Shallow Groundwater Areas Research Articles

Effects of Drip Irrigation Flow Rate and Layout Designs on Soil Salt Leaching and Cotton Growth under Limited Irrigation

Optimal drip irrigation management in shallow groundwater areas needs to clarify the effects of flow rate and layout designs on the soil moisture, salt distribution, cotton root length density, plant height, leaf area, and yield. In this study, a one-year field experiment was conducted from April to October 2018 in the fifth company of the 16th Regiment in Alar City, Xinjiang, to investigate the effects of various drip flow rates and layout designs of cotton growth. Two drip flow rates (2.8 and 5.6 L·h−1) and two layout designs (one film, two drip tapes, and six rows; one film, three drip tapes, and six rows) were applied to explore the optimal combination, resulting in a total of four treatments that were irrigated three times in the whole growth period. Soil moisture, salt distribution, cotton root length density, plant height, and leaf area were measured. The main results were as follows: (1) Under the same layout designs, the soil moisture content was higher and the soil salinity was lower when the drip flow rate was 5.6 L·h−1, and the cotton root length density, plant height, leaf area, and yield were significantly higher than that of 2.8 L·h−1. (2) Under the same drip flow rate, the soil desalination rate, cotton growth indexes, and yield under the three-tapes treatment were significantly higher than the values of the two-tapes treatment. The actual yield of treatment D was 21.56%, 19.23%, and 11.71% higher than that of treatments A, B, and C, respectively. (3) The crop evapotranspiration of cotton during the two irrigation cycles showed an increasing trend, and the groundwater contribution showed a smaller and then increasing trend. Overall, the combination of three tapes and a drip flow rate of 5.6 L·h−1 had the highest cotton yield and net income, which were 6211.36 kg·hm−2 and 4820.21 kg·hm−2 for the theoretical and actual yields. The results of this study can provide a reference for the management of limited irrigation leaching soil salinity and cotton cultivation in shallow groundwater areas.

Spatial allocation of bioretention cells considering interaction with shallow groundwater: A simulation-optimization approach

Green infrastructure (GI), as one type of ecological stormwater management practices, can potentially alleviate water problems and deliver a wide range of environmental benefits in urban areas. GIs are often planned and designed to reduce runoff and mitigate pollution. However, the influence of GI on groundwater hydrology and that of shallow groundwater on GI performance was seldom considered. This study utilized a calibrated surface-subsurface hydrological model, i.e., Storm Water Management Model coupled with USGS's modular hydrologic model (SWMM-MODFLOW) to consider the interaction between GI and groundwater into the process of GI planning. The optimal implementation ratio, aggregation level and upstream-downstream location of bioretention cells (BC, one type of GI) under different planning objectives and hydrogeologic conditions was explored. The consideration of groundwater management exerted a significant impact on the optimal spatial allocation of BCs. The results showed that when groundwater management was more concerned than runoff control, BCs were recommended to be allocated more apart from each other and more upstream in the catchment because more-distributed and upstream BCs can result in lower groundwater table rise which is beneficial. BCs were overall recommended to be allocated in areas of deeper groundwater tables, coarser soils, and flatter topographies. However, the spatial features of BCs are related to each other, the choice of them are affected by various hydrogeologic factors simultaneously. The exact location of BCs should be determined by considering the trade-off between runoff control efficiency and groundwater impact. The findings obtained in this study can provide guidance on GI planning in shallow groundwater areas.

Study on Water and Salt Transport Characteristics of Sunflowers under Different Irrigation Amounts in the Yellow River Irrigation Area

The control of irrigation volume is of significant importance in arid regions of northwest China. Particularly, it has a crucial impact on the salinization of shallow groundwater areas. In 2022 and 2023, field experiments were conducted to test three distinct under-membrane irrigation treatments. These treatments were assigned water quotas of HW (27 mm), MW (22.5 mm), and LW (18 mm). The HYDRUS-2D model was integrated with a field experiment to accurately simulate the dynamic fluctuations of soil water and salt in the sunflower root zone. The model’s performance was assessed and verified using real-field data from 2022 and 2023, and the simulation results closely matched the measured values. This research also used stable hydroxide isotopes to assess the water supply from various soil layers at different time intervals in sunflower plants. The results indicated that the three different levels of irrigation applied under the membrane had a significant impact on soil water content. Specifically, there was a significant difference in soil water content at a depth of 0–40 cm (p < 0.05), while there was little effect on the water content at a depth of 40–60 cm (p > 0.05). After irrigation, the average salt content in the top 0–20 cm of soil decreased by 7.0% compared to the medium and low irrigation levels, and by 10.8% compared to the medium irrigation level. Additionally, the medium irrigation level resulted in a 10.8% decrease in salt content compared to the low irrigation level, and a 4.1% decrease compared to the medium irrigation level. During the same period, the soil salinity levels at depths of 0–20 cm, 20–40 cm, 40–60 cm, and 60–100 cm in the area outside the membrane were measured to be 2.7~4.8 g·kg−1, 2.8~4.0 g·kg−1, 2.7~3.4 g·kg−1, and 1.7~2.6 g·kg−1, respectively. These levels decreased by 13.1~55.5%, 0.7~42.8%, −0.4~16.2%, and −72.7~7.5%, respectively. Following irrigation, the HW treatment mostly absorbed water in the 0–40 cm soil layer, while the MW and LW treatments absorbed water in both the 0–40 cm and 60–80 cm soil levels. The results indicated that the most optimal drip irrigation method beneath the membrane in this location was achieved when the amount of water applied was between 25–30 mm. This method demonstrated a combination of water conservation, high crop yield, and effective salt suppression.

Shallow groundwater characterisation and hydrograph classification in the coastal city of Ōtautahi/Christchurch, New Zealand

Groundwater is present at shallow depth under many coastal low-lying cities. Despite the importance of protecting coastal urbanised areas from flooding and climate-change-induced sea-level rise, the effects of shallow groundwater fluctuations are rarely investigated. The aim of this study was to determine characteristics of shallow groundwater, including spatial and temporal trends in depths to groundwater and their relationship to natural and anthropogenic stressors. The study uses depth to groundwater measurements from a uniquely extensive and densely spaced monitoring network in Ōtautahi/Christchurch, New Zealand. Data-driven analysis approaches were applied, including spatial interpolation, autocorrelation, clustering, cross-correlation and trend analysis. These approaches are not commonly applied for groundwater assessments despite the potential for them to provide insights and information for city-wide systems. The comprehensive approach revealed discernible clusters and trends within the dataset. Responses to stresses such as rainfall events and stream flow were successfully classified using clustering analysis. The time series analysis indicated that in areas of shallow groundwater, low variation in levels occurred and this was also found using clustering. However, attributing some clusters to specific hydrogeological attributes or stressors posed challenges. The primary feature in hydrograph classification proved to be the proximity to tidal rivers and their correlation with tidal signals. These results highlight the value of using large datasets to characterise spatial and temporal variability of shallow groundwater in urban coastal settings and to assist with monitoring infrastructure planning in the face of future climate-change hazards.

Effect of Soil Texture on Water and Salt Transport in Freeze—Thaw Soil in the Shallow Groundwater Area

Research on the variation in soil water, heat, and salt in unsaturated zones during the freeze–thaw process has great significance in efficiently utilizing water resources and preventing soil salinization. The freeze–thaw field experiment was carried out with the lysimeter as the test equipment to analyze characteristics of the soil freeze–thaw process, profile water content, main ion content, and salt content of three textured soils with the groundwater table depth of 0.5 m. The results showed that the soil temperature gradient and freezing depth were greater as the average soil particle size increased. The increment of water content at the depth of 0 to 30 cm in sandy loam and loamy sand decreased by 40.20~93.10% and 28.14~65.52% compared with that in sandy soil, and the average increment of salt content at the depth of 0 to 30 cm decreased as the average soil particle size increased during the freeze–thaw period. The average content of Ca2+, Na+, Cl−, and SO42− in loamy sand and sandy soil decreased by 4.37~45.50% and 22.60~70.42% compared with that in sandy loam at the end of the freeze–thaw period, and the correlation between soil salt content and water content decreased with the increase in the average soil particle size. The research results can provide a theoretical basis for soil salinization prevention and crop production in shallow groundwater areas.

Effect of the interlayer on soil temperature and the transformation between phreatic water and soil water under laboratory freeze-thaw action

To reveal the effect of interlayer on the temperature of freeze-thaw soil and the transformation between phreatic water and soil water in shallow groundwater areas, a freeze-thaw test was conducted with a groundwater table depth of 0.5 m under laboratory freeze-thaw action. The soil temperature and the transformation between phreatic water and soil water of sand columns under constant freezing temperature at −20°C lasted for 20 days, and the thawing process lasted for 15 days were monitored. The interlayers with a particle size of 0.1–0.5 mm (d50 = 0.3 mm) and a thickness of 5 cm were set at 5, 15, 20, and 25 cm away from the surface and these sand columns were marked as D5, D15, D20, and D25, which were compared with a homogeneous sand column (Ch) with a particle size of 0.5–1.5 mm (d50 = 1.0 mm). The results showed that the fine particle interlayer had thermal insulation on the soil profile and that it effectively inhibited upward migration of phreatic water to soil water during the freezing process. A sand column that had a near-surface interlayer had a better thermal insulation, a stronger inhibition effect on upward migration amount of phreatic water to soil water (UMA) and a larger cumulative downward movement amount of soil water to phreatic water (DMA). The cumulative UMA of D5, D15, D20, and D25 was 61%–84% of Ch during the freezing stage, and the cumulative DMA of D5, D15, D20, and D25 was 29%–57% of Ch during the thawing stage. The inefficient loss of groundwater increased exponentially with the depth of interlayer, the sand column with an interlayer that was farther away from the surface consumed more groundwater and stored more water in the unsaturated zone, and its DMA reached almost zero earlier. These research results were significant for the scientific evaluation of water resources in shallow groundwater areas.

Sustainable Development of Underground Coal Resources in Shallow Groundwater Areas for Environment and Socio-Economic Considerations: A Case Study of Zhangji Coal Mine in China.

Coal resources in China are developed in several regions with shallow groundwater, and large mining-related surface subsidence can have negative impacts on agriculture, land and water resources as well as existing and future socio-economic resources. All these are important for sustainable resource development. Dynamic subsidence reclamation (DSR) planning concepts are evaluated here for another case study with analyses over a 11-year period. In DSR topsoil, subsoil, farming, and water resources management are dynamically synergized concurrent with mining ahead of and behind the projected dynamic subsidence trough. The study area involved mining five longwall faces (and post-mining reclamation) to assess if DSR could have improved both the environment and socio-economic conditions for post-mining land use as compared to using traditional reclamation (TR) and TR-modified (TR(MOD)) approaches. The results show that: (1) Upon final reclamation, farmland area and water resources in DSR and TR (MOD) will have increased by 5.6% and 30.2% as compared to TR. Removing soils ahead of mining before they submerge into water is important for farmland reclamation and long-term economic development. (2) Due to topsoil and subsoil separation and storage in the DSR plan, reclaimed farmland productivity should recover quickly and agriculture production should be larger than TR and TR(MOD) plans. (3) For a simplified economic model, the total revenue in the DSR plan should be 2.8 times more than in TR and 1.2 times larger than in TR (MOD) plan. (4) The total net revenue of the TR(MOD) plan should be increased by 8.1% as compared with the TR plan. The benefits will be much greater for analyses over longer periods. Overall, the DSR plan will allow for an improved socio-economic environment for new businesses to support disrupted workforces during and after mining.

Impact of the geological and hydrogeological settings on the radon potential in Bulgaria

Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. One of the indicators for evaluating the impact of radon on a certain area/terrain, including on the biota, is the so-called geogenic radon potential. Different types of rocks and soils possess different 226Ra content and different permeability. Radon gas has high mobility and is driven by diffusion and convection with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore the geogenic radon potential at the surface could be affected by the geological settings as a content of uranium and also by the hydrogeological settings as a degree of saturation near the surface. The present study mainly deals with the different by genesis shallow groundwater in Bulgaria based on the published since 1960’s sources. After analysis of the collected data several distinct regions have been determined regarding lithological and geomorphological conditions, and the 0–3 m depth of the groundwater table. In addition, a GIS-based map was elaborated relating the rocks with expected geogenic radon potential and shallow groundwater areas.

Impacts of droughts on agricultural and ecological systems based on integrated model in shallow groundwater area

Agricultural and ecological developments are increasingly paid attention in light of climate change. It is expected to comprehensively macroscopically control agricultural and ecological developments in shallow groundwater area that ecology is closely related to agricultural development. This study synthesizes multi models, including process-based crop growth model, water status model of shelterbelt, and vegetation-soil-groundwater interactions to identify responses of crops, shelterbelt, and natural vegetation to different level droughts. Obtained results show that the rank of vulnerabilities to droughts is: maize (the most vulnerable crop) > wheat > sunflower > shelterbelt (the least vulnerable vegetation). Under three drought scenarios, the natural vegetation biomass is all in stable states that fluctuations of groundwater salinity and precipitation cannot largely change the natural vegetation biomass. The natural vegetation biomass in equilibrium states is decreased by 4.08 % and 9.19 % respectively when available irrigation water is reduced to 70 % and 50 % levels. The results indicate that controlling and decreasing initial soil salt content before crop growth may be an effective way to avoid the decrease in the yield loss caused by salinization. It is suggested that vulnerable crops and the possible evolution of natural vegetation towards degradation in extreme droughts should be concerned and taken certain measures. This study also implies that optimizing planting structure is a possible strategy to improve adaptabilities to droughts and decrease economic losses. The established model contributes to provide an effective approach to handle large-scale decision-making problems about comprehensively developing agriculture and ecology in changing environments. Obtained results can provide reference strategies for managers to achieve sustainable development.

Stackelberg equilibrium water allocation patterns in shallow groundwater area under uncertainties

The hierarchical agricultural water resource management problem in shallow groundwater area is expected to be solved through establishing a practical and feasible mathematical model. This study proposes a multi-level programming model with considerations of process-based crops growth model and uncertainties. The model is solved by a fuzzy approach that ensures the decision-making proceeds from top to bottom sequentially and the leader supervises the solution search direction. The leeway given by each level decision maker expands the decision-making space and lets Stackelberg equilibrium solution more satisfactory. The model is applied in Hetao Irrigation District in China. After optimization, the Stackelberg equilibrium water allocation pattern and satisfaction degrees of each level decision makers can be identified. Summarized conclusions are as follows: (1) under uncertainties of available water, the water diversion is allocated in a similar pattern, while the groundwater allocation has larger variabilities; (2) when available water decreases, local farmers can improve crop production through modifying or optimizing irrigation water amount in each growth period; (3) the combined use of water diversion and groundwater is expected to become an effective approach for achieving a win–win situation between government managers and local farmers. The proposed model performs well in generating Stackelberg equilibrium solutions satisfied by multi-level decision makers. It can be extended to provide decision makers a more complete decision support system and also has potential to be applied in other similar areas.

Response of groundwater to different water resource allocation patterns in the Sanjiang Plain, Northeast China

Study regionThe Sanjiang Plain, located at the confluence of Heilong, Songhua, and Wusuli Rivers, Northeast China. Study focusDue to the low and flat terrain, wetlands and swamps were widely distributed in plain areas in history. After decades of reclamation, farmland has replaced wetland as the dominant landscape. The competition of water resources between wetland ecological health and food security is very fierce, which is mainly reflected in the serious overexploitation of groundwater. This study used a new coupled surface water-groundwater model with an innovative function of irrigation and drainage simulation to research the changes of groundwater in the Sanjiang Plain under different water resource allocation schemes and paddy development scale in the future, which may provide a scientific basis for the planning of water resource allocation projects related to the restoration of groundwater and wetlands in this region. New hydrological insights for the regionWe established four prediction models for different water resource allocation schemes and paddy areas by replacing the water supply data and planting structure of the baseline model in the Sanjiang Plain. By comparing the groundwater balance and level of various schemes simulated by prediction models, it was found that the complete water diversion scheme covering the plain areas would greatly reduce groundwater exploitation, increase groundwater recharge, and turn groundwater storage from deficit to surplus, which would increase by 853 million m3/a. It would gradually compensate for the historical debts due to groundwater overexploitation while achieving a balance between groundwater recharge and discharge; thus, the groundwater depth in most part of the plain areas would be restored to less than 5 m. However, the scheme also had a defect, that is, it may cause soil secondary salinization in shallow groundwater areas. Therefore, the scheme needs to be further optimized to make full use of the low-cost groundwater.

A signature‐based approach to quantify soil moisture dynamics under contrasting land‐uses

AbstractSoil moisture signatures provide a promising solution to overcome the difficulty of evaluating soil moisture dynamics in hydrologic models. Soil moisture signatures are metrics that quantify the dynamic aspects of soil moisture timeseries and enable process‐based model evaluations. To date, soil moisture signatures have been tested only under limited land‐use types. In this study, we explore soil moisture signatures' ability to discriminate different dynamics among contrasting land‐uses. We applied a set of nine soil moisture signatures to datasets from six in‐situ soil moisture networks worldwide. The dataset covered a range of land‐use types, including forested and deforested areas, shallow groundwater areas, wetlands, urban areas, grazed areas, and cropland areas. Our set of signatures characterized soil moisture dynamics at three temporal scales: event, season, and a complete timeseries. Statistical assessment of extracted signatures showed that (1) event‐based signatures can distinguish different dynamics for all the land‐uses, (2) season‐based signatures can distinguish different dynamics for some types of land‐uses (deforested vs. forested, urban vs. greenspace, and cropped vs. grazed vs. grassland contrasts), (3) timeseries‐based signatures can distinguish different dynamics for some types of land‐uses (deforested vs. forested, urban vs. greenspace, shallow vs. deep groundwater, wetland vs. non‐wetland, and cropped vs. grazed vs. grassland contrasts). Further, we compared signature‐based process interpretations against literature knowledge; event‐based and timeseries‐based signatures generally matched well with previous process understandings from literature, but season‐based signatures did not. This study will be a useful guideline for understanding how catchment‐scale soil moisture dynamics in various land‐uses can be described using a standardized set of hydrologically relevant metrics.

Mapping shallow groundwater salinity in a coastal urban setting to assess exposure of municipal assets

Study regionChristchurch, New Zealand. Study focusLow-lying coastal cities worldwide are vulnerable to shallow groundwater salinization caused by saltwater intrusion and anthropogenic activities. Shallow groundwater salinization can have cascading negative impacts on municipal assets, but this is rarely considered compared to impacts of salinization on water supply. Here, shallow groundwater salinity was sampled at high spatial resolution (1.3 piezometer/km2), then mapped and spatially interpolated. This was possible due to a uniquely extensive set of shallow piezometers installed in response to the 2010–11 Canterbury Earthquake Sequence to assess liquefaction risk. The municipal assets located within the brackish groundwater areas were highlighted. New hydrological insights for the regionBrackish groundwater areas were centred on a spit of coastal sand dunes and inside the meander of a tidal river with poorly drained soils. The municipal assets located within these areas include: (i) wastewater and stormwater pipes constructed from steel-reinforced concrete, which, if damaged, are vulnerable to premature failure when exposed to chloride underwater, and (ii) 41 parks and reserves totalling 236 ha, within which salt-intolerant groundwater-dependent species are at risk. This research highlights the importance of determining areas of saline shallow groundwater in low-lying coastal urban settings and the co-located municipal assets to allow the prioritisation of sites for future monitoring and management.

An integrated model to optimize irrigation amount and time in shallow groundwater area under drought conditions

Drought is one of the main factors negatively affecting crop growth. Optimizing irrigation time and irrigation amount are two effective ways to improve crop yield and water use efficiency. In order to achieve process-based optimization in shallow groundwater area, a comprehensive model is established by combining EPIC crop growth module, soil and groundwater water-salt balance models, and multi-objectives 0–1 programming. Multi-objectives are set to maximize crop biomass accumulated in drought period and improve water use efficiency for saving water. The irrigation amount and irrigation time of maize during drought periods are optimized by the day. The results indicate that soil salinization can aggravate the water stress to crops. The optimized schemes show the significant difference of total biomass and water use efficiency when irrigating at different time during drought conditions. Water sensitivity coefficients can be used to roughly guide the irrigation strategies that irrigation should be conducted as early as possible during water sensitive periods, so as to guarantee the high crop biomass and water use efficiency. The integrated model established in this study provides a reference approach for optimizing irrigation time and irrigation amount based on dynamic changes. The established model and obtained results in this study seek to potentially provide effective strategies combating agricultural droughts

Retraction Note to: The change of groundwater quality in shallow layer based on parameter estimation and tennis physical fitness recovery

This paper mainly studies the parameters of active panel data. According to the activity panel data to create a balance model, through the use of two improved GMM evaluation algorithm and according to the original GMM evaluation algorithm, the activity panel regression model creation, and dynamic activity panel parameter evaluation creation process. Based on the research and analysis of groundwater exploitation and other related literature, this paper believes that the reasonable development and utilization of groundwater resources in the island is a major problem to be solved in the development process of groundwater resources. Therefore, in the shallow groundwater area, it plays a very important role in the protection of groundwater resources. There is a very close relationship between surface water and groundwater, and surface water and groundwater can interact and influence each other, making the water quality change to a certain extent. Groundwater is the main source of water supply in China. According to the literature, athletes have good physical fitness, which can help athletes get better results in the competition. Through the research and analysis of high-level tennis players’ physical fitness, we can find more scientific and effective training methods, and make the high-level athletes’ physical energy supply more comprehensive and reasonable, so as to improve the sports level and competitive ability of athletes. In this paper, through the study of traditional GMM evaluation algorithm, the parameters of regression model and data model can be accurately estimated by activity panel.

Optimization towards sustainable development in shallow groundwater area and risk analysis

The projected increasing food demand in the coming decades will require substantial water and energy resources. Practical approaches are expected to propose to realize enhancing crop production while towards sustainable development in shallow groundwater area. This study integrates a process-based model, multi-objectives, and fuzzy theory into optimization model to optimize crops water allocation pattern under uncertainties of water diversion and groundwater. The process-based model considers the water exchange between soil and groundwater, water stress and salt stress on crops, and ground water level changes. The multi-objectives defined in this study balances the conflicts of maximizing crop production, maximizing water use efficiency, and minimizing energy consumption. The uncertain amount of water diversion and groundwater is presented as fuzzy numbers. The optimized water allocation pattern of 3 crops in 12 water supply response units in Hetao Irrigation District show that the crop yield does not necessarily reach to the highest potential value, though wheat and maize are allocated more water than sunflower and have larger possibility to reach high crop yield. Significant energy investment is needed for extracting and purifying groundwater to ensure relatively high crop production at the case of possible low available water. Uncertainties of water diversion and groundwater will cause a greater range of ground water level in wheat field, a high risk of water stress in sunflower field and a high risk of very severe salinization in wheat field. The different changing directions of three sub-objectives demonstrate that optimal water allocation has no uniform rule but changes with available water.

RETRACTED ARTICLE: The change of groundwater quality in shallow layer based on parameter estimation and tennis physical fitness recovery

This paper mainly studies the parameters of active panel data. According to the activity panel data to create a balance model, through the use of two improved GMM evaluation algorithm and according to the original GMM evaluation algorithm, the activity panel regression model creation, and dynamic activity panel parameter evaluation creation process. Based on the research and analysis of groundwater exploitation and other related literature, this paper believes that the reasonable development and utilization of groundwater resources in the island is a major problem to be solved in the development process of groundwater resources. Therefore, in the shallow groundwater area, it plays a very important role in the protection of groundwater resources. There is a very close relationship between surface water and groundwater, and surface water and groundwater can interact and influence each other, making the water quality change to a certain extent. Groundwater is the main source of water supply in China. According to the literature, athletes have good physical fitness, which can help athletes get better results in the competition. Through the research and analysis of high-level tennis players’ physical fitness, we can find more scientific and effective training methods, and make the high-level athletes’ physical energy supply more comprehensive and reasonable, so as to improve the sports level and competitive ability of athletes. In this paper, through the study of traditional GMM evaluation algorithm, the parameters of regression model and data model can be accurately estimated by activity panel.

Use of the stable oxygen isotope method to evaluate the difference in water consumption and utilization strategy between alfalfa and maize fields in an arid shallow groundwater area

Returning farmland to grasslands (RFG)to restore soil fertility and prevent land degradation in overused agricultural lands is an important measure. However, the hydrological processes, water consumption and utilization in field systems are undoubtedly changed in shallow groundwater areas owing to RFG. Experiments in the Hetao irrigation district, Inner Mongolia, China, during 2017 (2-yr for alfalfa) and 2018 (3-yr for alfalfa) were conducted to evaluate the difference in soil water distribution, percolation, groundwater recharge, water consumption and water productivity between alfalfa (Medicago sativa L.) and maize (Zea mays L.) fields. The stable oxygen isotope method was used to reveal a strategy to utilize different water sources for alfalfa and maize in an arid shallow groundwater area. Compared with maize, the increase in water consumption by alfalfa increased the soil water consumption of the 0–100 cm soil layer and the groundwater recharge, which led to an increase of 9.44 mm and 65.32 mm, respectively. However, the leakage below 100 cm layer decreased by 44.91% compared with those of the maize field. The yield and WPc of alfalfa were 29.27% and 6.28% greater than that of maize in 2018, respectively. Percentages of 75.43%, 18.73% and 5.84% of irrigation water, groundwater and precipitation were taken up by alfalfa during the irrigation period, respectively, while it was 81.27%, 12.90% and 5.83% in the maize field, respectively. After irrigation, the crops primarily absorbed water from upper soil layer (0–40 cm), comprising 72.93% (alfalfa) and 69.8% (maize). However, more water from the deeper layers was used by alfalfa before irrigation, and the average contribution of 40–100 cm soil layer was 63.0%, an increase of 11.2% compared with maize. In addition, even though maize absorbed water by roots that could reach a soil depth of 80 cm, it primarily drew water from the 40–60 cm soil layer.

Evaluating crop-soil-water dynamics in waterlogged areas using a coupled groundwater-agronomic model

Waterlogging on croplands has been a known problem for a long time, leading to adverse social, physical, economic and environmental issues. To better solve the problem, the complicated plant-soil-water dynamics system needs to be better understood. The challenge is to simulate the interactions between the components in the systems. There are models that simulate plant-soil-water system but either run the processes independently leading to inaccuracy or has high invasiveness of using integrated models. This paper presents a tightly coupled model, DayCent-MODFLOW, that links a 3D ground-water flow (MODFLOW) model and a 1D agroecosystem model (DayCent). DayCent is responsible for plant-soil-water dynamic in the root zone, whereas MODFLOW simulates head and groundwater flow in the saturated zone of the aquifer. DayCent passes deep percolation from the soil profile to the water table and, under conditions of waterlogging in which the water table is within the soil profile, DayCent soil hydrologic processes are constrained by the presence of the water table simulated by MODFLOW. The coupling is achieved by adopting a parallel inter-process communication technique MPI (Message Passing Interface). The model is applied to a waterlogged agricultural area (22 km2) in northern Colorado, USA and tested against groundwater head and rates of evapotranspiration (ET). The model runs in parallel with multiple processes on the largest AWS Linux server. Groundwater heads match measured heads to a reasonable degree, and ET rates match reference ET and are highly correlated with crop type. Results show the strong hydrologic interaction between the two models. Greenhouse gas emissions from soil (N2O and CH4) were also estimated by the model under the waterlogged conditions. Although the model can be used to simulate any plant-soil-aquifer system, no matter the depth of the water table, results from this study show that the model can be used to assess crop productivity, recharge, ET, and greenhouse gas emissions in areas of shallow groundwater.

Influence of coarse‐textured soil layers under crop root zone on soil water and salt dynamics and crop yield in shallow groundwater areas

AbstractCoarse‐textured soil layers under crop root zone could modify soil water and salt dynamics and affect crop growth. However, the influence is not thoroughly investigated, especially under shallow groundwater table and soil salinization conditions. For this purpose, we calibrated and validated a one‐dimensional agro‐hydrological model, LAWSTAC, for soil water and salt movement, and their interactions with maize growth in Northwest China. Simulation results fitted well with the measured values of soil water content, salt concentration, leaf area index, and crop yield for the maize growing seasons of 2012 and 2013. Further simulations were conducted to evaluate the influence of buried depths (80, 90, 100, and 110 cm) and thicknesses (10, 20, 30, 40, and 50 cm) of a coarse sand layer under root zone on soil water storage, salt leaching, and crop yield. Results demonstrated that soil water and salt status in the root zone was related to the water content of the coarse‐textured soil layer. Water percolation increased rapidly when water content in the coarse layer was higher than a critical value, which could be beneficial for salt leaching but unfavorable for water retention in the root zone. These results could help understand the influence of the coarse‐textured soil layer on root zone water storage and salt leaching and provide guidance on the irrigation scheduling for salt leaching and crop growth in areas with salinization problems and shallow groundwater tables.