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Partitioning of evapotranspiration (ET) into soil evaporation (E) and plant transpiration (T) poses a significant challenge. This study proposed a novel approach that combines eddy covariance, micro-lysimeter, and high-resolution unmanned aerial vehicle (UAV) images within the flux footprint to optimize the canopy and soil resistances of the Shuttleworth-Wallace model (S-W) using a multi-objective optimization scheme. A two-year experiment was conducted at the Yucheng and Luancheng sites to investigate the effectiveness of the proposed method for the summer maize-wheat winter system in the North China Plain. Our results showed that the S-W model with multi-objective optimization by using high-resolution UAV images within the flux footprint significantly improved the estimation accuracy of ET components compared with the traditional one- and two-objective optimization schemes. The estimation of ET, T, and E of our method had an average root mean square error of 0.67 mm day−1, 0.66 mm day−1, and 0.28 mm day−1, respectively. The optimized S-W model using high-resolution UAV data within the flux footprint produced better ET partitioning than that optimized using Moderate Resolution Imaging Spectroradiometer (MODIS) data. We then applied the proposed method to estimate ET and ET components in the North China Plain. This study highlighted the importance of utilizing multi-source data (especially high-resolution UAV images) and multi-objective optimization for accurate ET partitioning.

The application of plant growth-promoting rhizosphere (PGPR) and Gamma-polyglutamic acid (γ-PGA) has a potential role in improving plant tolerance under abiotic stress, while their combined effects remain largely unexplored. This study aimed to evaluate the effects of the joint effects of PGPR and γ-PGA on maize growth and rhizosphere microbial communities under salt stress. A pot experiment consisting of two strain treatments (CK, M10), two γ-PGA treatments (γ0, γ1) and two salt treatments (S1, S2) was performed for this purpose. The results showed that under S1 treatment, the combined application of M10 and γ-PGA could increase plant height, leaf area and dry weight by 11.27%, 36.45% and 8.39% respectively (P

The implementation of current drip irrigation scheduling, which only considers crop water demands (referred to as empirical drip irrigation) during the growth period and uncontrolled leaching during fallow periods, exacerbates issues of soil salinization and water scarcity in the Xinjiang region. In pursuit of more scientifically effective irrigation and leaching methods, this study employed the H2DSWAP model coupled by the HYDRUS-2D and a Soil–Water–Atmosphere–Plant model (SWAP) for scenario experiments. Results showed that prolonged irrigation without drainage (winter-free irrigation) led to an annual upward trend in salt accumulation within the root zone (0–100 cm) through drip irrigation under film mulch. In regions with shallow groundwater levels (≤ 2.0 m), an exclusive focus on crop water requirements and neglecting leaching demands for salts led to a gradual reduction in crop yield, reducing by 86.8 % after 12 years of operation. Conversely, by considering both water and salt stress thresholds during the growth stage for irrigation, optimal crop yields can be maintained. However, salt predominantly accumulated within the 60–100 cm soil layer, inducing recurrent leaching during the growth period due to continual salt migration in this layer. This occurrence resulted in wasted water resources, uneven soil salt distribution, and ultimately diminished crop yields. The simulation findings for diverse winter irrigation scenarios suggested that the salinity content in the deep root zone (60–100 cm) could function as a leaching threshold for determining the necessity of winter irrigation, approximating a value of 11 g kg−1. In comparison to conventional irrigation and drainage practices, the irrigation and drainage coordinated regulation model proposed in this study contributes to salt removal, effectively restraining the waste of water resources caused by frequent winter irrigation.

Soil salinization is one of the main hazards affecting the sustainable development of agriculture in the Hetao Irrigation District (HID) of Inner Mongolia. To grasp the water and salt transport patterns and spatial–temporal distribution characteristics of the HID at the regional scale, the improved Soil and Water Assessment Tool with a salinity module (SWAT-Salt) model was used to establish the distributed water and salt transport model for the watershed in this study. The results demonstrated that the modified model could more accurately represent the process of water and salt changes in the HID. The coefficient of determination (R2) in the simulation of streamflow and discharge salt loading was 0.83 and 0.86, respectively, and the Nash–Sutcliffe efficiency (NSE) was 0.80 and 0.74, respectively. Based on this, different hydrological processes (surface runoff, lateral flow, groundwater, soil seepage) as well as spatial–temporal distribution characteristics of water salinity in groundwater and soil were analyzed in the HID. Differences in groundwater and soil salinity in different land uses and soil types were also compared. Of these, surface runoff and lateral flow salt discharge loading are concentrated in the southwestern portion of the basin, while groundwater salt discharge loading is concentrated in the eastern as well as southwestern portions of the basin. The salt discharge loading from groundwater accounts for about 98.7% of the total salt discharge loading from all hydrological pathways and is the major contributing part of salt discharge from the irrigation area. Soil salinity increases gradually from west to east. Groundwater salinity (2946 mg/L) and soil water electrical conductivity (0.309 dS/m) were minimized in the cropland. Meanwhile, rational allocation of irrigation water can appropriately increase the amount of salt discharge loading. In conclusion, the model could provide a reference for the investigation of soil salinization and water–salt management measures in irrigation areas.

Crop modeling is an effective tool for simulating crop growth under various agricultural water and salinity management practices. However, most crop models fail to describe the root dynamics in response to soil stresses adequately. To address this issue, field experiments were conducted by planting sunflowers in saline soils. Three machine learning (ML) models of random forest (RF), gaussian process regression (GPR), and extreme gradient boosting (XGBoost) were initially introduced for predicting root length density (RLD). Then, by coupling with a crop model SWAP, the soil salt content (SSC), soil water content (SWC), and crop growth indicators of leaf area index (LAI) and dry matter (DM) were simulated. Results show that RF and XGBoost models could predict RLD more accurately than the GPR model, with root mean square error (RMSE) lower than 0.473 cm cm-3. Compared to using a typical cubic polynomial function (CPF) of RLD in the SWAP model, similar SWC and SSC simulation results were obtained based on the ML models. However, for the crop growth simulation, the performances of ML models were significantly better than the CPF. Especially for LAI simulation in the high salinity fields, the relative root mean square error (RRMSE) in the RF model was 0.222–0.282 lower than in the CPF. Moreover, compared to the XGBoost model of RLD, more accurate and stable simulation results of SWC, SSC, and LAI were obtained based on the RF model. These results illustrate that ML models, especially the RF model, can be used to quantify RLD dynamics and improve crop modeling performances.

Intercropping radiation interception model is a promising tool for quantifying solar energy utilization in the intercropping system. However, few models have been proposed that can simulate intercropping radiation interception accurately and with simplicity. This study proposed a new statistical model (DRT model), which enables the simulation of daily radiation distribution by considering the geometric light transmission in the intercropping system. To evaluate model performance, the radiation interception and distribution in two wheat/maize strip intercropping experiments (A and B) were simulated with the DRT model and other two statistical models, including the horizontal homogeneous canopy model (HHC model) and the Gou Fang model (GF model). Experiment A was conducted in different intercropping configurations, while Experiment B was conducted in soils with different salinity levels. In both experiments, the HHC model exhibited the poorest performance (0.120 < RMSE < 0.172), while the DRT model obtained a higher simulation accuracy in the fraction of photosynthetically active radiation (PAR) interception, with RMSE lower by 0.008–0.022 and 0.022–0.125 than the GF and the HHC models, respectively. Especially, the DRT model showed stronger stability than the other two models under soil salinity stress, with R2 higher by 0.129–0.354 and RMSE lower by 0.011–0.094. Moreover, the DRT model demonstrated a relatively ideal simulation of the daily radiation distribution in Experiment A (0.840 < R2 < 0.893, 0.105 < RMSE < 0.140) and Experiment B (0.683 < R2 < 0.772, 0.111 < RMSE < 0.143), especially when the continuous canopy formed during the later crop growth stages. These results indicate the superiority of the DRT model and could improve our understanding of radiation utilization in the intercropping system.

Soil salinization is a pressing issue that needs to be addressed in current agricultural production. In this study, we utilized novel materials, unfunctionalized multi-walled carbon nanotubes (MWCNT) and functionalized multi-walled carbon nanotubes (MWCNT-OH), to explore the effects of soil carbon and nitrogen cycles in saline soil. We set up four treatments, which were exposed to two exposure doses of 1 g/kg and 1 μg/kg and two MWCNT types of functionalized MWCNT-OH and unfunctionalized MWCNT. Our results demonstrate that exposure of saline soil to 1 g/kg functionalized MWCNT-OH significantly increased the soil inorganic nitrogen (p < 0.05), while also promoting the soil microbial biomass. This exposure can also potentially enhance greenhouse gas emissions from saline soil. Moreover, exposure to MWCNTs significantly increased the proportion of Actinobacteria and Proteobacteria, two dominant phyla (p < 0.05), which in turn improved their contribution to the carbon and nitrogen cycling processes within saline soil. High exposure dose treatments (1 g/kg) significantly increased the abundance of functional genes associated with carbon metabolism, carbon fixation, methane metabolism, and nitrogen cycling processes within saline soil. In contrast, low exposure dose treatments (1 μg/kg) had no significant effect on the abundance of functional genes related to nitrogen cycling, but significantly increased the abundance of special functional genes related to carbon cycling. Redundancy analysis revealed that the microbial community composition within saline soil was significantly impacted by the soil total carbon, total nitrogen, and nitrate nitrogen content. Furthermore, it was observed that over 80% of the carbon and nitrogen cycling processes within the saline soil were contributed by the dominant phyla. In summary, our research confirms the potential applicability of MWCNTs within saline soil. Notably, exposure of saline soil to 1 g/kg functionalized MWCNT-OH exhibited the most significant promoting effect on the carbon and nitrogen cycles.

Presently, the effects of crop roots on crop root zone thermal characteristics are poorly understood, and new fertilizers are rarely considered from the perspective of changing crop root zone thermal characteristics. This study explored the effect of applying two new fertilizers, multiwalled carbon nanotubes (MWCNTs) and Bacillus atrophaeus (B. atrophaeus), on the crop root zone thermal characteristics of saline farmland soils through in situ measurements. The results showed that MWCNTs and B. atrophaeus could indirectly affect crop root zone thermal characteristics by changing the crop root growth. Combined application of MWCNTs and B. atrophaeus could promote both to induce positive effects, promote crop root growth, and significantly alleviate the adverse effects of soil salinization. The thermal conductivity and heat capacity of the shallow root zone were reduced due to the presence of crop roots, while the opposite was true in the deep root zone. For example, the thermal conductivity of the 0–5 cm rich root zone in the MWCNT treatment was 0.8174 W m−1 ·K−1, and the thermal conductivity of the poor root zone was 13.42% higher than that of the rich root zone. MWCNTs and B. atrophaeus can also change the spatial distribution of soil moisture, soil salt, and soil particle size characteristics by influencing the root-soil interactions and indirectly affecting crop root zone thermal characteristics. In addition, MWCNTs and B. atrophaeus could directly affect the root zone thermal characteristics by changing the soil properties. The higher the soil salt content was, the more obvious the effect of the MWCNTs and B. atrophaeus on the crop root zone thermal characteristics. The thermal conductivity and heat capacity of the crop root zone were positively correlated with the soil moisture content, soil salt content and soil particle specific surface area and negatively correlated with the soil particle size and the fresh and dry root weights. In summary, MWCNTs and B. atrophaeus significantly affected crop root zone thermal characteristics directly and indirectly and could adjust the temperature of the crop root zone.

Study region: Heidingzi, a typical seasonal freezing agricultural watershed in northeastern China. Study focus: This study’s objectives were to: (1) confirm whether nitrogen source areas and migration paths have changed with the melting of snow and frozen soil; (2) find an effective way to recognize the change points and separate nitrogen export processes to different periods during snowmelt; and (3) identify the source areas, migration paths, and critical influencing factors of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) in river water during these snowmelt periods. New hydrological insights for the region: The nitrogen export process during snowmelt can be divided into two stages according to the relationship between δ18O and nitrogen concentration. Nitrogen concentration had a linear relationship with δ18O during early snowmelt periods, while they varied within a small range during the late stages. Paddy field area proportion (PFP), Rural area proportion (RAP), Average Slope (AS), Slope area proportion 6°). Abundant nitrogen reserves near the river compensated for the negative impact of water shortage on nitrogen yield during early snowmelt periods. Water and nitrogen in rural areas came mainly from snow-scattered areas during early snowmelt periods, and from frozen domestic sewage or refrozen snowmelt in drainage ditches during late snowmelt periods.

Open-channel flow can be easily found in nature and engineering projects, and the channels’ cross-sections are of various shapes. Research on the flow capacity of open channels with different cross-sections can help deepen our understanding of the dependence of open channels’ general characteristics on cross-sectional shapes at a theoretical level. Furthermore, it has potential practical value in engineering projects. Through theoretical analysis, experimental research, and numerical calculation, two conclusions can be drawn in the present article: (1) A general expression for flow capacity was deduced based on viscous fluid theory, and a parameter describing the influence of cross-sectional shapes on flow capacity, CQ, was obtained. The advantage of our method is that the expression can be used to calculate the parameter directly, which varies with general and flow field characteristics. Another advantage is that the parameter can describe general and flow field characteristics in a uniform way. (2) The width-to-wetted perimeter ratio was selected to describe the cross-sectional shapes. The dependence of the parameter, CQ, on cross-sectional shapes can be summarized as follows: In laminar flow, the parameter depends on the width-to-wetted perimeter ratio only. In turbulent flow at a medium or low Reynolds number, the parameter varied with width-to-wetted perimeter ratio and Reynolds number. In turbulent flow at a high Reynolds number, the parameter was independent of the width-to-wetted perimeter ratio.

With the increasing shortage of land resources and people’s attention to the ecological environment, the application of microbial fertilizer with natural soil microorganisms as the main component has attracted increasing attention in saline agriculture. In this study, two salt-tolerant strains, YL07 (Bacillus atrophaeus) and YL10 (Planococcus soli), were isolated from maize (Zea mays L.) rhizosphere soil with a saturated conductivity (ECe) of 6.13 dS/m and pH of 8.32 (Xinjiang, China). The effects of B. atrophaeus WZYH01 (YL07) and Planococcus soli WZYH02 (YL10) on the growth and development of maize (Zea mays L.) under salt stress (ECe = 5.9 dS/m) were further studied. The results showed that compared with uninoculation, inoculation with B. atrophaeus WZYH01 and Planococcus soli WZYH02 significantly improved maize growth performance, biomass yield, and antioxidant levels under salt stress, and the effect of Planococcus soli WZYH02 was more prominent than the effect of B. atrophaeus WZYH01. Moreover, inoculation with B. atrophaeus WZYH01 and Planococcus soli WZYH02 protected maize from salt stress by regulating plant hormone [IAA and abscisic acid (ABA)] levels and increasing nutrient acquisition. In addition, the tested strains were most efficient for maize growth and health, increasing the content of K+ accompanied by an effective decrease in Na+ in maize tissues. The transcription levels of salt tolerance genes (ZMNHX1, ZMNHX2, ZMHKT, ZMWRKY58, and ZMDREB2A) in inoculated maize were also dramatically higher than the transcription levels of the specified salt tolerance genes in uninoculated maize. In conclusion, B. atrophaeus WZYH01 and Planococcus soli WZYH02 can alleviate the harmful effects of salt stress on crop growth, thereby promoting sustainable agricultural development.

The Three Gorges Reservoir region suffers from severe soil erosion that leads to serious soil degradation and eutrophication. Interrill erosion models are commonly used in developing soil erosion control measures. Laboratory simulation experiments were conducted to investigate the relationship between interrill erosion rate and three commonly hydraulic parameters (flow velocity V, shear stress τ and stream power W). The slope gradients ranged from 17.6% to 36.4%, and the rainfall intensities varied from 0.6 to 2.54 mm·min−1.

Submerged vegetation has strong vitality, and the root system is highly developed. Because this vegetation has a good bank-solidifying-and-beautifying effect, it is widely used in ecological river construction. However, the open channel flow field and water-blocking mechanism of submerged vegetation are complicated. It is not convenient to use this kind of original model directly in engineering calculation, but it can be much more convenient if the original model is generalized into a simple model. However, there are not many generalization models, so it is necessary to propose a simple generalization model of the water-blocking effect of submerged vegetation to facilitate engineering calculation. Upon theoretical analysis, numerical calculation and experiment data analysis, the following conclusions are obtained: As the basis of generalization, in order to make up for the deficiency of experimental results, a new numerical simulation model for the flow field of submerged vegetation open channel flow was firstly proposed. For the purpose of this research, a simple generalization model of the water-blocking effect of submerged vegetation was proposed. Finally, two parameters of generalized roughness coefficient and virtual channel elevation were obtained to reflect the water-blocking effect. They can be substituted directly into a planar two-dimensional model in engineering. It achieves the ultimate goal of convenient engineering calculation.

Open-ditch controlled drainage is an important water management measure used to reduce drought and waterlogging stress in many areas in the world. Such measures are essential to promote the crop yield, make full use of rainfall resources, reduce regional drainage discharge (Q) and reduce water environmental pollution. To quantify its effects, an open-ditch controlled drainage and crop yield simulation model was developed in an area located in Northern Huaihe River Plain (NHRP), Anhui Province, China. The model was calibrated and validated. The changes in crop yield and Q were simulated under different main-ditch water-depth control schemes, field ditch layout and outlet weir height control schemes from 1991 to 2021. Compared with the current situation, the change in crop yield caused by the main ditch schemes was significantly higher than that caused by the field ditch schemes. The change in Q caused by the field ditch schemes was greater than that caused by the main ditch schemes, with values of 60% and 0.02%, respectively. Combined control schemes could further increase the crop yield and reduce the Q. The results have practical application value for ensuring good crop yields and reducing farmland drainage in the NHRP and other similar regions.

Understanding salinity and fertilizer interaction is of great importance to improve crop production and fertilizer use efficiency in saline areas. To evaluate the interactive effects of different soil salinity levels and nitrogen (N) applications rates on the sunflower photosynthetic characteristics of N uptake and N use efficiency, a two-year field experiment was conducted in Hetao Irrigation District, China. The experiment consisted of three initial salinity (IS) levels expressed as the electrical conductivity of a saturated soil extract (ECe) (S0: 1.72–2.61 dS/m; S1: 4.73–5.90 dS/m; S2: 6.85–9.04 dS/m) and four N rates (45, 90, 135, and 180 kg/ha), referred as N0–N3, respectively. The results indicated that the net photosynthetic rate (Pn) of sunflowers treated with S0 and S1 levels both had a significant decrease in the bud stage, and then reached their maximum at anthesis. However, during the crop cycle, the Pn at S2 level only had small fluctuations and still remained at a high level (>40 μmol CO2/(m2 s)) at the early mature stage. When increasing IS levels from S0 to S1, the plant N uptake (PNU) under the same N rates were only decreased by less than 10% at maturity, whereas the decline was expanded to 17.2–45.7% from S1 to S2. Additionally, though applying the N2 rate could not increase sunflower PNU at the S0 and S1 levels, its N use efficiency was better than those under N3. Meanwhile, at the S2 level, the application of the N0 rate produced a higher N productive efficiency (NPE) and N uptake efficiency (NUPE) than the other N rates. Therefore, our study proposed recommended rates of N fertilizer (S0 and S1: 135 kg/ha, S2: 45 kg/ha) for sunflowers under different saline conditions.

Controlled drainage by regulating the groundwater level in open ditches is necessary to ensure the normal growth of crops in Northern Huaihe River Plain, China. The groundwater model MODFLOW was calibrated and validated in a representative area, and was then conducted to simulate the groundwater under different main drainage ditch water depth control schemes during the growth period of corn and wheat. Then the scenario with highest water depth (Scenario 20) from 1989 to 2019 was simulated, and the annual cumulative drought and waterlogging intensity (ACDWI) were analyzed in each decade and in different hydrological years. The results showed that the study area was dominated by drought stress. The lowest level of drought stress was achieved under Scenario 20. The frequency of drought gradually decreased from north to south in the study area. Moreover, the ACDWI decreased with increase of precipitation during 1989 to 2019. The results indicated that it was important to store water during the dry season, while it is also necessary to control the drainage in the rainy season to drain excess water on time. The results suggested that the water depth of the main drainage ditch should be regulated by zoning and by season to alleviate crop drought and waterlogging.

To investigate the diversity and structure of soil bacterial and fungal communities in saline soils, soil samples with three increasing salinity levels (S1, S2 and S3) were collected from a maize field in Yanqi, Xinjiang Province, China. The results showed that the K+, Na+, Ca2+ and Mg2+ values in the bulk soil were higher than those in the rhizosphere soil, with significant differences in S2 and S3 (p < 0.05). The enzyme activities of alkaline phosphatase (ALP), invertase, urease and catalase (CAT) were lower in the bulk soil than those in the rhizosphere. Principal coordinate analysis (PCoA) demonstrated that the soil microbial community structure exhibited significant differences between different salinized soils (p < 0.001). Data implied that the fungi were more susceptible to salinity stress than the bacteria based on the Shannon and Chao1 indexes. Mantel tests identified Ca2+, available phosphorus (AP), saturated electrical conductivity (ECe) and available kalium (AK) as the dominant environmental factors correlated with bacterial community structures (p < 0.001); and AP, urease, Ca2+ and ECe as the dominant factors correlated with fungal community structures (p < 0.001). The relative abundances of Firmicutes and Bacteroidetes showed positive correlations with the salinity gradient. Our findings regarding the bacteria having positive correlations with the level of salinization might be a useful biological indicator of microorganisms in saline soils.

Canal lining is commonly used to reduce seepage loss and increase water use efficiency. However, few studies have quantitatively estimated the seepage control effects of different lining materials under different service times. Ponding tests were conducted on the same canal section with four different lining statuses to investigate the canal lining effect on seepage control and its impact factors in arid areas. The cracks and holes in different lining materials were surveyed, and the canal seepage rates under the four test treatments were calculated by monitoring the water level change in the canal. The results show that the cracks in the joints of the two precast concrete slabs and holes in the geomembrane, which are located 0.25 m above the canal bottom on two sides of the canal, are responsible for the increased seepage loss. The new concrete and geomembrane lining combination reduces seepage by 86% compared with no lining, while seepage can be reduced by 68% using the concrete and geomembrane lining combination after three service years, and the amount decreases to 11% by using geomembrane lining with a three year service time. Based on the experiment and literature, a statistical relationship between the seepage reduction and lining service time was established, which provided a possible and easy way to estimate seepage losses from lined canals and improve the estimation accuracy using an empirical formula. Without considering the service time lining effect, the seepage loss is underestimated by 58%, and the canal water use efficiency is overestimated.

The dry drainage system (DDS) is an alternative technique for controlling salinization. To quantify its role in soil salinity control, a five-year field observation from 2007 to 2011 was completed in a 2900 ha experimental plot in Yonglian Experimental Station, Hetao Irrigation District, China. Results showed that the groundwater table depth in the fallow areas quickly responded to the lateral recharge from the surrounding croplands during irrigation events. The groundwater electrical conductivity (GEC) of fallow areas increased from 5 mS·cm−1 to 15 mS·cm−1, whereas the GEC below croplands produced small fluctuations. The analysis of water and salt balance showed that the excess water that moved to fallow was roughly four times that moved by an artificial drainage system and with 7.7 times the corresponding salt. The fallow areas act as a drainage repository to receive excess water and salt from surrounding irrigated croplands. Slight salt accumulation occurred in irrigated croplands and salts accumulated, with an accelerating trend over the final two years. The evaporation capability weakened, partly due to the salt crust in the topsoil, and the decrease in soil permeability in the soil column, which was almost impermeable to water. Using halophytes may be an effective method to remove salts that have accumulated in fallow areas, having great economic and ecological value. A DDS may be effective and sustainable in situations where the fallow areas can sustain an upward capillary flux from planted halophytes.

Monitoring and improving environmental stress in crops is vital for the sustainable development of agriculture and food security. Traditional experimental methods are costly and time-consuming, yet crop growth models focus mainly only on water and nutrient stresses. In this study, a new World Food Studies (WOFOST) model, WOFOST-ES, was developed by the addition of a general environmental stress factor (ES). To calibrate and validate WOFOST-ES, two-year micro-plot experiments and one-year field experiments with sunflower were conducted in the Hetao Irrigation District, China. The results of the micro-plot experiments indicated that the WOFOST model failed to simulate sunflower growth correctly but that the WOFOST-ES model was highly accurate in simulating both yield (R2 = 0.99, root mean square error (RMSE) = 56 kg/ha) and leaf area index (LAI) (R2 = 0.86, RMSE = 0.44). A statistical method for estimating ESs based on the dominant stress factor (salt at our study site) was also proposed as a supplemental tool for WOFOST-ES, and micro-plot and field experiments conducted in 2013 and 2017 both proved acceptable accuracy of the statistical method when using WOFOST-ES. Comparison between ESs and the water and salt stress factors of Feddes-type stress reduction functions indicated that ESs failed to reveal actual environmental stresses during the sunflower seeding stage but did reflect other environmental stresses in addition to water and salt during the bud, flowering, and maturity stages. Although the present WOFOST-ES model proved to be accurate, stable, and practical, future studies should be performed, focusing on the physical separation of ESs, their mechanistic quantification, and their evaluation at small time steps using more observations.

Crop coefficients (Kc) are important for the development of irrigation schedules, but few studies on Kc focus on saline soils. To propose the growth-stage-specific Kc values for sunflowers in saline soils, a two-year micro-plot experiment was conducted in Yichang Experimental Station, Hetao Irrigation District. Four salinity levels including non-salinized (ECe = 3.4–4.1 dS·m–1), low (ECe = 5.5–8.2 dS·m–1), moderate (ECe = 12.1–14.5 dS·m–1), and high (ECe = 18.3–18.5 dS·m–1) levels were arranged in 12 micro-plots. Based on the soil moisture observations, Vensim software was used to establish and develop a physically-based water flow in the soil-plant system (WFSP) model. Observations in 2012 were used to calibrate the WFSP model and acceptable accuracy was obtained, especially for soil moisture simulation below 5 cm (R2 > 0.6). The locally-based Kc values (LKc) of sunflowers in saline soils were presented according to the WFSP calibration results. To be specific, LKc for initial stages (Kc1) could be expressed as a function of soil salinity (R2 = 0.86), while R2 of LKc for rapid growth (Kc2), middle (Kc3), and mature (Kc4) stages were 0.659, 1.156, and 0.324, respectively. The proposed LKc values were also evaluated by observations in 2013 and the R2 for initial, rapid growth, middle, and mature stages were 0.66, 0.68, 0.56 and 0.58, respectively. It is expected that the LKc would be of great value in irrigation management and provide precise water application values for salt-affected regions.

Water and energy processes in frozen soils are important for better understanding hydrologic processes and water resources management in cold regions. To investigate the water and energy balance in seasonally frozen soils, CoupModel combined with the generalized likelihood uncertainty estimation (GLUE) method was used. Simulation work on water and heat processes in frozen soil in northern China during the 2012/2013 winter was conducted. Ensemble simulations through the Monte Carlo sampling method were generated for uncertainty analysis. Behavioral simulations were selected based on combinations of multiple model performance index criteria with respect to simulated soil water and temperature at four depths (5 cm, 15 cm, 25 cm, and 35 cm). Posterior distributions for parameters related to soil hydraulic, radiation processes, and heat transport indicated that uncertainties in both input and model structures could influence model performance in modeling water and heat processes in seasonally frozen soils. Seasonal courses in water and energy partitioning were obvious during the winter. Within the day-cycle, soil evaporation/condensation and energy distributions were well captured and clarified as an important phenomenon in the dynamics of the energy balance system. The combination of the CoupModel simulations with the uncertainty-based calibration method provides a way of understanding the seasonal courses of hydrology and energy processes in cold regions with limited data. Additional measurements may be used to further reduce the uncertainty of regulating factors during the different stages of freezing–thawing.

This research examines the simultaneous retrieval of surface soil moisture and salt concentrations using hyperspectral reflectance data in an arid environment. We conducted laboratory and outdoor field experiments in which we examined three key soil variables: soil moisture, salt and texture (silty loam, clay and silty clay). The soil moisture content models for multiple textures (M_SMC models) were based on selected hyperspectral reflectance data located around 1460, 1900 and 2010 nm and resulted in R2 values higher than 0.933. Meanwhile, the soil salt concentrations were also accurately (R2 > 0.748) modeled (M_SSC models) based on wavebands located at 540, 1740, 2010 and 2350 nm. When the different texture samples were mixed (SL + C + SC models), soil moisture was still accurately retrieved (R2 = 0.937) but the soil salt not as well (R2 = 0.47). After stratifying the samples by retrieved soil moisture levels, the R2 of calibrated M_SSCSMC models for soil salt concentrations improved to 0.951. This two-step method also showed applicability for analyzing soil-salt samples in the field. The M_SSCSMC models resulted in R2 values equal to 0.912 when moisture is lower than 0.15, and R2 values equal to 0.481 when soil moisture is between 0.15 and 0.2.