Drainage Control Research Articles

A coupled regional-scale numerical model for hydrological processes and interactions between groundwater and surface water in a controlled drainage district

Controlled drainage (CD) has emerged as an effective strategy to prevent field waterlogging and mitigate drought during crop growth by altering the hydrological process, while few studies have quantified its effect on groundwater-surface water interactions and groundwater recharge at a regional scale. In this study, a new model is developed for the coupled numerical simulation of water flow in ditches, soil, and underground aquifers under CD conditions. The domain is partitioned into horizontal sub-areas and two vertical layers, with ditches discretized into segments based on groundwater flow grids. The Saint-Venant equations, Richards equation, and MODFLOW are applied to describe water movement processes in ditches, soil, and underground aquifers, respectively. The proposed model is calibrated and validated using five years of observations of ditch water levels (DWL) and groundwater levels, demonstrating excellent agreement with observed data. Subsequently, water balance components of the shallow aquifer below 1 m depth (GW), 1 m of root layer soil profile (SW), and ditch water (DW) under seven scenarios with different control schemes during flood and dry seasons are analyzed to quantify variations in hydrological processes caused by CD. The results show that CD significantly impacts water within SW, GW, and DW, soil evaporation, infiltration, and net recharge from GW to SW (GtoS) by altering regional groundwater table depth (GWT) through the exchange between DW and GW (DtoG and GtoD). GWT and DW show moderate correlation with GtoD, while their correlation with DtoG varies significantly under different rainfall conditions. Smaller precipitation results that precipitation and GWT have a higher linear correlation with water balance components during the dry season compared to the flood season. The correlation values (r) between transpiration (T) and GWT range from −0.99 to 0.96 and −1 to −0.85 during the flood and dry seasons, respectively, indicating a pronounced influence of CD on crop growth. On average, a 1 m increase in DWL control scheme leads to a 0.51 m increase in DWL, and regional GWT decreases by 0.35 m and 0.24 m during flood and dry seasons, respectively. Furthermore, for every 1 m decrease in GWT, net GtoS increases by 36.1 mm and 28.1 mm, respectively, resulting in an increase in SW by 13.9 mm and 11.8 mm, respectively. Considering the varying main crop water stress and the impact of CD under different rainfall conditions, an appropriate CD scheme needs to be adjusted accordingly. These findings provide a quantitative reference for the effect of CD on regional hydrological process and serve as a typical case for similar areas aiming to implement CD strategies for waterlogging and drought control.

A New Concept of Flashboard Risers in Controlled Drainage Structures

Drainage water management (DWM), also known as controlled drainage (CD), is one of the edge-of-field strategies mainly designed to reduce the nitrate load from subsurface drainage systems. By limiting runoff, we also increase local retention, contributing to the sustainable management of water resources. For that purpose, CD involves using different kinds of controlled drainage devices. They are usually based on simple flashboard risers or stoplogs that regulate the drainage intensity by raising and lowering the drainage outlet. The problem with this type of device is the need for manual control, which can cause the CD system to be more demanding in terms of maintenance. A new approach to water management by CD allows the possibility of individual disassembly of each board without necessarily removing all of them. Thanks to the use of sideling runners, the water management process is much quicker. This is especially important when a farmer needs to manage water in a few controlled drainage devices in the field. The different variants of the design are shown here, as well as the way of stop-log assembly and control and the costs of maintaining similar devices. The advantages and disadvantages are described, and the usefulness of the new patented solution is assessed.

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 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.

Evaluating the Effects of Controlled Drainage on Nitrogen Uptake, Utilization, Leaching, and Loss in Farmland Soil

Controlling drainage during the growth stage is one of the means to provide suitable water and fertilizer conditions for crops, alleviate environmental pollution, and increase crop yield. Therefore, in this study, we studied three drainage treatments: free drainage (FD) and growth-stage subsurface controlled drainage (CD) at depths of 40 cm (CWT1) and 70 cm (CWT2). We used the HYDRUS-2D model to simulate the dynamic changes of NO3-N in the 0–100 cm soil layer as well as NO3-N uptake by crops, leaching after irrigation and fertilization, and loss through subsurface pipes in 2020 (model calibration period) and 2021 (model validation period). The degree of agreement between the simulated and measured values was high, indicating a high simulation accuracy. CD increased the soil NO3-N content and crop NO3-N uptake, and decreased NO3-N leaching and loss. We observed significant differences in the soil NO3-N content after irrigation at the budding stage of oilseed sunflower between CD and FD, with the largest difference seen for the 0–40 cm soil layer. CD increased crop yield, and the average oilseed sunflower yield of the CWT1 and CWT2 treatments increased by 4.52% and 3.04% relative to the FD treatment (p < 0.05). CD also enhanced nitrogen use efficiency. In moderately salinized soil, CD at 40 cm (CWT1) reduced the nutrient difference in vertical and horizontal directions while retaining water and fertilizer. CWT1 stabilized the groundwater depth, reduced the hydraulic gradient of groundwater runoff, and decreased the drainage flow rate. The NO3-N leaching and loss dropped, which promoted crop nitrogen uptake and utilization, improved nitrogen use efficiency, reduced nitrogen loss, and had a positive effect on protecting the soil and water environment. The results demonstrate that CD is a suitable drainage method for the experimental area.

Predicting the effect of weir management on the discharge of a controlled drainage system in a changing climate

Subsurface drainage in humid areas prevents field waterlogging but also transports nutrients to freshwater systems. Controlled drainage (CD) reduces drainage discharge and nutrient transport from fields. Some regions are expected to experience increased precipitation in the future, requiring CD to be evaluated under a changing climate. The objective of this study was to compare the performance of CD under two weir managements for a future period (2030–2059) and historical period (1992-2021) in southeast Michigan, USA. Climate projections were obtained for the shared socioeconomic pathway 245 emission scenario. Aggressive management involved maintaining the weir height at 40 cm during the growing season and 15 cm during the non-growing season, with a longer period of managed flow compared to common management, which maintained the weir height at 50 cm during the growing season and 30 cm during the non-growing season. It was predicted that the 30-year average annual precipitation would not change significantly in the future. The 30-year average mean monthly temperature would increase by 3.0°C in the future compared to the historical period. We performed simulations using the calibrated Root Zone Water Quality Model 2 (RZWQM2). The average drainage discharge in the future indicated a 20% increase in the 30-year average drainage discharge for a field with free drainage. The CD with common and aggressive managements reduced drainage discharge by 59% and 67% for the historical period, whereas the performance of CD was even better for the future period (63% and 72%, respectively). The improved future performance of CD can be attributed to a shift in precipitation patterns, with reduced precipitation during the growing season and increased precipitation during the non-growing season. As a result, the more aggressive weir management during this period created additional opportunities for reducing drainage discharge. In conclusion, aggressive management resulted in a slightly better flow-reducing performance than common management while indicating that both methods would effectively reduce drainage discharge in the likely future scenario.

Is Controlled Drainage of Agricultural Land a Common Used Practice?—A Bibliographic Analysis

Controlled drainage (CD) is one of the basic techniques used to manage groundwater levels. Farmers can optimize water levels for crop growth at different stages of the growing season. Proper drainage water management can reduce the risk of soil erosion and surface water pollution. By controlling drainage, sediment and nutrient runoff can be minimized, leading to improved water quality in nearby streams and rivers. A mixed methods approach was used, which was based on the bibliometric analysis and content analysis of 462 articles using the bibliometrix R package and VOSviewer software. The article aimed to analyze the Author Keywords and KeyWords Plus to indicate the resulting clusters of complex interdependence that emerge from the main research areas. Continuous research continues to improve drainage techniques and systems to optimize agricultural water use. The results indicated the importance of researching the feasibility of CD for agriculture. The innovation of this study is that it points out the relevance of taking up the possibility of changing the use of unilateral subsurface drainage systems with another method of controlling drainage outflows as a current global challenge, contributing to filling this gap in the literature.

Controlled Drainage Effectiveness in Reducing Nutrient Outflow in Light of Climate Changes

This modeling study focused on the hydrological and water quality effects of controlled drainage (CD) when operated using a subsurface drainage system in an agricultural field in the Wielkopolska region. The DRAINMOD hydrologic model was well calibrated and validated in an experimental field. This model was used in the performance of CD and free drainage (FD) combinations (108 and 27, respectively) in a near-future climate change scenario. The objective was to understand the potential of CD on the groundwater table (GWT), drainage outflow, surface runoff, and nitrogen and phosphorus reduction under projected climate conditions in Poland during the 21st century with shared socioeconomic pathway SSP370. The results indicated that the earliest start of CD practice is the most effective in increasing GWT. Compared to current climatic conditions, when applying CD on 1 March in the near future, with an initial GWT of 60 and 80 cm b.s.l. in wet years, drainage outflows will increase by 33% and 80% for the GFDL model, by 30% and 40% for the MPI model, and by 17% and 23% for the UKESM model. Comparing the surface runoff values obtained to current climate conditions, the MPI, GFDL, and UKESM models predict a significant increase in surface runoff in the near future, which is due to the predicted increase in precipitation. The annual NO3–N reduction was by 22, 19, and 15 kg per hectare for wet, normal, and dry years, respectively, in the near future. Among the climate scenarios, the UKESM model predicted higher NO3–N and PO4 leaching values compared to the MPI and GFDL models.

Nutrient release in drainage discharge from organic soils under two different agricultural water management systems

AbstractThe release of available nitrogen (N) and phosphorus (P) from agricultural tile drainage contributes to eutrophication in water bodies. To mitigate the harmful impact of nutrient release, drainage water management (DWM) has been proposed as a beneficial management practice that will limit N and P in tile drainage discharge. This study, conducted in the organic soils of the Holland Marsh, Ontario, assessed the nutrient water quality for 2 years (2015–2016) under DWM systems: controlled drainage (CD) comprising a series of stackable gates to manually control the water table level; and pumped drainage (PD) which uses a submersible pump within a collector well that discharges effluent when activated. The latter is the common method of field drainage in the Holland Marsh, however, there is limited comparable research for either DWM system. The data were separated into growing and fallow seasons as well as winter, spring, and summer seasons for trend analysis (winter: October–February; spring: March–May; summer: June–September). The nitrate (NO3‐N) concentrations, under CD, were found to be on average higher during the winter season (7.64 mg L−1) compared to the growing season (3.76 mg L−1). Furthermore, total N concentrations are positively correlated to discharge (R > 0.55). The average total P concentration increased during the summer period following fertilization; however, there was no correlation between P and drainage discharge throughout the duration of the study. The P concentrations depended more on nutrient inputs, rather than the discharge under CD. The log regression statistical relationship showed significant differences in nutrient levels compared to the mean at both sites, however, greater differences were found under CD. Under PD, the NO3‐N concentrations showed significant seasonal trends between the spring and winter (Pr > t: 0.0061) and summer (Pr > t: <0.0001). Overall, both CD and PD can reduce the amount of tile drain discharge, but the concentrations of N and P are not significantly reduced.

Controlled Drainage Mediates Cotton Yield at Reduced Nitrogen Rates by Improving Soil Nitrogen and Water Contents

Controlled drainage (CD) can reduce outflow and improve soil productivity, whereas its impacts on soil nitrogen (N), moisture contents, and cotton (Gossypium hirsutum L.) yield at reduced N rates remain largely unknown. To address the question, a field experiment was conducted to investigate the effects of N fertilizer rates (280, 252, 224, and 196 kg N ha−1, designated N1, N0.9, N0.8, and N0.7, respectively) on soil moisture, nitrate N (NO3−–N), and ammonium N (NH4+–N) contents and yield of cotton under CD and free drainage (FD). Compared to FD, CD increased the soil moisture, NO3−–N, and NH4+–N contents in the 0–40 cm soil depths, leading to greater plant N uptake at each N rate. The decreased total N loss through runoff due to CD accounting for the enhanced soil N contents. Moreover, CD had greater soil NO3−–N content at the reduced N treatments, contributing to the enhanced plant N accumulation, number of bolls, and lint percentage, and thus obtains a relatively high cotton yield. Remarkably, cotton yield reduced significantly with the decrease in N rates under FD, but it was comparable between N1 and N0.9 or N0.8 under CD. These suggested that CD helps to maintain high soil N and moisture contents in the 0–40 cm soil depths at 10–20% reductions in N fertilizer rate and thus without compromising cotton yield. The results also provide scientific basis for drainage water management mediates cotton yield at reduced N fertilizer rates.

Effectiveness of Controlled Tile Drainage in Reducing Outflow and Nitrogen at the Scale of the Drainage System

The impact of controlled drainage (CD) on the groundwater table (GWT), drainage outflow, surface runoff, and nitrogen reduction at the drainage system scale in the Wielkopolska region was analyzed in this study. Based on field research, mainly by monitoring of GWT changes in 2019–2020, the DRAINMOD model was calibrated and validated. Hydrological soil water balance simulations were carried out with 36 and 9 combinations for CD and free drainage (FD), respectively. The modelling period was March-September for 10 different dry, wet, and normal years from the period of 1961 to 2020. The next step was to use the results of drainage outflow modelling and chemical constituent analyses of drainage water samples to determine NO3-N concentrations and calculate NO3-N pollution loads. As a result of the simulations, the importance of the timing of the start of the outflow retention in the adopted model variants was determined, indicating the earliest assumed date of 1 March. The appropriate CD start date as well as the initial GWT has a significant impact on the effectiveness of CD application in reducing the volume of drainage outflow and reducing the amount of NO3-N entering open water with it. The application of CD under the conditions of the analyzed drainage facility makes it possible to retain up to 22 kg of NO3-N per hectare.

Optimizing water-saving irrigation schemes for rice (Oryza sativa L.) using DSSAT-CERES-Rice model

Rice is one of the major crops in China, and enhancing the rice yield and water use efficiency is critical to ensuring food security in China. Determining how to optimize a scientific and efficient irrigation and drainage scheme by combining existing technology is currently a hot topic. Crop growth models can be used to assess actual or proposed water management regimes intended to increase water use efficiency and mitigate water shortages. In this study, a CERES-Rice model was calibrated and validated using a two-year field experiment. Four irrigation and drainage treatments were designed for the experiment: alternate wetting and drying (AWD), controlled drainage (CD), controlled irrigation and drainage for a low water level (CID1), and controlled irrigation and drainage for a high water level (CID2). According to the indicators normalized root mean square error (NRMSE) and index of agreement (d), the calibrated CERES-Rice model accurately predicted grain yield (NRMSE=6.67%, d=0.77), , shoot biomass (NRMSE = 3.37%, d = 0.77), actual evapotranspiration (ETa) (NRMSE = 3.83%, d = 0.74), irrigation volume (NRMSE = 15.56%, d = 0.94), and leaf area index (NRMSE = 9.69%, d = 0.98) over 2 a. The calibrated model was subsequently used to evaluate rice production in response to the four treatments (AWD, CD, CID1, and CID2) under 60 meteorological scenarios which were divided into wet years (22 a), normal years (16 a), and dry years (22 a). Results showed that the yield of AWD was the largest among four treatments in different hydrological years. Relative to that of AWD, the yield of CD, CID1, and CID2 were respectively reduced by 5.7%, 2.6%, 8.7% in wet years, 9.2%, 2.3%, 8.6% in normal years, and 9.2%, 3.8%, 3.9% in dry years. However, rainwater use efficiency and irrigation water use efficiency were the greatest for CID2 in different hydrological years. The entropy-weighting TOPSIS model was used to optimize the four water-saving irrigation schemes in terms of water-saving, labor-saving and high-yield, based on the simulation results of the CERES-Rice model in the past 60 a. These results showed that CID1 and AWD were optimal in the wet years, CID1 and CID2 were optimal in the normal and dry years. These results may provide a strong scientific basis for the optimization of water-saving irrigation technology for rice. Key words: CERES-Rice, controlled irrigation and drainage, water-saving, long-term weather data, water use efficiency DOI: 10.25165/j.ijabe.20231602.7361 Citation: Gao S K, Gu Q Q, Gong X W, Li Y B, Yan S F, Li Y Y. Optimizing water-saving irrigation schemes for rice (Oryza sativa L.) using DSSAT-CERES-Rice model. Int J Agric & Biol Eng, 2023; 16(2): 142-151.

Canola yield and quality under tile drainage in the Canadian Prairies

For areas with seasonally shallow water tables and poorly drained soils, subsurface drainage systems are ideal for removing excess water from the root zone and improving soil workability, trafficability, and timeliness of field operations. With increased interest in tile drainage in southern Manitoba, the objective of this study was to evaluate the impacts of drainage on canola yield and canola oil qualities over three growing seasons (2019-2021) in Winkler, Manitoba. The study was carried out on replicated field plots with three different drainage treatments: controlled drainage (CD), free drainage (FD), and no drainage (ND). Subsurface drain tiles were installed at a depth of 0.9 m. The drains were spaced at 8 m for CD and 15 m for FD. Compared to FD plots (3.02 Mg/ha), the CD plots (3.51 Mg/ha) had significantly higher yields in 2019 with good rainfall. With low rainfall in 2020 and 2021, the impact of drainage, especially CD, diminished, with no significant differences between the treatments. In 2020, the average yields were 3.12, 2.52, and 2.97 Mg/ha for ND, CD, and FD, respectively. Similarly, in 2021, there was no significant difference between CD (1.14 Mg/ha), FD (1.52 Mg/ha), and ND (1.07 Mg/ha). The impact of CD under drought conditions was not significant. This could be related to the narrower drain spacing, which tends to remove water rapidly within the soil profile during short periods of high-intensity rainfall. The canola quality assessments (oil, protein, glucosinolate and fatty acid profile) showed no significant differences between ND, CD, and FD in each of the years. This suggests that environmental variables (mainly temperature and precipitation) may have masked drainage impacts on canola quality.

Impact of controlled drainage on corn yield under varying precipitation patterns: A synthesis of studies across the U.S. Midwest and Southeast

Controlled drainage (CD) is a valuable management practice for reducing drainage volume and nutrient loss, but its impact on corn (Zea mays L.) production is not completely understood. The objectives of this study were to investigate the regional effect of CD on corn grain yield compared to free drainage (FD), investigate the factors influencing corn yield response to CD, provide management recommendations for optimizing corn yield under CD, and identify future research needs for corn production on poorly drained soils with subsurface drainage systems. This synthesis included data collected from 13 field sites where corn was planted under both FD and CD in six U.S. Midwestern states and North Carolina totaling 55 site-years of data from 2006 to 2017. On average, there was no statistically significant difference in corn grain yield between CD (10.62 Mg/ha) and FD (10.53 Mg ha−1). However, 42% of the dataset indicated that CD either increased or decreased corn yield by 4% or more compared to FD. Further analysis was conducted on this subset of data in order to evaluate underlying factors (i.e., weather conditions during the season, soil type, and drainage system design and management) influencing corn yield response to CD. Results of this analysis showed that CD was effective in alleviating plant stress caused by mild to moderate drought conditions and subsequently increased corn grain yield by 4–14% in 12 site-years. In contrast, CD reduced corn grain yield by 4–10% during wet growing seasons (6 site-years). Variability in growing season precipitation has been identified as a key factor influencing corn grain yield under CD, and more active management or CD system automation is recommended. General recommendations are provided for managing manually operated CD systems in the U.S. Midwest to improve growing season water management and corn yield. Additional research to develop technologically advanced water management systems for crop production on poorly drained soils is needed in order to adapt to changing weather patterns.

Simulation and evaluation of soil water and salt transport under controlled subsurface drainage using HYDRUS-2D model

Controlled drainage is an important measure to improve salinized soil in arid and semi-arid areas. However, free drainage during the growth period leads to excessive water loss, and crops lack water in the later growth period, resulting in crop yield reduction. Therefore, in arid and semi-arid areas, soil salts should be leached during the non-growing period, and drainage should be controlled during the growing period to ensure that crops have adequate water absorption and utilization, improve soil water availability for optimal water supply and salinity control. In this study, through field trials in 2020 and 2021, 3 treatments were set up. The depth of free drainage (FD) is common subsurface pipe drainage and the controlled drainage in the growth period were 40 cm (CWT1) and 70 cm (CWT2), respectively, and the drainage depth in the non-growing period was 100 cm. Using the HYDRUS-2D model to simulate the dynamic changes of soil water and salts in the 0–100 cm range, the calibration and validation of the HYDRUS-2D model were performed using the measured soil water and salt content values of 2020 and 2021. The results showed that the simulated soil water and salt contents agreed well with the measured contents. Controlled Drainage (CD) is a new agricultural drainage management practice that involves periodically increasing the outlet elevation of subsurface drainage pipes, CD significantly increased the water content of the 0–100 cm soil layer—especially at 0–40 cm depth—after growth stage irrigation. Under FD, CWT1, and CWT2, the 2-year mean soil water content of the 0–40 cm soil layer after growth stage irrigation in 2020 and 2021 was respectively 0.263, 0.278, and 0.267 cm3 cm−3, with the latter two values being higher by 5.70 % and 1.52 % than the former value, respectively. Soil water uptake by sunflower after irrigation mainly occurred in the 0–40 cm soil layer, which contributed 55.88–78.51 % of the total soil water uptake. Soil re-salinization occurred in the late growth stage (the flowering stage) under different treatments, with a mean re-salinization rate (relative to the period before spring irrigation) of 29.29 %, 33.48 %, and 30.34 % under FD, CWT1, and CWT2, respectively. Although the re-salinization rate was relatively high under CWT1 and CWT2, it had a low effect on crop growth as well as crop yield. HYDRUS-2D simulation was performed to compare different drain depths in the growth stage in order to determine the optimal drain depth for sunflower in moderately saline soils. To this end, the following metrics were considered for the main root zone (0–40 cm): soil water content, soil salt content, soil de-salination rate during spring irrigation, and soil re-salination rate in the late growth stage. Reduce soil salt content during spring irrigation, increase soil water content after irrigation during growth period, and minimize soil salt return rate in late growth stage, that is, to provide suitable water conditions for crop growth and minimize salt stress. The optimal drain depth during the growth stage was ultimately determined to be 50 cm.

Linking soil phosphorus pools to drainage water quality in intensively cropped organic soils

Higher than average fertilization rates, as applied to mineral soils, are often recommended for cultivated organic soils (>20% organic matter), which over time, have led to phosphorus (P) pollution into receiving water bodies via subsurface tile drainage. Limited studies have documented the P pools within organic soils or their link to tile drainage water quality. This study quantified the different soil P pools found in organic soils under two water management practices: controlled drainage (CD) and pump drainage (PD) systems. Phosphorus availability in these soils was assessed by measuring inorganic P (Pi) and organic P (Po) via sequential fractionation; available P via Bray-1 P testing; and microbial P, along with crop root total P uptake. Drainage water samples were also analyzed for total P (TP) and dissolved reactive P (DRP). The results identified calcium (Ca) bound P as the largest P pool in these organic soils. Its correlation with other P pools suggests that it acts as a P sink in these soils. The correlation analysis further suggests that aluminum (Al) and iron (Fe) bound P is a driving force for P movement in the soil, as it had the most significant relationship with the P parameters in both the soil and drainage water. The regression analysis of TP found that the fertilizer and root P content were significantly related to the changes in drainage water quality at both sites. A P balance indicated that more fertilizer was being applied each year than was being used by the crops or released into the water, causing an accumulation of legacy P in the soil. Overall, the soil P pools affect the fluctuations of P concentration in the tile drainage water quality, featuring the complex relationship of the soil-water P dynamic.

Effects of modelling studies on controlled drainage in agricultural land on reduction of outflow and nitrate losses–a meta-analysis

A review with meta-analysis of outflow and nitrate loss reduction in controlled drainage (CD) vs conventional, free drainage (FD) was carried out in the study. Since the results of experimental field studies usually cover short periods of data collection, hence in this paper, meta-analyses were based on model studies that usually cover a longer time range. The databases Web of Science and Scopus were searched for eligible English articles, published until December 2020, that describe the quantity and quality of drainage water. The meta-analysis of outflow and nitrate loss reduction in CD vs FD using the mean difference (MD) with a confidence interval (CI) of 95%. The influence of each study was measured through heterogeneity, sensitivity analyses and publication bias using STATISTICA (version 13.3) for all analyses. Of the 107 works identified, 18 were finally included in the analysis based on established criteria required for an appropriate meta-analysis. In general the results indicate a reduction in average drainage outflow of 30.5% (MD = -71.26 mm; 95% CI, -103.49 –-39.04; p = 0.000) in arable land with CD in comparison to FD practice. In the case of nitrate load the reduction was 33.61% and in the drainage water there was lower content in CD practice by an average of 8.36 kg NO3 ha-1year-1 (95% CI, -9.93 –-6.79; p = 0.000). Subgroup analysis of two meta-analyses indicates that the results concerning these associations may vary with the calculated weight for each article, in which the number of years of study had the most significant impact.

Impact of controlled drainage on subsurface drain flow and nitrate load: A synthesis of studies across the U.S. Midwest and Southeast

Controlled drainage (CD), sometimes called drainage water management, is a practice whereby the drainage system outflow is managed during specific periods to retain more water in the field. Although CD has been shown to reduce downstream nitrate-N (NO3--N) load, seasonal patterns have been less consistent which can potentially impact the effectiveness of conservation practices. The main objective of this study was to assess the regional and seasonal impact of conventional free drainage (FD) and CD on drainage flow and nitrate-N load. Using experimental data from ongoing and historical CD experiments across the Corn Belt and in North Carolina, we evaluated subsurface drain flow, nitrate-N load, and performance of CD systems. Across the data set and regions, there was little difference in annual flow from FD conditions. Seasonally, more northern and western sites experienced a greater percentage of the annual flow occurring in the spring. There was no nitrate-N concentration reduction with CD. Flow and nitrate-N load reductions with CD did not vary by plant hardiness zone across the region, but the season with the greatest reduction did shift from winter to spring moving north and west in the study area. Absolute flow reductions (in mm) were similar regardless of precipitation category. Consequently, the percent reduction was lower as the amount of precipitation (category) increased. Overall, this analysis found CD to be an effective practice for reducing drain flow and nitrate-N loading directly delivered by the drains to downstream water bodies across the region.

Effects of Controlled Drainage on the Content Change and Migration of Moisture, Nutrients, and Salts in Soil and the Yield of Oilseed Sunflower in the Hetao Irrigation District

Controlled drainage (CD) is an important agricultural measure for maintaining soil moisture and nutrients, controlling groundwater level, and increasing crop yield. In arid regions, CD can be used to improve the water supply in agriculture and reduce environmental pollution. In this study, we investigated the effects of CD, including drainage depths of 40 cm (CWT1) and 70 cm (CWT2) during the plant growth stages, free drainage (FD), and open-ditch drainage (OD), on the migration of water, nutrients, and salts in the soil, the dynamics of the groundwater level, the loss of soil nitrogen, and the growth of oilseed sunflower plants. Compared with FD, CD increased the water and nutrient content in the soil, reduced nitrogen loss, and enhanced the ability of the soil to continuously supply nitrogen to the oilseed sunflower plants, which benefited plant growth at later growth stages and reduced environmental pollution. During the period between irrigation at the budding stage and the harvest stage, the average soil water content in the 0–20 cm soil layer in CWT1 increased by 3.67%, 4.78%, and 0.55%, respectively, compared with that in CWT2, FD, and OD. The soil mineral content in CWT1 was 25.17%, 35.05%, and 17.78% higher than that in CWT2, FD, and OD, respectively, indicating that higher soil salinity occurred at the later stage of plant growth in CWT1, which actually had little effect on the plants due to their enhanced salt tolerance and increased need for water and nutrients at that stage. In addition, CD delayed the decline in groundwater level, which allowed the plants to use groundwater at later growth stages, and as a result, the yield and water-use efficiency were improved. CWT1 significantly increased oilseed sunflower yield by 4.52–11.14% and increased water-use efficiency by 1.16–10.8%. Moreover, CWT1 also increased the survival rate of the oilseed sunflower plants by 2.62–2.92%, and the plants demonstrated good growth. Therefore, under CD conditions, plants used soil water and nitrogen more efficiently and, as a result, their productivity was increased, and the water quality was improved.

DRAINMOD modeling framework for simulating controlled drainage effect on lateral seepage from artificially drained fields

We demonstrated a DRAINMOD modeling framework to predict controlled drainage (CD) effect on the fate of water in artificially drained agricultural fields, which is key for determining the water quality benefits of the practice. To demonstrate this modeling framework, DRAINMOD simulated the hydrology of a subsurface drained grass field in Eastern North Carolina, U.S. under both free drainage (FD) and CD. Three scenarios were simulated for each water management: no lateral seepage (LS) and LS with constant and dynamic hydraulic head (Hr). For each scenario, predicted water table depth (WTD) and subsurface drainage were compared to observed values using Mean Absolute Error, Nash-Sutcliffe Efficiency, and Normalized Percent Error. Predicted water balance components for different scenarios were also investigated. Results clearly showed that LS was a significant component of the water balance for CD. Model predictions showed that 96% of the reduction in subsurface drainage due to CD could be attributed to LS (33.5 cm yr−1). The large values of LS predicted by the model were attributed to the presence of a permeable sandy layer in the soil profile, the shallow management depth of the drain outlet, and the small size of the experimental field plots. Agreement between predicted and observed WTD and subsurface drainage ranged from acceptable to excellent for FD with and without considering LS. In contrast, DRAINMOD simulations for CD yielded acceptable predictions only for the scenario considering LS with dynamic Hr. This study demonstrated the power of process-based simulation models, such as DRAINMOD, for interpreting and explaining data of experimental studies and underscored the importance of using a proper model calibration strategy for yielding reliable predictions. This study highlights the need for well-coordinated experimental and modeling research to further investigate how seepage affect CD performance for reducing drainage flow and nitrogen losses from artificially drained agricultural fields.