Subsurface Pipe Drainage Research Articles

An integrated approach through controlled experiment and LCIA to evaluate water quality and ecological impacts of irrigated paddy rice.

This study used an integrated approach to mainly assess the water quality of paddy field during cultivation and quantify its equivalent ecological damages. Accordingly, an isolated pilot area with 0.6 ha and subsurface drainage pipes was prepared for flow measurement and multiple pollutant examination (DO, EC, pH, COD, TKN, TN, TP, NO3, butachlor) under controlled condition during 94 days of rice cultivation. Based on life cycle impact assessment (LCIA) database, the indices of ReCiPe (2016) were used to convert the examined nutrient and herbicide pollution. Results showed that TKN and TP were significant pollutants and reached the maximum concentrations of 7.2 and 4.9 mg/L in pilot outflow, respectively. Here, their average discharged loads were 56.2 gN/day and 45.3 gP/day. These loads equal leaching 8.5% and 9.4% of applied urea and phosphate fertilizers, respectively. The nutrient export coefficients were 8.4 kgN/ha and 6.8 kgP/ha. Nevertheless, the majority of this pollution was transferred by inflow. The net export coefficients were 0.3 kgN/ha and 2.6 kgP/ha while net leaching rates were 0.3%TN and 3.3%TP. The trend of combined ecological damages also showed that the 11-17th day of cultivation imposed the highest ecological risks. The state-of-the-art index of ecological footprint per food production estimates the equivalent ratio of lost lives by impaired ecosystem against lives saved from starvation. This index showed that 7% of the potential of produced paddy rice in this area for saving lives would be spoiled by releasing pollution to the terrestrial ecosystem in the long term. Yet, it can be enhanced as a matter of direct discharge to the freshwater. Therefore, using suitable agricultural operations or improving farm management practices for pollution abatement or assimilation potential is highly recommended.

Application of Hydrus-2D Model in Subsurface Drainage of Saline Soil in Coastal Forest Land—A Case Example of Fengxian, Shanghai

The study aims to explore saline drainage modeling in coastal saline soils, particularly focusing on subsurface pipe drainage in the Shanghai coastal area. Utilizing Hydrus-2D/3D-2.05 software, dynamic changes in soil–water–salt under various subsurface pipe laying conditions in forested areas were simulated to identify optimal schemes. Indoor and outdoor experiments demonstrated the Hydrus model’s ability to effectively simulate soil–water–salt transport processes under complex conditions. Subsequent simulations under different parameters of underground pipe laying, including burial depths (D = 0.5/0.7/0.9/1.1/1.3/1.5 m) and pipe diameters (Ø = 8/10/12 cm), further corroborated model validation. Among the analyzed schemes, those with burial depths around 0.7 m and pipe diameters under 12 cm exhibited the most substantial salinity improvement. Regression analysis highlighted a significant impact of burial depth D on cumulative salt discharge, with a coefficient of 12.812, outweighing that of pipe diameter Ø. Furthermore, subsurface pipe laying schemes demonstrated long-term benefits and cost advantages, obviating the need for additional irrigation infrastructure. These findings underscore the significance of subsurface pipe drainage in enhancing soil quality, reducing construction expenses, and optimizing land utilization, providing a valuable foundation for the Shanghai Green Corridor development and related initiatives.

Research on Salt Drainage Efficiency and Anti-Siltation Effect of Subsurface Drainage Pipes with Different Filter Materials

Subsurface pipes covered with geotextiles and filters are essential for preventing clogging and ensuring efficient drainage. To address low salt discharge efficiency due to subsurface drainage pipes (SDPs) clogging easily, sand gravel, straw, and combined sand gravel–straw were set above SDPs, respectively, within a setting of uniform geotextiles. The influences of different filter materials on the drainage efficiency and salt discharge effect of the SDPs, as well as the effects of different filter materials on the salt drainage efficiency and anti-siltation effect of the SDPs were studied by performing simulation experiments in a laboratory. The results confirmed the following: (1) The salt removal rates of the SDPs externally wrapped with materials exceeded 95%. The subsurface pipe treated with the sand gravel filter material had the highest desalting rate (93.69%) and soil profiles with total salt contents that were 17.7% and 20.5% lower than those treated with the straw and combined sand gravel–straw materials, respectively. (2) The soil salinity of the sand gravel filter material around the SDPs was between 1.57 and 3.6 g/kg, and the drainage rate (R) was 0.97, so its salt-leaching effect was the best. (3) The sand gravel filter material increased the characteristic particle size of the soil above the SDP by 8.4%. It could effectively intercept coarse particles, release fine particles, and facilitate the formation of a highly permeable soil skeleton consisting of coarse particles, such as sand particles surrounding the soil. (4) The use of the straw filter material produced dense filter cake layers on the upstream surfaces of the geotextiles. When the sand gravel and combined sand gravel–straw filter materials were used, soil particles remained in the geotextile fiber structure, and a large number of pores were still retained. Therefore, the sand gravel filter material was the most suitable for the treatment of Yinbei saline–alkali soil in Ningxia Hui Autonomous Region.

Performance of surface, subsurface and trench‐type drainage systems in paddy fields for non‐rice farming

AbstractEffective drainage is a crucial factor in paddy fields, especially in regions with waterlogging or heavy clay soils. Identifying an effective drainage system is essential for the successful removal of excess soil water from paddy fields to prepare them for subsequent crops. This study aimed to evaluate three different drainage systems, shallow surface drainage (shallow ditch), conventional subsurface pipe drainage and trench‐type subsurface drainage (French drain), in paddy fields in terms of drainage water volume, water table depth, drainage intensity, soil moisture and cracks. Experiments were carried out in a physical model capable of simulation with a 7.5 m drain spacing. The findings indicated that trench‐type drainage was more effective in reducing soil moisture due to its higher drainage water volume compared to other systems. The time required for the topsoil to reach its lower plastic limit in the subsurface, trench‐type and shallow surface drainage systems was 14, 11 and 15 h after the depletion of excess water over the soil surface, respectively. Although shallow surface drainage represented faster depletion of excess water, trench‐type drainage eventually proved to be the most effective alternative for providing appropriate qualifications for secondary cultivation. Crack areas on the soil surface were twice as extensive in trench‐type and subsurface drainage systems as in shallow surface drainage systems, indicating their superior performance.

Determination of Winter Irrigation Quotas for Corn and Oil Sunflower Considering Crop Salt Tolerance Threshold under Subsurface Pipe Drainage Technology

Subsurface pipe drainage (SPD) is an important technique for the improvement of saline–alkali lands in China. Winter irrigation after crop harvest is a key measure used in the Yellow River irrigation area in northwest China to reduce soil salinity in the root zone of crops. To optimize winter irrigation under SPD, the calibrated HYDRUS-2D model was utilized in this study to investigate the effects of soil texture (clay loam, silt loam, loam, and sandy loam), initial soil salinity (1, 3, 5 g/kg), and the winter irrigation quotas (80, 100, 120, 150, 180 mm) on the rate of soil desalination. In this study, soil salinity levels during the stable production of common crops such as sunflower and corn in the Yinbei Irrigation District in Ningxia, China, were taken as the thresholds, efficient utilization of irrigation water was considered, and suitable crops and appropriate winter irrigation quotas for different soil textures and levels of soil salinity were proposed. Soil with a salt content of 1~3 g/kg is suitable for the planting of corn with 80 mm of irrigation water. Sandy loam soil with a salt content of 3~5 g/kg is suitable for sunflower–corn intercropping with 120 mm of irrigation water. Sandy loam soil with a salt content exceeding 5 g/kg is suitable for the planting of sunflower with 80 mm of irrigation water. Other types of soils need to be improved by reducing the spacing between subsurface pipes, using desulfurized gypsum, biochar, and other additives. People engaged in agriculture can utilize this research to determine the appropriate volumes of irrigation water, crop types, planting systems, and subsurface pipe parameters based on local conditions.

Simulating Water and Salt Migration through Soils with a Clay Layer and Subsurface Pipe Drainage System at Different Depths Using the DRAINMOD-S Model

Soil salinization affects more than 25% of land globally. Subsurface pipe drainage is known for its effectiveness in improving saline–alkali land. The red clay layer (RCL) hinders soil improvement in the Hetao Irrigation District of Inner Mongolia, China. The soil water and salt migration rules at different buried depths and RCL were studied based on the field subsurface pipe drainage test and simulation using the DRAINMOD-S model (Version 6.1). The following implications can be drawn from the results: (1) Although the RCL affected the accuracy of the model, the calibrated statistical results met the application requirements, and the DRAINMOD-S model can be used to analyze subsurface pipe drainage under different distribution conditions of the RCL. (2) The RCL can reduce the drainage efficiency of the subsurface pipe, specifically when the distribution is shallow. (3) The soil desalting rate increased with an increase in the buried depth of the subsurface pipe. The desalination effect of shallow soil was better than that of deep soil. The RCL reduced the drainage and salt removal efficiency of the subsurface pipe. Burying the subsurface pipe as far above the RCL as possible should be considered. Thus, it is feasible to apply the DRAINMOD-S model to relevant studies.

The effect of underground drainage on peat meadows and inactivation of the drainage in an attempt to restore these meadows, which failed as it reduced the ability of soils to retain water

Drainage is often used to increase agriculture production, but it has adverse effects on biodiversity and water retention. Here, the effect of subsurface pipe drainage on peat meadows near Senotín (Czechia), which were drained from the mid-1980s to 1990s, was studied. Attempts were made to restore the peat meadows by damming drainage pipes using clay-filled trenches in 1996. In this case study, the effect on the depth of the water table, soil water retention, infiltration and soil temperature were recorded. Measurements of the original peat meadow (undrained site), drained meadow (drained site) and restored meadow (restored site) before restoration and two decades after restoration were recorded. The water table in undrained areas was higher than at drained and restored sites, indicating that drainage had lasting effect on drained and restored sites. Infiltration was lowest at the undrained site, greater at the drained site, and highest at the restored sites. Field water capacity was lowest at the restored site, greater at the drained site and highest at the undrained site. Soil water content at maximum saturation was lowest at the restored site, greater at the drained site and highest at the undrained site. Soil temperature was highest at the restored site with no significant difference between the undrained and drained sites. Soil moisture levels were highest at the undrained site and lowest at the drained site. In addition, the undrained and restored sites did not differ significantly in soil moisture content. In conclusion, restoration did not have a significant effect on the level of the water table, initiation of peat formation or ability of soil to hold water.

Soil Water and Salt Transport in Severe Saline–Alkali Soil after Ditching under Subsurface Pipe Drainage Conditions

The subsurface pipe drainage project is essential in farmland drainage operations and is globally recognized as an effective saline–alkali land improvement measure owing to its efficient drainage capacity and low land occupation rate. This study aimed to establish enhanced methods for improving saline–alkali land by combining ditching with subsurface pipe drainage. The ditching was conducted at a depth of 60 cm based on the existing subsurface pipe arrangement. The calibrated DRAINMOD-S model was employed to simulate the test area with different ditching depths and subsurface pipe arrangement parameters. Furthermore, the law of soil water and salt transport in the subsurface pipe drainage system at different ditching depths was investigated. After ditching, the total unit drainage volume of leaching increased by an average of 14.65% over two years and the water storage of different soil layers in the different plots decreased by 1.37–1.48 mm on average. Ditching demonstrated a superior salt-leaching effect in areas with subsurface pipe layouts. The soil desalination rate of different soil layers increased by 6.40–13.40% on average, with a more significant impact on the surface soil desalination rate. The effect of the increased desalination rate was more apparent as the ditching depth increased. However, as the buried depth of the subsurface pipe increased, the relationship between the ditching depth and soil desalination rate became insignificant. Ditching improved the salt-leaching effect of subsurface pipe drainage projects, which can effectively reduce the cost of subsurface pipe burial, consequently promoting subsurface pipe use.

Efficient desalination method using a subsurface drainage pipe with rice husk in paddy fields

The 2011 tsunami from the Great East Japan Earthquake caused severe soil salinization in agricultural lands. Soil salt removal using a subsurface drainage pipe with rice husk has been widely used in many paddy fields. However, desalination was frequently decided based on the expertise of construction contractors in Japan resulting in inefficient desalination methods that led to a significant wastage of freshwater resources and a long duration for agricultural restoration. Previous studies have either simulated conventional subsurface drainage without considering the rice husk zone or focused only on rice husk subsurface drainage systems excluding pipes. However, no quantitative research on a subsurface drainage pipe with rice husk has been conducted using numerical simulations. Accordingly, this study proposes highly efficient desalination methods for reducing freshwater wastage using an indoor experiment and numerical simulation. The indoor experiment of the subsurface drainage pipe with rice husk was set up in a soil tank of 900 × 200 × 900 mm (length × width × height), with reproduced salinization using NaCl solution inundation and soil desalination using freshwater. Thereafter, calibration and validation using HYDRUS-2D confirmed the model's accuracy in reproducing the movement of water and salt in the soil profile. The effects at a ponding water depth of 50–300 mm under various conditions on desalination efficiency and leaching water quantity were simulated. The results suggested that as the same desalination effect is achieved, low ponding water depths with multiple desalting cycles will reduce the quantity of leaching water. Moreover, under low ponding water depth conditions, prolonging the flooding duration will cause a decrease in the desalination effect. In addition, for the same quantity of leaching water, increasing the pipe burial depth is more beneficial to desalination than expanding the rice husk zone width. This study provides theoretical guidance for water conservation and high-efficiency desalination using the subsurface drainage pipe with rice husk for post-disaster early restoration of paddy fields.

Effects of Subsurface Pipe Drainage Spacing on Soil Salinity Movement in Jiangsu Coastal Reclamation Area

The agricultural development of reclaimed coastal areas in Jiangsu Province is significantly hindered by high soil salinity and an inadequate irrigation and drainage infrastructure. Optimizing the layout of subsurface drainage systems has been identified as an effective means of reducing soil salinity, with the proper designation of engineering parameters being crucial. This study applied 12 treatments (T1–T12) consisting of four different spacings of subsurface drainage pipes (6 m, 11 m, 15 m, and no subsurface drainage pipes) and three observation wells at varying distances from the drainage outlet (5 m, 25 m, and 45 m). Results showed that all three subsurface pipe spacing treatments significantly reduced soil salinity compared to natural drainage, with a smaller subsurface pipe spacing treatment leading to better salt-reducing effects. The farther the distance from the measuring point to the drain, the higher the salinity. As the burial depth of the outlet decreased and spacing between the subsurface drainage pipes decreased, the salinization rate of the 0–60 cm soil layer was higher, while the salt accumulation in the 60–80 cm soil layer was more severe. Therefore, a subsurface drainage pipe spacing of 6 m and an outlet burial depth of 40 cm are recommended as more suitable choices to effectively control salt concentration in the soil. The research aimed to provide scientific reference data and technical support for the optimized design of subsurface drainage engineering parameters while promoting efficient desalination of saline-alkali areas worldwide.

Simulating the impact of subsurface pipe drainage systems on crop water productivity at a regional scale in the upper Yellow River Basin

AbstractSubsurface pipe drainage (SPD) could provide a suitable environment for crop production in arid and semi‐arid agricultural areas; however, less attention has been given to the design layout of SPD on the regional scale in Hetao Irrigation District (HID). In this study, the appropriate layout of the final subsurface pipe was determined using the distributed SWAP‐WOFOST (Soil–Water–Atmosphere–Plant and WOrld FOod STudies) model in HID. Subsequently, the impact of the proper SPD on crop yield and water productivity (WP) were evaluated. Finally, the crop zoning was adjusted to further enhance crop WP, and the corresponding newly added cultivated land area was preliminarily estimated based on the suggested SPD. The results indicated that after zoning in the suggested SPD, the annual average yields of spring wheat, spring corn and sunflower increased by 19%, 7% and 11%, respectively, and WP improved by 13%, 5% and 10%, respectively, compared to the traditional layout. The newly added cultivated land area was estimated to be approximately 3489 ha through the replacement of traditional end ditches with subsurface pipes in HID. Therefore, the suggested subsurface pipe designs and cropping pattern adjustment improved crop growth and led to an increase in the cultivated land area in HID.

Electrolysis characterization of saline wastewater discharged from a subsurface pipe in saline-alkali land

We improved the design of an ion membrane electrolysis device to assess its use for electrolytic desalination and hydrogen production utilizing wastewater discharged from a subsurface drainage pipe in saline-alkali land. The device can reduce the waste of water resources and agricultural non-point source pollution. The electrolysis performance is low due to the low concentration of salts and complex ionic species in the drainage water from subsurface pipes of farmland. A one-factor quantitative experimental study was conducted to assess the influence of the electrolysis parameters on the electrolytic characteristics. Multifactor synergistic optimization of the parameters was performed. The results indicate different degrees of linear correlations between the hydrogen and chlorine gas production rates and the current density (CD) for different process parameters. Different factors have different degrees of influence on the electrolysis characteristics, and factor interactions occur. The optimization model describing the effects of multiple factors on the final current density (FCD), pH value after reaction (ARP), and energy consumption rate (ECR) is reliable and stable. The optimized operating parameters included a brine concentration (BC) of 3.6 mol·L−1, before reaction pH (BRP) value of 9, working voltage (WV) of 12.2 V, and electrode immersion depth (EID) of 22.5 cm. Under these conditions, the FCD is 183.03 mA·cm−2, the ARP is 13.99, and the ECR is 24,586.50 kW·h/kg. The proposed method substantially improves the electrolysis performance. The results provide theoretical and technical support for utilizing saline wastewater discharged from saline-alkaline land.

Subsurface drainage pipe detection using an ensemble learning approach and aerial images

Subsurface drainage pipe detection using an ensemble learning approach and aerial images

N2O Emissions from Saline Soils in Response to Organic–Inorganic Fertilizer Application under Subsurface Drainage

Organic fertilizer applications and subsurface drainage are two important measures for improving coastal saline soil; however, nitrous oxide (N2O) emissions from saline soil under a combination of these two measures are seldom evaluated. In this study, saline soil cultivated with sunflowers (Helianthus annuus L.) was employed as an experimental system. Prior to the experiment, the saline soils were buried with three different spacings (10 m (S1), 15 m (S2), and 20 m (S3)) of subsurface drainage pipes. The nitrogen nutrients that are needed by sunflowers came from two different nitrogen sources (organic and inorganic fertilizer), including six application schemes of either 100% organic fertilizer (100%OF), 75% organic fertilizer combined with 25% inorganic fertilizer (75%OF), 50% organic fertilizer (50%OF), 25% organic fertilizer (25%OF), 0% organic fertilizer (0%OF), and no fertilizer (CK). The results show that the cumulative N2O emissions from the treatments under S1, S2, and S3 throughout the entire growth period were 8.9–15.8, 9.5–17.5, and 10.1–17.6 kg ha−1, respectively. A smaller spacing between adjacent drainage pipes or a higher replacement proportion of organic fertilizer reduced the accumulative N2O emissions. The increased replacement of organic fertilizer decreased the soil salinity, whereas it increased the C/N ratio and total carbon content. The fertilization treatments significantly increased the nitrogen uptake of sunflower plants, with increase ranges of 18.1–47.2%, 8.6–40.5%, and 8.8–34.5% under S1, S2, and S3, respectively, compared with CK. The highest yield of sunflowers was achieved under S2 combined with 25%OF, reaching 3.82 t ha−1. Correlation analysis showed that the N2O emission flux was positively correlated with the soil salinity, crop yield, and crop nitrogen uptake, whereas it was negatively correlated with the total carbon, C/N ratio, and organic carbon content. We concluded that using 25% organic fertilizer instead of inorganic fertilizer was beneficial for reducing N2O emissions while maintaining the crop yield under subsurface drainage.

Water and salt replacement through soil salt leaching under brackish water conditions with subsurface pipe drainage

AbstractTo explore the improvement effect of subsurface drainage and brackish water on saline alkali soil, an orthogonal experimental design was used to conduct soil column experiments under nine parameter combinations of the depth of the buried subsurface pipe, irrigation amount and salinity of brackish water. A numerical model of soil water and salt movement was established, and the physical parameters of the soil were verified by using the software HYDRUS‐1D. The results indicated that the salinity of the brackish water only affected salt replacement. The salt replacement associated with subsurface drainage decreases with increasing water and salt replacement area at a constant irrigation volume. The salt replacement amount through subsurface pipe drainage increased with the irrigation amount in constant water and salt replacement areas. When the burial depths of the subsurface pipes were 140 and 160 cm and the irrigation amounts were >3180 and 3990 m3 ha−1, respectively, the salt discharge through the subsurface pipes was greater than the salt content carried by the brackish water, and the salt content of the soil in the root zone reached the critical salt tolerance value of cotton, which can simultaneously show that the soil salt content would not affect cotton growth.

Numerical Simulation of Soil Water–Salt Dynamics and Agricultural Production in Reclaiming Coastal Areas Using Subsurface Pipe Drainage

Soil salinization induced by shallow saline groundwater in coastal areas can be managed using subsurface pipe drainage (SPD) for agricultural land reclamation. However, a reasonable SPD system layout should comprehensively consider local hydrological conditions and crop physiological characteristics based on long-term model evaluations. The objectives of this study were to test the applicability of a crop growth model (AquaCrop) for simulating winter wheat growth in SPD-applied fields by employing the water table behaviors predicted by the soil hydrologic model HYDRUS. Model calibration and validation based on field observations suggested that HYDRUS accurately predicted the distributions of soil water–salt dynamics, and the seasonal variations of canopy cover and biomass production predicted by AquaCrop were close to the measured values. The simulation scenarios considering the long-term effect of groundwater salinity (10.53, 21.06, and 31.59 g L−1 for low, medium, and high levels), drain spacing (10, 20, 30, 40 m, and no-SPD), and precipitation category (dry, normal, and wet year) on soil solute transport, grain yield (GY), water productivity (WP), and groundwater supply (GS) were further explored using a combination of HYDRUS and AquaCrop. The simulation results indicated that narrowing the drain spacing could improve the desalination performance of SPD, but there was no continuous downward trend of soil solute concentration during the long-term application of SPD when groundwater salinity was constant. The SPD application could improve grain yield by 0.81–1.65 t ha−1, water productivity by 0.13–0.35 kg m−3, and groundwater supply by 6.06–31.03 mm compared to the no-SPD scenarios, but such increases would be less pronounced in dry years with groundwater salinity at the low level. This study demonstrated that the co-application of hydrologic and crop growth models is a feasible method for revealing the effects of SPD on agricultural land reclamation in coastal areas.

Experimentally Based Numerical Simulation of the Influence of the Agricultural Subsurface Drainage Pipe Geometric Structure on Drainage Flow

The geometric structure of corrugated plastic pipes affects performance in agricultural subsurface drainage systems. To explore the influence of pipe geometry on flow field characteristics and the characterization of water movements, we developed a three-dimensional (3D) steady-state subsurface drainage model based on computational fluid dynamics (CFD). An analysis of the CFD and sand tank results indicated that the proposed model can accurately simulate the subsurface drainage process (R2 = 0.99). The corrugation structure parameters of the drainpipe, including the outside diameter, corrugation valley width and corrugation height, were taken as the objects for this study, and the influence of corrugation parameters on drainage discharge was orthogonally analysed. During drainage, the soil water initially collects in the corrugation valley and then approximately ninety percent of the water flows into the pipe through the bottom perforations; increasing the contact face area between the corrugation valley and soil can increase the flow rate of the drainpipe and the water table height above the pipe, which decreases the intersection position of the pipe and water table. The results of the analysis of the range and variance of the orthogonal experiment showed that the order of the primary and secondary factors influencing the drainage discharge was the outside diameter, corrugation valley width and corrugation height, with the outside diameter being most critical influencing factor.

Study on Soil Desalination Process of Saline-Alkaline Grassland along the Yellow River in Western Inner Mongolia under Subsurface Drainage

This study aimed to explore the characteristics of water and salt transport in saline-alkali grassland, effectively guide the ecological construction of saline-alkali grassland along the Yellow River in western Inner Mongolia, and provide a theoretical basis and technical support for the ecological restoration of saline-alkali grassland and regional environmentally sustainable development. The desalination process of saline-alkali soil under the condition of subsurface pipe drainage was simulated using an indoor soil tank test. The variation in soil leaching water consumption, the salinity of the leaching filtrate with time, the accumulation of the filtrate, and the desalination rate of the filtrate under the condition of continuous leaching with a 25 mm head were analyzed. At the same time, the variation process of soil conductivity at 0~40 cm (upper layer), 40~80 cm (middle layer), and 80~120 cm (lower layer) was analyzed. Subsurface pipe drainage can reduce the soil salt content, while reducing the control area of the subsurface pipes can accelerate the soil desalination rate, thus improving the quality of saline-alkali soil. In addition, the leaching effect under 30 cm partition spacing was better than that under 35, 40, and 45 cm partition spacing, and the corresponding desalination rate was higher. Under stable continuous leaching with a 25 mm head, the entire leaching process can be divided into three stages: the rapid desalination, moderate desalination, and stable stages. During the desalination process, the upper, middle, and lower layers were desalinated synchronously, and the desalination rate of the upper layer was the highest, followed by the desalination rate of the middle and lower layers.

Model-Based Optimization of Design Parameters of Subsurface Drain in Cotton Field under Mulch Drip Irrigation

In this study, the influence of the relevant parameters of a subsurface pipe layout on soil water and salt transport in a cotton field under mulched drip irrigation is explored. Based on the measured data of the changes in the groundwater level and salt in the field, the DRAINMOD numerical model has been used for simulating the water and salt dynamics of a salinized cotton field under subsurface pipe drainage. The results of the investigation show that the DRAINMOD model can accurately simulate the changes in the hydrological conditions and the salt-leaching process in the study area. The average deviation between the simulated and measured values of the groundwater depth in 2013 and 2014 was −1.72 cm and 2.43 cm, the average absolute deviation was 3.84 cm and 2.43 cm, the root mean square error was 5.14 cm and 3.63 cm, and the correlation coefficient was 0.87 and 0.94, respectively. The average deviation between the simulated and measured values of soil salinity in 2013 and 2014 was −0.68 g/kg and −1.86 g/kg, the average absolute deviation was 1.60 g/kg and 1.99 g/kg, the root mean square error was 1.95 g/kg and 2.99 g/kg, and the correlation coefficient was 0.82 and 0.86, respectively, which are all within the acceptable error range. After validation, the model was used to simulate and analyze the desalination process of a cotton field in the study area for 27 different subsurface pipe layout modes. The projection pursuit classification model has been combined with the accelerated genetic algorithm based on real-number coding. The comprehensive benefits of the subsurface pipe layout were evaluated using the construction cost, average desalination rate, and relative yield of cotton as the evaluation indices. The results show that C11 (buried depth 2.1 m, spacing 30 m) is the optimal layout of the subsurface pipe. The results of this study can provide theoretical support and scientific guidance for the popularization and application of subsurface pipe salt discharge technology and drip irrigation under film in the arid inland areas of northwest China.

Eight-year comparison of agroeconomic benefits of open ditch and subsurface pipe drainage in mulched drip irrigated saline–sodic farmland

Eight-year comparison of agroeconomic benefits of open ditch and subsurface pipe drainage in mulched drip irrigated saline–sodic farmland