Subsurface Drainage Research Articles

Temporal Stability of Grassland Soil Moisture Utilising Sentinel-2 Satellites and Sparse Ground-Based Sensor Networks

Soil moisture is important for understanding climate, water resources, water storage, and land use management. This study used Sentinel-2 (S-2) satellite optical data to retrieve surface soil moisture at a 10 m scale on grassland sites with low hydraulic conductivity soil in a climate dominated by heavy rainfall. Soil moisture was estimated after modifying the Optical Trapezoidal Model to account for mixed land cover in such conditions. The method uses data from a short-wave infra-red band, which is sensitive to soil moisture, and four vegetation indices from optical bands, which are sensitive to overlying vegetation. Scatter plots of these data from multiple, infrequent satellite passes are used to define the range of surface moisture conditions. The saturated and dry edges are clearly non-linear, regardless of the choice of vegetation index. Land cover masks are used to generate scatter plots from data only over grassland sites. The Enhanced Vegetation Index demonstrated advantages over other vegetation indices for surface moisture estimation over the entire range of grassland conditions. In poorly drained soils, the time lag between satellite surface moisture retrievals and in situ sensor soil moisture at depth must be part of the validation process. This was achieved by combining an approximate solution to the Richards’ Equation, along with measurements of saturated and residual moisture from soil samples, to optimise the correlations between measurements from satellites and sensors at a 15 cm depth. Time lags of 2–4 days resulted in a reduction of the root mean square errors between volumetric soil moisture predicted from S-2 data and that measured by in situ sensors, from ~0.1 m3/m3 to <0.06 m3/m3. The surface moisture results for two grassland sites were analysed using statistical concepts based upon the temporal stability of soil water content, an ideal framework for the intermittent Sentinel-2 data in conditions of persistent cloud cover. The analysis could discriminate between different natural drainages and surface soil textures in grassland areas and could identify sub-surface artificial drainage channels. The techniques are transferable for land-use and agricultural management in diverse environmental conditions without the need for extensive and expensive in situ sensor networks.

Inundation and nutrient assessment of farmed prairie potholes during a cropping season with high precipitation

AbstractEnclosed topographical depressions that retain water intermittently are abundant across the prairie pothole region of the United States. These depressional wetlands (potholes) are located at local minimum elevations with small contributing micro‐watersheds. These features are often located in areas where the primary land use is row crop agriculture; thus subsurface tile drainage has been implemented to improve crop production and field accessibility. However, even with drainage improvements, farmed potholes still tend to retain water during high precipitation periods. This study monitored 10 farmed potholes in 2018, a year with 32% more precipitation than the 30‐year average. Potholes were inundated between 12% and 81% of the monitored growing season; the highest inundation percentage occurred in a pothole without surface intakes. Nutrient concentrations in 2018 were lower on average than previously reported for the same potholes, possibly due to higher precipitation and less fertilizer applied because most of the potholes were in soybeans rather than corn. Total nitrogen and nitrate‐N median concentrations were 16.71 and 14.82 mg N L−1 lower (p‐value < 0.0001) during the early season (May 15–July 7) than concentrations in 2016–2017. Total phosphorus and dissolved reactive P median concentrations, conversely, were slightly but significantly lower during the late season (July 8–November 1) with 0.15 and 0.13 mg P L−1 difference (p‐value < 0.01), respectively. Observed DRP concentrations increased by 63% during multiday inundation periods. Our monitoring results suggest during seasons of heavy precipitation, farmed potholes might act as hotspots, contributing elevated levels of P to downstream waters.

Effects of Shallow Surface Drainage Ditches With Controlled Subsurface Drainage Management on Crop Yields in North Carolina

Highlights Shallow surface ditches with controlled subsurface drainage (SD) increased corn and soybean yields in eight of nine growing seasons compared to conventional drainage. The SD system increased corn yields on average by 0.4 Mg/ha, or 4% (0.7 Mg/ha, or 6.6%, excluding 2016). The SD system increased soybean yields on average by 0.5 Mg/ha, or 14.3%. Abstract. Agricultural drainage in the coastal areas of North Carolina (NC) is commonly achieved through large trapezoidal-shaped ditches. The coastal region of NC has limited topographic relief (slopes < 1%) with poorly drained soils that can cause substantial issues with surface water ponding during high-intensity or long-duration precipitation events without some form of surface drainage. Installation of large free flowing surface ditches (FD) with field crowning improves the drainage intensity but can create negative consequences such as over drainage and side slope scouring within the ditch. Large open ditches remove tillable land from production and serve as a primary transport pathway for pollutants. An alternative drainage design (SD) has been implemented that decreases the size of the surface ditches, limiting their drainage effect to only surface water and potentially improving equipment trafficability. The smaller ditches, installed with precision grade equipment, are placed on a grade sufficient to direct surface flow while keeping soil movement to a minimum. Lateral subsurface drainage tiles are installed to provide subsurface drainage and are connected to a main tile line operated with an outlet control structure for controlled drainage (CD). This study evaluates the crop yield and water table effects of the SD system compared to FD over nine crop seasons from 2014-2022. The SD treatment increased yield in eight of the nine crop seasons overall, four of five corn (Zea mays L.) crops, and all four soybean (Glycine max L.) crops. Overall, SD increased corn yields by 0.4 Mg/ha or 4% (0.7 Mg/ha or 6.6% with the exclusion of 2016) and soybean yields by 0.5 Mg/ha (14.3%). The effects of SD on crop yield and water table show that the system can be utilized to improve crop health and provide better management of cropland for producers. Keywords: Corn Yield, Drainage Water Management, Soybean Yield, Surface Drainage, Water Table.

Flow Rate and Volume Estimates from Variable Frequency Drive Operated Drainage Sump Pumps

Highlights This article provides an overview of operations and benefits of using a variable frequency drive to operate agricultural subsurface drainage system sump pumps. A methodology is proposed to monitor flow rates leaving agricultural subsurface drainage pump stations via a MATLAB algorithm. The results of this research were mixed because the algorithm estimates did not always match with the corresponding flowmeter measurements. Abstract. Subsurface drainage plays a crucial role in excess water removal through perforated pipes buried in the soil. The Red River Valley of eastern North Dakota and west central Minnesota often requires pumped drainage outlets due to its flat topography, with many modern systems incorporating variable frequency drives (VFD) for improved efficiency. VFDs adjust pump speeds to match drainage needs, but this dynamic operation complicates accurate flow rate estimation for edge-of-field monitoring. This project aimed to devise an automated method for calculating flow rate estimates from VFD pumping systems involving tank geometry, operational water levels, and pump duty cycling. Linear regressions with calibration data from a transit-time ultrasonic flowmeter produced mixed outcomes. Some linear regressions revealed errors in calculated versus measured flow rate of =14%, while other regressions showed errors nearing 40%. To address this, future efforts should explore methods incorporating the pump’s electrical characteristics. This approach would provide a more accurate representation of the unstable and intricate pumping operations during transient conditions. Keywords: Edge-of-field monitoring, Flow rate, Pump, Red River Basin, Subsurface drainage, Variable frequency drive

Predicted Contribution of Snowmelt to Subsurface Drainage Discharge in Two Subsurface-Drained Fields in Southern Quebec and Ontario

Highlights RZ-SHAW model delivered a satisfactory simulation for winter subsurface drainage discharge. Snowmelt dominated the drainage discharge during the winter and spring snowmelt seasons in southern Quebec. Snowmelt contributed to 29% and 18% of winter and annual drainage discharge, respectively, in southern Ontario. Abstract. Late winter/early spring has been recognized as a critical period for subsurface drainage discharge and associated nutrient losses due to snowmelt and rainfall in croplands under cold, humid climates in North America and Europe. Although the detachment and transport processes of soil particles under snowmelt and rainfall are known to be different, studies quantifying the contribution of snowmelt to winter drainage discharge are limited. This study aims to investigate the contribution of snowmelt to subsurface drainage discharge at two winterized experimental sites in southern Quebec and Ontario, Canada, using observed data and the Root Zone Water Quality Model-Simultaneous Heat and Water model (RZ-SHAW model). The RZ-SHAW model was calibrated and validated against the measured snow depth and year-round subsurface drainage discharge data from 2021 to 2023 at St. Emmanuel, Quebec, and from 2000 to 2003 at Harrow, Ontario. RZ-SHAW demonstrated satisfactory Nash-Sutcliffe model efficiency values (NSE = 0.50) for simulating snow depth, soil temperature, and winter subsurface drainage discharge. The calibrated RZ-SHAW model was used to simulate the contribution of snowmelt to subsurface drainage for the two sites from 1990 to 2022. The snowmelt was predicted to contribute 55% and 44% of the winter and annual subsurface drainage discharge for the cropland in Southern Quebec. In contrast, for the southern Ontario site, the contribution of snowmelt to winter and annual subsurface drainage discharge was 29% and 18%, respectively. Considering that snowmelt in Southern Quebec contributed a significant fraction of winter and annual subsurface drainage discharge, more attention should be devoted to adapting and developing new winter management for nutrient loss in future research in the region. Keywords: Cold region, Cropland drainage, Drainage partition, RZ-SHAW, RZWQM2, Snowmelt, Soil freeze and thaw, Winter subsurface drainage.

The Effect of Drainage and Subirrigation From a Small Drainage Water Recycling Reservoir on Corn and Soybean Yields in Eastern North Carolina

Highlights The Drainage Water Recycling (DWR) reservoir stored enough water to meet irrigation demand in three of four growing seasons. Subirrigation raised the groundwater table by an average of 15 cm. On average, DWR increased corn and soybean yields by 0.52 Mg ha-1 (8%) and 0.45 Mg ha-1 (17%), respectively. Subirrigation from the small size DWR reservoir did not protect corn from extended dry conditions during the growing season. Nutrients recycled back to the field via supplemental irrigation were not large enough to reduce fertilizer application rate. Abstract. Drainage water recycling (DWR) has been proposed as a source of supplemental irrigation to increase crop production resilience to extended and more frequent dry periods during the crop growing season; however, the system’s potential benefits have not been adequately quantified. The main objective of this study was to assess the performance of a DWR system for providing water for supplemental irrigation to corn and soybean at a research site in eastern North Carolina and quantify corn and soybean yield responses during 4 growing seasons (2018-2021) with varying weather conditions. Two treatments were implemented at the study site: DWR and the control (CT) treatment. The CT treatment was a 11.23 ha non-irrigated field that was primarily drained by a surface drainage system. The DWR treatment (11.48 ha) had a subsurface drainage system that provided drainage during the wet periods and subirrigation during the dry periods of the growing season. A small size reservoir (5,458 m3) was used to collect surface runoff and subsurface drainage and subirrigate the DWR treatment. Results showed that the DWR reservoir stored enough water to meet irrigation requirements in 3 of the four growing seasons and provided 5 to 73 mm of irrigation to the DWR treatment. Subirrigation raised the groundwater table by an average of 15 cm, which helped increase the upward movement of soil water to the root zone and meet crop evapotranspiration demand. DWR increased corn yields by 0.13 and 0.91 Mg ha-1 (1% and 79%) and soybean yields by 0.31 and 0.59 Mg ha-1 (9% and 30%). Subirrigation, which is generally less efficient than overhead irrigation methods, did not optimize the use of the limited water stored in the small reservoir and could not provide enough protection to corn against prolonged dry conditions in the 2019 growing season. The amount of nutrients recycled back to the field through subirrigation was not large enough to help reduce fertilizer application rate. Overall, the results demonstrated that DWR is a promising practice for increasing the resilience of crop production in the southeastern U.S. to the uncertainty in precipitation, which is expected to intensify by climate change. Monitoring the performance of DWR for longer periods with varying factors of weather, soil, and system design and management would help guide the design and management of the system to optimize the performance and minimize the implementation cost. Keywords: Drainage water management, Drainage water reuse, Irrigation reservoir, On-farm water storage, Subsurface drainage, Supplemental irrigation.

Impact of Controlled Drainage on Crop Yield Including Within-Field Variability

Highlights A 10-m grid system was developed for spatial and temporal analysis of crop yield impacts of controlled drainage. Yields were analyzed by annual wetness classification, soil drainage class, and elevation within the field. Overall, controlled drainage significantly increased corn yield by an average of 2.3%, but not soybean yield. The grid-based analysis with a linear mixed model identified characteristics influencing CD yield effect. Abstract. Controlled drainage is the practice of using a water control structure to raise the outlet in agricultural fields during periods when drainage is unnecessary, with the primary purpose of reducing nitrate loss. The use of this practice may increase crop yields compared to free drainage because controlled drainage can capture water from precipitation as soil water and store it for crop use later in the growing season. However, results from published studies of controlled drainage have shown mixed impacts on crop yields, and the effects of field characteristics and annual weather variation on these impacts are not well understood. To analyze crop yield impacts, two controlled and two free draining plots in eastern Indiana were compared. A grid system consisting of 10 by 10 meter cells was created to obtain a balanced data set and used to analyze crop yield by year, annual wetness classification, soil drainage class, and elevation. Controlled drainage significantly increased the corn yield in six out of nine years, and the nine-year corn yield average increased by 2.3%. Soybean yield was significantly higher under controlled drainage in three out of four years, but there was no significant difference in the four-year soybean average. Years were further classified as wet, normal, or dry based on growing season precipitation, and results indicated controlled drainage had the greatest significant impact on corn yield in the dry years. Analyzing yield by soil drainage class determined that yield had the greatest response to controlled drainage on the very poorly drained soils. Controlled drainage had a significant yield benefit in corn during dry years in areas in which the elevation is more than 30 cm above the surface elevation at the outlet, and did not lead to significant differences in normal or wet years at any elevation. The grid-based analysis with a linear mixed model accounting for autocorrelation was useful for understanding within-field variability of yield response. Keywords: Controlled drainage, Crop yield, Drainage water management, Soil drainage class, Subsurface drainage.

Assessment of the Potential Impacts of Climate Change on the Hydrology and Canola Yield Using the DRAINMOD Model

HighlightsTotal precipitation and average temperature are projected to increase in the Interlake region of Manitoba.DRAINMOD model results suggest that controlled drainage (CD) would significantly decrease subsurface drainage.Due to dry stress, canola yield is projected to decrease under free drainage (FD) and controlled drainage (CD).Simulation results suggest that capturing, storing, and reusing drainage water could be an adaptive and mitigative strategy for climate change impacts.Abstract.Climate change is a major concern for agricultural production regions like the Canadian Prairies. Therefore, understanding the hydrologic and crop yield response to climate change is important to developing adaptative and mitigative strategies. Downscaled climate model projections from two GCMs for historical (1981-2010), midcentury (2041-2070), and late-century (2071–2100) periods under three representative concentration pathways (RCP2.6, RCP4.5, and RCP 8.5) were used as climate inputs to drive a calibrated and validated DRAINMOD model under two water management scenarios: free drainage (FD) and controlled drainage (CD). Field data, including water table depth, was collected for two canola growing seasons at the PESAI (Prairies East Sustainable Agriculture Initiative) research site in Arborg, Manitoba, Canada. The model was calibrated and validated using the 2019 and 2020 water table depth. The projected changes in the climatic variables showed a slight increase in the mean annual precipitation and the mean temperature across the seasons. DRAINMOD simulation results suggest that CD would significantly decrease subsurface drainage, while water loss through evapotranspiration (ET) and surface runoff are projected to increase considerably under CD and FD. Furthermore, results showed that the relative canola yield would decrease under FD and CD. Stressor analysis showed that canola yield reduction was driven by dry stress due to the projected temperature rise, which outweighs the slight increase in precipitation. Simulation results suggest that the capture, storage, and reuse of drainage water could be an adaptive and mitigative strategy to address the predicted impacts. Keywords: Canola yield, Climate change, DRAINMOD model, Subsurface drainage.

Effects of Drainage System Design on Nutrient Leaching and Crop Yield

Highlights Tested drainage system designs had no clear effect on the total amount of drainage discharge. Tested drainage system designs had a clear effect on nutrient loads in drainage discharge. Corrugated plastic pipe drainage systems had higher N loads and lower P loads than tile drainage systems. Corrugated plastic pipe drainage systems gave higher yields than tile drainage systems and can be a profitable on-farm investment. Abstract. A clear strategy for adapting agricultural drainage to future climate change is important for environmental and economic reasons. In a study aimed at developing recommendations for the subsurface drainage design in clay soils, we evaluated the impact of replacing an old drainage system (1920) with new systems (2018) on nutrient leaching and crop yield. Our field experiment included 12 individually drained plots divided into four treatments: (A) old system with clay tiles at 10 m spacing, without an envelope; (B) new system with plastic pipes at 10 m spacing, gravel envelope; (C) new system with plastic pipes at 5 m spacing, gravel envelope; and (D) new system with plastic pipes at 10 m spacing, gravel envelope and lime incorporated in trench backfill. We conducted flow measurement and flow-proportional, logger-controlled water sampling of the drainage discharge from each plot at a measuring station. Preliminary results (first two years) show a clear effect of the new drainage systems on phosphorus and nitrogen loads in drainage discharge. The lowest total load of phosphorus and highest total load of nitrogen in all treatments were observed in treatment D (with 10 m drain spacing and lime incorporated in trench backfill). The highest total phosphorus load and lowest total nitrogen load in all treatments were observed for the old tile drainage system with 10 m drain spacing (treatment A). The environmental impact of new drainage systems on clay soils may thus be a trade-off between decreased phosphorus loads and increased nitrogen loads with more intensive drainage. Crop data from two experimental years indicated that investing in new drainage systems can be profitable for farmers, as crop yield was 3%-20% higher with new drainage systems compared with old tile drainage. More experimental years are needed to determine the long-term effects of the different drainage system designs. Keywords: Drain envelope, Drain spacing, Nitrogen load, Phosphorus load, Subsurface drainage.

Modeling the Potential Influence of Subsurface Tile Drainage Systems on Downstream Flooding in a Midwestern Agricultural Watershed

Highlights Tile flow was simulated to study the impacts of tile drainage on watershed hydrology and downstream flood days. Three tile drainage scenarios with varied extents of drained land were compared with a baseline scenario. The depth of tile flow contributing to streamflow was found to increase as the area of drained land increased. Results suggest that drainage systems decrease flood days when compared to the baseline scenario. Abstract. Subsurface tile drainage systems are common in agricultural regions of the Midwestern United States. Drainage systems remove excess water from the surface and soil profile of agricultural fields, allowing crop production in previously unsuitable locations. However, these systems impact watershed hydrology and could influence flooding events. Therefore, this study aimed to determine whether tile drainage systems influence downstream flood days in a Midwestern agricultural watershed, specifically the Skunk Creek watershed. The Soil and Water Assessment Tool (SWAT) model was used to simulate the hydrologic processes of the Skunk Creek Watershed for an 18-year period (2004–2021). The model was calibrated and validated using observed daily streamflow data with the SWAT Calibration and Uncertainty Program (SWAT-CUP) software and through the manual modification of missed precipitation data. Three tile drainage scenarios—ranging from 15% to 75% tile-drained agricultural land—were individually incorporated into the model. Results indicated that with increased tile drainage, surface runoff, groundwater flow, deep aquifer recharge, and percolation decreased, whereas lateral soil flow, tile flow, evapotranspiration, and water yield increased. A comparison of tile drainage scenarios suggests that increasing the area of tile-drained agricultural land decreases total flood days. However, the impact of tile drainage systems on downstream peak flood flows varied by event, with large precipitation events initiating flood days across all scenarios. While tile flow decreased flood days on a daily time step, flash floods might have occurred on a sub-daily time step but were not captured in this study. Future studies can replicate the approach with a sub-daily time step for simulating hourly flood events with various tile drainage scenarios. Keywords: Midwestern United States, Streamflow, SWAT, Tile drainage, Watershed hydrology.

Water Quality Sampling Provides Insight into Nutrient Sources and Pathways in an Agricultural Watershed in the Midwestern USA

HighlightsHysteresis and flushing indices were calculated for 23 storm events.Wetter conditions led to a dilution effect for nitrate during storm events.Travel times were faster for all nutrients during the winter, likely due to lack of vegetative cover.Results can be used to choose practices that effectively target specific nutrient sources and pathways.Abstract. Understanding where agricultural nutrients originate in the landscape can help mitigate downstream transport by selecting and installing best management practices that target nutrient sources. We collected flow and water quality data from 2017–2021 at two similar HUC-12 watersheds in northeastern Indiana, which provided an opportunity to link nutrient sources with transport processes in intensively managed agricultural watersheds. We calculated metrics to represent changes in nutrients during a storm event, including hysteresis (the change in concentration on the rising limb of the hydrograph compared to the recession limb) and the flushing index (the difference between concentrations at peak discharge and baseflow). We compared storm-based and annualized concentration-discharge (C-Q) relationships for NO3-N, soluble reactive phosphorus (SRP), total P (TP), and dissolved organic carbon (DOC) to land use and climate variables. Together, these provide insight into nutrient storage zones and transport pathways at the small watershed scale. Our results suggest these landscapes have plentiful and widely distributed sources of nitrogen (N) that are activated in the spring, which we observed as chemostatic behavior (i.e., concentration remained relatively constant during different flows). While this has been shown at larger scales in agricultural watersheds, these patterns are challenging to parse at the small watershed scale. We saw concentrating effects (i.e., increased concentrations as flow increased) for DOC, TP, and SRP during storms, suggesting activation of flow-paths connecting land-based sources to receiving streams. We also noted faster travel times in the winter for all four constituents when subsurface tile drains are most active and plant uptake is negligible. Our results differentiate nutrient delivery mechanisms and can aid management decisions by identifying environmental factors that most influence transport and selecting conservation practices that target these nutrient pathways. Keywords: Agriculture, Carbon, Concentration-discharge, Hysteresis, Nitrogen, Phosphorus, Watershed management.

Feasibility of Predicting Subsurface Drainage Discharge With DRAINMOD Parameterized by Uncalibrated SURRGO Soil Properties and ROSETTA3

Feasibility of Predicting Subsurface Drainage Discharge With DRAINMOD Parameterized by Uncalibrated SURRGO Soil Properties and ROSETTA3

Development of Drainage Tools for Facilitating the Creation of Topologically-Sound, Unidirectional Flow Tile Networks

HighlightsNew publicly accessible drainage design QGIS plugins were developed.These tools were successfully used to create topologically-sound subsurface drainage layout networks.The tools are easy to use and reduce the level of expertise required to prepare drainage networks that can be successfully sized and buried.Abstract. An important step in designing a drainage system is laying out the network. Successful installation and sizing of the system require that the network be topologically sound and unidirectional. Online digitization of drainage systems does not always result in networks that meet these criteria. Tile lines may not be consistently digitized from upstream to downstream, and there may be disconnected segments, dangles, and overshoots. We have developed a set of open-source tools (plugins) in QGIS that convert a series of laterals and mains digitized on a map into a topologically-sound drainage network to facilitate both burying and sizing the drainage lines. Steps include reversing node numbering, if necessary, to ensure that tile nodes are numbered from upstream to downstream, connecting the ends of tile lines that are within a certain tolerance of each other, correcting overshoots, and setting an order for burying or calculating cumulative flow in line segments. An application example is presented using a proposed tile network layout at the university farm to demonstrate the capacity of these new tools to fix topologically disconnected tile lines and generate sound tile networks that can be successfully buried and sized. These easy-to-use tools are compatible with all versions of QGIS3 and may be freely downloaded or installed from the official QGIS Plugin Repository. Keywords: Line Geometry, Plugins, QGIS Software, Tile Layout Routines, Tile Nodes and Lines.

Effectiveness Overview of Agricultural Conservation Practices for Water Quality Improvement Part II

Highlights This article summarizes ten agricultural conservation practices reviewed in both editions of the collection. Mean sediment load was reduced 73%-80% by residue and tillage management, filter strips, and cover crops. Mean nitrate-N load reduction ranged from 34%-46% for filter strips and water management practices. Phosphorus loads and concentrations were reduced by most practices, but dissolved P increased with two practices. Cost effectiveness varied widely, and these results may help in efforts to prioritize conservation implementation. Abstract. Although significant governmental investment has been provided to implement agricultural conservation practices (ACPs) for water quality improvement, eutrophication and hypoxia persist in coastal and fresh waters. A better understanding of the comparative effectiveness of ACPs is needed to improve environmental outcomes with the funding available. The objectives of this overview article are to (1) compare the performance and cost effectiveness among all the ACPs reviewed in both the first and second editions of the Special Collection and (2) present critical perspectives for researchers, policymakers, and funding entities seeking to improve water quality. The ten ACPs reviewed encompassed a range of goals, strategies, and landscape placement and varied widely in performance for their reduction of sediment, nitrogen (N), and phosphorus (P) and their cost-effectiveness. Three ACPs included performance measures for all three constituents: sediment, N, and P, whereas others focused only on N (nine ACPs) and/or P (six ACPs). The four ACPs that are considered “water management” practices: drainage water management, denitrifying bioreactor, saturated buffer, and constructed wetland were all effective in mitigating the effects of nutrients in subsurface drainage water and showed average nitrate-N load reductions of 40%-46%. In contrast, few practices were found effective in reducing dissolved P (DP) loss from agricultural fields. Four ACPs (residue and tillage management, conservation crop rotation, drainage water management, and nutrient management) demonstrated possible net economic benefits, while perspectives were provided for prioritizing financial assistance for other ACPs. Monitoring recommendations developed during the literature reviews highlighted the need for more long-term field-scale monitoring to better reflect multi-year climatic variability. Keywords: Constructed wetland, Cost effectiveness, Cover crop, Crop rotation, Denitrifying bioreactor, Drainage water management, Filter strip, Monitoring, Nitrogen, Nutrient management, Performance effectiveness, Phosphorus, Residue and tillage management, Saturat

Reduction of Nitrate Leaching and Threats to Surface Water Under Conservation Tillage

Highlights Conservation agriculture practice (NT) improved soil organic matter, a principal indicator of soil health, soil health score (SHS) and CO2 respiration, and other soil physical and chemical properties vs. conventional till (CT) practice. Conservation agriculture practice (NT) promoted soil health functions under sufficient precipitation distribution and ample temperature conditions and aided the soil's retention ability to resist nitrate leaching and loads in subsurface drainage discharge systems. Uneven weather conditions, drought, and other variable agronomic practices rendered soil conditions unfavorable to retain nitrate and induced adverse effects by increasing the nitrate leaching and loads in NT vs. CT. The limited experiment period presented significant challenges for the evaluation and synthesizing of soil health motivations and barriers in the NT vs. CT. Abstract. An edge-of-field subsurface drainage discharge system removes excess subsurface water from agricultural fields to improve the conditions of the soil system making them favorable for plant growth. Conversely, edge-of-fields can increase the nitrate (NO3 -) offsite movement to surface water bodies, which ultimately impacts water quality. In St. Johns, MI. Two on-farm large areas were initiated in 2013 for conservation (NT) and conventional till (CT) practices, of which two microscale fields, an area of 4 acres for each, were delineated in 2019 for NT and CT practices under a corn/soybean crop rotation. NT and CT fields were monitored and evaluated through full water years (WYs) 2019-2022. The objective was to use an innovative approach in coupling edge-of-field with soil health assessments to learn how improved soil health functions are influencing nitrate leaching and loads. NT practice enhanced SOM, other physical properties, and soil health parameters, promoting soil health functions compared to CT practice under conditions of adequate precipitation and favorable temperatures. Additionally, it improved the soil's ability to retain and resist nitrate loads in the 2020 water year, with reductions of 9.6 and 18.3 kg/ha, respectively. In 2021, WY nitrate loads reported nearly an equal value in NT vs. CT (4.8 and 4.4 kg/ha, respectively). Factors of uneven weather conditions and drought, variable agronomic practices, and residual nitrogen after corn, rendered soil conditions unfavorable to retain nitrate and induced adverse effects by increasing the nitrate leaching and loads in NT vs CT in 2022 WY (8.1 and 5.8 kg/h, respectively). Therefore, the limited evaluation period (2019-2022 WYs) presented significant challenges and revealed no affirmative evidence that the improved soil health functions under NT reduced the nitrate leaching loads in all WYs of this research. Further research is needed to prove the impact of NT on improving soil health functions to sustainably reduce nitrate leaching and loads in edge-of-fields. Keywords: Conservation no-till (NT), Conventional till (CT), Nitrate load, Soil health functions, Subsurface drainage discharge, Water quality.

Calibration of V-Notch and Compound Weirs for Subsurface Drainage Water Level Control Structures

Calibration of V-Notch and Compound Weirs for Subsurface Drainage Water Level Control Structures

Remote Sensing Contribution to the Detection of Karst Features and their structural Environment in the Area of the Bekaa Valley in Central-Lebanon

More than two-thirds of the area of Lebanon is covered by lime-and dolostones prone to karst processes, and, thus, developed surface karst features, such as poljes, dolines, uvalas, caves, and blind valleys. This study aims to map the surface karst features, especially sinkholes, and to identify their orientation and dimensions, as well as the tectonic pattern influencing their development based on remote sensing data and references. As karst affected areas are at a higher risk of environmental pollution of the aquifers in the densely populated area due to the karst specific surface and subsurface drainage conditions, the knowledge of the structural pattern and fault systems influencing surface infiltration and groundwater flow is important. This study is focused on the evaluation of optical satellite data (Landsat, Sentinel 2) as well as of radar images (Sentinel 1, ALOS PALSAR) and on Digital Elevation Model (DEM) data (SRTM, ASTER, ALOS PALSAR) and DEM derived morphometric maps aiming to detect traces of karst features, fault zones and their related structures, combined with other geoscientific data of Central-Lebanon. DEM derived maps support the detection of areas with higher surface water input due to their specific local morphometric disposition. The evaluations of the different data sets clearly show that sinkholes and springs in Central-Lebanon are concentrated along a nearly semi-circular belt along western part of the left-lateral Yammouneh shear fault zone. The main factors influencing the occurrence and distribution of surface karst features could be derived by the combined analysis of remote sensing data and reference information.

Evaluation of AnnAGNPS Wetland Nitrogen Removal Component on Farmed Prairie Potholes

Highlights AnnAGNPS offers a wetland module (AgWET) to simulate farmed prairie potholes soluble nitrogen dynamics. Three key parameters of the AgWET nitrogen removal components show high and very high Relative Sensitivity (Sr ). AnnAGNPS tends to underestimate the soluble nitrogen concentration at the beginning of the cropping season. Abstract. Farmed prairie potholes are common in northern Iowa and have been considered an impediment to agricultural development. Potholes have distinctive wetland characteristics where they might contain a high concentration of soluble nitrogen coming from agricultural upland runoff. With sub-surface drainage underneath them, providing short circuit nutrient transport downstream, Iowa poses a significant threat to nitrogen export to the Gulf of Mexico. Watershed models, such as AnnAGNPS, developed a wetland module allowing users to find the possible BMPs to accomplish nutrient reduction targets. Previous research indicates that AnnAGNPS may be used to mimic inundation depth fluctuations in potholes with moderate success. However, there has been little research on the wetland nitrogen removal components of the model. This study aims to evaluate the AnnAGNPS wetland module's performance in simulating the soluble nitrogen concentration in three farmed prairie potholes by comparing the simulation output with the observed data. The sensitivity analysis of the three key parameters of the model shows high and very high levels of sensitivity, with the temperature coefficient's relative sensitivity ranging from -6.7 to 8.6. Attempts in parameterization on the three targeted parameters indicated that the model poorly simulated the soluble nitrogen concentration. The comparison between observed and simulated data shows that the model fails to predict the high concentration of soluble nitrogen in the early cropping season. This conclusion is consistent with earlier research indicating that AnnAGNPS tends to underestimate the nitrogen concentration during the cropping season. Keywords: AnnAGNPS wetland module, Farmed prairie pothole, Soluble nitrogen concentration.

Assessing the Performance of Wasim and Drainmod Models for Subsurface Drainage Design and Analysis in a Data-Scarce Environment

Assessing the Performance of Wasim and Drainmod Models for Subsurface Drainage Design and Analysis in a Data-Scarce Environment

Subsurface drainage and nitrogen management affects corn and soybean yield in claypan soils in upstate Missouri

AbstractNitrogen (N) and subsurface drainage water management are crucial and challenging components of sustainable crop production on poorly drained claypan soils. During extreme precipitation events, N fertilizer management is difficult in a corn (Zea mays L.)–soybean (Glycine max L.) rotation that balances productivity and environmental quality. This 4‐year (2018–2021) experiment was conducted on a poorly drained soil to examine the interactive effects of drainage (subsurface tile drainage [SD] and no drainage [ND]) and corn N fertilizer treatments (non‐treated control [NTC], fall‐applied anhydrous ammonia [AA] at 190 kg N ha−1 with nitrapyrin [fall AA + NI], pre‐plant AA [spring AA] at 190 kg N ha−1, and top‐dressed urea [TD urea] as 42 kg N ha−1 SuperU and 126 kg N ha−1 ESN as a 25:75% granular blend) on yield and nutrient uptake. Corn grain yield was 1.22–1.53 Mg ha−1 greater with fertilizer treatments in SD compared to ND. Drought conditions in 2018 lowered corn grain yield compared to 2020. Average over 2 years, corn yield in SD soils was ranked as spring AA > fall AA + NI > TD urea > NTC. While soybean yield following corn was 13% greater in the NTC compared to TD urea. The SD treatment increased soybean yield by 0.6–2 Mg ha−1 compared to ND. This study results showed that fall AA + NI produced corn yields similar to spring AA in SD and ND soils in temperate humid climatic conditions.