Directory UMM :Data Elmu:jurnal:A:Agricultural Water Management:Vol46. Issue1.Nov2000:
Agricultural Water Management 46 (2000) 73±89
In¯uence of water table management on
corn and soybean yields
M.N. Mejia, C.A. Madramootoo*, R.S. Broughton
Department of Agricultural and Biosystems Engineering, McGill University,
Macdonald Campus, 21 111 Lakeshore, Ste-Anne-de-Bellevue Que., Canada H9X 3V9
Accepted 16 November 1999
Abstract
A 2-year ®eld study was conducted in eastern Ontario to evaluate the effect of water table
management (WTM) on the yields of strip-cropped corn (Zea mays L.) and soybean (Glycine max
Merr.). The WTM treatments consisted of two subirrigation treatments with water table controls set
at 0.50 m (CWT0.5) or 0.75 m (CWT0.75) from the soil surface, and a free drainage (FD) treatment
(water table1.00 m below the soil surface. Both corn and soybean yields were higher with CWT
than with FD for both years. In 1995, corn yields were 13.8% and 2.8% greater and soybean yields
8.5% and 12.9% greater, respectively, in the CWT0.5 and CWT0.75 plots than in the FD plots.
Similarly, in 1996, corn yields were 6.6% and 6.9% greater and soybean yields 37.3% and 32.2%
greater, respectively, in the CWT0.5 and CWT0.75 plots than in the FD plots. Yield increases
obtained during the study were attributed to greater crop water uptake in the CWT plots as a result
of the higher water tables. Comparison of 1995 and 1996 weather data with the long-term average
of the region shows that the years of study had wetter-than-average conditions in the critical months
of July and August, and that the yield increases due to WTM could be expected to be even greater
during drier years. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Controlled drainage; Glycine max Merr.; Subirrigation; Water table; Management; yield increase;
Zea mays L.
1. Introduction
Corn (Zea mays L.) and soybean (Glycine max Merr.) are economically important
crops in Ontario and Quebec, and, consequently, take up a large proportion of arable land.
In total, 0.81 million ha (Mha) of soybean and 0.98 Mha of corn were grown in 1995 in
*
Corresponding author. Tel.: 1-514-398-7778; fax: 1-514-398-8387.
E-mail address: cam@agreng.lan.mcgill.ca (C.A. Madramootoo).
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 1 0 9 - 2
74
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
these two provinces. In Ontario, the area cropped to soybean has increased from 0.42 in
1984 to 0.73 Mha in 1995 (Statistics Canada, 1996). For the same period in Quebec, land
cropped to corn has increased from 0.22 to 0.28 Mha, while the area cropped to soybean
has increased from 239 ha in 1976 to 0.08 Mha in 1995 (Statistics Canada, 1996).
Along with this expansion in cropped area, water quality degradation from drainage
and fertilizer use are likely to increase. Best management practices which reduce
pollution from agriculture, use water resources efficiently, as well as increase
productivity, are, therefore, needed for environmentally sustainable corn and soybean
production in the region. Water table management (WTM) has been shown by various
researchers to encourage the conservation of resources, increase productivity and reduce
pollution. The environmental and economic benefits of WTM through reduced pollution
and increased yields have been documented (Wright et al., 1992; Kalita and Kanwar,
1993; Tan et al., 1993; Drury et al., 1994; Broughton et al., 1995; Madramootoo et al.,
1995).
In the humid St. Lawrence lowlands of Quebec and Ontario, drainage is required to
remove excess water and is essential for field crop production. In summer, however,
droughty conditions often occur in the field due to lack of rain and high
evapotranspiration. The climatic factor most limiting to grain yields in fertilized corn
is insufficient rainfall during the growing season, particularly in July, when crop yields in
subsurface-drained fields are often reduced as a result of dry spells which can be
exacerbated by excessive drainage (Drury et al., 1996).
With WTM, the proper amount of aeration and soil moisture can be provided to the
crops in a more flexible manner. The water table can be lowered by drainage to facilitate
field operations in the spring and fall, and raised by controlled drainage and/or
subirrigation to provide plants with needed water during the growing season.
Thus, in addition to improving drainage water quality by reducing leaching of
agrochemicals from the soil profile, WTM can increase the efficiency of corn and
soybean production in two major ways: (i) by helping to retain more nitrate-N in the soil
for plant use, fertilizer costs can be reduced, and (ii) from water being made available to
plants during times of need, resulting in the improved crop yields. Under droughty
conditions, WTM by controlled drainage alone cannot provide adequate water to plant
roots. To supply plants with additional moisture in times of need, subirrigation can be
employed to pump water back into subsurface drains. Water table management, through
either controlled drainage or subirrigation minimizes the risk of crop losses from
uncertain rainfall, thereby stabilizing yields from year to year.
Farmers, water management specialists and environmentalists in eastern Canada have
expressed interest in WTM as a method of reducing agricultural pollution and boosting
crop yields. However, due to high capital cost and relatively low commodity prices,
farmers have generally refrained from investing in irrigation equipment for cereal and
grain production in eastern Canada. For subsurface-drained fields, however, WTM may
be the most efficient irrigation method for several reasons: (i) WTM eliminates water
losses by evaporation encountered when using surface irrigation, (ii) WTM uses rainfall
and drainage water more effectively, (iii) WTM distributes water uniformly, (iv) WTM
may reduce pesticide and fertilizer leaching to tile drains, and lastly (v) WTM does not
take up productive land area or create obstacles in the field as would above ground
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
75
irrigation systems, making it suitable for grain crops such as corn and soybean. Since
WTM requires less energy, labour and water, it is more economical than a sprinkler
system (Doty et al., 1983). WTM systems require flat topography, coarser textured soils,
an impermeable soil layer at 1±2 m in depth and the presence, or installation of a pipe
drainage system. Fortunately, these requirements are met in most of Ontario and Quebec.
For instance, in two counties in Quebec, it is estimated that 15 000 ha are well suited to
WTM (Papineau, 1988).
Lysimeter studies have been conducted to find optimum water table depths for corn
and soybean production in eastern Canada (Tan et al., 1993; Broughton et al., 1995). This
research supports the idea that there is a need for more field validation of potential crop
production levels with optimum water table depths. The objective of this study is to
evaluate the effects of three water table levels on corn and soybean grain yields under
eastern Canadian field conditions.
2. Materials and methods
2.1. Field layout
The study was conducted on a 3.5 ha field in Bainsville, eastern Ontario (458110 N,
748230 W) in 1995 and 1996. The average field slope of the site was 0.06% and the soil
was a stone free Bainsville silt loam (Dark Grey Glysolic soil group), underlain by a clay
layer at a depth of 1.0 m.
A ridge-till system with corn±soybean strip-cropping was practised for both years of
the study (1995, 1996), with rows strips perpendicular to drainage laterals running across
all treatment plots. In 1995, two-thirds of the experimental field was cropped to soybeans
and one-third to corn. The rotation was designed so that corn was cultivated on land that
had been cropped to soybeans the two previous years. In 1996, the field was planted half
to corn (C) and half to soybean (S) in alternating strips:
1994; 1995
1996
CSCSSSCSCSSSCSCSSSCSCSSSC
SCSCSCSCSCSCSCSCSCSCSCSCS
Each strip had six 0.75 m wide rows. The seeding rates were 72 000 seeds/ha for corn and
432 000 seeds/ha for soybean. Glyphosate herbicide was applied prior to seeding and preemergent herbicides were used during planting. Both corn and soybean were
mechanically cultivated twice to control weeds. The corn strips were fertilized with
28% urea/ammonium nitrate at a rate of 130 kg/ha in 1995 and 140 kg/ha in 1996. No
fertilizer or Rhizobium inoculant was applied to the soybean strips in either year.
2.2. Drainage system and controlled water table treatments
The drainage system consisted of 15 subsurface lateral drains that discharge
individually into a drainage ditch. Each lateral was 125 m long. The first 10 m section
from the outlet was made of 75 mm diameter non-perforated polyethylene pipe to
minimize water table drawdown by the ditch. The other 115 m section was made of
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Fig. 1. Experimental ®eld layout.
100 mm perforated polyethylene drainage pipe equipped with a filter sock. The average
drain depth is 1 m and the laterals are sloped at 0.10%. The lateral drains were spaced
18.3 m apart and were centrally located beneath each plot. Therefore, each lateral drains
an area 18.3 m wide by 115 m long, totalling about 0.21 ha.
The three treatments were: controlled water tables (CWT) at 0.5 m (CWT0.5) and
0.75 m (CWT0.75) below the soil surface, and conventional free drainage (FD) applied to
the 1.0 m deep laterals. Subirrigation maintained the water tables above the drains in the
CWT treatments. Each treatment consisted of three laterals and was separated by buffer
drains to isolate subsurface flows between the different treatment plots (Fig. 1). Laterals
A through J had water table control structures at the outlets and riser pipes to enable
subirrigation and maintain the water table treatments (Fig. 2), while drains K through O
drained freely into the ditch.
Subirrigation was initiated during the early vegetative stage and maintained until near
senescence. Water for subsurface irrigation was pumped from a ditch that was connected
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
77
Fig. 2. Control structure outlet.
to a nearby lake. A 0.75 kW Myers pump was used to convey lake water to the drain
laterals. At the field, a flowmeter recorded the total volume of water supplied. The
volume of drainflow was measured by tipping buckets at each of the monitored lateral
drain outlets, and recorded by a datalogger. The subirrigation system had a peak delivery
rate of approximately 0.95 I/s or 3.7 mm/day.
2.3. Field measurements
Water table depth from the ground surface was determined by lowering a graduated rod
with a water sensor at the tip into observation wells placed in the field. The observation
wells were 1.6 m long and made of 25.5 mm (1 in.) PVC pipes which were cut and
plugged at the bottom with drainage tape (Broughton, 1972). The pipes had drilled holes
of 6 mm in diameter along their lengths to let soil water in and were covered with
geotextile to keep silt out. The wells, installed to a depth of 1.5 m at lateral drain midspacing, protruded at the soil surface, and were capped to prevent rain or particulate
matter from entering. There were 43 wells in total, 12 observation wells per treatment, six
additional wells placed to monitor water table shape across CWT plots, and one 2 m well
used to monitor the water table level when it dropped below 1.5 m in the FD plot. The top
of each observation well was surveyed relative to a benchmark, to the bottom of the drain
outlets, and to the tops of risers of the water table control structures.
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Soil samples were collected throughout the growing season to compare soil moisture
contents across the treatment plots. The soil samples were taken at lateral drain midspacing, from three depths (0±20, 20±40 and 40±70 cm) and at 36 different locations in
each treatment field. Soil moisture contents were measured gravimetrically by weighing
the samples before and after oven-drying them at 1058C for 24 h (Gardner, 1965).
Rainfall and air and soil temperatures were recorded daily with an on-site datalogger to
compare the weather during the study to the long-term average conditions of the region.
Using the recorded daily temperatures, evapotranspiration (ET) and corn heat units
(CHU) were calculated for both years. The Blaney±Criddle equation (Schwab et al.,
1993) was used to calculate ET:
ET kp 0:46T 8:13
(1)
where ET is the monthly evapotranspiration, mm; k is the crop coef®cient for corn (0.42
for May; 0.8 for June; 1.15 for July, 0.87 for August; 0.55 for September; FAO, 1977); p
is the monthly percent of total daylight hours (Environment Canada Climatic Normals,
1960±1990 at McGill University Weather Station, Montreal, Que.), (Environment
Canada, 1993); T represents the average monthly temperature, 8C.
The corn heat units (CHU) were calculated using the following equation (Brown and
Bootsma, 1993)
q
(2)
CHU 1:80 Tmin ÿ 4:4 3:33 Tmax ÿ 10 ÿ 0:084 Tmax ÿ 102
where Tmin, Tmax are the minimum and maximum temperature, 8C
The CHU were accumulated from the date of seeding until the date of grain
physiological maturity. The dates of seeding were 11 May and 21 May in 1995, for corn
and soybeans, respectively, and 27 May for both crops in 1996. The grain maturity dates
were assumed to be 60 days after tasselling (Hanway, 1963). This date was 17 September
in 1995 and 28 September in 1996.
2.4. Yield parameters
The harvesting of corn and soybean was done by hand. Corn cobs were removed from
plants 2.5 m on either side of the laterals. This was done six times per treatment plot, for a
total of 30 m per treatment. Additionally, 60 corn plants were taken from each treatment
to determine the harvest index. The soybean plants were cut and shelled manually in
1995, but shelled by a combine harvester in 1996. The cobs were shelled using a corn
sheller and grain yields compared. The 100-seed weights for both corn and soybean were
also compared. Finally, dry matter weight comparisons were made for corn, and number
of pods per plant were compared for soybean.
2.5. Statistical analysis
Due to the drainage layout and limited number of drains, the placement of treatments
was constrained. The change in water table control height between two adjacent plots
necessitated two intervening buffer drains to maintain the water table at a constant level
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
79
in each of the monitored plots (Lalonde, 1993). This restriction, therefore, forced similar
water table treatments to be situated adjacent to each other.
Conventional statistical tests for significance were, therefore, not applicable due to the
lack of complete randomization. Therefore, a two-tailed Student's t-test was used to
determine if treatments were significantly different from one another (Agriculture
Canada, 1989; Lalonde, 1993). The treatments were compared in pairs: CWT0.5 versus
CWT0.75, CWT0.75 versus FD, and CWT0.5 versus FD. In cases where a certain outcome
was expected, an upper-tailed, or directional t-test was applied to test the hypotheses.
The compared samples were homoscedastic (from populations with the same variance),
were independent and normally distributed. The t-test is considered an appropriate
statistical method to test hypotheses under such conditions (Agriculture Canada, 1989;
Howell, 1989; Devore and Peck, 1990).
3. Results and discussion
3.1. Water table levels
The practice of WTM through controlled drainage and subirrigation was effective in
maintaining the water table levels in the CWT plots above the drains. Fluctuations of
water table levels and rainfall distribution for both years are shown in Figs. 3 and 4. The
water table fluctuations are reported as the mean value of all readings from each
treatment plot. Although the water table control structures at the drain outlets were set at
0.5 and 0.75 m below the soil surface, the moisture losses due to ET and deep and lateral
Fig. 3. Water table ¯uctuations and rainfall distribution in 1995.
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Fig. 4. Water table ¯uctuations and rainfall distribution in 1996.
seepage prevented static equilibrium at these levels. In 1995, the average water table level
for the CWT0.5, CWT0.75 and FD plots were 0.91, 1.03 and 1.30 m, respectively. In 1996,
the average water table level for the CWT0.5, CWT0.75, and FD plots were 0.75, 0.85 and
1.21 m, respectively. However, the water table levels occasionally reached target levels
and were significantly different (p0.05). In 1996, the CWT plots again produced the
largest grains. Grain size differences were significant (p0.05) for all comparisons. The
CWT0.5 and CWT0.75 plots produced soybean seeds that were 4.8% and 8.6% larger than
FD seeds, respectively.
3.11. Pods per plant
In 1995, the plants that produced the most pods were found in the CWT0.75 plots, followed
by those in the FD and CWT0.5 plots (Table 3). However, the differences in the number of
pods per plant were not significant. In 1996, the CWT0.5 and CWT0.75 plots produced the
most pods per plant. Although the difference in number of pods between the CWT0.5 and
CWT0.75 plots was not significant, both CWT's produced significantly more pods per plant
than FD plots (p0.05). In 1996, the CWT0.5 and CWT0.75 plots produced 32.0% and 82.2%
more pods per plant, respectively. Combined, the CWT plots produced 57% more pods per
plant than FD plots, which was reflected in the 35% increase in 1996 grain yields.
Yield increases were found with soybeans grown with WTM (Evans et al., 1991;
Madramootoo and Papadopoulos, 1991; Cooper et al., 1992; Madramootoo et al., 1995;
Tan et al., 1993; Drouet et al. (1989) and Kalita and Kanwar (1993) found similar yield
increases of approximately 30% for corn grown under WTM.
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
87
Improved crop preference can be attributed to the higher water availability provided by
WTM. More water reaches the crop roots by capillary rise from the shallower water
tables. It has been shown that stomatal conductance and transpiration rates of corn grown
with 0.3 and 0.6 m water table depths were greater than those grown with 0.8 m water
table depth (Tan et al., 1993). Some studies have shown that soybean yields were greatest
with a 0.6 m water table depth (Williamson and Kriz, 1970), while others found that a
water table depth of 0.15±0.30 m maximized soybean yields (Nathanson et al., 1984).
In both years of this study, the best yields for both corn and soybean crops were
achieved by setting a water table regime between 0.5 and 0.75 m. However, under our
field conditions, these design water table depths are actually between 0.75 and 1.03 m
since deep seepage and ET losses lowered the water tables. Research by Kalita and
Kanwar (1993) and Madramootoo et al. (1995) showed that the highest corn and soybean
yields were obtained with a water table depth of 0.6±0.9 m, and the lowest yields were
obtained with a water table depth of 0.2±0.3 m.
Climatic conditions greatly affected the effects of WTM on crop production.
Particularly in mid-July, 1995 and 1996, soil moisture content was much lower in the
free drainage plots than in the subirrigated area. However, sufficient soil moisture was
replenished in the free drainage area by timely rainfalls received in July to prevent wilting
in the non-subirrigated section. The combination of high temperatures in June along with
abundant rainfall in July resulted in very good crop growing conditions for both irrigated
and non-subirrigated crops. Although there were substantial yield increases with WTM,
the yield response to WTM was moderate and would most likely be higher in years when
July and August are drier than normal.
4. Conclusions
Compared to free drainage, corn and soybean yields were increased by water table
management in 1995 and 1996. In 1995, corn grain yield was increased by 13.8% and
2.8% by the CWT0.5 and CWT0.75 treatments, respectively, while soybean yield was
increased by 8.5% and 12.9% by the CWT0.5 and CWT0.75 treatments, respectively. In
1996, corn yields were higher in the CWT0.5 and CWT0.75 treatments than in FD by 6.6%
and 6.9%, respectively. Soybeans grown in the CWT0.5 and CWT0.75 treatments showed
yield increases of 37.3% and 32.2% over FD yields. The yield increases were also
reflected in the larger grains and kernels of the crops grown with WTM.
When compared to the long-term growing conditions of the region, the yield increase
responses during 1995 and 1996 are most likely moderate and could be higher in drier
years. For similar soils and climatic conditions, a water table level of 0.75 m was
recommended for corn and soybean production.
Acknowledgements
This research was supported by the Land Improvement Contractors of Ontario,
the Natural Sciences and Engineering Research Council of Canada and Agriculture and
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Agri-Food Canada. The assistance of the farm owner, Mr. R. McRae is appreciated. We
are grateful to Mr. J. Perrone and Dr. G. Dodds, Research Assistants at McGill University
for proof-reading and editing this manuscript.
References
Agriculture Canada, 1989. Statistical Methods for Food Quality Management. Agriculture Canada Publication
5268. Ministry of Supply and Services Canada, Ottawa, Ont., Canada, 99 pp.
Broughton, R.S., 1972. The performance of subsurface drainage systems on two St-Lawrence lowland soils.
Ph.D. Thesis, Department of Agricultural Engineering, Macdonald College of McGill University, Sainte
Anne-de-Bellevue, Que., Canada.
Broughton, S.R., Madramootoo, C.A., Papadopoulos, A., 1995. A Field Lysimeter System for Controlled
Drainage/Sub irrigation Research. In: Belcher, H.W., D0 Itri, F.M. (Eds.), Subirrigation and Controlled
Drainage, Lewis Publishers, Boca Raton, FL, pp. 453±458.
Brown, D.M., Bootsma, A., 1993. Crop heat units for corn and other warm-season crops in Ontario. Food
Factsheet Agdex 111/3 1. Ontario Ministry of Agriculture and Food, Queens Park, Ontario.
Cooper, R.L., Fausey, N.R., Streeter, J.G., 1992. Effect of water table level on the yield of soybean growth under
subirrigation/drainage. J. Production Agric. 5 (l), 180±184.
Devore, J., Peck, R., 1990. Introductory Statistics. West Publishing, St. Paul, MN
Doty, C.W., Caine, K.R., Farmer, L.J., 1983. Considerations for the design and operation of controlled drainagesubirrigation (CD-SI) system. ASAE Paper No. 83-2566, ASAE, St. Joseph, MI.
Drouet, M.P., Papineau, F., Broughton, R.S., 1989. Economic analysis of subsurface irrigation, maize. ASAE
Paper No. 89-2138, ASAE, St. Joseph, MI.
Drury, C.F., Tan, J.D., Gaynor, J.D., Oloya, T.O., Welacky, T.W., 1994. In¯uence of controlled drainage/
subirrigation on nitrate loss from Brookston clay loam soil. ASAE Paper No. 94-2068, ASAE St. Joseph, MI.
Drury, C.F., Tan, C.S., Gaynor, J.D., Oloya, T.O., Welacky, T.W., 1996. In¯uence of controlled drainagesubirrigation on surface and tile drainage nitrate loss. J. Environ. Qual. 25, 317±324.
Environment Canada, 1993. Climatic Normals 1961±1990. Canadian Climatic Program. Ministry of Supplies &
Services, Ottawa, Ont., Canada.
Evans, R.O., Skaggs, R.W., Sneeds, R.E., 1991. Stress day index models to predict corn and soybean relative
yield under high water table conditions. Trans. ASAE 34 (5), 1997±2005.
FAO, 1977. Guidelines for Predicting Crop Water Requirements. Irrigation and Drainage Paper 24. Food and
Agricultural Organization of the United Nations, Rome, Italy.
FAO, 1979. Yield Responses to Water. Irrigation and Drainage Paper 33. Food and Agricultural Organization of
the United Nations, Rome, Italy.
Gardner, W.H., 1965. Soil Moisture. In: Black, C.A. (Ed.), Methods of Soil Analysis, Part 2, Chemical and
Microbiological Properties, Agronomy Monograph 9, ASA, Ankeny, IA, pp. 82±127.
Hanway, J.J., 1963. Growth stages of corn (Zea Mays L.). Agronom. J. 22, 487±492.
Howell, D.C., 1989. Fundamental Statistics for the Behavioral Sciences. PWS-Kent Publishing, Boston, MA,
368 pp.
Kalita, P.K., Kanwar, R.S., 1993. Effect of water-table management practices on the transport of nitrate-N to
shallow groundwater. Trans. ASAE 36 (2), 413±422.
Lalonde, V., 1993. Some Hydrologic and Environmental Bene®ts of Water Table Management. M.Sc. Thesis,
Department of Agricultural Engineering, Macdonald Campus of McGill University, Sainte Anne-deBellevue, Que., Canada.
Madramootoo, C.A., Papadopoulos, A., 1991. Soil moisture and nitrate distributions under soybean-water table
management systems. ASAE Paper No. 91-2585, ASAE, St. Joseph, MI
Madramootoo, C.A., Broughton, S.R., Dodds, G.T., 1995. Water-table management strategies for soybean
production on a sandy loam soil. Can. Agric. Eng. 37 (l), 1±7.
Nathanson, K., Lawn, R.J., De Jabrun, P.L.M., Byth, D.E., 1984. Growth, nodulation and nitrogen accumulation
by soybean in saturated soil culture. Field Crops Res. 8, 73±92.
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
89
Papineau, F., 1988. Land and Water Appraisal for Irrigation in the Richelieu and St. Hyacinthe Counties,
Quebec. M.Sc. Thesis, Department of Agricultural Engineering, Macdonald Campus of McGill University,
Ste. Anne-de-Bellevue, Que., Canada.
Schwab, G.O., Fangmeier, D.D., Elliot, W.J., Frevert, R.K., 1993. Soil and Water Conservation Engineering, 4th
Edition. Wiley, New York
Statistics Canada, 1996. Grain Trade of Canada 1994±1995. Statistics Canada, Agricultural Division, Minister
Responsible for Statistics in Canada, Minister of Industry, Cat. No. 22-201-XPB, Ottawa, Ont.
Tan, C.S., Drury, C.F., Gaynor, J.D., Welacky, T.W., 1993. Integrated soil, crop and water management system to
abate herbicide and nitrate contamination of the Great Lakes. Water Sci. Technol. 28, 497±507.
Williamson, R.E., Kriz, G.J., 1970. Response of agricultural crops to ¯ooding, depth-of-water table and soil
gaseous composition. Trans. ASAE 13 (2), 216±220.
Wright, J.A., Shirmohammadi, A., Magette, W.L., Fouss, J.L., Bengston, R.L., Parsons, J.E., 1992. Water table
management practice effects on water quality. Trans. ASAE 35 (3), 823±830.
In¯uence of water table management on
corn and soybean yields
M.N. Mejia, C.A. Madramootoo*, R.S. Broughton
Department of Agricultural and Biosystems Engineering, McGill University,
Macdonald Campus, 21 111 Lakeshore, Ste-Anne-de-Bellevue Que., Canada H9X 3V9
Accepted 16 November 1999
Abstract
A 2-year ®eld study was conducted in eastern Ontario to evaluate the effect of water table
management (WTM) on the yields of strip-cropped corn (Zea mays L.) and soybean (Glycine max
Merr.). The WTM treatments consisted of two subirrigation treatments with water table controls set
at 0.50 m (CWT0.5) or 0.75 m (CWT0.75) from the soil surface, and a free drainage (FD) treatment
(water table1.00 m below the soil surface. Both corn and soybean yields were higher with CWT
than with FD for both years. In 1995, corn yields were 13.8% and 2.8% greater and soybean yields
8.5% and 12.9% greater, respectively, in the CWT0.5 and CWT0.75 plots than in the FD plots.
Similarly, in 1996, corn yields were 6.6% and 6.9% greater and soybean yields 37.3% and 32.2%
greater, respectively, in the CWT0.5 and CWT0.75 plots than in the FD plots. Yield increases
obtained during the study were attributed to greater crop water uptake in the CWT plots as a result
of the higher water tables. Comparison of 1995 and 1996 weather data with the long-term average
of the region shows that the years of study had wetter-than-average conditions in the critical months
of July and August, and that the yield increases due to WTM could be expected to be even greater
during drier years. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Controlled drainage; Glycine max Merr.; Subirrigation; Water table; Management; yield increase;
Zea mays L.
1. Introduction
Corn (Zea mays L.) and soybean (Glycine max Merr.) are economically important
crops in Ontario and Quebec, and, consequently, take up a large proportion of arable land.
In total, 0.81 million ha (Mha) of soybean and 0.98 Mha of corn were grown in 1995 in
*
Corresponding author. Tel.: 1-514-398-7778; fax: 1-514-398-8387.
E-mail address: cam@agreng.lan.mcgill.ca (C.A. Madramootoo).
0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 1 0 9 - 2
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
these two provinces. In Ontario, the area cropped to soybean has increased from 0.42 in
1984 to 0.73 Mha in 1995 (Statistics Canada, 1996). For the same period in Quebec, land
cropped to corn has increased from 0.22 to 0.28 Mha, while the area cropped to soybean
has increased from 239 ha in 1976 to 0.08 Mha in 1995 (Statistics Canada, 1996).
Along with this expansion in cropped area, water quality degradation from drainage
and fertilizer use are likely to increase. Best management practices which reduce
pollution from agriculture, use water resources efficiently, as well as increase
productivity, are, therefore, needed for environmentally sustainable corn and soybean
production in the region. Water table management (WTM) has been shown by various
researchers to encourage the conservation of resources, increase productivity and reduce
pollution. The environmental and economic benefits of WTM through reduced pollution
and increased yields have been documented (Wright et al., 1992; Kalita and Kanwar,
1993; Tan et al., 1993; Drury et al., 1994; Broughton et al., 1995; Madramootoo et al.,
1995).
In the humid St. Lawrence lowlands of Quebec and Ontario, drainage is required to
remove excess water and is essential for field crop production. In summer, however,
droughty conditions often occur in the field due to lack of rain and high
evapotranspiration. The climatic factor most limiting to grain yields in fertilized corn
is insufficient rainfall during the growing season, particularly in July, when crop yields in
subsurface-drained fields are often reduced as a result of dry spells which can be
exacerbated by excessive drainage (Drury et al., 1996).
With WTM, the proper amount of aeration and soil moisture can be provided to the
crops in a more flexible manner. The water table can be lowered by drainage to facilitate
field operations in the spring and fall, and raised by controlled drainage and/or
subirrigation to provide plants with needed water during the growing season.
Thus, in addition to improving drainage water quality by reducing leaching of
agrochemicals from the soil profile, WTM can increase the efficiency of corn and
soybean production in two major ways: (i) by helping to retain more nitrate-N in the soil
for plant use, fertilizer costs can be reduced, and (ii) from water being made available to
plants during times of need, resulting in the improved crop yields. Under droughty
conditions, WTM by controlled drainage alone cannot provide adequate water to plant
roots. To supply plants with additional moisture in times of need, subirrigation can be
employed to pump water back into subsurface drains. Water table management, through
either controlled drainage or subirrigation minimizes the risk of crop losses from
uncertain rainfall, thereby stabilizing yields from year to year.
Farmers, water management specialists and environmentalists in eastern Canada have
expressed interest in WTM as a method of reducing agricultural pollution and boosting
crop yields. However, due to high capital cost and relatively low commodity prices,
farmers have generally refrained from investing in irrigation equipment for cereal and
grain production in eastern Canada. For subsurface-drained fields, however, WTM may
be the most efficient irrigation method for several reasons: (i) WTM eliminates water
losses by evaporation encountered when using surface irrigation, (ii) WTM uses rainfall
and drainage water more effectively, (iii) WTM distributes water uniformly, (iv) WTM
may reduce pesticide and fertilizer leaching to tile drains, and lastly (v) WTM does not
take up productive land area or create obstacles in the field as would above ground
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
75
irrigation systems, making it suitable for grain crops such as corn and soybean. Since
WTM requires less energy, labour and water, it is more economical than a sprinkler
system (Doty et al., 1983). WTM systems require flat topography, coarser textured soils,
an impermeable soil layer at 1±2 m in depth and the presence, or installation of a pipe
drainage system. Fortunately, these requirements are met in most of Ontario and Quebec.
For instance, in two counties in Quebec, it is estimated that 15 000 ha are well suited to
WTM (Papineau, 1988).
Lysimeter studies have been conducted to find optimum water table depths for corn
and soybean production in eastern Canada (Tan et al., 1993; Broughton et al., 1995). This
research supports the idea that there is a need for more field validation of potential crop
production levels with optimum water table depths. The objective of this study is to
evaluate the effects of three water table levels on corn and soybean grain yields under
eastern Canadian field conditions.
2. Materials and methods
2.1. Field layout
The study was conducted on a 3.5 ha field in Bainsville, eastern Ontario (458110 N,
748230 W) in 1995 and 1996. The average field slope of the site was 0.06% and the soil
was a stone free Bainsville silt loam (Dark Grey Glysolic soil group), underlain by a clay
layer at a depth of 1.0 m.
A ridge-till system with corn±soybean strip-cropping was practised for both years of
the study (1995, 1996), with rows strips perpendicular to drainage laterals running across
all treatment plots. In 1995, two-thirds of the experimental field was cropped to soybeans
and one-third to corn. The rotation was designed so that corn was cultivated on land that
had been cropped to soybeans the two previous years. In 1996, the field was planted half
to corn (C) and half to soybean (S) in alternating strips:
1994; 1995
1996
CSCSSSCSCSSSCSCSSSCSCSSSC
SCSCSCSCSCSCSCSCSCSCSCSCS
Each strip had six 0.75 m wide rows. The seeding rates were 72 000 seeds/ha for corn and
432 000 seeds/ha for soybean. Glyphosate herbicide was applied prior to seeding and preemergent herbicides were used during planting. Both corn and soybean were
mechanically cultivated twice to control weeds. The corn strips were fertilized with
28% urea/ammonium nitrate at a rate of 130 kg/ha in 1995 and 140 kg/ha in 1996. No
fertilizer or Rhizobium inoculant was applied to the soybean strips in either year.
2.2. Drainage system and controlled water table treatments
The drainage system consisted of 15 subsurface lateral drains that discharge
individually into a drainage ditch. Each lateral was 125 m long. The first 10 m section
from the outlet was made of 75 mm diameter non-perforated polyethylene pipe to
minimize water table drawdown by the ditch. The other 115 m section was made of
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Fig. 1. Experimental ®eld layout.
100 mm perforated polyethylene drainage pipe equipped with a filter sock. The average
drain depth is 1 m and the laterals are sloped at 0.10%. The lateral drains were spaced
18.3 m apart and were centrally located beneath each plot. Therefore, each lateral drains
an area 18.3 m wide by 115 m long, totalling about 0.21 ha.
The three treatments were: controlled water tables (CWT) at 0.5 m (CWT0.5) and
0.75 m (CWT0.75) below the soil surface, and conventional free drainage (FD) applied to
the 1.0 m deep laterals. Subirrigation maintained the water tables above the drains in the
CWT treatments. Each treatment consisted of three laterals and was separated by buffer
drains to isolate subsurface flows between the different treatment plots (Fig. 1). Laterals
A through J had water table control structures at the outlets and riser pipes to enable
subirrigation and maintain the water table treatments (Fig. 2), while drains K through O
drained freely into the ditch.
Subirrigation was initiated during the early vegetative stage and maintained until near
senescence. Water for subsurface irrigation was pumped from a ditch that was connected
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
77
Fig. 2. Control structure outlet.
to a nearby lake. A 0.75 kW Myers pump was used to convey lake water to the drain
laterals. At the field, a flowmeter recorded the total volume of water supplied. The
volume of drainflow was measured by tipping buckets at each of the monitored lateral
drain outlets, and recorded by a datalogger. The subirrigation system had a peak delivery
rate of approximately 0.95 I/s or 3.7 mm/day.
2.3. Field measurements
Water table depth from the ground surface was determined by lowering a graduated rod
with a water sensor at the tip into observation wells placed in the field. The observation
wells were 1.6 m long and made of 25.5 mm (1 in.) PVC pipes which were cut and
plugged at the bottom with drainage tape (Broughton, 1972). The pipes had drilled holes
of 6 mm in diameter along their lengths to let soil water in and were covered with
geotextile to keep silt out. The wells, installed to a depth of 1.5 m at lateral drain midspacing, protruded at the soil surface, and were capped to prevent rain or particulate
matter from entering. There were 43 wells in total, 12 observation wells per treatment, six
additional wells placed to monitor water table shape across CWT plots, and one 2 m well
used to monitor the water table level when it dropped below 1.5 m in the FD plot. The top
of each observation well was surveyed relative to a benchmark, to the bottom of the drain
outlets, and to the tops of risers of the water table control structures.
78
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Soil samples were collected throughout the growing season to compare soil moisture
contents across the treatment plots. The soil samples were taken at lateral drain midspacing, from three depths (0±20, 20±40 and 40±70 cm) and at 36 different locations in
each treatment field. Soil moisture contents were measured gravimetrically by weighing
the samples before and after oven-drying them at 1058C for 24 h (Gardner, 1965).
Rainfall and air and soil temperatures were recorded daily with an on-site datalogger to
compare the weather during the study to the long-term average conditions of the region.
Using the recorded daily temperatures, evapotranspiration (ET) and corn heat units
(CHU) were calculated for both years. The Blaney±Criddle equation (Schwab et al.,
1993) was used to calculate ET:
ET kp 0:46T 8:13
(1)
where ET is the monthly evapotranspiration, mm; k is the crop coef®cient for corn (0.42
for May; 0.8 for June; 1.15 for July, 0.87 for August; 0.55 for September; FAO, 1977); p
is the monthly percent of total daylight hours (Environment Canada Climatic Normals,
1960±1990 at McGill University Weather Station, Montreal, Que.), (Environment
Canada, 1993); T represents the average monthly temperature, 8C.
The corn heat units (CHU) were calculated using the following equation (Brown and
Bootsma, 1993)
q
(2)
CHU 1:80 Tmin ÿ 4:4 3:33 Tmax ÿ 10 ÿ 0:084 Tmax ÿ 102
where Tmin, Tmax are the minimum and maximum temperature, 8C
The CHU were accumulated from the date of seeding until the date of grain
physiological maturity. The dates of seeding were 11 May and 21 May in 1995, for corn
and soybeans, respectively, and 27 May for both crops in 1996. The grain maturity dates
were assumed to be 60 days after tasselling (Hanway, 1963). This date was 17 September
in 1995 and 28 September in 1996.
2.4. Yield parameters
The harvesting of corn and soybean was done by hand. Corn cobs were removed from
plants 2.5 m on either side of the laterals. This was done six times per treatment plot, for a
total of 30 m per treatment. Additionally, 60 corn plants were taken from each treatment
to determine the harvest index. The soybean plants were cut and shelled manually in
1995, but shelled by a combine harvester in 1996. The cobs were shelled using a corn
sheller and grain yields compared. The 100-seed weights for both corn and soybean were
also compared. Finally, dry matter weight comparisons were made for corn, and number
of pods per plant were compared for soybean.
2.5. Statistical analysis
Due to the drainage layout and limited number of drains, the placement of treatments
was constrained. The change in water table control height between two adjacent plots
necessitated two intervening buffer drains to maintain the water table at a constant level
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
79
in each of the monitored plots (Lalonde, 1993). This restriction, therefore, forced similar
water table treatments to be situated adjacent to each other.
Conventional statistical tests for significance were, therefore, not applicable due to the
lack of complete randomization. Therefore, a two-tailed Student's t-test was used to
determine if treatments were significantly different from one another (Agriculture
Canada, 1989; Lalonde, 1993). The treatments were compared in pairs: CWT0.5 versus
CWT0.75, CWT0.75 versus FD, and CWT0.5 versus FD. In cases where a certain outcome
was expected, an upper-tailed, or directional t-test was applied to test the hypotheses.
The compared samples were homoscedastic (from populations with the same variance),
were independent and normally distributed. The t-test is considered an appropriate
statistical method to test hypotheses under such conditions (Agriculture Canada, 1989;
Howell, 1989; Devore and Peck, 1990).
3. Results and discussion
3.1. Water table levels
The practice of WTM through controlled drainage and subirrigation was effective in
maintaining the water table levels in the CWT plots above the drains. Fluctuations of
water table levels and rainfall distribution for both years are shown in Figs. 3 and 4. The
water table fluctuations are reported as the mean value of all readings from each
treatment plot. Although the water table control structures at the drain outlets were set at
0.5 and 0.75 m below the soil surface, the moisture losses due to ET and deep and lateral
Fig. 3. Water table ¯uctuations and rainfall distribution in 1995.
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M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Fig. 4. Water table ¯uctuations and rainfall distribution in 1996.
seepage prevented static equilibrium at these levels. In 1995, the average water table level
for the CWT0.5, CWT0.75 and FD plots were 0.91, 1.03 and 1.30 m, respectively. In 1996,
the average water table level for the CWT0.5, CWT0.75, and FD plots were 0.75, 0.85 and
1.21 m, respectively. However, the water table levels occasionally reached target levels
and were significantly different (p0.05). In 1996, the CWT plots again produced the
largest grains. Grain size differences were significant (p0.05) for all comparisons. The
CWT0.5 and CWT0.75 plots produced soybean seeds that were 4.8% and 8.6% larger than
FD seeds, respectively.
3.11. Pods per plant
In 1995, the plants that produced the most pods were found in the CWT0.75 plots, followed
by those in the FD and CWT0.5 plots (Table 3). However, the differences in the number of
pods per plant were not significant. In 1996, the CWT0.5 and CWT0.75 plots produced the
most pods per plant. Although the difference in number of pods between the CWT0.5 and
CWT0.75 plots was not significant, both CWT's produced significantly more pods per plant
than FD plots (p0.05). In 1996, the CWT0.5 and CWT0.75 plots produced 32.0% and 82.2%
more pods per plant, respectively. Combined, the CWT plots produced 57% more pods per
plant than FD plots, which was reflected in the 35% increase in 1996 grain yields.
Yield increases were found with soybeans grown with WTM (Evans et al., 1991;
Madramootoo and Papadopoulos, 1991; Cooper et al., 1992; Madramootoo et al., 1995;
Tan et al., 1993; Drouet et al. (1989) and Kalita and Kanwar (1993) found similar yield
increases of approximately 30% for corn grown under WTM.
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87
Improved crop preference can be attributed to the higher water availability provided by
WTM. More water reaches the crop roots by capillary rise from the shallower water
tables. It has been shown that stomatal conductance and transpiration rates of corn grown
with 0.3 and 0.6 m water table depths were greater than those grown with 0.8 m water
table depth (Tan et al., 1993). Some studies have shown that soybean yields were greatest
with a 0.6 m water table depth (Williamson and Kriz, 1970), while others found that a
water table depth of 0.15±0.30 m maximized soybean yields (Nathanson et al., 1984).
In both years of this study, the best yields for both corn and soybean crops were
achieved by setting a water table regime between 0.5 and 0.75 m. However, under our
field conditions, these design water table depths are actually between 0.75 and 1.03 m
since deep seepage and ET losses lowered the water tables. Research by Kalita and
Kanwar (1993) and Madramootoo et al. (1995) showed that the highest corn and soybean
yields were obtained with a water table depth of 0.6±0.9 m, and the lowest yields were
obtained with a water table depth of 0.2±0.3 m.
Climatic conditions greatly affected the effects of WTM on crop production.
Particularly in mid-July, 1995 and 1996, soil moisture content was much lower in the
free drainage plots than in the subirrigated area. However, sufficient soil moisture was
replenished in the free drainage area by timely rainfalls received in July to prevent wilting
in the non-subirrigated section. The combination of high temperatures in June along with
abundant rainfall in July resulted in very good crop growing conditions for both irrigated
and non-subirrigated crops. Although there were substantial yield increases with WTM,
the yield response to WTM was moderate and would most likely be higher in years when
July and August are drier than normal.
4. Conclusions
Compared to free drainage, corn and soybean yields were increased by water table
management in 1995 and 1996. In 1995, corn grain yield was increased by 13.8% and
2.8% by the CWT0.5 and CWT0.75 treatments, respectively, while soybean yield was
increased by 8.5% and 12.9% by the CWT0.5 and CWT0.75 treatments, respectively. In
1996, corn yields were higher in the CWT0.5 and CWT0.75 treatments than in FD by 6.6%
and 6.9%, respectively. Soybeans grown in the CWT0.5 and CWT0.75 treatments showed
yield increases of 37.3% and 32.2% over FD yields. The yield increases were also
reflected in the larger grains and kernels of the crops grown with WTM.
When compared to the long-term growing conditions of the region, the yield increase
responses during 1995 and 1996 are most likely moderate and could be higher in drier
years. For similar soils and climatic conditions, a water table level of 0.75 m was
recommended for corn and soybean production.
Acknowledgements
This research was supported by the Land Improvement Contractors of Ontario,
the Natural Sciences and Engineering Research Council of Canada and Agriculture and
88
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
Agri-Food Canada. The assistance of the farm owner, Mr. R. McRae is appreciated. We
are grateful to Mr. J. Perrone and Dr. G. Dodds, Research Assistants at McGill University
for proof-reading and editing this manuscript.
References
Agriculture Canada, 1989. Statistical Methods for Food Quality Management. Agriculture Canada Publication
5268. Ministry of Supply and Services Canada, Ottawa, Ont., Canada, 99 pp.
Broughton, R.S., 1972. The performance of subsurface drainage systems on two St-Lawrence lowland soils.
Ph.D. Thesis, Department of Agricultural Engineering, Macdonald College of McGill University, Sainte
Anne-de-Bellevue, Que., Canada.
Broughton, S.R., Madramootoo, C.A., Papadopoulos, A., 1995. A Field Lysimeter System for Controlled
Drainage/Sub irrigation Research. In: Belcher, H.W., D0 Itri, F.M. (Eds.), Subirrigation and Controlled
Drainage, Lewis Publishers, Boca Raton, FL, pp. 453±458.
Brown, D.M., Bootsma, A., 1993. Crop heat units for corn and other warm-season crops in Ontario. Food
Factsheet Agdex 111/3 1. Ontario Ministry of Agriculture and Food, Queens Park, Ontario.
Cooper, R.L., Fausey, N.R., Streeter, J.G., 1992. Effect of water table level on the yield of soybean growth under
subirrigation/drainage. J. Production Agric. 5 (l), 180±184.
Devore, J., Peck, R., 1990. Introductory Statistics. West Publishing, St. Paul, MN
Doty, C.W., Caine, K.R., Farmer, L.J., 1983. Considerations for the design and operation of controlled drainagesubirrigation (CD-SI) system. ASAE Paper No. 83-2566, ASAE, St. Joseph, MI.
Drouet, M.P., Papineau, F., Broughton, R.S., 1989. Economic analysis of subsurface irrigation, maize. ASAE
Paper No. 89-2138, ASAE, St. Joseph, MI.
Drury, C.F., Tan, J.D., Gaynor, J.D., Oloya, T.O., Welacky, T.W., 1994. In¯uence of controlled drainage/
subirrigation on nitrate loss from Brookston clay loam soil. ASAE Paper No. 94-2068, ASAE St. Joseph, MI.
Drury, C.F., Tan, C.S., Gaynor, J.D., Oloya, T.O., Welacky, T.W., 1996. In¯uence of controlled drainagesubirrigation on surface and tile drainage nitrate loss. J. Environ. Qual. 25, 317±324.
Environment Canada, 1993. Climatic Normals 1961±1990. Canadian Climatic Program. Ministry of Supplies &
Services, Ottawa, Ont., Canada.
Evans, R.O., Skaggs, R.W., Sneeds, R.E., 1991. Stress day index models to predict corn and soybean relative
yield under high water table conditions. Trans. ASAE 34 (5), 1997±2005.
FAO, 1977. Guidelines for Predicting Crop Water Requirements. Irrigation and Drainage Paper 24. Food and
Agricultural Organization of the United Nations, Rome, Italy.
FAO, 1979. Yield Responses to Water. Irrigation and Drainage Paper 33. Food and Agricultural Organization of
the United Nations, Rome, Italy.
Gardner, W.H., 1965. Soil Moisture. In: Black, C.A. (Ed.), Methods of Soil Analysis, Part 2, Chemical and
Microbiological Properties, Agronomy Monograph 9, ASA, Ankeny, IA, pp. 82±127.
Hanway, J.J., 1963. Growth stages of corn (Zea Mays L.). Agronom. J. 22, 487±492.
Howell, D.C., 1989. Fundamental Statistics for the Behavioral Sciences. PWS-Kent Publishing, Boston, MA,
368 pp.
Kalita, P.K., Kanwar, R.S., 1993. Effect of water-table management practices on the transport of nitrate-N to
shallow groundwater. Trans. ASAE 36 (2), 413±422.
Lalonde, V., 1993. Some Hydrologic and Environmental Bene®ts of Water Table Management. M.Sc. Thesis,
Department of Agricultural Engineering, Macdonald Campus of McGill University, Sainte Anne-deBellevue, Que., Canada.
Madramootoo, C.A., Papadopoulos, A., 1991. Soil moisture and nitrate distributions under soybean-water table
management systems. ASAE Paper No. 91-2585, ASAE, St. Joseph, MI
Madramootoo, C.A., Broughton, S.R., Dodds, G.T., 1995. Water-table management strategies for soybean
production on a sandy loam soil. Can. Agric. Eng. 37 (l), 1±7.
Nathanson, K., Lawn, R.J., De Jabrun, P.L.M., Byth, D.E., 1984. Growth, nodulation and nitrogen accumulation
by soybean in saturated soil culture. Field Crops Res. 8, 73±92.
M.N. Mejia et al. / Agricultural Water Management 46 (2000) 73±89
89
Papineau, F., 1988. Land and Water Appraisal for Irrigation in the Richelieu and St. Hyacinthe Counties,
Quebec. M.Sc. Thesis, Department of Agricultural Engineering, Macdonald Campus of McGill University,
Ste. Anne-de-Bellevue, Que., Canada.
Schwab, G.O., Fangmeier, D.D., Elliot, W.J., Frevert, R.K., 1993. Soil and Water Conservation Engineering, 4th
Edition. Wiley, New York
Statistics Canada, 1996. Grain Trade of Canada 1994±1995. Statistics Canada, Agricultural Division, Minister
Responsible for Statistics in Canada, Minister of Industry, Cat. No. 22-201-XPB, Ottawa, Ont.
Tan, C.S., Drury, C.F., Gaynor, J.D., Welacky, T.W., 1993. Integrated soil, crop and water management system to
abate herbicide and nitrate contamination of the Great Lakes. Water Sci. Technol. 28, 497±507.
Williamson, R.E., Kriz, G.J., 1970. Response of agricultural crops to ¯ooding, depth-of-water table and soil
gaseous composition. Trans. ASAE 13 (2), 216±220.
Wright, J.A., Shirmohammadi, A., Magette, W.L., Fouss, J.L., Bengston, R.L., Parsons, J.E., 1992. Water table
management practice effects on water quality. Trans. ASAE 35 (3), 823±830.