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Lignite−based amendments are promising soil conditioners for improving crop yield and nitrogen use efficiency, but there is limited knowledge regarding the potential effects of lignite−based amendment on nitrogen cycling−related microbial communities and their impacts on NH 3 volatilization and crop nitrogen uptake in saline−sodic farmland. Here, we investigated the influences of lignite bioorganic fertilizer (LBF) on NH 3 volatilization, nitrogen uptake, and microbial communities containing nifH , amoA , and nirS genes through a two−year field experiment. Three treatments were considered in the experiment, i.e., a control treatment with no organic fertilizer application (CK), a farmyard manure treatment (FYM) involving the application of sheep manure at a rate of 21 t ha−1, and a LBF treatment with optimal application rates of 3.0 and 4.5 t ha−1. Results showed that compared with the control treatment (CK), the LBF treatment reduced the total NH 3 volatilization by 22.3% and 13.5% in 2019 and 2020, respectively. In addition, the LBF treatment significantly increased sunflower nitrogen uptake by 52.5% and 114.2% in 2019 and 2020, respectively, in comparison with the CK treatment. Moreover, the LBF treatment not only increased the absolute abundance of the nifH gene by 111.5% and altered the core microbes in the nifH −containing community, but it also enhanced the complexity, stability, and cooperation of co−occurrence network of the nifH −containing community, which were positively related to the sunflower nitrogen uptake. The LBF and FYM treatments reduced NH 3 volatilization by improving the soil aggregate stability and saturate hydraulic conductivity. These results indicated that LBF may offer a feasible measure to improve the sunflower nitrogen uptake by constructing a complex, stable, and cooperative nitrogen fixation system, without the risk of NH 3 volatilization in saline−sodic farmland. • Lignite bioorganic fertilizer increased nitrogen uptake of sunflower and reduced NH 3 volatilization. • Lignite bioorganic fertilizer enhanced complexity, stability, and cooperation of nifH- containing community. • Aggregate stability was the main driver for changes in the nifH −and nirS −containing communities. [ABSTRACT FROM AUTHOR]

Water-saving irrigation is becoming more important in the upper Yellow River basin (YRB) due to reduced water allocation and growing water scarcity. However, drip irrigation as an efficient irrigation method, has not gained as much acceptance as one might expect. In this study, integrated approaches involving field experiments, agro-ecosystem modeling, and financial analysis were proposed to evaluate the multiple benefits of two irrigation methods. Field experiments on maize irrigated with border irrigation and drip irrigation under plastic mulching (i.e., BI-M and DI-M) were conducted in the Hetao Irrigation District (Hetao) of the upper YRB during 2021 and 2022. The AHC model was calibrated and validated using two-year experimental data, performing well in simulations of soil water-salt-nitrogen (N) dynamics and crop growth. An irrigation scheduling module was newly incorporated into AHC. Then the model was applied to analyze scenarios consisting of three classes of groundwater depth (GWD) and five N application levels. Optimal irrigation and N-fertilization strategies were suggested; and DI-M showed significant advantages over BI-M in terms of water-saving (56–66 mm), labor-saving, environmental benefits (50 kg ha−1 less N fertilizer and 19–25 kg ha−1 less N loss), and crop yields (<4%), both in experimental and scenario cases. However, the financial analysis revealed that the current smallholder BI-M could achieve higher net returns (about 12%) compared to DI-M, since the family labor is often not counted as a cost in smallholder farming. Additionally, the widespread adoption of BI-M is also partly attributed to its easy operation. Lastly, results indicated a trend where the advantages of drip irrigation would become more significant in the future, with the increasing agricultural population aging and rising labor costs in the YRB. • Experiments, surveys and AHC model were combinedly used for irrigation evaluation. • Water-salt-nitrogen fate and economic benefits were evaluated under various scenarios. • Optimal water-nitrogen strategies were suggested for border and drip irrigation. • Smallholder BI-M achieves higher net returns due to exclusion of family labor cost. • Drip irrigation has clear advantages in water, labor and eco-environmental benefits. [ABSTRACT FROM AUTHOR]

Climate change poses a challenge for resource utilization and environmental pollution issues caused by agricultural production, especially in arid to semi-arid regions. Farmland water, carbon and nitrogen balances are closely related to these resource and environmental issues. Thus, the Agro-Hydrological & chemical and Crop systems simulator was used to assess the response of water, carbon and nitrogen balances to climate change in a spring wheat farmland of arid to semi-arid Northwest China and to propose adaptation strategies. Five Global Climate Models from the Coupled Model Intercomparison Project 6 and two Shared Socioeconomic Pathways (SSP1–2.6 and SSP5–8.5) were used to establish scenarios with the Agro-Hydrological & chemical and Crop systems simulator to simulate farmland water, carbon and nitrogen balances for the 2025–2100 period. Various irrigation amounts and nitrogen fertilization rates were tested as compensation strategies. Results indicated that climate change could negatively affect farmland water, carbon and nitrogen balances, especially under the SSP5–8.5 scenario. Precipitation showed an increasing trend, thus percolation increased and soil water consumption decreased from 2025 to 2100. However, for the carbon budget, although the soil carbon dioxide emissions tend to decrease, the net primary production was also significantly reduced, which resulted in declining the net ecosystem carbon budget under future climatic conditions. In addition, higher temperature and increased precipitation enhanced soil inorganic nitrogen leaching and nitrous oxide emissions but reduced ammonia volatilization from 2025 to 2100. Overall, the soil total nitrogen loss was increased over time, whereas crop nitrogen uptake was significantly reduced. In relation to the SSP1–2.6 scenario, the SSP5–8.5 scenario accelerated the increase rates of soil water percolation and total nitrogen loss over time, as well as the decrease rates of crop nitrogen uptake and net primary production over time. The negative effects caused by climate change can be mitigated by reducing irrigation and increasing nitrogen fertilization. For the SSP1–2.6 scenario, 30% irrigation reduction and 30% nitrogen fertilization increase can effectively decrease soil water percolation and the related nitrogen losses while crop nitrogen uptake, net primary production and net ecosystem carbon budget increase in relation to the current management (irrigation = 240 mm and nitrogen fertilization = 200 kg ha–1). For SSP5–8.5 the strategy with 45% irrigation reduction and 45% nitrogen fertilization increase can also decrease nitrogen losses and increase crop nitrogen uptake, net primary production and net ecosystem carbon budget. • The responses of farmland water-carbon-nitrogen balances to climate change were assessed. • Climate change increased soil water percolation and total nitrogen loss from 2025 to 2100. • The future crop nitrogen uptake and net primary production showed a decreasing trend. • Net ecosystem carbon budget was rapidly reduced over time under the SSP5–8.5 scenario. • Compensation strategies to climate change were proposed under different SSP scenarios. [ABSTRACT FROM AUTHOR]

• Coupling AHC and SHAW models simulates year-round agro-hydrological processes in cold arid areas. • Coupled model performance was evaluated with two-year field experiments. • The impacts of various irrigation and groundwater management strategies were assessed. • Appropriate irrigation and groundwater management strategies for farmland were suggested. Quantitatively assessing the impact of irrigation and groundwater management strategies is crucial for improving water productivity and soil salinity control in cold arid areas with shallow groundwater tables (CAASGT). However, existing studies often focus on specific periods, either the crop growth period or the freeze–thaw period, due to the lack of appropriate models that can accurately represent both soil freeze–thaw and crop growth processes. This limited focus results in incomplete year-round insights, given the significant differences and interactions in hydrological processes during these two periods. In this study, we coupled the agro-hydrological model (i.e., the AHC model) and the cold region hydrological model (i.e., the SHAW model) to simulate the year-round agro-hydrological processes and crop growth in CAASGT. The coupled model was rigorously calibrated and validated using two years of field experiment data collected from a maize field in the upper Yellow River basin (YRB). Subsequently, the validated model was employed to analyze the effect of different irrigation and groundwater management scenarios on crop yield, soil salinity, and water productivity in two hydrological years (dry and wet years). Results indicated that increasing groundwater depth was beneficial for soil salinity control in all scenarios but reduced maize yield at low irrigation levels. Autumn irrigation proves essential for soil salinity control, with reducing the irrigation amount in autumn irrigation period having a more significant impact on maize yield than that in growing season. Additionally, soil thawing time significantly affects soil salt accumulation and crop yield, with earlier thawing time leading to more severe salt accumulation at the end of the freeze–thaw period, restraining maize seedling growth and decreasing maize yield. These results are expected to offer year-round insights into improving water productivity and soil salinity control in CAASGT. [ABSTRACT FROM AUTHOR]

Abstract: Tide-induced airflow is commonly seen in coastal lands and affects ground stability especially with a less permeable pavement on the ground surface. A tide-induced airflow model in a two-layered unsaturated zone consisting of a highly permeable layer underneath a less permeable layer was established by Li and Jiao [Li HL, JJ Jiao. One-dimensional airflow in unsaturated zone induced by periodic water table fluctuation. Water Resour Res 2005;41:W04007. doi:10.1029/2004WR003916 ] to describe the one-dimensional airflow with constant atmospheric pressure at the ground surface. In this study, we expand the Li and Jiao model by considering the realistic atmospheric pressure fluctuations and the initial condition. A new transient solution to the airflow model is developed for an initial boundary value problem (IBVP). The transient solution can be used not only to calculate the subsurface air pressure at a future time with a known initial condition, but also to evaluate the asymptotic air pressure variations when time becomes long. The amplitude ratio and phase lag of the subsurface air pressure relative to the tide-induced hydraulic head variations inside the unconfined aquifer below the unsaturated zone are investigated. The results reveal that effect on the subsurface pressure due to changes of atmospheric pressure amplitude depends on the configurations of air resistance in the less permeable layer and the air-filled porosity difference in the two layers. The introduction of atmospheric pressure fluctuations into the airflow model leads to insignificant influence on water table level. A field application of the new solution at Hong Kong International Airport in Hong Kong, China is demonstrated. It indicates that the new transient solution can be conveniently used to evaluate the subsurface air pressure with discrete atmospheric pressure data at the ground surface. [Copyright &y& Elsevier]

Summary: Constant-head test is a commonly used aquifer testing method in groundwater hydrology. A mathematical model for constant-head test in a leaky aquifer with a finite-thickness skin was developed in this study. Three different aquifer–aquitard systems were considered and the Laplace-domain solutions were obtained and then inverted numerically with the Stehfest method to yield the time-domain solutions. The well discharges for different cases were computed and a sensitivity analysis of the well discharge on different parameters was performed. The results indicated that the dimensionless transmissivity of the aquitard had little effect on the well discharge at early times while a larger transmissivity of the aquitard leaded to a larger well discharge at late times. The well discharge for the positive skin was smaller than that without the skin while the well discharge for the negative skin was larger than that without the skin, where positive and negative skins refer to the cases in which the permeability values of the skin zones are less and greater than that of the formation zone, respectively. A thicker skin resulted in a smaller well discharge for the positive skin case but leaded to a larger well discharge for the negative skin case at late times. We also found that the drawdown for the positive skin case was less than that for the negative skin case at the same time, and a positive skin might result in delayed response of the aquifer to pumping. The sensitivity analysis indicated that the well discharge was sensitive to the properties of the skin zone, but not sensitive to the properties of the aquitards for the aquifer–aquitard system presented in this study. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with two-dimensional solute transport in an aquifer–aquitard system by maintaining rigorous mass conservation at the aquifer–aquitard interface. Advection, longitudinal dispersion, and transverse vertical dispersion are considered in the aquifer. Vertical advection and diffusion are considered in the aquitards. The first-type and the third-type boundary conditions are considered in the aquifer. This study differs from the commonly used averaged approximation (AA) method that treats the mass flux between the aquifer and aquitard as an averaged volumetric source/sink term in the governing equation of transport in the aquifer. Analytical solutions of concentrations in the aquitards and aquifer and mass transported between the aquifer and upper or lower aquitard are obtained in the Laplace domain, and are subsequently inverted numerically to yield results in the real time domain (the Zhan method). The breakthrough curves (BTCs) and distribution profiles in the aquifer obtained in this study are drastically different from those obtained using the AA method. Comparison of the numerical simulation using the model MT3DMS and the Zhan method indicates that the numerical result differs from that of the Zhan method for an asymmetric case when aquitard advections are at the same direction. The AA method overestimates the mass transported into the upper aquitard when an upward advection exists in the upper aquitard. The mass transported between the aquifer and the aquitard is sensitive to the aquitard Peclet number, but less sensitive to the aquitard diffusion coefficient. [Copyright &y& Elsevier]

• The accuracy of analytical expression of transient S y is effectively improved. • Expressions are based on the MVG model and can be used at any WT changes. • The expressions of ultimate S y,u and the time t d required to reach S y,u are given. This paper presents the new analytical expressions to improve the description of transient specific yield (S y) in shallow groundwater drainage. A new expression of the transient S y (i.e. S y,G (t)) that only considers the gravity effect is first derived based on the modified van Genuchten model. This analytical expression is still valid when water table depth (WTD) is less than the soil air-entry pressure head, and thus completes the lack of description in the near-saturated segment in previous expressions. Further, we propose an approximate method to dealing with the diffusivity (capillary) effect, and derive an improved approximate expression of S y with both considering the gravity and diffusivity (capillary) effects. The accuracy of the improved expression of S y,GD (t) is evaluated with the test cases that cover all of soil types (under the USDA soil classification system) and different changes in water table, also compared with the expression derived with only considering the gravity effect. The comparisons show that the S y,GD (t) expression could more accurately capture the dependence of the transient S y on time and WTD, and significantly reduce the errors of ignoring the diffusivity effect. In addition, the analytical expression of ultimate S y and the final time t d required to reach its ultimate value are both derived based on the initial and final equilibrium states. Results indicate that our improved expressions can expand the application range of analytical expression and significantly improve the calculation accuracy of transient S y in the shallow groundwater environments. [ABSTRACT FROM AUTHOR]

The triangle/trapezoid framework model (TFM) is a widely used approach for mapping regional evapotranspiration (ET) based on thermal infrared remote sensing imagery. However, the homogeneity assumption for meteorological forcing and surface properties involved in TFM contradicts the characteristics of heterogeneous regions, leading to high uncertainty at regional scale, especially under energy-limited or strong advection conditions. Therefore, this study examined the linear relationship between soil moisture availability (Λ SM), evapotranspiration efficiency (Λ ET) and radiation surface temperature (T rad), and developed an Independent Framework-based dual-source ET Model (IFEM) for heterogeneous regions. By fixing two key meteorological forcing variables, air temperature (T a) and vapor pressure deficit (VPD), and three surface characteristic parameters, aerodynamic resistance (r a), albedo (α) and the ratio of soil heat flux to net radiation (Γ), the IFEM constructs a uniform fractional vegetation cover (f c)- T rad space. In this uniform f c -T rad space, isolines of Λ SM and Λ ET are aligned with those of T rad , and an independent trapezoid framework is constructed for each pixel of RS images. It avoids the systematic bias caused by the distorted trapezoid space involved in traditional TFMs. The proposed model was applied in a hydrologically semi-enclosed irrigation area, the Hetao Irrigation District, with Landsat and MODIS datasets from 2016 to 2020 to evaluate its performance at the field and region scales. Firstly, the IFEM was capable of retrieving latent heat with a mean absolute error (MAE) of 34.43 W m−2 and a mean absolute percentage error (MAPE) of 8.68%, compared with the measurements from flux towers. Secondly, the IFEM reasonably separated the soil (MAPE = 21.33%) and canopy (MAPE = 14.33%) components from ET, compared with the soil evaporation observed by micro-lysimeters and the plant transpiration calculated by sap velocity upscaling technology. Thirdly, the IFEM showed high accuracy in estimating annual total ET with a percentage error range within ±3.0%, compared against the regional water balance calculations. Overall, the IFEM demonstrated high robustness and accuracy for field-scale and regional-scale applications, validating its potential as a reliable method for mapping regional ET in heterogeneous regions. • The IFEM is developed for remote sensing-based duan-source ET estimation in heterogeneous regions. • The IFEM constructs a uniform f c - T rad space. • Where an independent trapezoid framework is constructed for each pixel. • Based on which, the evaporation efficiency could be more accurately estimated. • The LE could be more reasonably partitioned into soil and canopy components. [ABSTRACT FROM AUTHOR]

• GHG emission value account for 75–80% of the total negative ESV in Northwest China. • Reducing irrigation by 33.3–53.3 % and N fertilization by 29.4–41.2 % can achieve REF trade-offs. • Wet years increased the water-saving potential but reduced the N-saving potential. Excessive irrigation and nitrogen (N) fertilization have caused severe reductions in farmland water and N productivity, and functional degradation of agroecosystems in arid to semi-arid regions. Thus, a process simulation-based framework for resource, food, and ecology (RFE) trade-offs was used to optimize the irrigation and N fertilization strategy (IRNF). A scenario study was conducted based on the framework that was developed in our previous companion study in the arid to semi-arid regions of Northwest China. Based on the local IRNF (i.e., 450 mm irrigation and 340 kg ha−1 N fertilization), reduced irrigation and N fertilization management scenarios were proposed considering eleven irrigation depth reduction cases and ten N fertilization reduction cases in three hydrological years (wet, normal, and dry). The integrated responses of spring wheat yield, water and N productivity, and ecosystem service value (ESV) to various IRNFs were quantified and assessed. The results showed that the local IRNF obtained higher yields and positive ESVs, but was also produced higher greenhouse gas (GHG) emissions, N losses, and water consumption, thus resulting in lower water and N productivity and higher negative ESVs. Among the negative ESVs, GHG emission value accounted for the largest proportion of the total negative ESV (75–80 %), followed by water consumption and fertilizer loss values. Compared with the local IRNF, the scenarios with 210 mm irrigation and 240 kg ha–1 N fertilization in wet years, 240 mm irrigation and 200 kg ha–1 N fertilization in normal years, and 300 mm irrigation and 200 kg ha–1 N fertilization in dry years could not only reduce negative ESVs, improve water and N productivity, and save water and fertilizer resources, but also maintain acceptable yields and positive ESVs. These recommendations reduced the total negative ESV by 4.8–7.7 %, increased water and N productivity by 4.0–8.9 % and 44–69 %, and saved irrigation water and N fertilizer resources by 33.3–53.3 % and 29.4–41.2 % in three hydrological years in relation to the local IRNF, respectively. This study indicates that the framework is a reliable tool for achieving farmland RFE trade-offs and generating appropriate IRNFs for different hydrological years in arid to semi-arid regions. Therefore, sustainable development goals in RFE systems may be achieved by optimizing irrigation and fertilization management. [ABSTRACT FROM AUTHOR]

• Long-term changes in the water cycle of an arid irrigation district were analyzed. • The major drivers of surface and subsurface hydrological processes were identified. • Approximately 60% of the variation in ET resulted from climate variability. • Human activities induced over 70% changes in subsurface hydrological processes. Climate variability and human activities are the two major driving forces of changes in the hydrological cycle. However, how these two factors separately influence the water cycle in arid irrigation districts with shallow groundwater tables is still unknown. This study aimed to investigate the long-term changes in the water cycle and then quantify the individual contributions of climate variability and human activities to the changes in the water cycle in a large irrigation district. The Hetao Irrigation District (HID), located in the upper Yellow River Basin in Northwest China, was selected as the case study area, and an agro-hydrological model (SWAT-AG), which has powerful capabilities to model complex agro-hydrological processes, was employed as the simulation tool. The results showed that from 2000 to 2018, evapotranspiration (ET) of growing season in the HID remained relatively stable, but there were significant decreases in evaporation and dramatic increases in transpiration. For the subsurface hydrological processes, deep percolation and capillary rise of growing season both showed a decreasing trend, while groundwater drainage showed an increasing trend. The water exchange between the atmosphere layer and the root zone (i.e., ET, including evaporation and transpiration) was more significantly dominated by climatic conditions. In contrast, the subsurface hydrological processes were mainly affected by human activities, e.g., irrigation management, canal seepage, farmland area and cropping pattern. Climate variability contributed to approximately 60% of the changes in ET, whereas human activities introduced over 70% of the changes in deep percolation, capillary rise, and groundwater drainage, respectively. This study provides valuable insights into the impacts of climate variability and human activities on the changes in the water cycle and enhancements of water management practices in arid irrigation districts with shallow groundwater tables. [ABSTRACT FROM AUTHOR]

Color printing based on stacked-films has attracted much attention due to its advantage in fabrication. It is still an open question regarding how to achieve full colors in flexible substrate for practical applications with low cost. In this paper, structural colors based on an asymmetric Fabry–Perot (F–P) cavity using two-layer stacked films are proposed, and vivid colors as cyan, magenta, yellow, and black are experimentally achieved in reflection by varying the thickness of the dielectric layer. Meanwhile, the proposed structural colors present a good angular tolerance of up to 45°, especially for TM-polarized incident light. Remarkably, the feasibility of this device fabricated on a flexible substrate is also experimentally investigated, wherein the reflective color is almost unchanged even the radius of curvature reaches up to 4 mm. Therefore, the device we proposed here can make significant contributions to various applications for color printing, flexible display, wearable electronic equipment, and other related fields with low cost. • Structural color using two-layer stacked films is proposed and demonstrated. • Vivid colors as cyan, magenta, yellow, and black are experimentally achieved. • The fabricated flexible structural color shows an ultra-wide bending tolerance. [ABSTRACT FROM AUTHOR]

A silicon-based light source using simple manufacturing process and having excellent luminous efficiency is significantly desired for the development of optoelectronic integrated circuits. In this paper, an integrated poly-silicon avalanche mode light-emitting-device (poly-SiAMLED) is fabricated using a complementary metal oxide semiconductor (CMOS) process. It utilizes the poly-silicon p-n junctions in avalanche breakdown to achieve illumination and employs the carrier injection technology to achieve about 2.9 × 10−7 external quantum efficiency and about 2.2 × 10−8 power conversion efficiency. Moreover, it is easy to fabricate because the process is compatible with the existing integrated circuit process. The proposed device can be used as one of the components of the optoelectronic interface in optoelectronic integrated circuits. • The light-emitting wavelength range of 400~1000 nm is in good agreement with the detection range of silicon-based photodetectors. • The poly-SiAMLED can serve as good electro-optical interfaces in standard silicon-CMOS integrated circuitry. [ABSTRACT FROM AUTHOR]

Quantifying surface and subsurface water dynamics is essential to design and manage furrow irrigation systems. Many furrow irrigation models estimate infiltration using empirical functions without considering the variable ponding depth and the initial soil moisture. Other models, such as the detail coupled models, which describe subsurface flow with the 2D Richards equation, are complex and difficult to apply in practical use. In this paper, we propose a modified furrow irrigation model (MFIM) that couples the approximate furrow infiltration model with the zero-inertia model. The finite difference method and an iterative procedure were used to couple computations of surface flow and infiltration. The influence of time resolution on simulating results was also examined. Results showed that the simulated water advance of the MFIM agreed reasonably well with that of the detail coupled model. More accurate simulation results were obtained by using smaller time step size. The proposed model has shown high computational efficiency. The MFIM may be an effective alternative tool for furrow irrigation design and management. [ABSTRACT FROM AUTHOR]

Hydrological processes in hilly watersheds are significantly affected by variations in elevation; however, the hydrological functions of different vertical vegetation belts, have rarely been reported. The distributed hydrological model WEP-L (Water and Energy transfer Process in Large river basins) was applied to analyse vertical variations in the hydrological processes of Qingshui River basin (QRB), Wutai Mountain (altitude: 3058 m a.s.l.), China. The results show that the highest ratio of evapotranspiration to precipitation occurs at 1800 m a.s.l. Below 1800 m, evapotranspiration is mainly controlled by precipitation, and in regions above1800 m it is controlled by energy. The runoff coefficients for different vertical vegetation belts may be ranked as follows: farmland > grassland > subalpine meadow > evergreen coniferous shrub forest > deciduous broad-leaved forest. Grassland is the largest runoff production area, contributing approximately 39.10% to the annual water yield of the QRB. The runoff from forested land decreased to a greater extent than the grassland runoff. Increasing forest cover may increase evapotranspiration and reduce runoff. These results are important, not only for further understanding of the hydrological mechanisms in this basin, but also for implementing the sustainable management of water resources and ecosystems in other mountainous regions. [ABSTRACT FROM AUTHOR]

The enclosure and ungrazing practices for grassland management result in accumulation of plant litter on soil surface thus affecting the available soil water and nutrients for plant production. We experimentally investigated the effects of litter on soil properties and plant growth in a prolonged enclosure grassland of Loess Plateau, China. Three different litter manipulations were conducted including removal of all litter, an untreated in-situ control with original litter levels, and a double litter treatment. Litter treatment experiments demonstrated that plant litter affected the superficial soil water. Soil water content in plots with in-situ or double litter is generally higher than that with litter removal. The depletion of soil water up to five days post rainfall is fastest in litter removal plots for the top soil, but no evident difference for the deep ones. Different litter treatments have no significant impact on soil total carbon, nitrogen as well as carbon/nitrogen ratio for consecutive two years experiments. Both above- and below-ground biomasses in plots of litter removal were less than those in the plots of in-situ and double litter treatment. Litter affects plant production mainly through the mechanical barrier regulating root zone soil moisture. Therefore, prolonged litter manipulation experiments are desirable to understand the long-term response of plant growth on litter from nutrient aspect. [ABSTRACT FROM AUTHOR]

Under long-term agricultural water saving strategy implemented in the Yellow River basin (YRB), this study analyzed long-term regional groundwater responses and their ecological impacts in an arid irrigation district (Hetao) in the upper YRB. The Mann-Kendall trend test was adopted to examine the trends of the monitoring data of climatic-anthropogenic factors and groundwater depth-salinity, as well as the modeling and remote-sensing results of natural vegetation growth. Results indicated significant decreasing net water diversion while increasing drainage since agricultural water saving, which is a major cause of groundwater reduction instead of climatic factors. This reduction was further confirmed with significant increasing groundwater depth (GWD) trends found in about 90 out of the total 224 monitoring wells across Hetao during 1970–2015. An overall salt accumulation was recognized for Hetao, but groundwater salinity only significantly changed in a few areas with insignificant trends found for more than 70 out of the total 114 monitoring wells during 1995–2015. Meanwhile, significant large-scale decreasing trends were detected for both simulated natural vegetation biomass and remote-sensing derived vegetation index, and wetland loss problem was also found. Particularly, relatively strong similarities were found among the spatial distributions of significant increasing GWD, decreasing vegetation biomass and index, and losing wetlands. This further suggested that the reduction might have caused negative ecological impacts. Overall, the results provided important information regarding long-term regional groundwater responses and their ecological impacts under agricultural water saving, which is significant for agricultural water management for arid irrigation districts. • Long-term groundwater response to water saving was analyzed in an arid region. • Impact on natural vegetations was analyzed by modelling and remote-sensing methods. • Groundwater showed significant depth increase but insignificant salinity change. • Natural vegetation biomass and index showed significant decreasing trends. • Increased GWD and decreased vegetation biomass and index showed strong relations. [ABSTRACT FROM AUTHOR]

• The combined algorithm can extract crop planted structure in the YRB. • Spring wheat planted area decreased over 2001–2020, other food crops were opposite. • Water-saving measures and other factors jointly affect the crop planted structure. Accurate extraction of crop planting structure is the fundamental for estimating regional crop yield and crop water consumption in the Yellow River Basin (YRB). However, the planted area of the main food crops in the YRB in recent 20 years is still unclear. Therefore, the MODIS image data was used to extract the growing area of the main food crops (winter wheat, summer maize, spring wheat and spring maize) in the YRB over 2001–2020 by the combination of the differential algorithm, spectral mutation algorithm and threshold method. The results revealed that the combined method could be used to track the planted area of the main food crop in the YRB, with R 2 and RMSE values ranged from 0.51 to 0.82 and 11.01 to 68.92 × 103 hm2, respectively. The planted area of winter wheat and summer maize in the down-stream irrigation district accounted for 74.7% and 86.7% of the total in the YRB, respectively. Inner Mongolia and Ningxia autonomous regions are the main producing areas for spring wheat and spring maize, accounting for 73.8% and 83.5% of the total in the YRB, respectively. The planted area of winter wheat, summer maize and spring maize had an increasing trend with the rate of 1.440 × 104 hm2 per year, 2.375 × 104 hm2 per year and 2.257 × 104 hm2 per year over 2001–2020. Whereas, the planted area of spring wheat had a decreasing trend with the rate of −2.019 × 104 hm2 per year. Implementation of water-saving irrigation measures, variations of diverted water from the Yellow River, local policies improvement and agricultural market might be the main driving forces for the changes of the planted area for food crops. The results can provide a fundamental agricultural information dataset for further study of regional crop water consumption in the YRB. [ABSTRACT FROM AUTHOR]

B U (2) u b In addition, Eq. (4) was described as: HT ht , while the " I NGWP i " should be should be revised as " I net GWP i " The correct equations [i.e., Eq. (1) and Eq. (4)] are shown as follow: 1 HT ht Graph 4 HT ht Graph The original article has been corrected. [Extracted from the article]

• Enhanced hydrological model (SWAT-AG) is proposed based on SWAT framework. • Close interactions of soil water, groundwater and plant growth are well described. • Hydrological processes in watershed with shallow aquifer are reasonably simulated. • SWAT-AG improves the model performance in agro-watershed compared with SWAT. This article introduces the SWAT-AG (a modified SWAT for agro-hydrological modeling) as an enhanced hydrological model for simulating the hydrological processes in agricultural watershed with shallow water tables. The model is developed based on the framework of the SWAT with significant improvements on describing the interactions of the vadose zone water, groundwater, salt and plant growth. The main features of the SWAT-AG include that it can simulate the close interactions of soil water and shallow groundwater with considering the capillary rise effects; it provides functions to simulate the soil salt movement and salt-stress on plant growth; and it incorporates a balance-based module on a sub-basin scale for shallow aquifer with involving canal seepage and ditch drainage calculation. Model testing and application were conducted in Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, northwest China. The comparison between simulated and observed data showed that the SWAT-AG performed well and obviously better than the original SWAT in simulating the soil water and salt dynamics, groundwater depth fluctuations, and plant growth and water consumption. The results showed that the NSE averagely increased from −17.57 to 0.57 and from 0.71 to 0.79 for soil water storage and leaf area index, respectively, in typical croplands and natural patches. In addition, the effects of shallow groundwater in sustaining the agro-ecosystems were reasonably revealed with the spatial analysis of evapotranspiration, capillary rise and salt accumulation. The test case proved that the proposed SWAT-AG could efficiently enhance the functionality and practicality of hydrological models for agricultural watersheds with shallow groundwater. [ABSTRACT FROM AUTHOR]

In this study, we developed a comprehensive three-dimensional vehicle-track coupled dynamics model considering the traction drive system and axle box bearing. In this model, dynamic interactions between the axle box bearing and other components, such as the wheelset and bogie frame, are considered based on a detailed analysis of the structural properties and working mechanism of the axle box bearing. A few complicated dynamic excitations, such as the time-varying mesh stiffness of gears, time-varying stiffness of bearing, bearing gaps and track irregularities, are considered. Then, the dynamic responses of the vehicle-track system are demonstrated via numerical simulations based on the established dynamics model. The results indicate that the traction drive system and track irregularities can significantly influence the dynamic interactions of the axle box bearing. The necessity of considering the excitation caused by gear meshing and track irregularities when assessing the dynamic performance of the axle box bearing is demonstrated. [ABSTRACT FROM AUTHOR]

Highlights • A conceptual soil hydrological model considering under field-capacity redistribution (CSHMUR) is developed. • The CSHMUR-EPIC model can effectively simulate AWP by considering upward flows and the subfield-capacity deep percolation. • Some optimized irrigation amount can be determined with the CSHMUR-EPIC model. Abstract Agricultural water productivity (AWP) model is an essential tool for irrigation water management that is highly dependent on soil water processes. Soil hydrological models based on numeric solution to the Richards' equation are time-consuming and difficult to measure, and models based on soil water balance approach are favored especially for crop water simulation because of the less parameters requirement and higher operational efficiency. In most of the soil water balance models such as Williams-Ritchie water balance model, AquaCrop model and Hydrobal model, the under field-capacity redistribution (the redistribution during the period of soil water content below the field-capacity) is omitted and this treatment does not adequately simulate AWP for arid and semi-arid areas with deep groundwater. In these areas, AWP is the ratio between crop yield achieved and the sum of actual evapotranspiration and deep percolation at field scale. Since no more water supply for crop growth except for low frequency irrigation and tiny amount of precipitation, high evapotranspiration will aggravate an upward flow that can enhance transpiration and thus benefit crop growth while deep percolation not available for crop is sustainably accumulated to a considerable volume in under field-capacity redistribution process. To take into consideration the beneficial effects of upward flow on crop growth and the considerable under field-capacity deep percolation loss, a conceptual soil hydrological model considering under field-capacity redistribution (CSHMUR) is developed and coupled with the EPIC crop growth model. In CSHMUR model, soil water redistribution is characterized by two sequential water flows: downward flows affected by the gradient of gravitational potential and upward flows affected by the gradient of matric potential. These two flows are mainly used to simulate deep percolation occurring in redistribution processes and upward flows resulting from matric potential, respectively. The CSHMUR-EPIC model is calibrated and validated with field data for a typical arid area of northwestern China, and it is then applied for the simulation of seven irrigation scenarios. The study highlights that the upward flows aggravated by drought conditions and the under field-capacity deep percolation are remarkable enough and should not be neglected in the AWP estimation for arid and semi-arid areas with deep groundwater. The developed CSHMUR-EPIC model can effectively simulate upward flows and the under field-capacity deep percolation, and thus soil water content (SWC) both in lower and upper soil profiles, actual evapotranspiration and crop growth, resulting in an precise estimation of AWP. As upward flows and the under field-capacity deep percolation vary with irrigation schedule, the model is also helpful in exploring various irrigation schedule to obtain a sustainable agricultural water resources management. [ABSTRACT FROM AUTHOR]

Highlights • HYDRUS-dualKc model was extended to be used in the regional scale. • Model was validated using experimental data and remote sensing ET. • Hydrological complexities caused by fragmented land covers were discussed. • New insights were provided for agro-hydrological modelling. Abstract Hydrological effects caused by fragmented land cover types in human-dominated agro-ecosystems are poorly understood. In this study, based on visual interpreted high-resolution land cover map, an agro-hydrological model (HYDRUS-dualKc) was used in a distributed manner to investigate the hydrological complexities caused by fragmented land cover types and shallow groundwater. An irrigation system located in the upper Yellow River basin was chosen as a case study area, where field observations were conducted in 2012 and 2013. Combined effects of vegetation, soil, irrigation and groundwater were considered. Simulations of soil moisture and soil salinity fitted well with field observations; evapotranspiration (ET a) was also comparable with remote sensing data. Results showed that the growing season ET a varied from 162 to 567 mm among the different vegetation covers with the values for crop fields usually higher than those for natural lands. The soil evaporation was obviously larger in natural land and the natural vegetation growth was seriously stressed. Through lateral groundwater exchange, the cropland functioned as a stable groundwater recharge zone while the natural land functioned as a discharge zone during the growing season. As a result, 21% of the total water diverted to Jiyuan migrated to natural lands through groundwater due to field percolation and canal seepage, along with 50–75% of the total salt introduced. The fragmented land covers and complex hydrological processes bring many challenges to remote sensing and model simulation. Future land planning and water resources management should consider the hydrological effects caused by the fragmented land cover types and the associated management strategies. [ABSTRACT FROM AUTHOR]

Highlights • Distributed modeling of agro-hydrological processes was conducted in MOIS. • Spatial distribution of ET a , crop yield and deep percolation was analyzed. • Irrigation water use efficiency was systematically evaluated in MOIS. • Regional irrigation water budget was obtained and discussed for entire MOIS. • Suitable water-saving amount and improved irrigation strategies were proposed. Abstract Water use conflicts between agriculture and ecosystem have become a more severe and acute problem in the Heihe River basin (HRB). Excessive irrigation water use in the middle oasis of the HRB has caused gradual deterioration of water quality and eco-environment both in middle and lower HRB. The urgent issue is to make a quantitative analysis and an improvement of irrigation water use in middle oasis. In this paper, distributed agro-hydrological modeling was conducted to access the irrigation water use and potential water-saving in the major irrigation system of middle HRB (MOIS), using the GIS-based SWAP-EPIC model. The modeling work was based on the abundant data from field experiments, remote sensing, surveys and statistics, and previous eco-hydrological studies. The reliability of the distributed simulation was evaluated using the remote sensing data of actual evapotranspiration (ET a). Then, spatial distribution of irrigation water depth, ET a , deep percolation and crop yield and the related impact factors were systematically analyzed in MOIS. Results indicated that only 53% of total applied water was efficiently used through ET a , whereas deep percolation loss and canal conveyance loss accounted for 22% and 25% of the total applied water, respectively. The beneficial water use fraction was still low in MOIS, averaging only 0.70 on field scale and 0.52 on district scale. Water-saving analysis predicted that 15% of irrigation amount could be saved efficiently, with especial emphasis on the rational water allocation and distribution. In addition, our results related to agro-hydrological processes could provide very valuable information for improving the existing watershed hydrological modeling in the HRB. [ABSTRACT FROM AUTHOR]

Highlights • A new model system (named AHC) was proposed for agro-ecosystem simulation. • AHC is suitable for both salinity and nitrogen issues and other various conditions. • AHC provides mature functions to efficiently handle the parameter calibration. • AHC is well tested using a salinity case and a nitrogen case as exemplifications. Abstract This article introduces the AHC model as a new tool for modeling and assessing the agroecosystem processes. The AHC, as a one-dimensional numerical physical model, simulates the soil water and salt/nitrogen dynamics, heat transport, and crop growth and yield in various soil-crop environments. The key features of the AHC include that it provides the optional function for simulating the fate of salt or nitrogen; it has an efficient global method for sensitivity analysis and parameter estimation; and it is useful in a wide range of field conditions, especially for those in northern China. A menu-driven program is developed as a user-friendly interface for efficient data manipulation. This paper primarily describes the main structures and algorithms of the AHC and presents its field applicability. Model testing and application was conducted with two cases: (1) a salinity case with maize growing in salt-affected fields under arid and shallow groundwater environments (Hetao, upper Yellow River basin, northwest China); and (2) a nitrogen case with a wheat-maize rotation system in the semihumid monsoon region (Tai'an, North China Plain). Good agreement was obtained between the simulated and observed data, including the soil water contents, salt/nitrogen contents, and crop growth indicators. The soil water and salt/nitrogen dynamics, crop growth processes, and their complex interactive effects were also well interpreted using the AHC. Rational simulation proves the good applicability of the AHC for practical field use. [ABSTRACT FROM AUTHOR]

Highlights • Long-term water saving irrigation and groundwater decline reduced regional ET. • Reduced water diversion caused soil water deficit over the crop growth period. • Contribution of shallow groundwater to ET increased by ∼10% in past 15 years. Abstract Evapotranspiration (ET) is an important component of the water budget process and is characterized by complex spatiotemporal changes, especially in irrigated agricultural areas. The impact of various hydrological processes and human activities on ET is still a meaty theme to study and investigate. A typical agricultural irrigation district with shallow groundwater and arid climate conditions was selected as the case study area in this work. The impact of the supplied irrigation water, shallow groundwater, crop planting pattern, and weather conditions on regional ET was determined after the regional ET was estimated by a Surface Energy Balance Algorithm of Land (SEBAL) model with Moderate Resolution Imaging Spectroratiometer (MODIS) data. The results show that the regional ET in Hetao kept declining in the past 15 years. The positive correlation between the water input (water diversion and precipitation) and ET indicated that reduced water diversion controls the declining ET , also causing the drop of groundwater level. Due to capillary forces and root uptake, the shallow groundwater tended to move upward to support the crop water consumption because the soil suffered from a water deficit. Furthermore, we quantified the contribution of shallow groundwater to regional ET and found that the water supplied from shallow groundwater increased from 5% to 15% during the period of water–saving irrigation. However, the long–term decrease of irrigation water supply and groundwater level caused a soil water deficit over the crop growth period, and the variation of crop planting pattern reduced ET as well. Therefore, groundwater plays an important role in sustainable agricultural development in arid and semiarid areas and the contribution of shallow groundwater to regional water consumption cannot be neglected. [ABSTRACT FROM AUTHOR]

Biochar is proposed as a soil amendment to improve soil physical-chemical properties and crop productivity. However, the effect of biochar on crop yield is not consistent and the mechanisms affecting plant growth are still not well-understood. In this paper, field experiments were carried out to investigate the impact of biochar addition on soil properties, water and fertilizer productivity of tomato in semi-arid area of Inner Mongolia, China. The tested biochar was made from maize straw by slow pyrolysis. Four biochar treatments were conducted including addition of 10, 20, 40 and 60 t ha −1 and no biochar as a control. Addition of biochar reduced the bulk density and increased the porosity of soil. Electrical conductivity of soil increased with increasing biochar application rate. Soil pH was not affected by addition of biochar in one growing season. Yield, crop water productivity and partial factor productivity for fertilizer were nonlinearly (quadratic) proportional to application rate of biochar. Highest water and fertilizer productivity obtained from the 40 t ha −1 biochar treatment. Comprehensive analysis of biochar impact on yield, water and nutrient productivity, and cost-benefit for the grower indicate that addition of approximate 30 t ha −1 is an appropriate rate for tomato production in the study area. This suggestion is based on the relatively short term effect and local market conditions. A prolonged experiment is desirable to understand the long term response of soil and crop to biochar addition. [ABSTRACT FROM AUTHOR]

Agricultural water productivity (WP) is an important indicator to evaluate the implementation of agricultural water saving in arid regions. However, the role of groundwater capillary rise to crop water use and WP is unclear at the regional scale, as the soil texture, irrigation amount, planting pattern and groundwater depth is various for different fields. Based on the calibrated Agricultural Water Productivity Management for Shallow Groundwater (AWPM-SG) model, a five-year regional WP and water budgets assessment was performed. The results showed that the groundwater contribution to crop evapotranspiration (ET) would be up to 65% with a groundwater depth of 1.0–1.5 m, but the agricultural productivity would be relatively low resulting from a waterlogged root zone. Additionally, deep groundwater could result in a reduced WP due to less capillary rise, while WP would be 2.02 and 1.98 kg/m 3 with groundwater depth of 2.5–3.0 m and 3.0–4.5 m under irrigation amount of 100–300 mm. Furthermore, limited irrigation can enhance the contribution of groundwater to WP and irrigation water productivity (IWP), which is significant with groundwater depth increasing. While the average IWP were 5.83, 3.62, 2.54 and 1.77 kg/m 3 , respectively for irrigation amount of 100–300, 300–500, 500–700 and 700–900 mm and the average IWP decreased from 4.79 m to 3.18 kg/m 3 with groundwater depth increasing 0.5–1.0 m to 3.0–4.5 m. However, irrigation effective utilization ( C ieu ) was affected by groundwater depth weakly with irrigation water increasing. Furthermore, the optimal groundwater depth of 2.5–3.0 m was obtained by the impact of groundwater on irrigation water productivity (IWP) and C ieu . Thus at the regional scale, the spatial distribution of groundwater levels needs to be considered for making irrigation decisions. [ABSTRACT FROM AUTHOR]

Soil salinization, severe NO 3 --N leaching and low water-fertilizer use efficiency are constraints to sustainable maize production in the upper Yellow River basin (YRB) of Northwest China. Agro-hydrological models have been proven to be a promising decision tool for water and fertilizer management of farmland. In this paper, the AHC (Agro-Hydrological & Chemical and Crop Systems Simulator) model was calibrated and validated by measured soil water, salt, nitrogen (N) and crop growth data and used for scenario analysis to search for the appropriate irrigation and N fertilization strategies for drip-irrigated saline maize farmland. The scenarios were designed with different soil matric potential thresholds (SMPT) for irrigation, different saline degrees (i.e., slightly and moderately saline soils), and with or without additional salt leaching (ASL) in different hydrological years (wet, normal and dry). The results indicated that increasing SMPT and ASL increased the frequency and total amount of irrigation, thus favoring soil salt leaching. NO 3 --N was leached out of the root zone soil as SMPT exceeded –20 kPa, especially for the cases with ASL. For the case of –20 kPa SMPT, compared with the irrigation scenario without ASL, the irrigation scenario with ASL could significantly increase maize yield and water use efficiency (WUE) in moderately saline farmland. However, for the case of –15 kPa SMPT, the irrigation scenario with ASL caused a significant decrease in WUE for both saline farmlands. Maize yield increased as the N application rate increased from 150 kg ha–1 to 250 kg ha–1 and remained stable as the N application rate continuously increased, resulting in high NO 3 --N leaching and low partial factor productivity of N fertilizer (PFP n). Comprehensively considering crop yield, WUE, PFP n , soil desalting and environmental impacts, in wet and normal years, the appropriate irrigation and N fertilization strategy is irrigation under –20 kPa SMPT and a 250 kg ha–1 N application rate without ASL for slightly saline maize farmland and with ASL for moderately saline maize farmland, respectively. In dry years, the appropriate irrigation and N fertilization strategy is irrigation without ASL under –15 kPa SMPT and a 250 kg ha–1 N application rate for both slightly and moderately saline maize farmlands in the study and relevant areas. • Increasing additional salt leaching favored soil desalting and maize production. • Excessive high soil matric potential thresholds caused severe NO3--N leaching. • Irrigation practices were optimized for two salinized soils in three hydrological years. • Proper nitrogen input rate was determined for food-resource-environmental trade-offs. [ABSTRACT FROM AUTHOR]

Oasis areas of arid inland river basins in northwest China have been facing intensified water use conflicts between agricultural sector and eco-environmental systems since 1990s. The reduction of river water allocation to oasis has resulted in the undesirable declines of groundwater levels (GWLs) with the increase in irrigated area and groundwater pumping. Improving water management and restoring GWLs become a great concern for those areas. In this study, the middle oasis of Heihe River basin (HRB) was selected as the representative case for such an endeavor. A three-dimensional groundwater flow model was established for the Zhangye basin, a sub-basin of HRB to obtain a better understanding of groundwater dynamics in middle oasis, particularly for investigating the effects of agricultural water use. A major advantage of this model is that the spatial and temporal recharge from irrigation has been described in details with considering the result obtained by an ago-hydrological model (SWAP-EPIC) simulation. The model was well calibrated and validated over the period of 1991–2010. Simulation of GWLs matched well with the observed 20-year GWLs in the 50 wells. Then, spatiotemporal groundwater dynamics and groundwater budget were quantitatively analyzed for the Zhangye basin during 1991–2010. In particular, the modeling results revealed three different changing trends of GWLs based on the analysis of groundwater dynamics and budget for four representative zones. Results indicated that negative balance of groundwater was mainly caused by over exploitation of groundwater for irrigation, resulting in a GWL decline of 9 cm a −1 in average and even 2 m decline in some years at local areas. The area with critical groundwater depth (e.g. <5 m) has reduced about 30% in 2010 as compared to that in 1991. Finally, recommendations on how to restore GWLs were proposed with emphasis on irrigation water and land use adjustment and groundwater pumping control. Our results are expected to provide implications for recovering the groundwater status in oasis areas of inland river basins in arid northwest China. [ABSTRACT FROM AUTHOR]

Water scarcity and salt stress are two main limitations for agricultural production. Groundwater evapotranspiration (ET g ) with upward salt movement plays an important role in crop water use and water productivity in arid regions, and it can compensate the impact of deficit irrigation on crop production. Thus, comprehensive impacts of shallow groundwater and deficit irrigation on crop water use results in an improvement of irrigation water productivity (IWP). However, it is difficult to quantify the effects of groundwater and deficit irrigation on IWP. In this study, we built an IWP evaluation model coupled with a water and salt balance model and a crop yield estimation model. As a valuable tool of IWP simulation, the calibrated model was used to investigate the coupling response of sunflower IWP to irrigation water depths (IWDs), groundwater table depth (GTDs) and groundwater salinities (GSs). A total of 210 scenarios were run in which five irrigation water depths (IWDs) and seven groundwater table depths (GTDs) and six groundwater salinities (GSs) were used. Results indicate that increasing GS clearly increases the negative effect on a crop's actual evapotranspiration (ET a ) as salt accumulation in root zone. When GS is low (0.5–1 g/L), increasing GTD produces more positive effect than negative effect. In regard to relatively high GS (2–5 g/L), the negative effect of shallow-saline groundwater reaches a maximum at 2 m GTD. Additionally, the salt concentration in the root zone maximizes its value at 2.0 m GTD. In most cases, increasing GTD and GS reduces the benefits of irrigation water and IWP. The IWP increases with decreasing irrigation water. Overall, in arid regions, capillary rise of shallow groundwater can compensate for the lack of irrigation water and improve IWP. By improving irrigation schedules and taking advantages of shallow saline groundwater, we can obtain higher IWP. [ABSTRACT FROM AUTHOR]

Due to water scarcity, water saving practices (WSPs) are being implemented in the irrigation districts of the upper Yellow River basin, causing a series of consequences, e.g. the reduction of field irrigation amount and groundwater depth (GWD) increase. The impacts of irrigation water reduction and GWD increase in canal systems with heterogeneous land covers is complex and remains unclear, thus the need to be elucidated to efficiently promote WSPs. Based on the two-year field observations in 2012 and 2013 and former studies, the HYDRUS-dualKc model, which has been well calibrated and validated in a typical canal system in Hetao, was used to predict the changes in transpiration, evaporation and salt accumulation considering scenarios with various GWDs and irrigation strategies. Results showed that under present irrigation scheduling, plant transpiration of maize, watermelon, tamarisk and sunflower had an initial slight increase, then reached a peak value, and finally decreased in the two years with GWD increase, while soil evaporation and salt accumulation both declined continuously. Based on integration results from the three crops and the natural vegetation simulation scenarios, an optimum GWD of between 1.7–2.3 m for the crop fields and 1.4–2.0 m for the natural land was recommended. With optimum GWD, 15%–30% of water diversion from the Yellow River during the growing season can be saved each year. When considering the irrigation strategies, salt accumulation increased and crop transpiration declined with irrigation reduction, yet the impact on soil evaporation was limited. It also showed that only sunflower had the potential to reduce irrigation amount (about 20%). Future water saving should pay more attention to the water delivery process and the optimization of irrigation during the non-growing season. An additional irrigation to watermelon during its development stage and a pre-season irrigation to tamarisk can largely improve their growth, and the recommended irrigation depths were 100 mm and 250 mm, respectively. These results can be reference criterion for the further implementation of WSPs. [ABSTRACT FROM AUTHOR]

Improving the efficiency of water consumption and water productivity is the key approach to satisfy sustainable water resource supply and food demand. As effective measures, water saving practices are implemented in arid and semi-arid regions. For areas with shallow groundwater, water used for irrigation is not entirely consumptively used. The majority of irrigation water infiltrations below the root zone are stored in shallow groundwater. This can be reused as groundwater based evapotranspiration (ET g ) at the regional scale. Thus, actual regional efficiency of water consumption (REWC) based on all water within the hydrological system is greater than based on consumptive use only. Accurately evaluating the response of REWC and regional water productivity (RWP) to water saving practices is essential due to the complexity of the hydrological system. In this study, regional ET g and regional evapotranspiration (ET) of the past 20 years were reproduced in a typical arid irrigation district with shallow groundwater based on the water balance method. Furthermore, REWC and RWP were estimated to investigate the impact of water saving practices to regional water use. Simulation results show that groundwater is a significant water source of regional ET in arid regions with a shallow aquifer and contributes more than 16% of regional ET for the irrigation district. Water saving practice implementation enhances the contribution of groundwater to ET. After water saving practices implementation, annual REWC and RWP have been improved by 0.07 and 0.1 kg/m 3 , respectively. Furthermore, negative correlation between REWC and I + P (the total water supply including rainfall and irrigation water diversion) and positive correlation between RWP and REWC demonstrate that water saving practices can reduce the non-beneficial water losses by evaporation and enhance productivity by a lower groundwater table. Overall, shallow groundwater plays an important role to enhance REWC and RWP and the contribution of groundwater to regional water use needs to be considered as part of a reasonable water saving strategy towards a sustainable agricultural system. [ABSTRACT FROM AUTHOR]

Relatively low-lying zones of natural vegetation within irrigated areas are not only carriers of biodiversity but also dry drainage areas of excess water and salts applied to nearby croplands. It is thus useful to have a correct understanding of the soil water-salt dynamics and plant water use for keeping the sustainability of those natural areas. The HYDRUS-dualKc model that couples the HYDRUS-1D model with the FAO-56 dualKc approach was extended to simulate the eco-hydrological processes in natural patches of Hetao Irrigation District (Hetao), upper Yellow River basin. Field experiments were conducted in a tamarisk (Tamarix chinensis Lour.) dominated area during the growing seasons of 2012 and 2013. The model was calibrated and validated using the two-year experimental data, and applied to analyze the water and salt dynamics and the tamarisk water consumption for the present situation. Then, various groundwater depth (i.e. the depth from groundwater surface to water table, GWD) scenarios were simulated while considering the fluctuating and constant regimes of GWD changes, as well as variations of the rooting depth. Results indicated that this natural land functioned efficiently as a drainage area for subsurface flow and excess salt from surrounding croplands. However, the present GWDs were too shallow leading to high soil evaporation and severe salt stress. The soil evaporation accounted for 50% of the total evapotranspiration ( ET a ) while root zone salt storage increased about 50% during growing seasons. On the basis of scenario analysis, an optimum groundwater depth of 140–200 cm with smaller fluctuation was suggested for the growing seasons of natural patches. In addition, tamarisk growth could be largely improved if the roots can grow deeper with water table decline in the future. We demonstrated that monitoring and modeling could be used to support the development of water management strategies in Hetao aimed at conserving water while sustaining local ecosystems. [ABSTRACT FROM AUTHOR]

• The SHAW model was modified with considering changes in soil hydrothermal properties. • Hydrothermal properties in frost heave soil can be evaluated with altered bulk density. • The modified model can accurately capture soil water-heat-salt dynamics. • The modified model can be used for water management in obviously frost heave areas. Traditional agricultural or eco-hydrological models usually ignore soil deformation and its impact on hydrothermal properties when simulating soil water, heat, and salt transport under freeze–thaw conditions. As a result, significant errors may occur when these models are used in areas with considerable frost heave, such as arid areas with shallow groundwater tables. In this study, the simultaneous heat and water model (SHAW model) was modified with considering soil deformation and its impact on hydrothermal properties during the freeze–thaw period. The modified SHAW model was then validated using the experimental data collected at the Hetao Irrigation District, in the upper Yellow River basin. Comparison between the simulated and observed data showed that the modified SHAW model performed well and obviously better than the original SHAW model in simulating the soil water, heat, and salt transport. As compared with the SHAW model, the modified SHAW model averagely decreased the RMSE value by 37.5% and 23% for soil water content and soil temperature, respectively. The modified model can be used as a decision tool for water management and salinity control of farmland in cold areas with significant frost heave. [ABSTRACT FROM AUTHOR]

Unreasonable irrigation water saving and salinity control practices (IWS-SCPs) have resulted in a shallow groundwater table, severe soil salinization and low water use efficiency in the upper Yellow River basin (YRB), Northwest China. In our study, a framework was developed by coupling the agro-hydrological model, i.e., AHC (Agro-Hydrological & chemical and Crop systems simulator) with a decision-making method, i.e., VIKOR (VlseKriterijuska Optimizacija I Komoromisno Resenje), and then a comprehensive evaluation index was calculated to assess the IWS-SCPs for maize and sunflower in the upper YRB. The AHC model was calibrated and validated with two years of field measured data, and then it was used to perform the simulations of agro-hydrological processes corresponding to the designed scenarios considering the irrigation depth and groundwater table depth (GWD) under the conditions of different hydrological years and degrees of soil salinization. The simulated crop yield, soil salinity variation, and crop water productivity were used as the evaluation indicators to search for appropriate IWS-SCPs of the target crops. The results showed that the recommended IWS-SCPs for maize were those with GWDs between 2.1 − 2.3 m and irrigation depths approximately 10% lower for non-saline soils in wet years and 10% higher than the present irrigation for slightly and moderately saline soils in normal and dry years. Whereas, the IWS-SCPs with GWD between 1.5 − 2.2 m and an irrigation depth of approximately 10 − 30% lower than the present situation could be recommended for sunflower in wet years and normal years regardless of saline soils and in dry years of non-saline soils. The developed framework and the obtained results are expected to provide a decision tool and implications for improving irrigation efficiency and salinity control in the arid upper YRB as well as other areas with similar climate conditions and shallow groundwater. • Coupling AHC model and VIKOR method provided a decision tool for water saving and salinity control. • The framework could be used as a decision tool for irrigation management and salinity control. • The appropriate groundwater depth for maize is 0.6 m deeper than that for sunflower. • Approximately 10%− 30% of irrigation water can be saved for sunflower in the upper Yellow River basin. [ABSTRACT FROM AUTHOR]

[Display omitted] • A process simulation-based framework was developed for RFE trade-off. • Farmland water–carbon–nitrogen processes and ecosystem service values were quantified. • The negative ESV of local practices accounts for approximately 10% of the positive ESV. • The optimal FINS for spring wheat farmland was obtained by using the framework. • Approximately 53 % irrigation water and 32 % N fertilizer can be saved for wheat in the upper Yellow River Basin. Improving food production and resource utilization efficiency and mitigating the functional degradation of agroecosystems are major challenges worldwide. However, few studies have reconciled the conflicts among resources, food, and ecology (RFE) in agricultural production. This study develops a water–carbon–nitrogen process simulation-based framework for RFE trade-off by coupling the agro-hydrological model, i.e., AHC (Agro-Hydrological & chemical and Crop systems simulator) with the ecosystem service value (ESV) assessment method and decision-making method, i.e., VIKOR (VlseKriterijuska Optimizacija I Komoromisno Resenje). The framework is capable of (1) quantifying farmland ESVs; (2) reconciling conflicts among resource utilization, food production and ecosystem development by optimizing farmland irrigation and nitrogen (N) application strategies (FINS). The framework was used to analyze the FINS, and then to obtain the compromise decision focusing on a lower negative ESV and the maximizing group utility decision focusing on a higher yield and positive ESV for spring wheat farmland in Northwest China. Results indicated that under the local FINS, i.e., 450 mm irrigation and 340 kg ha−1 N application, the total ESV generated by spring wheat farmland per season was [4.76, 4.87] × 104 CNY ha−1. Among these ESVs, every 1 CNY ha−1 positive ESV generation was accompanied by approximately 0.11 CNY ha−1 negative ESV. Compared with the local FINS, the compromise decision, i.e., the FINS with 210 mm irrigation and 200 kg ha−1N application, significantly reduced negative ESV but caused slight losses in yield and positive ESV, while the maximizing group utility decision, i.e., the FINS with 210 mm irrigation and 260 kg ha−1N application, increased yield and positive ESV but resulted in a small negative ESV mitigation. Moreover, both FINSs could save irrigation water and N fertilizer resources, and improve water and N productivity to various degrees. This framework has excellent performance in reconciling conflicts among RFE systems and generating coordinated solutions and has potential to achieve sustainable development goals in agricultural RFE systems. [ABSTRACT FROM AUTHOR]

Appropriate plant density is essential for crop production in rainfed areas. However, it is quite difficult to obtain the optimal plant density under plastic film mulch in different hydrological years through field experiments due to its limited treatments, and time and labor costs. Therefore, mathematical models are generally used for searching the optimal alternatives. In this paper, the Agro–Hydrological & chemical and Crop systems simulator (AHC) was adopted to model soil water dynamics, rainfed maize growth, and yield under plastic film mulch and various plant density conditions in Northeast China for different hydrological years. The results showed that the AHC model can simulate rainfed maize water use and growth under plastic film mulch and various plant density conditions, i.e., 60,000 (D1), 67,500 (D2), 75,000 (D3), 82,5000 (D4) and 90,000 plants ha−1 (D5). The average maize yields of all treatments in the severely dry (SD), moderately dry (MD), normal (N), moderately wet (MW), and severely wet (SW) years were 11440.3, 13685.4, 13821.5, 14704.8, and 14014.3 kg ha–1, respectively. Compared with non–mulch, plastic film mulch increased the maize basal crop coefficient by 0.08–0.11 and decreased the soil evaporation coefficient by 0.26–0.32, from SD and SW years, respectively. Thus, plastic film mulch augmented maize transpiration by 46.2–76.8 mm, while reduced evaporation by 163.5–186.8 mm across the simulated years. Ultimately, the maize yield under plastic film mulch was 5.9–17.4% higher than that without mulch. From D1 to D5 treatments, the decrease of soil evaporation coefficient was within 0.02 under plastic film mulch and was over 0.05 without mulch. Under plastic film mulch, the relations between plant density and net profit could be well described by the parabolic curves, and the recommended optimal plant densities of maize in the study area were 91, 101, 101, 105, and 101 thousand plants ha–1 in the SD, MS, N, MW, and SW years, respectively. Our findings provide management implications for maize cultivation in the rainfed areas of Northeast China. • The highest maize yield was observed in the moderately wet year. • Plastic film mulch increased maize optimal plant density. • Higher increase in maize yield was obtained in higher plant density with film mulch. • The highest optimal maize plant density was obtained in moderately wet year. [ABSTRACT FROM AUTHOR]

Agricultural water conservation is important in arid and semi-arid areas where water resources are deficient and agriculture irrigation accounts for a high proportion of water use. Thus, efficient deficit irrigation methods, which the supplied water is less than potential evapotranspiration have been developed. In semi-arid areas, groundwater can contribute to crop’s water consumption but less is known about impact of deficit irrigation on the contribution. We conducted, therefore, a two-year field experiments with deficit flood irrigation for maize in an arid district with shallow groundwater in China. Four irrigation practices were tested with water applied at approximately 82.5%, 75%, 67.5% and 60% of the 540 mm potential evapotranspiration (PET) in 2014 and the 500 mm in 2013 over the crop growing season. We found that the upward flux between soil water and groundwater varied from 5 mm with input water of 488 mm to 60 mm with input water of 353 mm. The yield of maize decreased by only 15% from 10.0 to 8.5 t/ha for the WS treatment (irrigated at 60% of PET) compared with the WH treatment (irrigated at 82.5% of PET) due to more groundwater contribution to the crop growing with less irrigation. As a consequence, the water use efficiency (WUE), defined as quotient of the yield and plant evapotranspiration was not significantly different among different irrigation treatments. However, the irrigation water use efficiency (IWUE), which is the yield per unit of water applied, increased significantly with the decreasing amount of water applied due to the contribution of upward fluxes. The implication is that deficit irrigation enhances the contribution of groundwater to crop water use and will not produce an obvious reduction of yield within a stable shallow groundwater level. [ABSTRACT FROM AUTHOR]

Numerical simulation is an efficient approach for investigating the salt and water movement through soil profile and predicting of crop response to soil water deficit and salinity. In this study a coupled model that describes the soil water and solute transport by means of HYDRUS-1D model and crop growth process by means of growth module of EPIC was used. The model was calibrated and validated against field data, collected during two growing seasons in field plots of winter wheat irrigated with four levels of irrigation amount and water salinity of 5 ds m −1 at the Fengqiu State Key Agro-Ecological Experimental Station, in North China Plain. The model was also used to evaluate the salinity stress on evapotranspiration (ET), grain yield and water use efficiency (WUE) and long-term use of saline water on grain yield and salt accumulation. Visual inspection and the obtained statistical parameters values showed that good agreement between measured and simulated data of soil water content, salt concentration, ET and grain yield. Evapotranspiration values of winter wheat were reduced under salinity stress conditions, mainly by reducing crop transpiration. The grain yields were reduced due to salinity stress, but the change trend of WUE was associated with precipitation amount. Increasing per saline water irrigation amount is an effective way to reduce the WUE decline rate under the low rainfall growing season as like that in simulation year. The average of ten years grain yield confirmed that a yield potential exceeding 86% could be maintained by saline water with 5 ds m −1 when per irrigation volume more than 0.8 E, E denotes evaporation from an uncovered, 20 cm diameter pan positioned 0–5 cm above the crop canopy. There has a slight salt build-up after ten years simulation, and the quantity of salt accumulation decreased with the increase of irrigation volume. Thus, more attention should be paid to the sustainability of irrigated agriculture with low irrigation volume when using saline water irrigation. On the whole, field observations combined with the coupled model could be used to evaluate different agricultural managements on grain yield and soil salinity. [ABSTRACT FROM AUTHOR]

Hetao Irrigation District (HID) is characterized by less rainfall and high evaporative, but it is a main grain production region in China. Increasing water use efficiency is an appropriate way to fulfill the sustainable agriculture development because the allocated water for HID will be reduced in the future. In this study six irrigation treatments with irrigation amounts being the 20, 40, 60, 80, 100, and 120% of crop water requirement (ET c ) were carried out for maize crop ( Zea mays L.) in the HID under mulch-dripped irrigation condition in 2013 and 2014 years. Soil water and electrical conductivity, plant growth factors, harvest factors and yield were investigated, and crop actual evapotranspiration (ET cact ), water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated. Results showed that soil water and salt mainly varied in the upper 60 cm soil layer. At harvest, salt accumulation was found in the upper soil layer and the highest salt accumulation was in the least irrigation treatment. Growth factors and harvest factors were reduced significantly (P < 0.05) for irrigation depth of less than 40%ETc compared to 80–120%ETc, but they were not significantly (P > 0.05) different from 80 to 120%ETc. The highest grain yield were found at 100%ETc, then yield decreased with irrigation depth decreasing due to the reductions of ear size and 100-grain weight. ET cact ranged from 200 to 430 mm in the two seasons, and linearly increased with the irrigation depth increasing. The highest WUE was found at 60%ETc, while IWUE was decreasing with irrigation depth increasing. Fully considering maize yield, water use efficiency, soil salt balance and water resources availability of Yellow river, full irrigation with 100%ETc is recommended with the objective of the highest yield when water resources can satisfy water demand of irrigation and economic development, while water deficit of 20–30% is recommended with the objective of getting the highest WUE and little yield loss (4–8%) under mulched drip irrigation in HID. [ABSTRACT FROM AUTHOR]

• An enhanced soil-water-nitrogen-crop coupling model (named ORYZA-N) was proposed. • Soil temperature, solute transport, and soil C&N modules were newly developed. • ORYZA-N was tested and applied in N simulation for the JRC with two years of data. • Nitrogen (N) parameter values were specific and recommended for cold region rice. • N dynamics, balance, and use efficiency were quantitatively analyzed with ORYZA-N. This article introduces ORYZA-N as an enhanced soil-water-nitrogen-plant coupling model to simulate agro-hydrological processes and crop growth in rice paddy fields. The model is developed based on the ORYZA2000 (a widely-used rice model with an open-source code) with significant improvements in modeling the nitrogen (N) fate and related processes. Three new modules were designed in ORYZA-N for simulating N transport and transformation processes, including a soil temperature module, a solute module for ammonium nitrogen (NH 4 -N) and nitrate nitrogen (NO 3 -N) transport, and a soil nitrogen module for organic carbon and nitrogen turnover. The mechanics of root water uptake and soil water drainage also were improved to better describe the soil water movement and its effects on root N uptake. The ORYZA-N model was then tested and applied in simulating the fate of water and nitrogen and crop growth for Japonica rice in cold regions (JRC) in the Northeast China Plain (NECP), for a two-year field experiment (during 2018 and 2019). Model evaluation shows a good performance was achieved with the ORYZA-N model. The simulated values for pond water depths, N uptake and partitions, and various organ productions were in particularly good agreement with the observed values (R2 > 0.68, NSE > 0.50); meanwhile, the simulated fluctuation trends for NH 4 -N and NO 3 -N concentrations were reasonable as well. The calibrated/obtained nitrogen-related parameters for JRC were obviously different from those for rice varieties in warmer regions, which can efficiently complement the parameter dataset for rice modeling in cold regions. Finally, the N dynamics, balance, and utilization efficiency were interpreted and assessed for the two experimental years, and possible improvement measures for N use for JRC were proposed. The total aboveground N content was about 160 kg N ha−1 at harvest, while the N content in the stems, green leaves, dead leaves, and panicles accounted for about 15, 5, 25, and 55% of the total aboveground N content, respectively. Overall, rational simulation proved the enhanced functionality and practicality of ORYZA-N for modeling the N fate and utilization. [ABSTRACT FROM AUTHOR]

Water scarcity has been a crucial issue for sustainable irrigated agriculture in the arid regions. In these regions where conserving water is paramount, optimal allocation and utilization of irrigation water is particularly important. In this study, a process-based regional economic optimization (PBREOP) model was developed for maximizing irrigation water use efficiency and economic benefit of an irrigation system. The PBREOP model is a two-level optimization model with combined use of an agro-hydrological model (SWAP-EPIC). The first level (farm scale) dealt with the optimal distribution of irrigation water and cropping pattern considering various crops and soils in a subsystem, using a non-linear programing technique. The second level (district scale) sought out the optimal strategy for irrigation water allocation among different subsystems using a dynamic programing algorithm. The crop water production functions (CWPFs) were an important component of the first-level objective function. They were derived with the SWAP-EPIC model considering different irrigation alternatives. The model was solved using the decomposition-harmonization method for large systems. The Yingke Irrigation District (YID) in the middle Heihe River basin, Northwest China was used as a case to test the PBREOP model. Nine CWPFs for three major crops and three major soils were firstly derived based on the simulations of different irrigation levels and climate conditions (20 years). Next, the PBREOP model for YID was established with 11 subsystems, and applied to the irrigation water use optimization under five water supply scenarios. Results showed that the total economic benefit in YID could be increased by 15% on average through the optimization of water allocation and cropping pattern with the same water supply amount as that of the current situation. A variation range of the risk was also obtained with considering the impacts of climate uncertainties. Scenario analysis showed that the total irrigation water could be reduced by 23% on average without benefit reduction when compared to the benefit of the present situation. Model test indicated that the proposed PBREOP model can efficiently optimize irrigation water use and cropping pattern on a regional scale. [ABSTRACT FROM AUTHOR]

• An improved SPAC model (named SHAW-SC) is proposed based on modifying SHAW. • New crop module and modifications of ET and solute transport/leaching are included. • Coupled processes of soil heat-water-salt transport and crop growth are well described. • Continuous, dynamic simulation of SPAC was realized on an entire agr-year scale. • Water-salt dynamics and water use are quantitatively analyzed in ASF regions. The soil–plant-atmosphere continuum (SPAC) that is a dynamic, interactive and coupled system is particularly complicated in arid seasonally frozen regions (ASF regions) with the effects of soil freeze–thaw process and salinity. A quantitative understanding of heat-water-salt transport and crop growth in the SPAC over an entire agricultural year (agr-year) is an importance of promoting best practices for water use and crop production. In this paper, an improved coupled SPAC model (SHAW-SC) is presented and applied for continuously simulating the SPAC system of ASF regions over an agr-year. The model is developed based on modifying the SHAW model (version 3.0) and incorporating the EPIC crop growth module. The main new features of the SHAW-SC include extending the model capability for canopy growth and yield formation, improving the description of soil solute transport in the shallow groundwater systems, and providing functions to describe the effects of surface mulching on soil evaporation and salinity stress on crop growth and transpiration. Model testing and application were conducted with two agr-year data at the sunflower experimental field in irrigated areas of the upper Yellow River basin, northwest China (with an arid and cold climate). Simulations of soil water content, temperature, and crop growth indicators fitted well with the observations both in calibration and validation (with NSE > 0.64 and sufficiently small RMSE); meanwhile, simulation of salinity concentration was also satisfactory (NSE: 0.32 and 0.83; RMSE: 1.09 and 2.44 g L−1), despite the complexity of salt transport and the measurement difficulty. In addition, the comparison with previous experimental results also showed the reasonability of modeling results. Then, a comprehensive and quantitative analysis of the SPAC dynamics was conducted over an agr-year, with identifying five characteristic periods (i.e. pre-freezing, soil-freezing, soil-thawing, pre-planting and crop growth periods). Results provided a fuller understanding of the characteristics of water-salt dynamics and balance components, and the related issues of crop stress, water use and salinity control on an entire agr-year scale. Model testing and application proved that the proposed SHAW-SC was an efficient tool to simulate coupled processes of heat-water-salt transport and crop growth for ASF regions, and as well an enhancement of current SPAC models for practical field applications. [ABSTRACT FROM AUTHOR]