Drainage and Water Quality in Northern United States and Eastern Canadaa

Journal of Irrigation and Drainage Engineering / July/August 1995 / 296

By W. F. Ritter,1 R. P. Rudra,2 P. H. Milburn,3 and S. Prasher,4 Member, ASCE

Abstract

Drainage has been used in the northeastern United States and Canada since colonial times. It has only been since the 1970s that substantial quantities of subsurface drains have been installed annually in Quebec. Drainage in Ontario was first installed in the early 1900s. Today there is an increasing concern that drainage is harmful to the environment. II has only been in recent years that projects have been initiated to evaluate the environmental impacts of agricultural drainage. Both nitrates and pesticides have been detected in agricultural drainage waters, sometimes at concentrations exceeding drinking-water standards. Research has identified the need for integrated management of water quality and quanl1ty. There is a need to quantify the role of preferential flow as a mechanism of pollutant transport in surface and subsurface drainage water and to develop a modeling approach that is applicable at the field and watershed scale.

Introduction

The northeastern United States includes the states of Maine, Vermont, New Hampshire, Massachusetts, Connecticut, Rhode Island, New York, and Pennsylvania. According to the U. S. Department of Commerce (USDOC), in 1987 in these states with a total agricultural land area of 8,315,000 ha there were over 114,000 farms and 5,159,000 ha of cropland (USDOC, 1989). Dairy is the largest livestock industry in these states with New York and Pennsylvania having over 1,400,000 dairy cows (USDOC, 1989). Hay is the leading crop grown on 2,110,000 ha followed by corn on 670,000 ha (USDOC, 1989). The 1991 value of agricultural products sold was $8.46 billion (North Carolina 1992).

For the purposes of this paper, Eastern Canada has been defined as encompassing all of the provinces east of and including Ontario. The moderate climate of southern Ontario influenced by the Great Lakes has led to the development of a diverse agricultural economy. Ontario has the most diverse and largest agricultural industry in Canada with total receipts of U. S. $4.0 billion in 1991. According to the Ontario Ministry of Agriculture and Food (OMAF) in 1991 there were 68,600 farms in Ontario with 5,455,000 ha of land (OMAF 1992). About one half of Ontario farms have livestock with about one third of the livestock operations in dairy production and the remaining two thirds in meat production. There has been a dramatic change over the years crop in production from forage and cereal grains to corn and beans. About 47% of the agricultural land in Ontario is in corn and bean production.

Quebec is the largest Province in eastern Canada. Of a total of 136,000,000 ha, however, only 5%, or about 7,000,000 ha. is farmland. At present, only 2,100,000 ha are cultivated for crop production, or improved pasture and hay (Shady 1989). Most of this productive land is located along the St. Lawrence River and its major tributaries. Quebec had 38,000 farms in 1991 with agricultural receipts of over U. S, $3.7 billion. Dairy products make up over 30% of the agricultural receipts (OMAF 1992). Corn and vegetables are the two leading crops. Quebec's agriculture is not as diversified as Ontario's agriculture but is similar to the agriculture in most of the northeastern states.

The Atlantic Provinces of Canada, Newfoundland (NF), Prince Edward Island (PEI). Nova Scotia (NS), and New Brunswick (NB), produce approximately 3.5% of the total gross value of Canadian agricultural products sold and account for 1% of the improved agricultural land in Canada. The proportion of land used for agricultural production varies from 48% of the total land area in PEI to less than I% of the total land area in NF. Total agricultural land in the Atlantic province is 1,134,000 ha with 524,700 ha of improved farmland (land subject to various general imputs such as cultivation and fertilization) and may include drainage improvement (Statistics Canada 1987). According to the Canada Land Inventory Capability of Agricultural Soil Classification (Nowland 1975),5,600,000 ha are rated suitable for general arable use. Only about 9% of the potentially arable soils are in current agricultural use, with the remainder under forest. Drainage limitations of soils are common to one half of all the potentially arable land including existing agricultural lands (Nowland 1975; Milburn 1989; Milburn et aL 1989).

This paper is designed to discuss the history of drainage in the northeastern U. S. and eastern Canada and to summarize drainage and water-quality research in the region: A limit~d discussion on future research needs will also be Included In the paper.

History of Drainage Development

Early drainage work was constructed in Massachusetts under the authority of colonial and state laws. Early settlers In New York and New England used subsurface drainage in addition to open ditches. Material used for buried drains prior to the use of fired clay tile pipes included poles, logs, brush, lumber of all sorts, stones laid in various patterns, bricks, and straw.

The first use of clay tile for farm drainage is attributed to John Johnston who lived in the Finger Lakes region of New York. Johnston imported patterns for horseshoe-type drain tile from Scotland in December 1835. Tiles were made from these patterns at the B. F. Whartenby pottery at Waterloo, N. Y. in 1835. They were made entirely by hand. A crude molding machine was installed in 1838 in the Whartenby factory that made the process cheaper and faster (Weaver 1964).

The first tilemaking machine, the "Scraggs," was brought to America in 1848 from England. The machine operated on the extrusion process (Weaver 1964). Many locally manufactured tilemaking machines were patterned after the Scraggs machine, with most of the early manufacturers located in New York state. The first mole plow in the United States was introduced in 1867 in Steuben County, N.Y. (Beauchamp 1987).

New York state has the largest amount of agricultural drainage in the Northeast with 370,600 ha drained in 1985. Approximately 55% of the drained area is subsurface drainage while the remainder is surface drainage (Pavelis 1987). Maine has 2 intensively drained agricultural counties while Vermont, Pennsylvania, and New York have 4, 4, and 7 intensively drained counties, respectively.

Ontario was the first of the eastern Canada provinces to introduce drainage. The history of drainage development in Ontario is related to the development of agriculture. Agricultural drainage in Ontario has been practiced for more than one and a half centuries. Manufacturing of tile drains started in the middle of the last century. A plant to manufacture clay tile was first established in 1844. By the beginning of the 20th century there were about 150 tile manufacturing plants. Up to the 1960s most of subsurface drainage systems used clay tiles or concrete pipes. After the Agricultural Rehabilitation Development Act of 1967, corrugated plastic tubing was introduced. Up to the end of the last century subsurface drainage tiles were installed manually. In 1902, the first Buckeye Traction Ditcher, capable of laying about 1,100 mid of tile, was imported to Ontario.

Of the 5,500,000 ha of farmland in Ontario, 61% is cultivated. Most of the cultivated land has drainage improvements. Systematically spaced subsurface drainage systems is the most common drainage practice used.

Initial installation of subsurface drainage systems in Quebec started around 1912. However, the early installations proceeded at a rather slow pace. In 1965, for example, the annual rate of installation was 1,900 ha. However, it jumped to 22,000 ha/yr in 1975, almost a twelvefold increase in 10 years. The 1970s saw a growth rate of subsurface drainage unequalled in any other Canadian province. It is estimated that subsurface drainage systems have been installed in over 600,000 ha of agricultural land by 1988 (Shady 1989).

The early history of drainage in the Atlantic Provinces of Canada (NS, NF, PEI, and NB) is not well documented. However, some facts have been established. The first tile drain was installed in NS in 1888 at the Canada Agriculture Experimental Farm, Nappan. Clay tile was first manufactured in NS in 1915. Provincial Departments of Agriculture of both NB and NS purchased mechanized drainage trenchers in the early 1900s and continued to provide drainage contracting services to farmers until the early 1970s, when private drainage contractors became established (Milburn 1989). Systematic subsurface drainage became more common with the advent of private drainage contractor services; consequently, average annual job size per farm in NB increased from approximately 500 m in 1960 to 3,500 m in 1985 (Milburn and Gartley 1988). Similarly, total annual installation in Atlantic Canada also increased dramatically, from 600 km/yr in 1970, to 2,000 km/yr for the period 1985-88 (Milburn 1989).

Institutional and Social Constraints

Improved drainage of agricultural land purposes is increasingly viewed as being against the public's best interest. The pendulum has swung away from development in the last 20 years as a balance has been sought between development, reclamation, and drainage on one hand and preservation of environmental values on the other. The U. S. National Environmental Policy Act of 1969, the Clean Water Act as amended in 1977, and the Food Security Act of 1985 all have had an effect on agricultural drainage development. The Food Security Act of 1985 and 1990 Farm Bill deny price support and other farm program benefits to producers who grow crops on converted or drained wetlands. Also the elimination of investment tax credits and estrictions on expending farm conservation investment under the Tax Reform Act of 1986 are further disincentives to bring new lands into production through drainage.

OMAF and the Ontario Agriculture College have played an important role in the development of subsurface drainage and the drainage industry in Ontario. In Ontario, land drainage is performed by specialized contractors, entirely in the private sector. Initially there were no regulations for tile drainage work. The Tile Drainage Installation Act was passed in 1972. This legislation requires licensing of drainage businesses, drainage machinery, and drainage machine operators. In 1988, the province had 150 drainage businesses and more than 600 drainage operators. The OMAF offers certificate courses on the design of drainage systems and training for drainage machine operators. The Ontario Farm Drainage Association provides educational programs to contractors to effectively discuss and address industry problems.

Before future needs for subsurface drainage in Quebec can be determined, detailed information about the soils that do not benefit from subsurface drainage are required and a number of socioeconomic factors need to be considered. A 1966 survey estimated about 1,350,000 ha would benefit from drainage. About 600,000 ha have been drained, leaving a total of 850,000 ha to drain. The need for draining these soils will depend on up-to-date information and future requirements for food production. Surface drainage will be important to provide waterways that serve as outlets for drainage systems.

In the Atlantic Provinces of Canada utilization of subsurface drainage has increased under the combined influence of two factors: (1) readily available, rapid, and high-quality installation capacity from the drainage contracting sector; and (2) federal and/or provincial government cost-sharing that has promoted good on-farm land drainage practices. Continuance of cost sharing is not assured. Loans for drainage improvements are available from most agricultural lending agencies, subject to credit eligibility. Technical services such as on-farm consultation, preliminary topographic surveys, system layout and design are provided through drainage contractors, private consultants, and/or Department of Agriculture extension personnel, depending on location. Due to the rolling topography of the Atlantic region, natural gravity outlets are available for the vast majority of on-farm drainage projects, and subsurface drainage is not constrained nor serviced by artificial "main drain" networks.

Research Results

A few studies have addressed water-quality implications of drainage discharge on surface water stream biology (Lakshimarayana et at. 1992), but in most cases drainage effluent from systematically subdrained land has been analyzed as a preliminary means of estimating leaching losses of nutrients and pesticides from the root zone. Steenhuis et at. (1988) measured pesticide and nitrate concentrations in suction Iysimeters, and ground water and tile outflow under conventional tillage and conservation tillage on Rhinebeck sandy clay loam and variant clay loam soils. Low concentrations of atrazine (0.2-0.4 f..lglL) and alachlor (0.1 f..lg/L) were detected in the ground water 1 month after application. Only atrazine was detected in the conventional tillage in ground water in low concentrations (0.4 f..lg/L) in November. Nitrate concentrations were above 10 mglL in the unsaturated zone soil water solution but near zero in the ground water. Comparison of bromide tracer and nitrate concentrations indicated denitrification was occurring. They concluded pesticide leaching to the ground water was by macropore flow.

Bolton et al. (1970) were the first to study the effect of agricultural drainage on water quality in Ontario. They measured nutrient losses in tile drainage on a Brookston clay soil in continuous corn, continuous bluegrass and a four-year rotation of corn, oats, alfalfa, and alfalfa. No fertilization was compared with fertilizer application rates of 17 kg/ha of nitrogen and 67 kg/ha phosphorus for all crops except first- and second-year alfalfa in the rotation. The corn received an additional 112 kg/ha of nitrogen. The average annual nitrogen and phosphorus losses are presented in Table 1. Nitrogen losses increased with fertilizer applications in four of the six cropping seasons. Nitrate concentrations in the tile outflow were above 10 mg/L for fertilized rotation corn and secondyear alfalfa. Cropping systems had little effect on phosphorus concentrations. Fertilizer application caused a small increase in phosphorus losses. During the next 15-20 years from the early 1970s , in Ontario the focus of agriculture was production agriculture and the agricultural industry was defensive about pollution of water resources. Pollution due to subsurface drainage has received more attention in the 1990s. Recently, a number of projects have been initiated to study the correlation between tile drainage and land management systems on the quality and quantity of drained water.

A project in the eastern Ontario region on Ontario is studying the effect of tillage on the pesticides atrazine and metolachlor and nitrates in ground water and tile outflow (Patni et al. 1992 and Masse et al. 1992). The first two years indicated that concentrations and loadings of atrazine and deethylatrazine were higher for no tillage than conventional tillage. Cumulative loading rates and average concentrations of atrazine, deethylatrazine, metolachlor, and nitrates in the tile outflow are summarized in Table 2. The loading rate of atrazine was significantly different between the conventional tillage and no tillage while for deethylatrazine the loading rate was not significantly different between the two tillage systems. Atrazine and deethylatrazine concentrations were significantly different for the two tillage systems in 1991 but not in 1992. Metolachlor was detected only for a short period during the winter of the second year. Nitrate loads and concentrations were higher in conventional tillage than no tillage. The nitrate loads were not significantly different between tillage systems but the nitrate concentrations were significantly different in 1991.

Ground water was sampled at depths of 1.2, 1.8, 3.0, and 4.8 m (Masse et al. 1992). Atrazine was detected in 71% of the samples. Average concentrations decreased with depth. Concentrations were significantly higher under no tillage than conventional tillage at the 3.0 m and 4.8 m depth. The Environmental Protection Agency (EPA) drinking water standard of 3 µg/L was only exceeded in 7 out of 418 samples. Deethylatrazine was detected in 85% of the samples. Average deethylatrazine concentrations were higher than average atrazine concentrations at all depths. There was a significant difference at all depths between tillage systems with the no tillage having the higher deethylatrazine concentrations. Metolachlor was detected in only 4% of the samples. All concentrations were below the EPA health advisory limit of 10 µg/L. Nitrate concentrations exceeded the drinking water standard of 10 µg/L in 93% of the samples collected at 1.2 m, 80% at 1.8 m, 76% at 3.0 m, and only 15% at 4.6 m. Average nitrate concentrations under no tillage and conventional tillage, respectively, were 29.4 and 35.6 mg/L at 1.2 m, 19.6 and 26.5 mg/L at 1.8 m, 18.5 and 13.9 mg/L at 3.0 m, and 2.4 and 4.5 mg/L at 4.6 m. The difference between tillage systems was only significant at the 4.6 m depth. More data are needed to determine the long-term effect of tillage on ground-water and tile-drain-water quality.

TABLE 1. Average Annual Nitrogen and Phosphorus Losses in Tile Drains (Bolton et al. 1970)

Nitrogen Phosphorus
Crop (1) No fertilizer (kg/ha) (2) Fertilizer (kg/ha) (3) No fertilizer (kg/ha) (4) Fertilizer (kg/ha) (5)
a Rotation
Corn 8.5 14.0 0.13 0.24
Oats and alfalfa 6.4 8.5 0.13 0.13
Alfalfa-first year 6.3 5.8 0.13 0.15
Alfalfa-second year 9.3 10.1 0.08 0.22
b Continuous
Corn 4.4 8.9 0.26 0.24
Bluegrass 3.5 1.1 0.01 0.12

TABLE 2. Total Nitrate and Herbicides in Tile Effluent (Patni et al. 1992)

1991 1992a
Chemical (1) Conventional tillage (kg/ha) (2) No tillage (kg/ha) (3) Conventional tillage (kg/ha) (4) No tillage (kg/ha) (5)
Atrazine 0.90b 1.82b 0.58b l.48b
Deethylatrazine 1.55 2.05 0.06 1.20
Metolaehlor 0.00 0.00 0.04 0.49
Nitrates 29.0 20.0 21.6 25.5
aJanuary to July for herbicide and January to August for nitrates.

bSignificant at the 0.05 level.

A completed project in the southern region of Ontario did not show a significant difference in the total drainage water between the no tillage (NT) and moldboard-tillage (MB) treatments Kachanoski and Rudra 1991). However, NT had a significantly higher average concentration and flow-weighted concentration of nitrates in the tile outflow during spring and early fall periods than MB. The opposite trend was observed for late-fall and early-winter periods when MB had significantly higher nitrate concentrations than NT. Yearly f1owweighted concentrations were similar for both treatments and the average ground-water nitrate concentrations between 1 m and 5 m depth were similar. Tracer experiments revealed more preferential flow occurred in the MB tillage treatment. Overall bulk average velocity was higher in the case of the NT treatment.

Recently, subsurface drainage systems have been examined for their possible contribution to pollution of surface water. It is believed that some of the agricultural chemicals that leach beyond the crop root zone into the shallow ground water migrate with the drain water to the local streams, rivers, and lakes as part of drain effluent. Masse et al. (1990) reported that atrazine and its dealkylated-N metabolites were found in the shallow ground-water zone of a corn field on a clay loam soil in Quebec. At many times, the concentrations were found to be higher than the 3 µg/L advisory limit of EPA. Muir and Baker (1976) observed atrazine concentrations in tile-drain water in the range of 0.20 to 3.85 µg/L in Quebec corn fields. In eastern Ontario, Patni et al. (1987) detected atrazine and deethylatrazine in 75% and metolachlor in 32% of the tile-drain water samples from a clay loam soil where corn was being grown under conventional tillage.

Several field-scale studies have been initiated in the last few years to investigate the role of water-table management systems in reducing pesticide and nutrient discharges from subsurface-drained farmlands. One of the hypotheses driving these investigations is that the drain effluent will become less toxic if the water can be within the farm boundaries for extended periods of time, a typical phenomenon with subirrigation and controlled drainage systems. Most pesticides have a field half-life of a few weeks to a few months, under aerobic conditions, and therefore, the tile effluent would contain lesser concentration of pesticides if the drainage water is prevented from escaping the farm boundaries for ail extended period of time. With subirrigation and controlled drainage systems, it is possible to maintain favorable moisture content levels in the soil profile which, in turn, can lead to higher adsorption and microbial degradation rates of pesticides in such fields. Many studies consistently have shown higher rates of denitrification result by keeping the drain pipes submerged with water for extended periods of time, and lower nitrate concentrations in drainage effluent.

Arjoon et al. (1993) found that the leaching of prometryn herbicide in water-table-managed plots was slower than in subsurface-drainage plots in an organic soil in Quebec. Similar results were obtained by Aubin and Prasher (1993) for the herbicide metributzen in a potato field in Quebec. However, Arjoon and Prasher (1993) found there was no difference in the leaching of metolachlor in controlled drainage and regular subsurface drainage in a loamy sand soil.

Ng et al. (1994) found total atrazine and metolachlor losses did not differ between controlled and noncontrolled drainage in a Brookston clay loam in southwestern Ontario. The controlled drainage increased the amount of surface runoff compared to the uncontrolled drainage. For the controlled drainage, 23% of the rainfall was lost as surface runoff, whereas 12% of the rainfall was lost as surface runoff with the uncontrolled drainage.

Applying liquid manure to fields with tile drainage may have an increased impact on tile effluent water quality. Dean and Foran (1990) found higher concentrations of bacteria and nitrogen and phosphorus in tile drainage discharge when rainfall occurred shortly before or shortly after manure spreading. McLellan et al. (1993) in a study in southwestern Ontario on a Brookston clay loam soil found tile discharge ammonia concentrations increased from 0.2 to 0.3 mg/L before spreading to a peak of 53 mg/L shortly after manure was spread. Land application of liquid manure did not increase nitrate concentrations in the tile effluent but significantly increased the fecal coliform bacteria. Blocking the drains to simulate controlled drainage decreased ammonia and bacteria concentrations.

In a three-year study in southern Ontario, Fleming (1990) found no significant relationship between nitrate levels and either time of year or number of weeks after spreading of manure. He sampled 14 tile lines on a weekly basis and six stream sites. Only five of the sites had nitrate levels above 10 mg/L. Total phosphorus concentrations in the tile water were significantly higher at sites receiving regular applications of manure compared to sites receiving only occasional manure applications or none at all. Sites where manure was spread regularly had higher fecal coliform concentrations in the tile effluent. but the results were not significantly different. Fecal coliform concentrations were higher in six stream sites than the tile water, but nitrate and total phosphorus concentrations were lower. The stream flow consisted of tile discharge, surface runoff, and ground water.

Madramootoo et al. (1992) measured nitrogen, phosphorus, and potassium losses in subsurface drainage from two potato fields. Nitrogen concentrations in the tile effluent ranged from 1.70 to 40.02 mg/L. Phosphorus concentrations ranged from 0.002 to 0.052 mg/L. Potassium concentrations ranged from 2.98 to 21.4 mg/L. The total nitrogen loads in subsurface drainage during the growing season (April-November) from the two fields were 14 and 70 kg/ha in 1990. Phosphorus loads were less than 0.02 kg/ha.

Bastien et al. (1990) detected metribuzen in the tile flow at concentrations up to 3.47 I-lg/L in the two potato fields where Madramootoo et al. (1992) measured nutrient losses. Concentrations in surface runoff samples were much higher (33.6 to 47.1 I-lg/L). Aldicarb, fenvalerate, and phorate were not detected in the drainage waters.

In a 2-yr study involving five farm sites in NB (Milburn et al. 1990), flow-weighted average nitrate concentrations of the subdrain discharge (April-December) were greater than 10 mg/L for established potato rotation sites, both in the year of potatoes and in the subsequent nonpotato year when the rotation crop received little or no fertilizer. Corresponding average nitrate concentrations at low input, nonpotato rotation sites were approximately 3 mg/L. The total mass of nitrates removed in the drainage water are summarized in Table 3. The annual nitrate load varied from 1 kg/ha in a hay, hay, potato, winter wheat, and hay five-year rotation to 33 kg/ha in a potato, potato, oats, hay, and potato rotation. Herbicides dinoseb and metribuzin used in potato production were also detected in the drain discharge (95% of positive samples <2 I-lg/L) both during the year of application and again the following spring, but concentrations were less than detection limits 12-18 months after application (Milburn et al. 1991).

The fungicide chlorothalonil was detected at low concentrations in subsurface drainage water 7 months after application to potatoes in PEI (0.005 to 0.008 I-lg/L, 4 of 66 samples) (O'Neill et al. 1992). In another ongoing study in PEI, the average annual flow-weighted nitrate concentration of the subdrain discharge associated with a potato crop was reduced by 30%, to below 10 mg/L by planting a cover crop of winter wheat immediately following potato harvest (MacLeod et al. 1991; Milburn and MacLeod 1991).

Lakshminarayana et al. (1992) investigated the impact of subdrainage discharge containing atrazine on planktonic drift of the receiving natural stream. Maximum measured atrazine concentrations were 13.9 µg/L in the subdrain discharge and 1.89 µg/L in the stream. No negative impacts on plankton populations were evident beyond 50 m downstream from the drainage outlet. A section 20 m downstream was affected during low flow conditions. Ambient environmental conditions as well as atrazine were thought to be contributing to the measured results. Flow-weighted nitrate concentrations of the subdrain discharge associated with corn production in the preceding study was approximately 5 mg/L (Milburn and Richards 1991).

Research results to date in Atlantic Canada indicate that concentrations (and mass fluxes) of pesticides leaching from the root zone, as evidenced by analysis of subsurface drainage water, are relatively low compared to the current maximum health advisory limits established by Health and Welfare Canada (1987). Nitrate leaching losses are potentially more critical and widespread, especially in the concentrated areas of potato production in NB and PEI.

One question concerning tile drainage effluent is the impact it has on receiving waters. Although nitrate concentrations may be high in the tile effluent, dilution may play an important role in the receiving water. The receiving water may meet all water quality standards, so the tile-water quality may be of little concern in some cases. Lakshminarayana et al. (1992) found high atrazine concentrations in the tile effluent had very little effect on the receiving streams. In most cases the effect of high tile effluent nitrate or pesticide concentrations on receiving waters has not been investigated.

TABLE 3. Nitrates Removed by Tile Drainage for Different Cropping Rotations (Milbern et al. 1990)

Crops N Applied NO3-N Removed
Site No. (1) 1987 (kg/ha) (2) 1988 (kg/ha) (3) 1987 (kg/ha) (4) 1988 (kg/ha) (5) 1987 (kg/ha) (6) 1988 (kg/ha) (7)
(a) Established Potato Rotation Sites
1 potato barleya 110 45 16 28
2 potato barley 150 35 33 25
3 fall rye fall rye, peas 0 60 11 10
(b) Nonpotato Rotation Site
4 hay potato 0 200 1 5
5 potato peas 165 50 11 7
aUnderseeded to clover grass mixture

Research Needs

A review of research projects completed or in progress, indicate many questions concerning water quality impacts and agricultural drainage remain to be answered. Milburn et al. (1990) concluded that there is a need to determine year-round leaching losses of nitrates and pesticides from various production systems common to Atlantic Canada. Water-table management systems may reduce pollution from agricultural chemicals, but more field experience is needed. There may be a significant increase in crop yields from subirrigation and controlled drainage systems (Memon 1985). The systems are not very expensive and they can be adopted without asking farmers to drastically change their current farming practices. However, water-table management systems are restricted to relatively flat land.

Research has also confirmed that land-management practices can have significant impact on the concentrations and pathways of agricultural chemicals. Hydraulic characteristics of soils including preferential flow pathways indicate chemicals may move more rapidly to ground water. Comparison of different tillage systems indicates that in some cases no tillage may have higher loading rates than conventional tillage and vice versa (Patni et al. 1992; Steenhuis et al. 1988). Therefore, no tillage may not be a cure-all farming practice. Further work is needed to document the effect of these tillage practices on water quality.

Other major research needs identified are:

  1. Quantification of the role of preferential flow in the pollution of surface and subsurface drainage water.
  2. Development of modeling approaches to pollution control strategies that are applicable at the field and watershed scale.
  3. Development of technical means and methods to properly interface the use of agrichemicals with livestock manures where tile drainage is used, to minimize the impact on ground-water and receiving-stream water quality.
  4. Investigations in several areas of the United States have shown the effectiveness of cover crops in reducing nitrate leaching (Brinsfield et al. 1988). The role of cover crops for water-quality management in the northeastern United States and eastern Canada needs further investigation.
  5. Continued efforts to determine the water-quality consequences of agricultural production systems common to a region, particularly consequences of the concentration and total flux of leaching losses have on groundwater and receiving-stream water quality.
  6. Determination of subdrainage effects on runoff and soil erosion, and the edge-of-field transport of pesticides adsorbed to eroded sediment.

Appendix. References

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aPresented at the July 21-23. 1993 ASCE National Conference on Irrigation and Drainage Engineering. Park City. Utah. 1Prof., Agric. Engrg. Dept.. Univ. of Delaware. Newark. DE 19717. 2Prof., School of Engrg., Univ. of Guelph. Guelph. Ontano NIG 2Wl. Canada. 3Soils Engr., Agric. Canada Research Station. Fredericton. NB E3B 4Z7. 4Assoc. Prof., Agric. Engrg. Dept., Macdonald Coli. of McGill Univ. 21.111 Lakeshore Road. Ste-Anne de Bellevue. Quebec. H9X 3V9.

Note. Discussion open until January 1. 1996. To extend the closing date one month. a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on May 12. 1994. This paper is part of tbe Journal of Irrigation and Drainage Engineering, Vol. 121. No.4. July/August 1995. ©ASCE. ISSN 0733-9437/95/IKl04-0296-0301/$2.IKl + $.25 per page. Paper No. 8458.

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