Subirrigation Research Articles

Impact of Controlled Drainage and Subirrigation on Water Quality in the Red River Valley

The potential impact of controlled drainage (CD), which limits drainage outflow, and subirrigation (SI), which provides supplemental water through drain tile, on surface water quality are not well known in the Red River Valley (RRV). In this study, water samples were collected and analyzed for chemical concentrations from a tile-drained field that also has controlled drainage and subirrigation modes in the RRV of southeastern North Dakota from 2012–2018. A decreasing trend in overall nutrient load loss was observed because of reduced drainage outflow, though some chemical concentrations were found to be above the recommended surface water quality standards in this region. For example, sulfate was recommended to be below 750 mg/L but was reported at a mean value of 1971 mg/L during spring free drainage. The chemical composition of the subirrigation water was shown to have an impact on drainage water and the soil, specifically on salinity-related parameters, and the impact varied between years. This variation largely depended on the amount of subirrigation applied, soil moisture, and soil properties. Overall, the results of this study show the benefits of controlled drainage on nutrient loss reduction from agricultural fields.

Nutrient retranslocation in Larix principis-rupprechtii Mayr relative to fertilization and irrigation

Nutrient retranslocation from senescing foliage to perennial organs is critical for nutrient conservation and a mechanism of plant adaptation to low-fertility soils. And it has been well documented for evergreen species and for deciduous broadleaf tree species. Meanwhile, subirrigation (SI) and fertilization are used to improve the production efficiency of seedlings, however, little is known about how retranslocation in deciduous conifer seedlings is affected by SI or soil fertility. We fertilized Larix principis-rupprechtii Mayr seedlings with 50, 100, and 150 mg N per seedling using SI and overhead irrigation (OI). Seedling growth and nutrient status, at both pre-senescence (T1) and post-abscission (T2) moments, and growing media electrical conductivity were measured to (1) explore relationships between foliar nutrient retranslocation and (a) growth, (b) nutrient status, and (c) media fertility, and (2) examined how these are affected by irrigation method and fertilizer rate. Fertilizer rate and irrigation method had little effect on seedling growth, with the exception of root mass, but N, P, and K concentrations increased with increasing soil fertility and both concentrations and contents were greater under SI compared to OI. Foliar N and K retranslocation was lower under SI compared to OI across all fertilizer rates, while foliar P retranslocation was lower only at the highest fertilizer rate for SI-seedlings. For OI-seedlings, retranslocation was unaffected by fertilizer rate, with average N, P, and K retranslocation efficiencies of 71%, 29%, and 55%, respectively. However, retranslocation in SI-seedlings declined as fertilizer rates increased. Foliar nutrient retranslocation directly correlated with seedling biomass accumulation over the growing season (up to T1) and inversely correlated with soil fertility, shoot biomass accumulation during hardening (from T1 to T2), and T1 nutrient concentration in roots (N, P, and K) and stems (N and K). Understanding nutrient retranslocation dynamics for deciduous woody plants informs more effective nutrient management regimes for seedling production under SI.

Subirrigation Effects on Larch Seedling Growth, Root Morphology, and Media Chemistry

Subirrigation (SI), where water is provided to container seedlings from below and rises through the growing media via capillary action, is regarded as an environmentally-responsible method of delivering water and fertilizer to nursery-grown plants, resulting in more uniform crops and improved production efficiency. While a concern around adopting this method is that a potential higher salt concentration in the upper layers of growing media under SI may inhibit root growth and result in decreased plant quality, few studies have focused on how root morphology is altered by SI. Therefore, a balanced two-factor factorial design with three rates of fertilization (50, 100, and 150 mg N seedling−1) and two irrigation methods (SI or overhead irrigation (OI)) was used to examine the growth response of Prince Rupprecht’s larch (Larix principis-rupprechtii Mayr) seedlings for one nursery season. Associated changes between rhizosphere electrical conductivity (EC) and root morphology of different root size classes were analyzed. Results show that (1) height, root-collar diameter, and root volume were similar between seedlings grown under SI and OI. However, (2) compared to seedlings receiving OI, SI-seedlings had less root mass, length, and surface area but greater average root diameter (ARD). (3) Morphological differences were evident primarily in root diameter size classes I–III (D ≤ 1.0 mm). (4) Fertilizer rate influenced root length and surface area up to 130 days after sowing but affected ARD throughout the growing season such that seedlings treated with 50 mg N had smaller ARD than seedlings treated with 100 mg N. (5) As the growing season progressed, SI-media had significantly higher EC compared to OI-media and EC increased with increasing fertilizer rate under SI but not under OI. These results indicate that SI can produce larch seedlings of similar height and root collar diameter (RCD) compared to OI, but root systems are smaller overall with fewer small-diameter roots, which may be related to high EC levels in SI-media, which is exacerbated by the use of high rates of fertilizer. Therefore, the EC in the media should be monitored and adjusted by reducing fertilizer rates under SI.

Comparison of Four Systems for Propagation of Coleus by Stem Cuttings

Overhead mist (OM) facilitates the propagation of stem cuttings by preventing transpirational water loss. However, drawbacks to OM include the application of large volumes of water, potentially unsanitary conditions, irregular misting coverage, and leaching of foliar nutrients. We explored three alternatives to OM that might avoid these problems by applying moisture below, rather than overhead. These included 1) a submist (SM) aeroponic system configured to provide intermittent mist only to the rooting zone, 2) a subirrigation (SI) system that provided water via capillary action through perlite from a reservoir maintained below the base of each cutting, and 3) a subfog (SF) aeroponic system that was configured to provide constant fog only to the rooting zone. To initiate each system, we wetted perlite or filled reservoirs using either water or quarter-strength Hoagland solution. Stem cuttings of ‘Wizard Mix’ coleus (Plectranthus scutellarioides) were propagated in the systems for 21 days. Cuttings in the SM system produced more than three times as many roots as cuttings in the OM system, with roots more than six times the length. Root dry weights averaged 28 mg for cuttings in the SM system, compared with only 3.5 mg among cuttings receiving OM. The SF and SI systems produced results broadly comparable to the OM. Fertilizer did not consistently improve rooting measures across the systems. Although we observed few fine roots on cuttings rooted using SM, they transplanted well into a soilless substrate and quickly produced new root growth. The SM system used less than 1/5 the water used by the SI system, and less than 1/50 the water used by the SF system. In comparison, a single OM nozzle operating for 10 seconds released about one-third of the total water lost through transpiration from each SM system over the entire experiment. Our results show that SM systems merit further evaluation for propagation of plants by stem cuttings.

Subirrigation System Performance and Evaluation in the Red River Valley of the North

Abstract. Using a subsurface drainage system, subirrigation (SI) applies water below the ground surface and raises the phreatic water to within or near the root zone. SI is relatively new to the Red River Valley (RRV) of the North in eastern North Dakota (ND) and west central Minnesota (MN). In 2011, two SI field sites in the RRV were installed and have shown promising results in optimal water management and increasing agricultural production. Unlike a surface irrigation system, SI supplies water below the ground surface over a long duration; water loss is generally through crop transpiration; and SI leads to negligible water loss via wind, surface runoff and evaporation. Therefore, a new method was developed to evaluate the SI system performance. Water application efficiency (Ea) was calculated through the soil moisture changes in the root zone before and after the SI application with known amounts of SI, precipitation, and evapotranspiration (ET). Uniformity coefficient (UC) and distribution efficiency of low quarter (DULQ) were estimated from the total depth of water stored in the root zone. The SI system performance in 2014 and 2015 showed that the Ea was over 100% in 2014 and 78% for the ND 2015 site-year. The Ea values were high, indicating that the SI system either performed better than typical surface irrigation systems with minimal water loss, or the SI system and/or the methods need improvement in accurate ET estimation to help close the water budget. The UCs were 67% to 86%, and the DULQs were 48% to 78%, much lower than typical sprinkler and surface irrigation systems, possibly due to the unique SI flow path. Overall, the evaluation indicated that a SI system is effective as a water supply, but the uniformity needs to be improved with a longer SI duration or smaller flow rate or an alternative SI system design. Keywords: Red River Valley of the North, Subirrigation, Uniformity, Water use efficiency.

Subsurface Drainage and Subirrigation Effects on Water Quality in Southeast North Dakota

Rising water tables, increased soil salinity, and poor trafficability have prompted rapid expansion of subsurface drainage in the Red River Valley of the North in eastern North Dakota and northwestern Minnesota. A conventional subsurface drainage (CD) and subirrigation (SI) field study was conducted in southeast North Dakota from 2008 to 2010 to investigate drainage and subirrigation effects on water quality. Water samples were collected biweekly from a sump pump structure (used as the water inlet and outlet) and 16 observation wells within the field. Water quality variables included chloride (Cl-), electrical conductivity (EC), total dissolved solids (TDS), sodium adsorption ratio (SAR), sodium (Na+), orthophosphate (PO4-P), ammonium (NH4-N), nitrite and nitrate (NOx-N), Kjeldahl nitrogen (TKN), and total nitrogen (TN). A three-factor partially nested design and a general linear model with random effects were employed to compare the effects of water management treatment, distance to drain, and well locations (soil heterogeneity) on water quality. The most significant water quality difference was found at the outlet structure, where a significant difference (p < 0.001) between the CD and SI water was found for all ten variables. The water quality of the drainage water was better than the subirrigation water from the aquifer, except for the NOx-N, EC, and TDS concentrations. Well water Cl- concentrations inside the field were significantly greater in SI compared with CD water; EC, TDS, SAR, and Na+ were not. In contrast, EC, TDS, SAR, and Na+ were significantly higher at two well locations, indicating that soil heterogeneity affected the water quality. Due to SI practice, a significant difference for Cl-, SAR, and Na+ was found between the locations closest to and farthest from the drains during the SI practice, which implies that the SI process may cause soil properties to change in the future. Overall, well locations significantly affected PO4-P, NOx-N, and TN, indicating that the soil physical and chemical properties affected the water quality, and these effects could overcome the difference due to different water treatments.

Modeling Water Table Depth, Drain Outflow, and Nitrogen Losses in a Cold Climate Using DRAINMOD 5.1

The performance of the DRAINMOD 5.1 model was tested for conditions, including freezing and thawing, that prevailed at a 4.2 ha field research facility located at St. Emmanuel, Quebec, Canada. Using two years (1998 and 1999) of data collected from the site, the model's ability to predict water table depth (WTD), drain outflow, and nitrate (NO3--N) loads in drain water was tested. The site was arranged in a split-plot design, with two N fertilizer rates (120 and 200 kg ha-1, main plots) factorially combined with two modes of water table management: sub-irrigation (SI) at a WTD of 0.6 m vs. free drainage (FD) at a drain depth of 1.0 m (subplots). The model was calibrated using water table depth and subsurface flow data from 1998 and validated with 1999 data. The model's accuracy was evaluated using the coefficient of determination (R2), modeling efficiency (E), and other statistical parameters. DRAINMOD 5.1 performed well at simulating the number and timing of drainage events in both snowmelt and later-season periods. The model underestimated annual drain outflow under free drainage and sub-irrigation by 12 mm and 20 mm, respectively, in both years. The model simulated the pattern of water table fluctuations fairly well, with R2 values ranging from 0.81 to 0.91, indicating good model fit. The model performed well in predicting total NO3--N loads in subsurface flow, even though there was a tendency to underestimate loads under both free drainage and sub-irrigation treatments.

Water Table Management to Improve Drainage Water Quality in Semiarid Climatic Conditions of Iran

A lysimeter study was conducted in the field in Karaj, Iran to investigate the effects of water table management on water quality of subsurface drainage effluents. Drain volumes, nitrate-N concentration, phosphorus concentration, and electrical conductivity of drain effluents were monitored during the growing seasons of alfalfa (Medicago scutellata). Totally 12 lysimeters consisted of four treatments were used in this study, of which nine of them were equipped with subirrigation (SI) and the other three with free drainage (FD) systems. Annual alfalfa (Medicago scutellata) was planted in all lysimeters. Water table levels were kept at 30 cm (SI30), 50 cm (SI50), and 70 cm (SI70) below the soil surface in SI-lysimeters and more than 100 cm below the soil surface in FD-lysimeters. The results of this 2-year study showed a significant reduction in nitrate-N concentrations in SI-lysimeters compared to FD-lysimeters. In 2005, the mean nitrate-N concentrations in drainage effluent were reduced by 84% in the SI30 and by 82% in the SI50, relative to FD. Similarly, in 2006, drain water depth and nitrate-N concentrations were significantly reduced relative to FD. The forage dry matter production from SI30 and SI50 were significantly higher than those from FD in both years. In 2006, the average of dry matter production was increased by 69 and 89% by the SI30 and SI50, respectively, relative to FD. The average electrical conductivity of drainage water was reduced in SI lysimeters compared to FD lysimeters that meet Iranian standard level (3 dS/m). There are no statistically significant differences in phosphorous concentration in drainage water of different treatments. Finally, the results of this 2-year study indicate that the water table management practices are economically and environmentally feasible in Iran in order to have a sustainable agriculture.

Water Use and Fertilizer Response of Azalea Using Several No-leach Irrigation Methods

Although research has shown that plants grown with subirrigation systems such as ebb-and-flow and capillary mat require less water and fertilizer inputs than traditional overhead irrigation methods, similar information for capillary wick irrigation has not been available. We compared the growth and water use response of azalea (Rhododendron sp. ‘George Tabor’) grown in 6.5-inch-diameter “azalea” containers with three irrigation methods [overhead (OVR), subirrigation (SUB), and capillary wick (WCK)] and four fertilizer nitrogen (N) rates 0.5 to 2.0 lb/yard3 supplied by an incorporated, resin-coated, controlled-release fertilizer (Nutricote 17N–3.1P–6.7K, 180 d at 77 °F). OVR volume was adjusted to deliver 100% of evapotranspiration (ET) loss. For all irrigation treatments, the lowest N rate resulting in maximum plant growth was 1.0 lb/yard3, which was less than the label recommendation of 1.5 lb/yard3. At the N-limiting N rate of 0.5 lb/yard3, irrigation method had no effect (P &lt; 0.05) on azalea growth. At N rates higher than 1.0 lb/yard3, decreased growth was observed for OVR compared with SUB and WCK. This negative effect on plant growth was attributed to salt injury as indicated by excessive pour-through electrical conductivity (EC) levels in OVR containers. At the end of the experiment, substrate EC was highest in the uppermost layer of SUB and WCK containers, reflecting the upward movement of water associated with these two irrigation methods. Water use efficiency, which ranged from 1.9 to 2.8 g shoot dry weight per liter of water lost through ET, was unaffected (P &lt; 0.05) by irrigation method at the N rate of 1.0 lb/yard3. We concluded that the growth response of azalea to fertilizer N rate was similar for WCK and SUB despite periodic pour-through EC tests indicating higher substrate nutrient levels with WCK.

(307) NFT versus Subirrigation: II. Tomato Fruit Quality Grown in Closed Soilless Systems under Salinity or Water Stress

Nutrient solutions (NS) containing moderate to high concentrations of salts are frequently supplied to improve the taste of tomato fruits grown in soilless systems. The aim of this study was to determine whether salinity and water stress affect the tomato fruit quality similarly. The research was conducted in Mola di Bari, Italy, during Autumn 2004, and compared the nutrient film technique (NFT) with the trough-bench technique [Subirrigation (SUB)] in terms of tomato (Lycopersicon esculentum Mill. cv. Kabiria) fruit quality. In the NFT, the plants were grown with two electrical conductivity (EC) levels (2–4 and 6–8 dS·m-1) of NS. The highest EC was obtained by increasing all the ions in the NS. In the SUB system, two water tensions (-4 and -8 kPa) of substrate (perlite) were examinated. At harvest, in each cluster (six/plant), fruit dry matter (DM) and total soluble solids (TSS) were determinated. In the fourth and sixth cluster, vitamin C content and titratable acidity were determined. Total yield was not influenced by either soilless system, while the average weight of the fruit was lower in the SUB. The DM and TTS were influenced by soilless system (on average, 6.6 vs 7.3 g/100 g of fresh matter and 5.3 vs. 5.9 °Brix, with NFT and SUB, respectively). Both of the stresses resulted in the increase of DM and TSS, principally in SUB (water stress) in respect to NFT (salinity stress), while vitamin C and titratable acidity were not influenced by soilless system or water/salinity stress (25.2 mg/100 g fresh matter and 0.45 g/100 mL of citric acid juice, respectively). Results of NFT with the highest EC of NS exceeded 9 dS·m-1, without any stress symptoms in the plants, while EC in the SUB system remained unchanged (about 2.5 dS·m-1).

(306) NFT versus Subirrigation: I. Yield and Water Use Efficiency of Tomato Grown in Closed Soilless Systems under Salinity or Water Stress

Sustainability of the soilless greenhouse system is under discussion in open cycle systems, where excess nutrient solution (NS) draining from the substrate is released into the environment. Closed growing systems (CGS) lead to the saving of water and fertilizers. The aim of this research was to compare two CGS: nutrient film technique (NFT) and trough-bench technique [Subirrigation (SUB)]. We report the results of yield and water use efficiency (WUE) of tomato (Lycopersicon esculentum Mill. cv. Kabiria) plants. NFT plants were grown with two electrical conductivity (EC) levels (2-4 and 6-8 dS·m-1) of NS (its highest EC was obtained by increasing all the ions therein). In the SUB system, two water tensions (-4 and –8 kPa) of susbtrate were compared; a NS with an electrical conductivity level of 2 dS·m-1 was used. The tensions were measured through tensiometers. Tomato plants were transplanted at the fourth to fifth true-leaf stage into pots containing 8 L of perlite for SUB. In both CGS, the plants were placed on steel gullies (slope of 2%). Six clusters per plant were harvested. Total and commercial yield were not influenced by the CGS (on average, 1959 and 1853 g/plant, respectively). The average weight of the fruit was lower in the SUB system's plants (40 vs. 43 g/fruit, respectively, for SUB and NFT). Salinity and water stresses resulted in a reduction of 26% of the yield and 16% of the average weight of fruits. The WUE was higher in SUB than NFT (30.7 vs. 26.0 g·L-1, respectively). Salinity stress reduced WUE (29.4 v.s 22.6 g·L-1 with 2–4 and 6–8 dS·m-1, respectively), whereas water stress did not.

Impacts of Water Table Management on N2O and N2 from a Sandy Loam Soil in Southwestern Quebec, Canada

Nitrous oxide (N2O) is primarily produced as intermediate in denitrification and, to a lesser extent, through nitrification processes. Nitrous oxide emission and, consequently, its atmospheric impacts depend on the extent to which N2O is reduced to dinitrogen gas (N2) by denitrifiers. Field experiments were conducted from 1998 through 2000 growing seasons at St. Emmanuel, Quebec, Canada, to investigate the combined impact of water table management (WTM) and N fertilization rate on the soil denitrification (N2O + N2) rate, rate of N2O production, and the N2O:N2O + N2 ratio. Water table treatments included subirrigation (SI) with a target water table depth of 0.6 m and free drainage (FD) with open drains. The tile drains (75 mm diameter) were laid at a 1.0 m depth from the soil surface. Nitrogen fertilizer was applied at two rates:120 and 200 kg N ha−1 as ammonium nitrate (34-0-0). The N2O + N2 evolution rates were greater in SI (12.9 kg N ha−1) than in FD (5.8 kg N ha−1) plots. The percentages of N2O relative to overall N2O + N2 evolution were 35 and 11% for 1998, 29 and 8% for 1999, and 37 and 20% for 2000, under FD and SI, respectively. The reduced N2O production under SI was due to a greater reduction of N2O to N2. Results indicate that greater N2O + N2 evolution under shallow water tables are not necessarily accompanied by higher N2O emissions.

Assessment of Denitrification Gaseous End‐Products in the Soil Profile under Two Water Table Management Practices Using Repeated Measures Analysis

The denitrification process and nitrous oxide (N2O) production in the soil profile are poorly documented because most research into denitrification has concentrated on the upper soil layer (0-0.15 m). This study, undertaken during the 1999 and 2000 growing seasons, was designed to examine the effects of water table management (WTM), nitrogen (N) application rate, and depth (0.15, 0.30, and 0.45 m) on soil denitrification end-products (N2O and N2) from a corn (Zea mays L.) field. Water table management treatments were free drainage (FD) with open drains and subirrigation (SI) with a target water table depth of 0.6 m. Fertility treatments (ammonium nitrate) were 120 kg N ha(-1) (N120) and 200 kg N ha(-1) (N200). During both growing seasons greater denitrification rates were measured in SI than in FD, particularly in the surface soil (0-0.15 m) and at the intermediate (0.15-0.30 m) soil depths under N200 treatment. Greater denitrification rates under the SI treatment, however, were not accompanied with greater N2O production. The decrease in N2O production under SI was probably caused by a more complete reduction of N2O to N2, which resulted in lower N2O to (N2O + N2) ratios. Denitrification rate, N2O production and N2O to (N2O + N2) ratios were only minimally affected by N treatments, irrespective of sampling date and soil depth. Overall, half of the denitrification occurred at the 0.15- to 0.30- and 0.30- to 0.45-m soil layers, and under SI, regardless of fertility treatment level. Consequently, sampling of the 0- to 0.15-m soil layer alone may not give an accurate estimation of denitrification losses under SI practice.

Water and Fertilizer Nitrogen Management to Minimize Nitrate Pollution from a Cropped Soil in Southwestern Quebec, Canada

Nitrate-N (NO3--N) pollution of water resources is a widely recognized problem. Water and nitrogen fertilizer are the two most important factors affecting NO3--N movement to surface and groundwater. Field trials were conducted from 1998 to 2000 growing seasons to investigate the combined impacts of water table management (WTM) and N fertilization rate on NO3--N concentration in the soil profile and in drain discharge. There were two water table treatments: free drainage (FD) with open drains at a 1.0 m depth from the soil surface and subirrigation (SI) with a target water table depth of 0.6 m below the soil surface, and two N fertilizer rates: 120 kg N ha-1 (N120) and 200 kg N ha-1 (N200) in a split-plot design. Compared to FD, SI reducedNO3--N concentration in the soil by up to 50% averaged over the two N rates. Concentrations of NO3--N in drainage water fromSI plots were lower than those from FD by 55 to 73%. These findings suggest that SI can be used as a means of reducing soil NO3--N pollution and drainage water NO3--N concentrations.

Environmental and agronomic implications of water table and nitrogen fertilization management.

Nitrate (NO3-) pollution of surface and subsurface waters has become a major problem in agricultural ecosystems. Field trials were conducted from 1996 to 1998 at St-Emmanuel, Quebec, Canada, to investigate the combined effects of water table management (WTM) and nitrogen (N) fertilization on soil NO3- level, denitrification rate, and corn (Zea mays L.) grain yield. Treatments consisted of a combination of two water table treatments: free drainage (FD) with open drains at a 1.0-m depth from the soil surface and subirrigation (SI) with a design water table of 0.6 m below the soil surface, and two N fertilizer (ammonium nitrate) rates: 120 kg N ha(-1) (N120) and 200 kg N ha(-1) (N200). Compared with FD, SI reduced NO3(-)-N concentrations in the soil profile by 37% in spring 1997 and 2% in spring 1998; and by 45% in fall 1997 and 19% in fall 1998 (1 mg NO3(-)-N L(-1) equals approximately 4.43 mg NO3- L(-1)). The higher rate of N fertilization resulted in greater levels of NO3(-)-N in the soil solution. Denitrification rates were higher in SI than in FD plots, but were unaffected by N rate. The N200 rate produced higher yields than N120 in 1996 and 1997, but not 1998. Corn yields in SI plots were 7% higher than FD plots in 1996 and 3% higher in 1997, but 25% lower in 1998 because the SI system was unable to drain the unusually heavy June rains, resulting in waterlogging. These findings suggest that SI can be used as an economical means of reducing NO3- pollution without compromising crop yields during normal growing seasons.

Water Table Management as a Natural Bioremediation Technique of Nitrate Pollution

Abstract Nitrate-nitrogen (NO3--N) pollution of water resources is a worldwide problem. Field trials were conducted from 1997 to 1998 to investigate the combined impacts of water table management (WTM) and N fertilization rate on soil NO3--N level and concentration of NO3--N in drainage water. Treatments consisted of two water table treatments: free drainage (FD) with open drains at a 1.0-m depth from the soil surface and subirrigation (SI) with a design water table of 0.6 m below the soil surface, and two N fertilizer rates: 200 kg N ha-1 (N200) and 120 kg N ha-1 (N120) in a split-plot design. Subirrigation reduced NO3--N concentration in the soil compared to FD by 37% in the spring of 1997 but not significantly (2%) in 1998; and 45% and 19% in the fall of 1997 and 1998, respectively. Higher rates of fertilization (N200) resulted in greater levels of NO3--N in the soil profile than the N120. Nitrate-N concentrations in drainage water from SI were 74% and 80% lower than those from FD in 1997 and 1998, respectively. Water table management can effectively reduce NO3--N pollution of water.

Modelling nitrate losses in drainage water using DRAINMOD 5.0

The appropriateness of the DRAINMOD-N computer model for the southwestern Quebec region was assessed by comparing field data and simulated results. Four years of field data were collected from a 4.2 ha field research facility located at St. Emmanuel, Que. The experimental layout contrasted two different fertilizer and water table treatments in a split plot design. Nitrogen fertilizer was applied at rates of 120 and 200 kg N/ha. The water table was either maintained at 0.6 m by a subirrigation (SI) system or was under free drainage (FD) at a drain depth of 1.0 m. The model was calibrated using data from 1996 to 1997. Simulated output for 1998 and 1999 were compared to measured values based on the mean residual error (MRE), coefficient of efficiency ( C eff=1.0 represents a perfect match; C eff≤0 a poor match) and other statistical parameters. Except for FD plots in 1998 (MRE=−0.225 m, C eff=−0.198), water table depths (WTDs) were predicted to 0.17 m (23%) with C eff ranging from 0.035 to 0.846. DRAINMOD correctly predicted the pattern, but underestimated the magnitude of daily drainflow in both years. On a monthly basis total drain flow was underestimated by up to 5 mm in 1998 and 1.2 mm in 1999. Except for the 1998-SI plots ( C eff=−0.021) simulations were excellent ( C eff>0.8). With the exception of two FD-year-N combinations, DRAINMOD overestimated leached nitrogen by 0.01–1.09 kg ha −1 month −1 (0.02–5.01%). Nitrate leaching predictions were poor in 1998 (−0.20> C eff>−7.83), but good to excellent in 1999 (0.95> C eff>0.56). The poor performance in 1998 compared to 1999 is attributed to significant rainfall events occurring soon after surface fertilizer application in 1998, but not in 1999. DRAINMOD largely overpredicted monthly total denitrification. Predictions were poor in 1999 (−0.25> C eff) and very poor in 1998 (−139.7> C eff) and mostly attributable to poor simulation of June and July, the peak months of measured denitrification. DRAINMOD performed well in the prediction of hydrological parameters, but fared less well in terms of nitrate leaching and denitrification.

Influence of water table and nitrogen management on residual soil NO 3− and denitrification rate under corn production in sandy loam soil in Quebec

Nitrate-N (NO 3 −) effluents from agricultural ecosystems contributing to the degradation of water quality has become a serious environmental problem. A field experiment was conducted in 1996 and 1997 at St. Emmanuel, Que., Canada, to investigate the combined effects of water table management (WTM) and N fertilization on soil NO 3 − level and denitrification rates in the top soil layer (0–0.15 m). The field was planted to corn ( Zea mays L.) in both years. Treatments consisted of a factorial combination of two water table treatments, free drainage (FD) at about 1.0 m and subirrigation (SI) at 0.6 m below the soil surface, and two N fertilizer rates, 200 kg ha −1 (N 200) and 120 kg ha −1 (N 120). SI reduced NO 3 − concentration in the top soil layer by 42 and 16% in 1996 and 1997, respectively. Nitrate levels in soil were 50% lower in N 120 plots in 1996, and 20% in 1997 compared to the N 200 plots. Denitrification was higher in SI compared to FD, but not influenced by N rate. As a consequence, WTM practices have implications for both water quality and greenhouse gas emissions. Climatic conditions played a large role in regulating N dynamics in the soil. Due to drier and cooler conditions in 1997, denitrification rates were lower than in 1996, leaving higher residual NO 3 − in the soil profile following corn harvest.

Evaluation of Four Irrigation Systems for Containerized Ornamentals

Containerized Cotoneaster dammeri `Coral Beauty' and Forsythia `Northern Gold' were grown in a 2 bark: 1 peat: 1 sand (by volume) medium containing 5 kg·m–3 Nutricote 16N–4.4P–8.1K, Type 140, under four irrigation regimes: drip (DR; 20 min/day; two periods), overhead (OV; 90 min/day; two periods), overhead pulse (OP; 28 min/day; four periods), and subirrigation (SU). Volumes of 0.33, 0.35, and 0.14 liters·day–1 were delivered to each container in the DR, OV, and OP systems, respectively. SU was supplied from a geotextile-covered sand bed. End-of-season dry weights of Cotoneaster and Forsythia were 41% and 55% greater, respectively, in SU-grown plants compared to their OV-irrigated counterparts. Differences in growth between the other three regimes were minor for both species. Pre-dawn and dusk water potentials did not differ between plants in the four regimes, but midday potentials were slightly lower in SU- and DI-irrigated plants. End-of-season foliar N and P content differed only slightly between irrigation treatments, but K levels were significantly higher in SU plants. The reasons for better growth under SU remain obscure but may be related to improved medium nutrient retention and improved fertilizer use efficiency under an irrigation regime in which water moves upwards from the pot base to top.

GERANIUM PRODUCTION AS INFLUENCED BY THREE METHODS OF IRRIGATION USING A CONTROLLED RELEASE FERTILIZER

Seed geraniums (Pelargonium × hortorum Bailey `Scarlet Elite') were grown in 10-cm pots in a 1 pine bark : 3 peat moss : 1 perlite medium from 18 March until 5 May 1993. Plants received Osmocote 14N-6.1P-12.5K and either conventional overhead (CO), drip (DI), or subirrigation (SI). Subirrigation produced greater shoot and root dry weights than CO or DI. Plants grown using DI produced fewer branches than plants grown using CO or SI. Plants receiving SI reached anthesis before plants receiving CO or DI. Method of irrigation had no influence on total root, soil, or leachate N, but SI did increase total shoot N.