared with D treatments (105 mm), but reduced tile drainage 34% from 1992 to 1993. Total runoff was not changed. The increased surface runoff in the CDS treatment was because of the high water table from rainfall since no subirrigation was applied in 1992 (Drury et al., 1996). For the 1993 to 1994 period, CDS reduced tile drainage 31% and total runoff 18% compared with D treatments but had no significant effect on surface runoff (P > 0.05). Controlled drainage–subirrigation treatments received an average of 129 mm subirrigation in 1993. Surface runoff was increased 61% by CDS for the 1994 to 1995 period but the decrease in tile drainage or total runoff was not significant. In this year, 114 mm subirrigation was applied. The increased surface runoff from the CDS treatments was related to shallower water table depths as a result of rainfall for the 1992 to 1993 period and subirrigation for the 1993 to 1994 and 1994 to 1995 periods (Drury et al., 1996).

Herbicide is most susceptible to aqueous transport shortly after application (Wauchope, 1978; Gaynor et al., 1992, 1995a; Moorman et al., 1999; Jaynes et al., 1999). Eighteen collection events were monitored from herbicide application in May 1992 to application in May 1993 with 2091 surface and 2489 tile samples collected from the 16 plots and analyzed for herbicide concentration. Thirty seven percent of the surface samples and 35% of the tile samples were collected during the growing season (May to September). Twelve runoff events occurred in the 1993 to 1994 season with 871 surface and 954 tile samples. Of these, 47% of surface and 25% of tile samples were collected during the 1993 to 1994 growing season. Six runoff events occurred in the 1994 to 1995 period with 410 surface and 1447 tile samples collected. Although the amount of runoff (6 to 22%) and tile drainage (7 to 38%) during the growing season constituted a small proportion of the total rainfall, it accounted for a large proportion (49 to 99%) of total herbicide loss (Table 2). This supports the growing body of evidence that the nature and intensity of rainfall events within months after herbicide application is one of the most significant factors in herbicide loss (Gaynor et al., 1992, 1995a; Triplett et al., 1978; Wauchope, 1978; Olson et al., 1998; Moorman et al., 1999; Jaynes et al., 1999).


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  		Table 2. Rain (mm), runoff (mm), drainage (mm), and accompanying herbicide losses (g ha-1, % of annual loss in parentheses) before and after herbicide application (DAA) for each significant rainfall event. Values averaged over treatment and water table control. Period totals are from herbicide application in May to May of the next year

 
Rainfall Events after Application
Greater amounts of herbicide were lost for the 1992 to 1993 and 1993 to 1994 periods than for the 1994 to 1995 period. On average, 9.0 g ha-1 of atrazine were lost from 1992 to 1993, 13.8 g ha-1 from 1993 to 1994, and 2.2 g ha-1 from 1994 to 1995 (Table 2). The small (5 to 280 mg ha-1) quantities of herbicide lost before application in 1992 are from herbicide applied in 1991. The proportion of des-ethyl atrazine lost (1 to 64%) increased as the amount of atrazine loss decreased. Thus, the atrazine metabolite becomes more significant to the total loss in years when atrazine losses are small. A similar observation was made in previous studies (Gaynor et al., 1992, 1995a; Jayachandran et al., 1994). Similar amounts of metribuzin were lost for the 1992 to 1993 and 1994 to 1995 periods (2.4 and 2.1 g ha-1, respectively), with greater loss in the 1993 to 1994 period (6.3 g ha-1). Metolachlor loss averaged 7.6, 13.9, and 4.4 g ha-1 for the 1992 to 1993, 1993 to 1994, and 1994 to 1995 periods, respectively.

Most of the herbicide transport occurred immediately after application before the herbicide had reacted with soil constituents and undergone degradation (Fig. 4 and 5) . Two small rainfall events 25 DAA in 1992 totalling 58 mm produced 1.7 mm tile drainage (Table 2). Because little tile drainage was produced in this event, it accounted for less than 2% of the total herbicide loss (2.5 to 9.0 g ha-1). A 39.5-mm rainfall 39 DAA produced 6.8 mm combined surface and subsurface runoff, which removed 23 to 35% of the herbicide lost. Another 95.5-mm rainfall removed a further 28 to 45% of the herbicides. A larger proportion of metribuzin (75%) and metolachlor (70%) than atrazine (51%) was removed in these rainfall events. In 1993, 79 mm of rainfall was received 22 DAA, which produced 17.4 mm of combined runoff and drainage accounting for 83 to 87% of the total herbicide loss (6.3 to 13.9 g ha-1). The next 48-mm rainfall 52 DAA produced 3.8 mm of runoff and drainage and removed a further 10 to 16% of the herbicides. In 1994, several small rainfalls accumulated 108 mm up to 47 DAA, but only 4.3 mm of runoff and drainage was recorded, which transported 35 to 53% of the herbicide loss (2.1 to 4.4 g ha-1). Thus, the data substantiates simulation studies (Zhang et al., 1997) and literature reviews (Triplett et al., 1978), which show that rainfall that produces no surface runoff close to herbicide application greatly reduces herbicide loss in subsequent rainfalls.



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  		Fig. 4. Cumulative surface runoff and herbicide loss in the runoff from May 1992 to April 1995 with either drainage (D) or controlled drainage–subirrigation (CDS). Arrows denote time of herbicide application. Vertical bars are standard error of treatment means (n = 8)

 


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  		Fig. 5. Cumulative tile drainage and herbicide loss in the drainage from May 1992 to April 1995 with either drainage (D) or controlled drainage–subirrigation (CDS). Arrows denote time of herbicide application. Vertical bars are standard error of treatment means (n = 8)

 
Herbicide Concentration in Surface Runoff and Tile Drainage
Herbicide concentrations (expressed as flow-weighted concentrations for each collection period) were largest in runoff or tile drainage events soon after herbicide application (Fig. 2 and 3). In these events, concentration exceeded the Canadian interim maximum acceptable concentration (IMAC) of 5 µg L-1 for atrazine and metribuzin and 50 µg L-1 for metolachlor. The proportion of samples exceeding the Canadian IMAC in runoff and drainage was similar for atrazine (5 to 33%) and metribuzin (8 to 29%) (Table 3). The similar frequency of samples exceeding the Canadian IMAC for atrazine and metribuzin is noteworthy since metribuzin was added at half the rate of atrazine. This probably reflects the higher solubility of metribuzin (1220 vs. 33 mg L-1; Weed Science Society of America, 1989) relative to atrazine and its lower affinity for adsorption to this soil (Gaynor et al., 2000). Des-ethyl atrazine exceeded the IMAC less frequently (0 to 25%) than atrazine, whereas metolachlor exceeded the Canadian IMAC in 0 to 22% of the samples. Drainage control had no consistent effect on the frequency of samples exceeding the Canadian IMAC in runoff or tile drainage (Table 3).


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  		Table 3. Proportion of runoff and tile drainage samples with herbicide concentration greater than the Canadian interim maximum acceptable drainage (IMAC; 5 µg L-1 for triazines and 50 µg L-1 for metolachlor)

 
Herbicide Losses Related to Crop Tillage
Crop-tillage treatments only affected total runoff and herbicide loss in the 1992 to 1993 season (Tables 4 to 7), probably because of the nature of the runoff events and low antecedent moisture content conditions. Except for metribuzin, soil saver reduced total herbicide loss 32 to 38% (p < 0.05) compared with moldboard plow (Tables 4 to 7). Most all of the reduction occurred from surface runoff. Smaller herbicide loss has been reported in surface runoff from no-till compared with conventional till (Malone et al., 1996a), but drainage losses are increased (Malone et al., 1996b), which results in little or no change in total herbicide loss from no-till (Malone et al., 1996a,b; Kanwar et al., 1997). Also, larger herbicide concentrations in surface runoff from no-till counters the effect of reduced runoff so that a reduction in herbicide loss from tillage may not be consistently realized (Sauer and Daniel, 1987).


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  		Table 4. Annual atrazine loss in surface runoff, tile drainage, and total runoff from mold board plow (MB), soil saver (SS), mold board plow with annual ryegrass intercrop (MB + IC), and soil saver with annual ryegrass intercrop (SS + IC) treatments with drained (D) or controlled drainage–subirrigation (CDS) from 1992 to 1993, 1993 to 1994, and 1994 to 1995. F statistics and probability levels for tillage cropping treatments (TMT), water management (WT), and their interaction are included

 

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  		Table 7. Annual metolachlor loss in surface runoff, tile drainage, and total runoff from mold board plow (MB), soil saver (SS), mold board plow with annual ryegrass intercrop (MB + IC), and soil saver with annual ryegrass intercrop (SS + IC) treatments with drained (D) or controlled drainage–subirrigation (CDS) from 1992 to 1993, 1993 to 1994, and 1994 to 1995. F statistics and probability levels for tillage cropping treatments (TMT), water management (WT), and their interaction are included

 

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  		Table 5. Annual des-ethyl atrazine loss in surface runoff, tile drainage, and total runoff from mold board plow (MB), soil saver (SS), mold board plow with annual ryegrass intercrop (MB + IC), and soil saver with annual ryegrass intercrop (SS + IC) treatments with drained (D) or controlled drainage–subirrigation (CDS) from 1992 to 1993, 1993 to 1994, and 1994 to 1995. F statistics and probability levels for tillage cropping treatments (TMT), water management (WT), and their interaction are included

 

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  		Table 6. Annual metribuzin loss in surface runoff, tile drainage, and total runoff from mold board plow (MB), soil saver (SS), mold board plow with annual ryegrass intercrop (MB + IC), and soil saver with annual ryegrass intercrop (SS + IC) treatments with drained (D) or controlled drainage–subirrigation (CDS) from 1992 to 1993, 1993 to 1994, and 1994 to 1995. F statistics and probability levels for tillage cropping treatments (TMT), water management (WT), and their interaction are included

 
The ryegrass intercrop reduced total herbicide loss 14 to 25%, with the lowest herbicide loss from the SS + IC, D treatment (Tables 4 to 7). The intercrop was reseeded each year and establishment in the early part of the growing season was slow when runoff and herbicide loss are most dynamic. The intent of the intercrop was to reduce runoff and to increase infiltration of water (Wall et al., 1991) and thereby reduce herbicide loss. This occurred in the 1992 to 1993 period but not in other years (Tables 1 and 4 to 7). No studies on water quality have been published with ryegrass intercrop, but established grassed filter strips reportedly reduced herbicide concentration and loss (Arora et al., 1996; Barfield et al., 1998; Dillaha et al., 1989; Hayes et al., 1984).

Sediment phase transport was not measured in our study because erosional losses (390 kg ha-1 yr-1) from this soil and slope are low (Gaynor and Findlay, 1995) and previous studies found little (<0.001 g ha-1) herbicide transported by sediment (Gaynor et al., 1992). Wauchope (1978) reviewed the early literature and determined that herbicides with large water solubility and low adsorption affinity were most susceptible to aqueous transport. Zhang et al. (1997) found greater than 85% of atrazine and 72% of metolachlor loss in the aqueous phase from a silt loam and sandy loam soil, indicating sediment transport may be significant for some soil types.

Drainage Control and Rainfall Effects on Herbicide Loss
Controlled drainage–subirrigation resulted in greater herbicide loss through surface runoff than tile drainage in all years (Fig. 4 and 5), except for atrazine and metolachlor in 1993 (p > 0.05, Tables 4 to 7). Controlled drainage–subirrigtion increased surface runoff but decreased tile drainage losses so that no significant change in total herbicide loss was detected. Thus, CDS would be expected to affect source but not total herbicide loss. We did observe (p = 0.05) a 27% increase in total des-ethyl atrazine loss with CDS compared with D (0.92 g ha-1) in 1993 (Table 5). The cumulative herbicide loss profiles in surface runoff and tile drainage (Fig. 4 and 5) emphasize the importance of rain events soon after herbicide application in herbicide loss. Management practices that alter the hydrology early in the growing season will be most effective in reducing herbicide losses.

Banded Herbicide Application
The same amount of herbicide was applied to all treatments in 1992 and 1993. However, in 1994 the MB + IC and SS + IC treatments received 50% less herbicide through band application then the MB and SS treatments. The herbicide rate in the band was similar in all treatments but less area was treated in the band application. The beneficial effect of banding vs. broadcast application could not be directly assessed because 1994 was a dry year and herbicide losses were low (2.1 to 4.4 g ha-1) (Tables 4 to 7). No significant benefit of banding vs broadcast application was apparent in that year. The sum of atrazine + des-ethyl atrazine loss averaged 3.64 g ha-1 from broadcast and 3.68 g ha-1 from band application (Tables 4 and 5). Metribuzin loss averaged 2.05 and 2.08 g ha-1, respectively (Table 6). Metolachlor loss averaged 4.72 and 4.16 g ha-1, respectively (Table 7). With rainfall simulation, Gaynor and vanWesenbeeck (1995) reported that atrazine and metribuzin, but not metolachlor, loss in surface runoff was reduced in direct proportion to the area treated. A 50% reduction in area treated reduced triazine loss in surface runoff by 50%, but the percentage loss remained unchanged. Smaller herbicide concentrations and lower losses in tile drainage were reported from the Walnut Creek watershed study in Iowa when herbicide was band-applied (Moorman et al., 1999). Hall et al. (1972) found that aqueous and sediment loss of broadcast-applied herbicide decreased with lower herbicide rates. In that study, a greater percentage of the quantity of herbicide applied was lost at higher than at lower rates of application, indicating that the reduction in loss was not in direct proportion to herbicide rate. Atrazine loss from their studies was only measured in surface runoff. In our study, less than 3% of atrazine and metribuzin applied and 2% metolachlor applied were lost through surface and subsurface transport.


   SUMMARY
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
REFERENCES
 
Controlled drainage–subirrigtion on fine-textured soil may change the distribution of herbicide loss between surface runoff and tile drainage, but total herbicide loss does not seem to be affected. Soil saver tillage combined with a ryegrass intercrop has potential in some years to decrease total herbicide loss by at least 49% compared with conventional moldboard plow tillage by reducing surface transport. In this study, maximum triazine and metolachlor loss in combined surface runoff and tile drainage was 3.8 and 2.3%, respectively, of that applied. Of the cultural practices studied, reduced herbicide input by band application will reduce herbicide loss irrespective of environmental factors (Moorman et al., 1999; Gaynor and vanWesenbeeck, 1995). The integrated management practice for corn production incorporating a ryegrass intercrop and band application of herbicide holds potential for improving water quality of surface runoff and tile drainage.


   ACKNOWLEDGMENTS
 
This research has been supported by grants from the Preservation Fund of the Great Lakes Water Quality Action Plan. Appreciation is expressed to the following individuals: M. Soultani, V. Bernyk, D. MacTavish, G. Stasko, T. Oloya, K. Rinas, J. St. Denis, J. Stowe, S. Mannell, W. McLean, A. Szabo, M. Bissonnett, S. Duransky, and J. Elliott, who contributed through technical, secretarial and field support. Appreciation is further extended to Big "O" Inc., which donated some of the nonperforated pipes used in this project, and to Novartis Crop Protection Canada Inc., for analytical standards of the herbicides.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY
 REFERENCES
 




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