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Long-Term Benefits of Controlled Drainage

Chandra A. Madramootoo1,*, Mfon Essien1, Kosoluchukwu Ekwuknife1

Published in Journal of the ASABE 67(3): 565-571 (doi: 10.13031/ja.15542). Copyright 2024 American Society of Agricultural and Biological Engineers.

1    Department of Agricultural and Environmental Studies, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada.

*    Correspondence: chandra.madramootoo@mcgill.ca

Submitted for review on 17 January 2023 as manuscript number NRES 15542; approved for publication as a Research Article and as part of the “Advances in Drainage: Selected Works from the 11th International Drainage Symposium” Collection by Associate Editor Dr. Mohamed Youssef and Community Editor Dr. Zhiming Qi of the Natural Resources & Environmental Systems Community of ASABE on 6 February 2024.

Citation: Madramootoo, C. A., Essien, M., & Ekwuknife, K. (2024). Long-term benefits of controlled drainage. J. ASABE, 67(3), 565-571. https://doi.org/10.13031/ja.15542

Highlights

Abstract. Conventional tile drainage is essential for crop production in Eastern Canada. It is of increasing interest for cereal and grain producers, especially in light of potential agronomic and environmental benefits. Based on data collected over a 13-year period at an intensive maize production site in southern Quebec, we found that controlled drainage has an overall positive effect on grain yield. In some years, depending on precipitation intensities and timing, nitrous oxide (N2O) fluxes under controlled drainage were greater than under conventional tile drainage. In other years, controlled drainage had 43% lower N2O emissions. Controlled drainage significantly reduced NO3-N contamination and tended to increase crop yield. It can be a beneficial management practice to be adopted on subsurface-drained croplands.

Keywords.Controlled drainage, Crop yield, Environment, Greenhouse gases, Subsurface drainage, Water quality.

Controlled drainage is a water management strategy with the potential to increase crop yields and offer environmental benefits on relatively flat, poorly drained soils. Subsurface or conventional tile drains are required to remove excess precipitation in the spring, to enable field operations and planting at the start of the growing season, as well as remove excess precipitation during the summer growing season. These tile-drained lands can benefit, not just through increased crop yields, but also from reduced nitrate-nitrogen (NO3-N) and reduced nitrous oxide emissions. In the Eastern Canadian provinces of Quebec and Ontario, corn (Zea mays) and soybean (Glycine max L.) are predominantly grown under intensive tile drainage. The two provinces produce over 90% of corn and 80% of soybean; these are important agro-ecological zones in Canada (Statistics Canada, 2021).

Controlled drainage is recommended as a reliable technology to reduce subsurface discharge and nitrate leaching (Skaggs et al., 2012). Several researchers, including Drury et al. (2009), Elmi et al. (2005), Mejia et al. (2000), Stämpfli and Madramootoo (2006), Sunohara et al. (2015), and Creze and Madramootoo (2019), have shown the crop yield and water quality benefits of CD on experimental fields in Quebec. Controlled drainage has been reported to have a significant impact on nitrate leaching, with reductions of over 50%.

Further environmental benefits of CD include a reduction of greenhouse gas emissions, particularly N2O due to N fertilizer applications, which can vary from 130 to 270 kg N/year. There have only been a few studies that have examined the effects of water table control on N2O emissions (Elmi et al., 2005; Nangia et al., 2013; Van Zandvoort et al., 2017; Abbasi et al., 2020). Many of these studies show partial to moderate reductions of N2O due to CD and SI. The rate and timing of N applications have a significant impact on N2O emissions, particularly if there was heavy rainfall after fertilizer application.

The adoption of CD by large-scale farmers in Canada remains relatively low, despite the potential of CD to reduce nitrate pollution and nitrous oxide emissions (Madramootoo et al., 1993; Tait et al., 1995). The slow adoption may be attributed to the operation of CD control structure, which is regarded as labor intensive, requiring the manual removal/addition of riser boards from/to the control structure. Earlier designed control structures froze internally during the winter, resulting in unmovable swollen or frozen boards in early spring, thereby making it difficult to manually adjust. More recently, composite or aluminum gates that do not swell have alleviated many of these issues.

There are other impediments to large-scale commercial adoption of CD. These barriers are largely attributed to a lack of consensus over yield gains (Poole et al., 2013; Wesstrom et al., 2014). A few studies that reported increased yields due to CD found that the yields were not sufficient to offset investment costs (Breve et al., 1998). Marmanilo et al. (2021) opined in their study that the yield benefits of CD may be masked due to rainfall being more intense than historical average rainfall intensities, making drainage more important. Recent studies have found CD to be profitable (Crabbe et al., 2012; Kitchen and Kitchen, 2017); however, large commercial growers are still not convinced of the yield and subsequent economic benefits.

The objective of this study is to evaluate the long-term effects of CD on grain yields, water quality, and greenhouse gases using data from a large experimental field in Quebec. The significance of this research is that it provides farmers, drainage professionals, technology users, and policy makers with an analysis of the impacts of CD as a beneficial water management strategy for drained agricultural soils. The results can be used to support economic and environmental policy decision-making.

Materials and Methods

Study Area and Field Management

The study data was derived from research conducted over a 13-year period from 1993 to 2018. Corn was seeded continuously from 1993–2002, followed by 5 years (2003–2008) of soybean, then a corn-soybean rotation of 3 years. Yellow bean was planted in 2012 and 2015. The experimental site of 4.2 ha is located on a commercial farm located in Coteau-du-lac, Quebec, Canada (lat 74°11'15”, long 45°21'0”). Nitrate leaching data and nitrous oxide emissions were collected separately over a four-year period.

The slope of the field is approximately 0.5%. The soil type is classified as Soulanges sandy loam soil of the Gleysol order. It was characterized by a very fine sandy loam alluvium parent material, underlain by marine clay at depths of 60 to 180 cm. Soil physical properties such as bulk density, organic matter content, saturated hydraulic conductivity, porosity, and textural class were measured. The bulk density was 1.27 g cm-3, the soil pH was 6.4, and the soil C/N ratio was 7.49 at 15 cm depth. In 2018, soil chemical properties were measured, including available NO3-N, which ranged from 5 mg kg-1 at a soil depth of 0-20 cm to 1 mg kg-1 at 40-60 cm, and available NH4-N, which was about 1 mg kg-1 at both 0-20 cm and 40-60 cm soil depths. The relevance of these measurements are the impacts that available and reactive N have on nitrate leaching and nitrous oxide emissions in the field. The field was under conventional tillage; chisel-plowed in the fall and harrow disked in the spring immediately prior to seeding. The field management system included two water management practices: conventional tile drainage (FD) and controlled drainage (CD). The same fertilizer was applied to both CD and FD, with FD as the control treatment, representing conventional farm drainage practiced in the region. All treatments followed a randomized controlled block design (RCBD). The experiment consisted of three blocks (Blocks A, B, and C) and two treatments (FD and CD), with repeated measures, as shown in figure 1.

Figure 1. Experimental layout of the study field and arrangement (adapted from Jiang et al., 2019).

Agronomic Practices and Meteorological Data

Seed varieties were selected each year following projected heat units and recommendations from the seed provider. The distance between the rows was 76.2 cm. Each year, the crops were planted in May and typically harvested at the end of the growing season in October. Fertilizer was banded at seeding in early May, and the rest of the fertilizer was usually incorporated when the plant was around the V6 stage (about 6 weeks after emergence). Each year, the crop fertilizer needs were determined based on soil tests at the site, adhering to Quebec compliance guidelines. The fertilizers were applied taking into consideration the corn heat units (CHU) projections and target yield. The total fertilizer applied ranged from 130 kg N ha-1 to 270 kg N ha-1 using the split fertilizer method. Drainage outflow, residual N, and yields were measured annually. Pesticides and herbicides were applied according to local recommendations. The crop residue was typically left on the field and plowed in the fall season after harvest. Information on the soil properties and fertilizer applications is shown in tables 1 and 2. Precipitation and temperature data were collected from the Côteau-du-Lac Environment Canada weather station (Station ID: 7011947), approximately 500 m from the experimental site. The soil temperature was obtained using a hand-held thermometer. Soil water-filled pore space was obtained using a ThetaProbe (Model ML2x, Delta-T Devices Ltd.) inserted in the top 6 cm of the soil. The probe was calibrated to the soil of the site.

Water Management

There were primarily two water table management systems studied: FD and CD. The existing tile drainage system consisted of 0.076 m diameter tiles laid at the center of each plot at an average depth of 1.0m below the soil surface with a spacing of 15 m. The field layout is shown in figure 1. In FD, tile drains were left open throughout the year to facilitate the free outflow of water from the field. In CD, tile drains were left open during the spring to ensure that water drained freely from the field due to snowmelt and to allow for field trafficability during seedbed preparation and planting. The site had three blocks with buffer separations of 30 m between blocks. Each block was subdivided into eight plots of 15 m by 75 m, separated by a vertical plastic sheet to a depth of 1.5 m. Complete details of the experimental site are described by Tait et al. (1995).

Table 1. Soil physical and chemical properties at varying depths on the experimental site. (Soil properties correspond to data derived from Creze and Madramootoo, 2019).
PropertyDepth
0-20 cm20-40 cm40-60 cm
ClassificationSoulanges series; Gleysol type
Physical
Soil texture%
Sand 557169
Silt 332522
Clay749
Bulk density, g cm-31.361.601.46
Textural classSandy loamSandy loamSandy loam
Chemical
Mean pH7.07.27.3
Organic matter, %3.514.511.32
Carbon, %2.02.60.8

Table 2. Information on the quantity of Nitrogen fertilizer applied and water level depth is provided below.
YearQuantity Applied
(Kg ha-1)
N: P: K		Water Table Depth
(m)
CDFD
1993270:52:146 0.71.00
1994270:52:1460.81.00
1995130:60:601.001.3
1996140:130:900.751.00
1997200:130:900.751.00
1998200:130:900.61.00
1999150:130:900.61.00
2000169:130:900.751.00
2001199:75:1030.81.00
2002253:75:1030.81.00
2008186:70:500.61.00
2009179:60:700.81.00
2018180:60:6011.2

Greenhouse Gas and Water Quality Sampling

Greenhouse gas (GHG) data was collected using a vented, non-steady-state closed chamber. The chambers with dimensions of 0.556 m x 0.556 m x 0.140 m (W x L x H) were inserted to a depth of 10 cm in the soil, leaving 4 cm of chamber height above the surface. The chambers were placed approximately 3 m from the tile drains within the 15 m drain spacing (see fig. 1). Auxiliary measurements, including soil temperature and soil water content, were collected alongside gas samples. Gas sampling frequency was carried out weekly. The concentration of the N2O in each sample was determined using a Bruker 450-Gas Chromatograph system.

Tipping buckets were placed at the outlet of each subsurface drain to measure the drainage discharge. Water sampling was set according to the accumulated volume of drain flow. Water samples were collected in plastic jars connected to tipping buckets; one for each drain tile. The samples were taken to the laboratory weekly or bi-weekly, depending on tile flow rate, and analyzed for NO3-N in triplicate using a Lachat flow injection auto-analyzer (Elmi et al., 2002).

Statistical Analysis

Comparisons between controlled and conventional drainage were conducted on an annual or seasonal basis using an ANOVA. The ANOVA was estimated using SAS (SAS Institute, Cary, NC) to test the homogeneity of variances of emissions comparing CD and FD systems. An ANOVA was also used to determine if there was a significant difference between the water management systems because the sample size was small. A t-test was then employed to evaluate the genuine effects of the observed differences between the two means of the water management systems.

A regression analysis was used to test the impact of crop yields, as the data had a larger sample size. The dependent variable in the regression model was crop yields, which was hypothesized to be influenced by a change in water table management and fertilizer management. Our model is specified as follows:

    ???? = ??0 + ??1???? + ??2???? + ??3???? + ????    (1)

where

ei= error term.

Pi= precipitation

Fi = fertilization rate

???? = the effect on crop yields, measured by the change in yields

Ni = a dummy variable where 1 represents the implementation of CD (controlled drainage) and 0 represents the absence

of the technology (i.e., conventional tile drainage)

i indexes the observations.

The regression analysis was performed using the STATA software. The correlation of fertilizer, precipitation, and CD on crop yields was also assessed.

Results and Discussion

Climatic Data

The magnitude and timing of precipitation varied over the 12 growing seasons (May–November). Variations in rainfall, temperature, and evapotranspiration are presented in table 3. The daily climatic data for the wettest year (1998) and the driest year (2001) are shown in figures 2a and 2b for precipitation and evapotranspiration. The total seasonal rainfall was lowest in 2000 and 2001 by 22%, compared to the 30-year normal, with more than 51% occurring in July and August. The month of June was 79% drier than the 30-year normal. Total seasonal rainfall in 1996–1998 was 21%, 13%, and 24% greater than normal, respectively. About 32% of the rainfall occurred in May and June, while in some years, it rained more uniformly from May to October than the rest of the year. Air temperatures varied substantially from the 68-year average, with normal being 3.5 °C warmer in May 2012 and about 2.0 °C cooler in November 2013. The monthly average of these years was within ± 0.1 °C of the long-term monthly average temperatures for the past 68 years (1946–2011). June, July, and August were warm months with air temperatures higher than 20.0 °C in all years, especially in 2012, where temperatures were above normal. The air temperature caused an increase in the soil temperature, with similar values in all treatment plots.

Daily precipitation data for 1998 and 2001
(a)
Daily evapotranspiration data for 1998 and 2001
(b)
Figure 2. (a) Total precipitation (mm) for the years 1998 and 2001. (b) Total evapotranspiration (mm/day) for the years 1998 and 2001.
Table 3. Rainfall and corn yields measured at the field site between 1993 and 2018. (The data sources from the relevant publications are also given).
YearRainfall
(mm)		Yield
(Mg Ha-1)		Difference
in Yields
(%)		Reference
CDFD
19934828.282.5%Zhou et al.
(2000)
19944448.99.4-5.3%
199547911.411.12.7%Mejia et al.
(2000)
19965117.36.87.4%
19986186.68.8-25.5%Madramootoo
et al. (2001)
Elmi et al. (2005)
19994829.59.7-2.1%
20013609.46.936.2%Stampfli and
Madramootoo (2006)
200247610.17.632.9%
200843312.312.5-1.6%Singh et al.
(2014)
200946510.411.3-8.0%
201836510.911-0.9%Current study

Observed Effects of Controlled Drainage on Crop Yields, Nitrous Oxide, and Nitrate Leaching

Crop Yields

Corn yields varied between FD and CD, depending on annual rainfalls, temperature, and evapotranspiration. In the drier years of 2001 and 2002, controlled drainage showed higher grain yields. In 2002, average annual rainfall was comparable to the 30-year average; however, it is described as a drier year because most of the rainfall was recorded in May/June before the crucial months (late June–August) of crop growth, which recorded lower rainfall. Accordingly, CD was applied during the crucial crop growth stage due to insufficient soil moisture, and the benefits can be observed in the yields, which are presented in table 3. Conversely, in wetter years such as 1998, FD showed greater grain yields. In those relatively wet years, the impact of CD on yield compared to FD was up to -25.5%, whereas in relatively dry years, its impact was over 30%. Rainfall timing is extremely important. In a relatively wet year where most of the annual rainfall occurred in the early spring, tile drainage is essential early in the season, but CD during the growing season would support higher yields, due to capillary rise with an elevated water table.

A very modest increase in crop yields was observed with controlled drainage in drier years, such as 2001. However, the mean differences were not significant across treatments at the 0.05 level using the t-test statistic; the observed value of the test statistic was 0.4 while the critical value was 2.09. The increased benefit of CD with respect to corn yield was approximately 3% to 7% from 1993 to 1996 (Zhou et al., 2000; Mejia et al., 2000), while in 2001 and 2002 corn yield was 32.9%-36.2% higher in CD than FD, due to extremely dry conditions during both growing seasons (Stampfli and Madramootoo, 2006). The results were consistent with studies on corn yields in Ontario and Iowa (Jaynes et al., 2010; Sunohara et al., 2010). Controlled drainage on yields were statistically lower than FD in 1998, when precipitation was the highest, as shown in table 3. This indicates that CD plots may be prone to waterlogging if not managed effectively, as the water level rose too close to the root zone (Sunohara et al., 2010). Other studies found significant crop yield improvements associated with CD in similar regions because the quantity of nutrients which would have been lost to subsurface drainage remained available for crop uptake when CD was employed (Sunohara et al., 2014).

Effects on Nitrate Leaching

As can be seen from table 4, controlled drainage reduced total nitrate loss by approximately 58% compared to FD (Mejia and Madramootoo, 1998; Elmi and Madramootoo, 2000). We estimated the effect of CD and FD on NO3 - N leaching using a least square regression approach and found CD to have a significant (P = 0.006) effect on leaching with a slope coefficient of -18, implying that CD reduced nitrogen pollution by over 17 times that of FD. There was no significant relationship between precipitation and leaching. Although, intuitively, soil moisture influences nitrification and denitrification, which affect the movement of nitrogen within the soil profile.

Table 4. Nitrate leaching data between 1997 and 2000. (Data sources from the relevant publications are also given).
YearRainfall
(mm)		Fertilizer
Applied
N		NO3-N Losses
N kg ha-1		Difference
(%)		References
CDFD
19974692001.43.0+53.3Madramootoo et al., 2001
Elmi et al., 2000
Elmi et al., 2002
Elmi et al., 2005.
19986182001.57.2+79.17
19994821501.43.0+74.29
20005541691.52.6+23.33

When the fertilizer variable was analyzed in combination with CD, the results showed that there was a significant effect (P = 0.012), and it was negatively correlated to leaching. Using ANOVA to test the correlation coefficient, nitrate was negatively correlated with CD, with a p value of 0.0018. We tested the homogeneity of variances for CD and FD and obtained a P <0.0001. The mean values for the pooled variances showed that P > t = 0.0013. Thus, the results from table 4 show that there is no significant difference between FD and CD. Water table management using control drainage structures is a potential beneficial management practice (BMP) due to its ability to reduce nonpoint source pollution from croplands.

The N fertilizer applied, precipitation, and soil type influence the movement of N within the soil profile and ultimately the N leaving the soil. Annual variations in NO3-N concentration are due to the crop planted and the quantity of fertilizer applied. Residual soil N, rainfall, and drainage volume are also factors.

Effects on Nitrous Oxide Emissions

The results of our measurements under FD and CD are shown in table 5. An ANOVA showed that there was no significant difference (P = 0.5355) between the variance from FD and CD. Our results showed that the average topsoil NO3-N under CD was slightly lower than under FD, though this difference was not significant (P > 0.05). An earlier study at the study site also reported topsoil NO3-N tending to be lower under CD than FD, observed denitrification (N2O+N2) rates to be twice as high under CD than FD (Elmi et al., 2005). However, N2O emissions in that study were not necessarily higher under CD, denoting a greater reduction of N2O to N2 in the CD plots. Notably, the three years of their study were either wet or normal, such that the potential for complete denitrification was greater than in a dry year. Therefore, the difference in topsoil NO3-N between FD and CD may not be adequate to explain the differences in observed N2O fluxes. Weier et al. (1993) noted that complete denitrification from N2O to N2 is dependent on soil moisture and available carbon. In three of the six years of measurements, N2O fluxes under CD were greater by 49% than those under FD, but up to 43% lower in the other three years.

Elmi et al. (2005) showed greater daily mean N2O emissions from the CD (vs. FD) plots in 2000 but lower N2O fluxes in 2018 (0.025 and 0.035 mg m2 hr-1) for CD and FD, respectively. The higher mean N2O fluxes under FD may be explained by a peak N2O flux observed at the beginning of the growing season (fig. 3). Such short-term peak fluxes originate in microbial hotspots, where process rates are ten- to a hundred-fold greater than in the surrounding bulk soil. The hotspots are influenced by soil factors such as moisture and the availability of carbon (C) substrate and reactive N. Other major peaks in N2O fluxes were observed in both CD and FD after fertilizer was applied in June. These elevated fluxes continued for about two weeks before returning to baseline values. They further observed that peak fluxes coincided with high rainfall events. However, 2018 had lower growing season precipitation compared to a normal or wet year. Therefore, the occurrence of N2O fluxes in the field may depend more strongly on the availability of soil N and the rate and timing of fertilizer application, particularly when associated with rainfall events.

Table 5. Nitrous oxide data between 1997–2000, and 2018. (Data sources from the relevant publications are also given).
YearRainfall
(mm)		Fertilizer
Applied
N		NO2-N Emissions
N kg ha-1		Difference
(%)		References
CDFD
19986182001.61[a]1.89[a]- 14.81Madramootoo et al., 2001
Elmi et al., 2000; Elmi et al., 2002
Elmi et al., 2005.
19994821501.81[a]0.93[a]+ 94.62
20005541693.12[a]1.84[a]+ 69.57
20183601800.025[b]0.035[b]- 28.57Ekwunife and Madramootoo, 2023

    [a]    Indicates emissions.

    [b]    indicates fluxes.

Figure 3. N2O fluxes from tile drainage (FD) and controlled drainage (CD) treatment plots over the 2014, 2015, and 2018 growing seasons (Ekwunife and Madramootoo, 2023).

Conclusions

This study highlights the substantial and long-term benefits of controlled drainage (CD) in enhancing drainage water quality and sustaining crop yields without contributing to greenhouse gas (GHG) emissions. Our findings reveal that CD led to a 3% increase in crop yield, a significant 17% reduction in drainage volume, and, importantly, did not result in elevated GHG emissions. Moreover, our observations align with simulations conducted by researchers in eastern Canada, positioning CD as a robust pollution control and abatement technology. Notably, the insignificant difference in N2O emissions between free drainage (FD) and CD over the study period positions CD as a "win-win" technology, offering lasting co-benefits. These include not only enhanced yield resilience in drier years but also the potential to reduce NO3-N leaching and N2O emissions from grain fields. Looking forward, our study suggests that the adoption of CD may see increased relevance in the face of changing climatic conditions, characterized by heightened annual precipitation and temperatures. As climatic patterns evolve, particularly with increased growing season temperatures and unpredictable precipitation distribution, CD's effectiveness in managing soil water storage for optimal crop utilization becomes increasingly valuable. Additionally, the study highlights the need for practical water table control structure management during wetter springs to mitigate NO3-N concentrations while facilitating timely spring field operations. In essence, CD emerges not only as a current solution but as a strategic approach to adapt to future climatic shifts and optimize agricultural practices for sustained productivity and environmental stewardship.

Acknowledgments

The authors are grateful to the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, and the Agricultural Greenhouse Gas Program of Agriculture and Agri-Food Canada for their financial support of the work reported in this paper.

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