Water Table Management Practices Research Articles

Drainage water management impacts soil properties in floodplain soils in the midwestern, USA

Subsurface drainage is one of the most commonly used water table management practices in the Midwest U.S. Subirrigation through the subsurface drainage system using drainage water recycling (DWR) was developed to meet crop production goals and address environmental concerns. The objective of this study was to examine differences in soil properties after seven-years of subsurface drainage treatments [no drainage (ND), drainage only (DO), and drainage plus subirrigation (DWR)] in continuous corn production in Knox County, Missouri. Soil samples were collected at 0–10, 11–20, 21–40, and 41–60 cm depths periodically from 2015 to 2021 and were analyzed for soil pH, cations, cation exchange capacity (CEC), nitrate-N (NO3-N), phosphorus (P), organic matter (OM), total carbon (TC), bulk density (BD), penetration resistance, and soil texture. A significant shift in soil texture from 2015 to 2021 was observed with a 26% and 11% increase in the clay content at a 41–60 cm soil depth in DWR and DO treatments, respectively, compared to ND. Accelerated soil OM and TC mineralization was observed with DWR which may be due to soil acidification, increased soil moisture, and aeration compared to DO and ND. This was further supported by increased CEC at deeper soil depths. In addition, increased reservoir water pH and electrical conductivity in 2016 and 2017 may have amplified the water table fluctuation effects on soil properties. The mean concentration of sodium (Na), potassium (K), bicarbonate, sulfate, nitrate, and phosphate were in an acceptable range for use as irrigation water. In conclusion, continuous corn production under DWR affected soil texture and enhanced soil acidification, which in turn amplified the mineralization of soil OM and TC.

Soil nutrients and plant uptake parameters as related to greenhouse gas emissions.

Fertilizer and water management practices have short- and long-term effects on soil chemical and physical properties and, in turn, greenhouse gas (GHG) emissions. The goal of this 4-yr field study was to establish the relationships between soil properties, agronomic practices, and GHG (CO2 and N2 O) emissions under different fertilizer and water table management practices. There were two fertilizer treatments: inorganic fertilizer (IF) and a mix of solid cattle manure and inorganic fertilizer (SCM), combined with tile drainage(DR) and controlled drainage with subirrigation(CDS). The cropping system was a maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Nitrogen in biomass (BMN) and N in grain (GRN) were measured and used to calculate other plant N parameters. Nitrous oxide and CO2 fluxes were collected weekly, and their respective cumulative emissions were calculated. The results show that soil organic matter (OM), soil total carbon (C), and soil total nitrogen (N) were greater in SCM than IF by 23.7, 35.2, and 24.4%, respectively. Water table management did not significantly affect soil N and C. Increased CO2 emissions were witnessed under higher soil OM, soil total C, and total N. Plant N uptake parameters were negatively correlated with N2 O and CO2 emissions. Higher plant N uptake can reduce environmental pollution by limiting N2 O and CO2 emissions.

An economic analysis software for evaluating best management practices to mitigate greenhouse gas emissions from cropland

Many recent studies on soil and crop management practices have demonstrated their possibility in mitigating greenhouse gas emissions (GHG) from cropland. The response of GHG emissions to management practices can be quantitatively simulated using biophysics-based agricultural system models. However, the economic feasibilities of such management adoption are yet to be evaluated, especially when the producers have to adopt only one profitable management plan. This paper presents a field-scale economic analysis software that is capable of estimating the net benefits under various greenhouse gas mitigating management practices. The calculated net benefits are based on the benefit-cost analysis (BCA), where GHG emissions are converted to the CO2 equivalent and priced using the information from the current carbon trade market. GHG emissions and crop yield are simulated using the Root Zone Water Quality Model (RZWQM2), an agricultural system model coupled with the BCA software. A case study for a cornfield at the Saint Emmanuel site near Montreal, Canada, from 2012 to 2015 under two water table management practices, i.e., free-drainage (FD) and controlled drainage (CD), results showed that FD was more profitable than CD. Although fewer greenhouse gases were emitted under CD than under FD, the potential benefit under current carbon credit payment from GHG reduction under CD was far less than the additional cost from installing new instruments and excessive maintenance fees. This study suggests that the government subsidy is needed to provide further incentives for producers to adopt new greenhouse gas emission mitigating management practices.

Educational interactive vector simulation of water table control designs using LabView

AbstractThis research study spots the light on the possibility of approximating the Fourier series solutions, of the partial differential equations that are used for the design and control of different water table management practices, by a single quadratic vector equation which can very simply take into consideration all various soil hydrological and boundary conditions of any water table management design. To achieve this task, an educational interactive LabView program is designed for the quadratic vector simulation of the water table control (WTC) designs. The program is mathematically based on two types of equations, the linearized form of the Boussinesq equation and the “approximate” quadratic interpolation function vector equation. The program enabled the ease of use, offered an interesting interactive graphical visualization, and provided a high degree of accuracy of the results, which made the program very suitable for teaching and learning. All WTC designs are included in one single LabView graphical user interface representing a typical cross‐section design of a pipe drainage field between irrigation and drainage canals. The WTC designs performed in this virtual cross‐sectional field and simulated in the interface are activated by using LabView digital controllers simulating switches, pumps, valves, a water table sensor, a tensiometer for checking soil‐water stress, and (irrigation/drainage) field pipes. Several numerical design examples solved by the program indicated the exactness and suitability of using the parametric vector simulation for the design of WTC designs.

Evaluating RZ-SHAW model for simulating surface runoff and subsurface tile drainage under regular and controlled drainage with subirrigation in southern Ontario

The response of both surface runoff and subsurface drainage as affected by water table management practices in tile-drained fields is poorly documented. Widely used to simulate management effects on crop production and water quality, the Root Zone Water Quality Model (RZWQM2) has recently been equipped with a subirrigation component. Coupled with Simultaneous Heat and Water (SHAW) model to improve its hydrological responses to cold climates, the hybrid RZ-SHAW has never been tested for simulating surface runoff and subsurface drainage under controlled drainage with subirrigation system. The objective of this study was to evaluate the model performance in predicting surface runoff, subsurface tile drainage, and crop yield under regular drainage (DR) and controlled drainage with subirrigation (CDS) for the first time. The RZ-SHAW model was calibrated and validated against tile drainage, surface runoff and crop yield data collected in a tile-drained field in Harrow, Ontario from June 2008 to December 2011 under DR and CDS treatments. Despite occasional underestimation in winter and overestimation in summer, the model was performing generally satisfactorily in simulating the accumulated subsurface drainage and runoff under both DR and CDS treatments with percent bias (PBIAS) within ±15 %, Nash-Sutcliffe model efficiency coefficient (NSE) >0.5 and the index of agreement (IoA) >0.75. Overall, the RZ-SHAW was capable of predicting the subsurface drainage and surface runoff under both DR and CDS treatment, and it provided reliable estimation for the impact of water table management practice on ET and crop yield, but its accuracy for simulating events of peak flow was not as precise for the CDS treatment than DR treatment.

Mitigating greenhouse gas emissions in subsurface-drained field using RZWQM2

Greenhouse gas (GHG) emissions from agricultural soils are affected by various environmental factors and agronomic practices. The impact of inorganic nitrogen (N) fertilization rates and timing, and water table management practices on N2O and CO2 emissions were investigated to propose mitigation and adaptation efforts based on simulated results founded on field data. Drawing on 2012–2015 data measured on a subsurface-drained corn (Zea mays L.) field in Southern Quebec, the Root Zone Water Quality Model 2 (RZWQM2) was calibrated and validated for the estimation of N2O and CO2 emissions under free drainage (FD) and controlled drainage with sub-irrigation (CD-SI). Long term simulation from 1971 to 2000 suggested that the optimal N fertilization should be in the range of 125 to 175 kg N ha−1 to obtain higher NUE (nitrogen use efficiency, 7–14%) and lower N2O emission (8–22%), compared to 200 kg N ha−1 for corn-soybean rotation (CS). While remaining crop yields, splitting N application would potentially decrease total N2O emissions by 11.0%. Due to higher soil moisture and lower soil O2 under CD-SI, CO2 emissions declined by 6% while N2O emissions increased by 21% compared to FD. The CS system reduced CO2 and N2O emissions by 18.8% and 20.7%, respectively, when compared with continuous corn production. This study concludes that RZWQM2 model is capable of predicting GHG emissions, and GHG emissions from agriculture can be mitigated using agronomic management.

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.

Agricultural drainage management, quality and disposal issues in North America

The North American continent, comprising Canada and the United States of America, has a wide range of climatic, soils and cropping conditions. Surface and subsurface drainage is required to remove excess soil water in the wetter regions of the continent, as well as to maintain a favorable salt and water balance in the crop root zone in the drier irrigated regions. Drainage and water table management practices are essential for the production of food and fiber. However, these practices may sometimes cause third-party impacts, which are largely of a water quality nature. Drainage practices have therefore evolved from removal of water for increased crop productivity, to a method of environmental control. Consequently, much effort over recent years has been in designing and installing drainage systems, which have multiple objectives. A very recent notable institutional development is the formation of the Agricultural Drainage Management Systems (ADMS) Coalition, comprised of farmers, drainage contractors and the drainage industry, government advisors, and water management and agricultural specialists, to promote research, education and adoption of drainage water management as a practice that can reduce the delivery of pollutants to streams. This paper describes the need, extent and status of drainage in North America, including water quality issues, drainage water management and disposal problems. Copyright # 2007 John Wiley & Sons, Ltd.

Simulation of nitrate-N movement in southern Ontario, Canada with DRAINMOD-N

DRAINMOD-N, a mathematical model to predict nitrate-N concentrations in surface runoff and drain outflows from subsurface-drained farmlands, has been tested against field data collected in southern Ontario. The data was collected in a corn field from 16 conventional drainage and subirrigation plots in Woodslee, Ontario, from 1992 to 1994. The model performance was evaluated by comparing the observed and simulated nitrate-N concentrations in surface runoff and drain outflows. A precise calculation of water-table depth is an essential prerequisite for a model to obtain a proper prediction of nitrate-N movement. For the simulation of water-table depth, the lowest root mean square error and the highest correlation coefficient of linear regression were 173 mm and 0.51 for the subirrigation plots; and 178 mm and 0.84 for the subsurface drainage plots. Therefore, the performance of DRAINMOD-N for soil hydrologic simulations was satisfactory and it could be used for assessing nitrogen fate and transport. For the simulation of nitrate-N losses in the subirrigation plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.74 kg/ha and 0.98 for surface runoff; and 6.53 kg/ha and 0.91 for drain outflow. For the simulation in the subsurface drainage plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.70 kg/ha and 0.96 for surface runoff; and 6.91 kg/ha and 0.92 for drain outflow. The results show that DRAINMOD-N can perform satisfactory simulation of soil hydrology and nitrate-N losses in surface runoff under various water-table management practices. The model can, therefore, be used to evaluate different water pollution scenarios and help in the development and testing of various pollution control strategies for fields in cold weather such as that in southern Canada.

APPLICATION OF MARS IN SIMULATING PESTICIDE CONCENTRATIONS IN SOIL

Efforts were made to predict pesticide concentrations at three different depths in the soil profile, using models developed with Multivariate Adaptive Regression Splines (MARS), a regression analysis model. The models were developed with independently collected data from the Eugene F. Whelan Experimental Farm (Agriculture and Agri-Food Canada, Woodslee, Ontario, Canada) from 1992 to 1994. Data from 16 plots, subjected to four different tillage treatments and two different water table management practices, were used. The fate of three herbicides, namely atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine], metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4- triazin-5(4H)-one], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(-2-methoxyl-1-methylethyl) acetamide], at three different soil depths were studied. The input variables for the models included Julian day, days after application of pesticide, measured herbicide concentrations, and cumulative figures for rainfall depth, air temperature, soil temperature, and potential evapotranspiration. Considering the limited size of the data set, a 10-fold cross-validation was performed to test and validate the model. Model predictions at the 0-10 cm depth were very close to the measured values, with model efficiencies varying from 83% to 99%. The predictions at the 10-15 cm depth generally varied from 33% to 83%, while the ones at the 15-20 cm depth were within 42% to 95%, with a few exceptions where the model predicted a single value, of the average observed concentrations. These results demonstrate that MARS was able to do a commendable job in simulating pesticide fate and transport in soil with limited data.

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.

Bioremediation of nitrate-contaminated shallow soils and waters via water table management techniques: evolution and release of nitrous oxide

Nitrate (NO 3–N) commonly accumulates in soils because of fertilizer additions or when crop demand is much less than the rate of NO 3–N production. Water table management (WTM) has been proposed to stimulate denitrifying bacteria, thus removing the accumulated NO 3–N by converting it to N 2O (a greenhouse gas) and N 2. We studied the emission of N 2O and N 2 as affected by water table depth. Undisturbed soil columns (30 cm dia by 90 cm long) from three soil series (Blount, somewhat poorly drained Aeric Ochraqualf; Clermont, poorly drained Typic Glossaqualf; and Huntington, well drained Fluventic Hapludoll) were treated with 2.11 g N (as KNO 3) applied as a band 10 cm below the surface. Two different WTM schemes were studied: static (WTM1) and dynamic (WTM2). We repeated WTM2 using 15N and this treatment, applied to the Huntington soil only, was designated WTM3. In general, N 2O concentrations in a soil column responded to fluctuations in water table depth. Concentrations of N 2O were usually higher in soils immediately below, as compared to above, the water table. The Clermont columns departed from this general trend. Maintaining the water table at 50 cm depth resulted in N 2O emission rates (1.8–44 mg N 2O–N m −2 d −1) comparable to those reported for cultivated fields. A water table only 10 cm below the surface caused N 2O emission rates to increase considerably (60–560 mg N 2O–N m −2 d −1). Four days after imposition of a water table 10 cm below the soil surface, N 2O comprised 95% of the N gas emitted (i.e. N 2O mole fraction was 0.95). One week later, however, the N 2O mole fraction was 0.35 which was significantly ( P≤0.05) lower than the mole fraction (0.68) measured prior to raising the water table. These results suggest that when using WTM practices, the best option to maintain high NO 3–N removal rates and to reduce the proportion of N 2O in the emitted gases is to maintain a high water table for a prolonged period in the most biologically-active portion of the soil profile.

Simulation of pesticide concentrations in groundwater using Agricultural Drainage and Pesticide Transport (ADAPT) model

A water quality model for subirrigation and subsurface drainage, ADAPT (Agricultural Drainage And Pesticide Transport), was tested with field data collected under various water table management practices near Ames, IA. Atrazine and alachlor concentrations at various soil depths for water table depths of 30, 60, and 90 cm were simulated using ADAPT model for corn growing seasons of 1989 through 1991. Daily pesticide concentrations in groundwater predicted by the model were compared with available observed data for the same site. Predicted values of atrazine and alachlor concentrations in groundwater decreased when shallow water table depths were maintained in the lysimeters. Similar trends were noticed with the observed data. Reasonable agreement was obtained between the observed and predicted values of atrazine and alachlor for 1989 to 1991. However, in few cases, results showed a wide variation between observed and predicted values. Because no observed data was available for pesticide concentrations in the unsaturated zone, predicted results could not be compared. Based on our investigation, it appears that ADAPT may be used for predicting subsurface water quality under water table management practices; however, further validation is necessary with more field observed data from similar studies before wider application of this model is made.

ROLE OF SOIL AND GRASS STRIPS IN REDUCING NITRATE-N POLLUTION IN SUBSURFACE DRAINED FARMLANDS: LYSIMETER RESULTS

A two-year study was carried out to investigate the role of soil and grass strips, coupled with water table management, in reducing nitrate-N residues from agricultural drainage waters. Twelve lysimeters, 1 m long and 450 mm diameter, were packed with a sandy soil and subjected to two water table management practices: free drainage and controlled drainage. Each treatment had either grass (sod) cover or bare soil in triplicate. Nitrate-N contaminated water was applied at the top to each lysimeter and samples of drain effluent were collected at the bottom. Significant reductions (1% level) in nitrate-N concentrations were found in all treatments. However, the controlled drainage treatment was found to be more effective for reducing nitrate levels than the free drainage treatment.In the second year, the cumulative volume of applied water and drain outflow was used to perform a mass balance and estimate the nitrate residues in drainage waters after treatment. The total amount of nitrate applied to each column, 13 g, was reduced to one-third in the controlled drainage lysimeters, and to one-half in the free drainage lysimeters. The controlled drainage lysimeters covered with grass were found to be the most effective for reducing nitrate residues. The results of this study reinforce the contention that grass filter strips can reduce nitrate-N pollution of drainage water from agricultural land.

GROUNDWATER RESIDUES OF ATRAZINE AND ALACHLOR UNDER WATER-TABLE MANAGEMENT PRACTICES

This study was conducted to investigate the effects of various water-table management (WTM) practices on the concentrations of two surface-applied herbicides, atrazine and alachlor, in a shallow groundwater system. Groundwater samples were collected by installing piezometers and suction tubes at Iowa State University’s research centers near Ames and Ankeny during three corn-growing seasons, 1989-1991. At the Ames site, experiments were conducted by maintaining constant water-table depths (WTD) of 0.3, 0.6, and 0.9 m in nine field-type lysimeters, and groundwater samples were collected from various depths during the corn-growing seasons. At the Ankeny site, a dualpipe subirrigation system was installed on a 0.85 ha field, and variable water-table depths were maintained. Analysis of water samples collected in 1989, 1990, and 1991 clearly indicates that atrazine and alachlor concentrations in groundwater could be substantially reduced by maintaining shallow WTD during the growing season. It was also observed that atrazine concentrations were higher than those of alachlor. Alachlor was not detected in many samples; however, atrazine was detected in all samples, with high concentrations at the Ames site at the 0.9 m WTD, and at the Ankeny site at deeper WTD. Pesticide concentrations in groundwater decreased with soil depth and time. Results of this study suggest a positive influence of WTM practices in reducing pesticide concentrations in groundwater.

LINKFLOW, A Water Flow Computer Model for Water Table Management: Part I. Model Development

A computer simulation model, LINKFLOW, was developed to calculate the movement of water during various water table management practices, namely subsurface drainage, controlled drainage, and subirrigation. The model can simulate water movement through a heterogeneous and anisotropic saturated soil and includes an unsaturated flow component with a zone of water extraction by plant roots. The computer program links a newly developed one-dimensional unsaturated water flow model to an existing but modified three-dimensional saturated water flow model, MODFLOW. The water movement is simulated for a region of the field, and results obtained define water conditions in the root zone for a wide range of soil, topography, drain location, and weather conditions. LINKFLOW is unique among soil water flow models because of the following features: 1) it can simulate soil-water conditions beneath a crop on land with varying topography; 2) it can determine 3-D flows from drains in a heterogeneous, anisotropic soil; and 3) it can simulate the effects of different automated control strategies for subirrigation. Results can be presented in tabular format, contour map format, and/or a 3-D surface format to help understanding flow behavior of the system. A subirrigation case simulation is presented to illustrate just one example of the models use in water table management studies. This article focuses on the development of the simulation model.

EVALUATION OF DRAINMOD FOR SOUTHERN ONTARIO CONDITIONS

DRAINMOD, a well-known water table management model, was evaluated with field measurements made in a subsurface-drained corn field in southern Ontario, Canada. Four test plots were monitored from July to October 1991 and from May to September 1992 for midspan water table levels and drain outflows under two water table management practices, i.e. subsurface drainage and subirrigation in 1991 with two replicates each and subsurface drainage and controlled drainage in 1992, also with two replicates each, under conventional (fall mouldboard plough) tillage treatment.The average absolute deviations between the average measured midspan water table depths and the predicted values ranged from 24 to 100 mm for conventional drainage, and 82 to 353 mm for controlled drainage/subirrigation. The corresponding standard errors ranged from 32 to 118 mm for conventionally drained and 98 to 435 mm for controlled drained/subirrigated plots. The average absolute deviation between the measured and predicted drain outflows and the corresponding standard errors ranged from 0.28 to 0.36 mm/d and 0.76 to 0.90 mm/d, respectively, for the conventionally drained plots.The above values for the statistical parameters are comparable to the values obtained elsewhere in similar studies. From the two years of evaluations, therefore, it appears that DRAINMOD holds a lot of promise for designing and/or evaluating water table management systems in southern Ontario. However, the model should be evaluated at other sites in southern Ontario before any concrete conclusions are drawn.

Simulating Corn Yields for Two Iowa Soils

Corn yields in Iowa often could be improved with better water table management practices, but many soils in this region do not have adequate information about their yield potential. This study was conducted to evaluate the applicability of DRAINMOD in simulating crop yields for artificially drained soils of central and northeastern Iowa. Ten years of field data on crop yields from two drainage experimental sites in Iowa were used to compare relative crop yields with yields predicted by DRAINMOD. Data on saturated hydraulic conductivity, soil-moisture tensions, soil infiltration, and other physical properties were collected either at the experimental sites or in the laboratory on disturbed soil samples. Data on upward flux and infiltration constants for the Green and Ampt equation were calculated by using the infiltration data and soil-moisture retention characteristics of the surface layer. Relative crop yields predicted by DRAINMOD were reasonably close to the observed relative yields for both Iowa sites. Standard error of the estimates of relative yields was 17.41% and the average deviation was 12.99%. The coefficient of determination, r2, between the predicted and measured yields was 0.54. Overall performance of the model suggests that DRAINMOD can be used successfully for predicting yields for different locations if data on site characteristics, soil-water properties, and plant growth functions are available.

Effect of Water-table Management Practices on the Transport of Nitrate-N to Shallow Groundwater

Field experiments were conducted for three years (1989-91) at the research farms of Iowa State University near Ames and Ankeny to evaluate water-table management (WTM) effects on groundwater quality. Water-table depths of 0.3, 0.6, and 0.9 m were maintained in field lysimeters at the Ames site, and variable water-table depths were maintained in a subirrigation field at the Ankeny site. Water samples were collected from various soil depths to analyze NO3-N concentrations in groundwater. Concentration of NO3-N in groundwater changed with WTM practices. The lowest NO3-N concentrations were observed under the shallow water-table depths. NO3-N concentrations in groundwater generally decreased with increased depths and time during the growing season under all WTM practices. Crop yields were higher under water-table depths of 0.6 to 0.9 m than under other water-table depths, and corn yields decreased under shallow water-table depths of 0.2 to 0.3 m. Results of this study indicate that WTM practices can be used to substantially reduce the concentrations of NO3-N in groundwater. Results also strongly support the need for further research with WTM practices for water quality and crop production.

Energy balance concept in the evaluation of water table management effects on corn growth: Experimental investigation

The effects of water table management practices (WTMP) on corn growth in 1989 and 1990 at two field sites, Ames and Ankeny, Iowa, were evaluated by calculating crop water stress index (CWSI) and monitoring plant physiological parameters during the growing seasons. Experiments were conducted on field lysimeters at the Ames site by maintaining water tables at 0.3‐, 0.6‐, and 0.9‐m depths and in a subirrigation field at the Ankeny site with 0.2‐, 0.3‐, 0.6‐, 0.9‐, and 1.1‐m water table depths, and periodically measuring leaf and air temperature, transpiration rate, stomatal conductance, and photosynthetically active radiation (PAR) using leaf chamber techniques. Net radiation of canopy was estimated using the leaf energy balance equation and leaf chamber measurements and then correlated with PAR. Analysis of data revealed that net radiation, leaf air temperature differential, transpiration rate, stomatal conductance, and CWSI were strongly related to WTMP during vegetative and flowering stages of corn growth. Excess water in the root zone with a water table depth of 0.2 m caused the maximum crop water stress and ceased crop growth. Both water and oxygen could be adequately maintained for favorable crop growth by adopting the best WTMP. Results indicate that plant physiological parameters and CWSI could be used to evaluate the effectiveness of WTMP and develop the best WTMP for corn growth in the humid region.