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In arid and semi-arid regions, rainfall takes on a critical significance to both agricultural and engineering construction activities, and the transport process and driving mechanism of soil water under rainfall conditions are in need of further investigation. To clarify the variations in soil moisture, temperature, and liquid and vapor flux under various rainfall scenarios, the Mu Us Sandy Land was selected as the study region, and a water–vapor–heat transport model was established using the Hydrus-1D software with in situ observed soil and meteorological data. The simulated results were in good agreement with the measured data during both the calibration and validation periods, suggesting that the model was accurate and applicable to the study region. The variations in the selected dry and rainy periods proved the significant effect of rainfall events on soil matric potential, temperature, and driving forces. When rainfall occurred, the hydraulic conductivity for liquid water rose by three to five orders of magnitude, driving the liquid water flow downward. In contrast, the vapor flux played a vital role in soil water movement, accounting for about 15% of the total water flux in the shallow layer when the soil was dry, while it became non-significant during rainy periods due to the reduction in hydraulic conductivity for vapor and the temperature gradient. These results clarified the mechanisms of soil liquid water and vapor movement in arid areas, which could provide scientific support for future studies on vegetation restoration and ecosystem sustainability in ecologically fragile areas. [ABSTRACT FROM AUTHOR]

Exploring the components of evapotranspiration (ET) is essential but challenging because of the difficulties in ET partitioning. This study aims to improve the accuracy in partitioning ET under farmland and apple orchards by the hydrological model HYDRUS-1D constrained with isotopes, and further identify the effects of land use change on soil water balance (SWB). In particular, the long-term average SWB was first decoupled by combining multiple isotopes (δ2H, δ18O, and δ3H), and then used to constrain HYDRUS-1D to improve model performance. With the isotope-based partitioned SWB, some hydrological model parameters difficult to be obtained experimentally were inversely optimized. Consequently, the performance of HYDRUS-1D in ET partitioning was greatly improved. Specifically, with the isotope method as a reference, the HYDRUS-1D with optimized parameters had errors of 20%±2.1, 4%±2.0, and 6%±0.8 for evaporation (E), transpiration (T), and ratio of transpiration to evapotranspiration (T/ET), which were much smaller than those from the model with default parameter (171%±34.5, 57%±5.8, and 58%±5.8). The apple orchards increased T by decreasing other SWB components. The framework of optimizing hydrological model by isotope-based SWB decoupling is promising in improving model accuracy, and the partitioned SWB components can be used to promote our understanding of ecohydrological processes. [Display omitted] • Combination of multiple isotopes for SWB partitioning is effective. • HYDRUS-1D was constrained by isotope-based water balance decoupling. • Optimized hydrological model is promising in accurately partitioning ET. • Other SWB components decreased to satisfy the increased transpiration. [ABSTRACT FROM AUTHOR]

Water resources are becoming increasingly scarce, and improving water productivity (WP) is crucial to the development of dryland farming on the Chinese Loess Plateau. Fertilization and cropping systems are important measures to improve WP, and tracking their long-term effects on water balance components is helpful for water use and risk management. In this study, the calibrated and validated Hydrus-1D model was used to simulate the dynamic changes of water balance components under four different fertilization treatments (without fertilization, CK; 120 kg ha−1 N and 26.2 kg ha−1 P, NP; 75 t ha−1 manure, M; 120 kg ha−1 N, 26.2 kg ha−1 P, and 75 t ha−1 manure, NPM) and three cropping systems (winter wheat monoculture, WWM; spring maize monoculture, SMM; wheat-wheat-maize rotation, WMR) from 1985 to 2020, with differences in crop yields and WP analyzed. Compared to CK, NPM, NP, and M treatments increased the average yield by 201.9%, 161.7%, and 130.6%; increased the inter-annual yield variations by 191.2%, 149.3%, and 144%; increased transpiration by 80.4%, 58.7%, and 37.5%; reduced evaporation by 18.8%, 5.6%, and 2.3%; decreased deep percolation in the 3 m profile by 44.7%, 60.7%, and 41.1%; and increased WP by 174.5%, 130.8%, and 110.2%, respectively. Values under the three cropping systems occurred in the order SMM>WWM>WMR for normalized crop yield, SMM>WMR>WWM for transpiration, WWM>WMR>SMM for evaporation, and SMM>WWM>WMR for annual average WP. Our results suggest fertilization significantly increases crop yield and WP, with NPM fertilization treatment having the highest WP, but results in large inter-annual yield variations in dryland farming. Spring maize monoculture had the highest yield and WP in this study, while the rotation system balanced the water use differences. These results provide useful information for formulating water management practices for regional dryland farming. • Fertilization increased crop yield and yield variability in dryland farming due to the variations in precipitation. • Maize monoculture had the highest yield and WP among three cropping systems. • The rotation system balanced water use by crop growing season differences and uneven precipitation distribution. • ET a significantly increased over time due to the increasing climate evaporation demand. [ABSTRACT FROM AUTHOR]

California is increasingly experiencing drought conditions that restrict irrigation deliveries to perennial nut crops such as almonds and pistachios. During drought, poorer quality groundwater is often used to maintain these crops, but this use often results in secondary salinization that requires skilled management. Process-based models can help improve management guidelines under these challenging circumstances. The main objective of this work was to assess seasonal soil salinity and root water uptake as a function of irrigation water salinity and annual rain amounts. The manuscript presents a comparison of three-year experimental and numerically simulated root zone salinities in and below the root zone of almond and pistachio drip-irrigated orchards at multiple locations in the San Joaquin Valley (SJV), California, with different meteorological characteristics. The HYDRUS-1D numerical model was calibrated and validated using field measurements of soil water contents and soil solute bulk electrical conductivities at four root zone depths and measured soil hydraulic conductivities. The remaining soil hydraulic parameters were estimated inversely. Observations and simulations showed that the effects of rain on root zone salinity were higher in fields with initially low salinities than in fields with high salinities. The maximum reduction in simulated root water uptake (7%) occurred in response to initially high soil salinity conditions and saline irrigation water. The minimum reduction in simulated water uptake (2.5%) occurred in response to initially low soil salinity conditions and a wet rain year. Simulated water uptake reductions and leaching fractions varied at early and late times of the growing season, depending on irrigation water salinity. Root water uptake reduction was highly correlated with the cumulative effects of using saline waters in prior years, more than salt leaching during a particular season, even when rain was sufficient to leach salts during a wet year. [ABSTRACT FROM AUTHOR]

Extensive sand layers are widely distributed over the impact plain of the Yellow River, particularly for Hetao Irrigation Areas in Inner Mongolia of western China. The migration of water and salt under the soil sand layer has posed a great influence on soil water utilization, soil salinization control, and crop growth. In this study, a numerical model of soil water movement was proposed to investigate the field evapotranspiration, crop water consumption, water supply, and deep soil water leakage in the sand layer using the data of field monitoring and laboratory experiments during the growth period of spring maize. Taking the cultivated land of the typical sand layer in the Hetao Irrigation Area as the research object and planting crop as spring corn, two gradients of buried depth were selected: S1 (40-95 cm) and S2 (60-110 cm) of the sand layer in the soils. Three irrigation levels were also set to carry out the field experiment, and then to compare with BWI without sand layer, including W1 (252.5 mm), W2 (315.85 mm), and W3 (378.75 mm). A HYDRUS-1D model was selected to simulate the field evapotranspiration during the growth period of spring maize, deep seepage of soil water, groundwater recharge, and root water absorption. In addition, the temporary water deficit and water productivity were calculated during the whole growth period. Water use in the cultivated land with sand layer was then compared with that without sand layer. The results showed that the soil evaporation loss between grains decreased, whereas, the leaf transpiration water increased, with the increase of buried depth of the sand layer. Specifically, the soil layer above the sand layer was thicker, the soil water storage was larger, the surface soil moisture content was higher, and the soil negative pressure was lower when the buried depth of the sand layer was larger. As such, the deep soil water was less replenished upward through the capillary action. At the same time, there was less leakage to the deep layer below the sand layer after irrigation. Furthermore, the upstream water supply of maize in the field without sand layer increased by 57.01% and 118.53%, respectively, compared with the treatment of shallow (40-95 cm), and deep sand layer (60-110 cm). More importantly, the deep-water leakage of soil under the treatment of sand layer was the least, when the irrigation amount was 315.85mm. Correspondingly, the water absorption of maize roots decreased with the increase in the buried depth of the sand layer, where the largest was found without sand layer during the growth period. Specifically, the shallow (40-95 cm) and deep sand layer (60-110 cm) treatment were 55.51% and 61.31% of evapotranspiration, respectively, whereas, the treatment without sand layer was 66.69%. The irrigation system can be determined for spring maize in the sand layer, according to the sand layer distribution and local conditions. Particularly, the recommended irrigation quota of spring corn can be 315.85 mm during the growth period, when the sand layer was similar to the S1WI and S2WI treatment. The recommendation can be attributed to avoiding the leakage loss of irrigation water in the deep soil water of the farmland with the sand layer. The findings can also provide important theoretical guidance for the formulation of a farmland irrigation system with the sand layer in the Hetao Irrigation District. [ABSTRACT FROM AUTHOR]

To explore the impact of land- use change on the long- term soil water balance in Northern China's Loess Plateau, we used the H ydrus-1 D model to simulate the soil water dynamics at depths of 0--4 m under the scenario of arable land-alfalfa land-natural grassland located in the Liudaogou watershed. The evolution characteristics of hydro logical variables including soil water storage, deep seepage and evapotranspiration were quantified from 1981 to 2050. The results showed that soil water fluctuated with rainfall levels during arable land periods, with 88% of the annual precipitation consumed through evapotranspiration, and 11 % was lost to deep seepage. The first stage of soil water change during the alfalfa land period was 1--6 years after plantation, during this period, evapotranspiration accoun ted for 108 % of the annual rainfall, leaving the soil water in a negative balance. And the soil water storage of 0--4 m decreased at a rate of 52 mm/a. The second stage was 7- 13 years after plantation, almost all rainfall was consumed by evapotranspiration. Eight years after alfalfa land transitioned into natural grassland, annual evapotranspiration de creased by 31 %, and soil water storage gradually recharged at 45 mm/ a. Subsequently, 92% of the annual rainfall was used for evapotranspiration, with the remaining 8% was lost to deep seepage. The soil water remained in a rela tively stable state. These indicated that the soil water balance modes varied under different vegetation types. Planting vegetation with high-water-consumption could cause negative balance of soil water and led to serious soil desiccation, which then had a negative effect on soil water supply. However, the formed dry soil layer could be completely re stored by changing the vegetation type. [ABSTRACT FROM AUTHOR]

The Loess Plateau is the main rain-fed agricultural area in western China, and water shortage is a critical factor restricting vegetation establishment and growth in this region. Under the influence of global climate change in recent years, significant changes have taken place in climate characteristics of the Loess Plateau, which will have a far-reaching impact on evaporation and transpiration under different vegetation conditions. Therefore, there is needed to make a in-depth research on the response of evaporation and transpiration to climate change for typical afforestation tree species, which has remarkable theoretical and practical significance in providing useful indications for tree species selection, water use efficiency improvement and ecosystem restoration. In order to evaluate the effects and mechanism of climate change on evaporation and transpiration of typical artificial afforestation tree species, a field experiment was carried out in the growing season of 2015－ 2016 (April 15th-October15th) at Nanxiaohegou basin (35°41′-35°44′N,107°30′-107°37′E), a typical small basin in gully region of the Loess Plateau selected by the Yellow River Water Conservancy Commission of China. In three sample plots of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis, soil physical parameters of three soil depth (0-40 cm, >40-100 and >100-200 cm) and the distribution of root density were measured, and soil moisture content, leaf area index, evaporation, precipitation and meteorology data were observed during the study period, from which simulation models of transpiration and evaporation in three experimental plots were established using Hydrus-1D software. The uncertainty of models parameters were analyzed through the Morris method, and the results showed that parameters of pore size distribution (40–100 cm) (n2), saturated water content (40-100cm) (θs2), field water capacity (θf), optimum threshold for root water absorption (h1), lower threshold for root water absorption (h2), soil water potential for permanent wilting (h3), extinction coefficient (μ), and parameter of vegetation interception model (a) had a great influence on transpiration, and the parameters related to the physiological characteristics of vegetation (h1, h2, h3, μ, and a) were the important reasons for the differences in transpiration of three tree species. The measured soil moisture content and evaporation data from 2015 were used to calibrate the model, and the data from 2016 were used to validate the model. Nash-suttcliffe efficiency coefficients were all above 0.700. The calibrated models were used to simulate evaporation and transpiration process under different presupposition scenarios derived from related research on climate characteristics of the study area, and the results showed that: 1) The effects of climate change in the future and different hydrological years on Robinia pseudopodia transpiration were greater than that in evaporation, while the opposite was true for Platycladus orientalis and Pinus tabuliformis. 2) Under all climate scenarios, the amount of transpiration for above tree species were distributed in 128.8-282.6, 99.3-200.3 and 140.5-220.5 mm, respectively, while the amount of evaporation were distributed in 94.6-135.4, 116.5-187.3 and 123.8-212.5 mm, respectively, and the transpiration and evaporation were both shown in the following aspect: the wet year > the normal year > the dry year. 3) As for transpiration, the response degree of three tree species to the climate characteristics of the future and different hydrological years was: Robinia pseudoacacia > Platycladus orientalis > Pinus tabuliformis, when it came to the evaporation, it was just the opposite. 4) In the same period of the future climate scenarios, the amount of transpiration in Robinia pseudoacacia plot was the largest among all tree species in wet and normal year, while in the dry year, the tree species with largest amount of transpiration was Pinus tabulaeformis. 5) The influence of precipitation on the transpiration and evaporation in growing season was stronger than that of temperature, and regression analysis indicated that the precipitation in growing season had a very significant linear function (P<0.01) with transpiration and evaporation for all 3 tree species. This study may provide valuable information for rational management of artificial afforestation tree species and restoration of the local ecological environment. [ABSTRACT FROM AUTHOR]

[Objective]This paper aimed to evaluate the water retention capacity of stratified soils. [Method] Indoor saturated drainage experiments were conducted in three types of layered soil columns (two layers, four layers and eight layers of sandy loam and sand, respectively). Compared with homogeneous sandy loam and sand columns, the soil water changes from 0 to 120 hours in different time interval were observed, the final soil moisture content profiles was measured, and a HYDRUS-1 D model was employed to imitate the drainage process for different soil columns. [Result]The combination of sand layer with sandy loam layer enhanced the soil water retention, and the increase of fine and coarse grained layers was supportive to soil water content. Furthermore, laboratory observation and software simulation confirmed that comparing soil moisture profiles, water drainage was mainly from sand layers more than sandy loam layers, which indicated that the capillary hairier between coarse grained layer underlying fine grained layer positively impacts water retention capacity for layer soil columns. [Conclusion]The results would be meaningful for water resource exploitation, polluted soil remediation and landfill contaminants prevention in arid and semi-arid areas. [ABSTRACT FROM AUTHOR]

• Hydrus-1D model provides an alternative approach for estimating deep percolation in a flood-irrigated field. • Penman-Monteith formula is an important parameter in coupled Hydrus-1D and CROPWAT. • Hydrus-1D in combination with CROPWAT can optimum amount of water required to meet the crop water demand in the field. • CROPWAT model can improve irrigation scheduling in a flood-irrigated field under flood irrigation conditions in dry climates. Demand for irrigation water has been steadily increasing in arid regions where intensification of crop production is supported by flood-irrigation. An assessment of irrigation performance, water productivity, and irrigation schedules is critical to water conservation in dry climates. In this study, we conducted a field experiment to compare soil water balance in a flood-irrigated wheat-maize rotation system during the growing season of 2015–2016. We then modeled the soil water balance and improved irrigation strategies by coupling Hydrus-1D with the CROPWAT model, and using evapotranspiration calculated from climatic data. The calibrated Hydrus-1D model was used to simulate the temporal and spatial variation of evapotranspiration and deep percolation based on measured soil water distribution of soil profiles in the unsaturated zone. Results showed that using soil hydraulic parameters from inversion modeling can simulate soil water flow in multi-layer soil during a crop growing season. Simulation results indicated that about 36.6 and 40.6% (478.6 and 680.1 mm) of total water input in 2015 and 2016, respectively, was consumed by evapotranspiration. Furthermore, simulated deep percolation amounted for approximately 32.3 and 42.9% (403.9 and 696.6 mm) of the total amount of irrigation water in 2015 and 2016, respectively. These results indicated that only a small proportion of irrigation water was used by crops for transpiration. In addition, irrigation performance indicators such as relative water supply, relative irrigation supply, depleted fraction, and overall consumed ratio values indicated poor performance of irrigation practices in the study area. Particularly, crop yields did not increase with increases in irrigation water in flood-irrigated fields during the last ten years. Results of the CROPWAT model indicated that combinations of a fixed irrigation depth and timing, of 40 mm every 10 days, and 50 mm every 10 days were reasonable for wheat and maize, respectively, given the sandy soil in the study area. The improved irrigation strategies will limit water irrigation loss to 20% without significant effects on crop yields. This study provides an alternative approach for estimating deep percolation and crop water requirements supporting management efforts in water conservation in dry climates. [ABSTRACT FROM AUTHOR]

Highlights • Soil salt dynamics were dominated by seasonal precipitation and hydrological year. • Soil salt accumulated during the growth period, and leaching out under abundant rainfall during growth period of maize. • Soil salt accumulated in dry and normal years and leached in wet years, especially in the extremely wet year. • The effect of irrigation times of brackish water was greater than that of soil texture on soil salt accumulation. • It is feasible that using brackish water for long-term irrigation in the lowland area of the North China Plain. Abstract In the North China Plain (NCP), increased water shortages and food yield increase present serious threats to the sustainability of cultivated lands. Irrigation by brackish or saline water is a possible solution to alleviate freshwater shortages. It is critical to understand the soil salt variations and the characteristics of salt accumulation and leaching under long-term brackish water irrigation in cultivated croplands. In this study, the HYDRUS-1D model was calibrated and validated, and then applied to evaluate that how 20 years of irrigating with brackish water affects soil salinity and soil salt transport in wheat-maize cultivated lands with different texture layers in the lowland of NCP. The results showed that the simulations of soil matric potential and soil salt concentrations fitted well with the measured values. Soil salt dynamics were dominated by seasonal precipitation and hydrological years. Seasonal rainfall distribution determined seasonal characteristics of salt changes in shallow layers (0–100 cm). Soil salt accumulated during the growth period of winter wheat corresponding to the dry season, and was greatest at the harvest. Soil salt leached down to deeper soil layers under abundant rainfall during growth period of maize. The annual soil salt in 300 cm profiles were driven by hydrological years, and soil salt could be accumulated in dry and normal years and leached in wet years, especially in the extremely wet year. Soil salt accumulation was higher under two brackish water irrigations compared to one irrigation for winter wheat, and soil salinity in homogeneous soils was less than in the heterogeneous soil with clay loam interlining. The results showed the effect of irrigation times of brackish water was greater than that of soil texture on soil salt accumulation. Our results demonstrated that wheat and maize could be grown well under one irrigation with brackish water a year. Salt accumulation increased with the number of irrigation events that used brackish water for winter wheat. The brackish water irrigation was evaluated and the results demonstrated that partial substitution of fresh water by brackish water for irrigation is feasible in the lowland area of the NCP. It is more suitable for long-term brackish water irrigation in relatively homogeneous soil than in heterogeneous soil. These simulated results are helpful to provide appropriate management measures for long-term brackish water irrigation and fresh water saving, and provide a basis for assessing the environmental effect under long-term brackish water irrigation. [ABSTRACT FROM AUTHOR]

The Loess Plateau is the main rain-fed agricultural area in western China, and water shortage is a critical factor restricting vegetation establishment and growth in this region. Under the influence of global climate change in recent years, significant changes have taken place in climate characteristics of the Loess Plateau, which will have a far-reaching impact on evaporation and transpiration under different vegetation conditions. Therefore, there is needed to make a in-depth research on the response of evaporation and transpiration to climate change for typical afforestation tree species, which has remarkable theoretical and practical significance in providing useful indications for tree species selection, water use efficiency improvement and ecosystem restoration. In order to evaluate the effects and mechanism of climate change on evaporation and transpiration of typical artificial afforestation tree species, a field experiment was carried out in the growing season of 2015－ 2016 (April 15th-October15th) at Nanxiaohegou basin (35°41′-35°44′N,107°30′-107°37′E), a typical small basin in gully region of the Loess Plateau selected by the Yellow River Water Conservancy Commission of China. In three sample plots of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis, soil physical parameters of three soil depth (0-40 cm, >40-100 and >100-200 cm) and the distribution of root density were measured, and soil moisture content, leaf area index, evaporation, precipitation and meteorology data were observed during the study period, from which simulation models of transpiration and evaporation in three experimental plots were established using Hydrus-1D software. The uncertainty of models parameters were analyzed through the Morris method, and the results showed that parameters of pore size distribution (40-100 cm) (n2), saturated water content (40-100cm) (θs2), field water capacity (θf), optimum threshold for root water absorption (h1), lower threshold for root water absorption (h2), soil water potential for permanent wilting (h3), extinction coefficient (μ), and parameter of vegetation interception model (a) had a great influence on transpiration, and the parameters related to the physiological characteristics of vegetation (h1, h2, h3, μ, and a) were the important reasons for the differences in transpiration of three tree species. The measured soil moisture content and evaporation data from 2015 were used to calibrate the model, and the data from 2016 were used to validate the model. Nash-suttcliffe efficiency coefficients were all above 0.700. The calibrated models were used to simulate evaporation and transpiration process under different presupposition scenarios derived from related research on climate characteristics of the study area, and the results showed that: 1) The effects of climate change in the future and different hydrological years on Robinia pseudopodia transpiration were greater than that in evaporation, while the opposite was true for Platycladus orientalis and Pinus tabuliformis. 2) Under all climate scenarios, the amount of transpiration for above tree species were distributed in 128.8-282.6, 99.3-200.3 and 140.5-220.5 mm, respectively, while the amount of evaporation were distributed in 94.6-135.4, 116.5-187.3 and 123.8-212.5 mm, respectively, and the transpiration and evaporation were both shown in the following aspect: the wet year > the normal year > the dry year. 3) As for transpiration, the response degree of three tree species to the climate characteristics of the future and different hydrological years was: Robinia pseudoacacia > Platycladus orientalis > Pinus tabuliformis, when it came to the evaporation, it was just the opposite. 4) In the same period of the future climate scenarios, the amount of transpiration in Robinia pseudoacacia plot was the largest among all tree species in wet and normal year, while in the dry year, the tree species with largest amount of transpiration was Pinus tabulaeformis. 5) The influence of precipitation on the transpiration and evaporation in growing season was stronger than that of temperature, and regression analysis indicated that the precipitation in growing season had a very significant linear function (P<0.01) with transpiration and evaporation for all 3 tree species. This study may provide valuable information for rational management of artificial afforestation tree species and restoration of the local ecological environment. [ABSTRACT FROM AUTHOR]

The Loess Plateau is the main rain-fed agricultural area in western China, and water shortage is a critical factor restricting vegetation establishment and growth in this region. Under the influence of global climate change in recent years, significant changes have taken place in climate characteristics of the Loess Plateau, which will have a far-reaching impact on evaporation and transpiration under different vegetation conditions. Therefore, there is needed to make a in-depth research on the response of evaporation and transpiration to climate change for typical afforestation tree species, which has remarkable theoretical and practical significance in providing useful indications for tree species selection, water use efficiency improvement and ecosystem restoration. In order to evaluate the effects and mechanism of climate change on evaporation and transpiration of typical artificial afforestation tree species, a field experiment was carried out in the growing season of 2015－ 2016 (April 15th-October15th) at Nanxiaohegou basin (35°41′-35°44′N,107°30′-107°37′E), a typical small basin in gully region of the Loess Plateau selected by the Yellow River Water Conservancy Commission of China. In three sample plots of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis, soil physical parameters of three soil depth (0-40 cm, >40-100 and >100-200 cm) and the distribution of root density were measured, and soil moisture content, leaf area index, evaporation, precipitation and meteorology data were observed during the study period, from which simulation models of transpiration and evaporation in three experimental plots were established using Hydrus-1D software. The uncertainty of models parameters were analyzed through the Morris method, and the results showed that parameters of pore size distribution (40–100 cm) (n2), saturated water content (40-100cm) (θs2), field water capacity (θf), optimum threshold for root water absorption (h1), lower threshold for root water absorption (h2), soil water potential for permanent wilting (h3), extinction coefficient (μ), and parameter of vegetation interception model (a) had a great influence on transpiration, and the parameters related to the physiological characteristics of vegetation (h1, h2, h3, μ, and a) were the important reasons for the differences in transpiration of three tree species. The measured soil moisture content and evaporation data from 2015 were used to calibrate the model, and the data from 2016 were used to validate the model. Nash-suttcliffe efficiency coefficients were all above 0.700. The calibrated models were used to simulate evaporation and transpiration process under different presupposition scenarios derived from related research on climate characteristics of the study area, and the results showed that: 1) The effects of climate change in the future and different hydrological years on Robinia pseudopodia transpiration were greater than that in evaporation, while the opposite was true for Platycladus orientalis and Pinus tabuliformis. 2) Under all climate scenarios, the amount of transpiration for above tree species were distributed in 128.8-282.6, 99.3-200.3 and 140.5-220.5 mm, respectively, while the amount of evaporation were distributed in 94.6-135.4, 116.5-187.3 and 123.8-212.5 mm, respectively, and the transpiration and evaporation were both shown in the following aspect: the wet year > the normal year > the dry year. 3) As for transpiration, the response degree of three tree species to the climate characteristics of the future and different hydrological years was: Robinia pseudoacacia > Platycladus orientalis > Pinus tabuliformis, when it came to the evaporation, it was just the opposite. 4) In the same period of the future climate scenarios, the amount of transpiration in Robinia pseudoacacia plot was the largest among all tree species in wet and normal year, while in the dry year, the tree species with largest amount of transpiration was Pinus tabulaeformis. 5) The influence of precipitation on the transpiration and evaporation in growing season was stronger than that of temperature, and regression analysis indicated that the precipitation in growing season had a very significant linear function (P<0.01) with transpiration and evaporation for all 3 tree species. This study may provide valuable information for rational management of artificial afforestation tree species and restoration of the local ecological environment. [ABSTRACT FROM AUTHOR]

In order to overcome the barriers on conducting field irrigation experiments including limited number of treatments and level setting, a large number of influencing factors as well as the high cost of human and material resources, this paper establishes an irrigation scheduling analysis method through combination of field observation and numerical simulation. The method was applied to analyze the water consumption characteristics and irrigation scheduling of pepper under the condition of border irrigation in the Shule River Basin. Field observations included soil volumetric moisture content, crop plant height, meteorological data, and soil physical parameters. The Hydrus-1D model was adopted in the method to simulate the water movement process during crop growth period. The calibration and verification of the model were conducted by using data of measured soil volumetric moisture content in the first and second half of pepper growth period, respectively. RMSE (root mean square error) and RMSD (root mean square deviation) were used to quantitatively evaluate the performance of the model. RMSE reflected the average degree of absolute error between the simulated value and the measured value. RMSD was the standardization of RMSE, and reflected the degree of deviation between the simulated value and the measured value. The calibrated and validated model was used to analyze the water consumption law of the crop growth process, and numerical experiments of the irrigation scheduling scenario were conducted to find the better irrigation scheduling with minimum water stress and deep percolation. The amount of water stress was defined as the cumulative amount of soil water content less than 60% of field capacity in the maximum root layer. The results of the method application showed that the total water consumption of pepper during the whole growth period was 456.76 mm under current irrigation scheduling. The ranking of average daily water consumption intensity was swelling stage > fruit setting stage > flowering stage > maturity stage > seedling stage. The results also showed that there was serious deep percolation loss, and water stress occurred in several growth periods, for the amount of deep percolation in the current scheduling during the whole growth period was 171.56 mm and that of water stress was 39.46 mm. In order to obtain the better irrigation scheduling, 96 new scenarios for irrigation scheduling were developed, which included 6 irrigation amounts for each application and 16 irrigation time intervals. With the increase of TIA (total irrigation amount), WC (water consumption) showed an increasing trend, and then became steady, and the range of TIA for WC peaks was 950-1 120 mm. WS (water stress) showed a trend of rapidly decreasing with the increase of TIA, and became extremely small after TIA exceeded 750 mm. With the increase of TIA, DP (deep percolation) showed a trend of slowly increasing first and then rapidly increasing linearly. According to the principle of minimum amount of deep percolation and water stress, taking into account the operating intensity and acceptability of the farmers, this paper proposed that the border irrigation scheduling of pepper in Shule River Basin should be: 525 mm for the total irrigation amount, 9 times irrigation per year, 30-day interval between 2 irrigations in the seedling period, 15-day interval in other growth periods, and 45-80 mm for the irrigation amounts for each application. In practice, it can be adjusted according to specific climatic conditions and soil moisture monitoring. [ABSTRACT FROM AUTHOR]

The Loess Plateau is the main rain-fed agricultural area in western China, and water shortage is a critical factor restricting vegetation establishment and growth in this region. Under the influence of global climate change in recent years, significant changes have taken place in climate characteristics of the Loess Plateau, which will have a far-reaching impact on evaporation and transpiration under different vegetation conditions. Therefore, there is needed to make a in-depth research on the response of evaporation and transpiration to climate change for typical afforestation tree species, which has remarkable theoretical and practical significance in providing useful indications for tree species selection, water use efficiency improvement and ecosystem restoration. In order to evaluate the effects and mechanism of climate change on evaporation and transpiration of typical artificial afforestation tree species, a field experiment was carried out in the growing season of 2015－ 2016 (April 15th-October15th) at Nanxiaohegou basin (35°41′-35°44′N,107°30′-107°37′E), a typical small basin in gully region of the Loess Plateau selected by the Yellow River Water Conservancy Commission of China. In three sample plots of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis, soil physical parameters of three soil depth (0-40 cm, >40-100 and >100-200 cm) and the distribution of root density were measured, and soil moisture content, leaf area index, evaporation, precipitation and meteorology data were observed during the study period, from which simulation models of transpiration and evaporation in three experimental plots were established using Hydrus-1D software. The uncertainty of models parameters were analyzed through the Morris method, and the results showed that parameters of pore size distribution (40-100 cm) (n2), saturated water content (40-100cm) (θs2), field water capacity (θf), optimum threshold for root water absorption (h1), lower threshold for root water absorption (h2), soil water potential for permanent wilting (h3), extinction coefficient (μ), and parameter of vegetation interception model (a) had a great influence on transpiration, and the parameters related to the physiological characteristics of vegetation (h1, h2, h3, μ, and a) were the important reasons for the differences in transpiration of three tree species. The measured soil moisture content and evaporation data from 2015 were used to calibrate the model, and the data from 2016 were used to validate the model. Nash-suttcliffe efficiency coefficients were all above 0.700. The calibrated models were used to simulate evaporation and transpiration process under different presupposition scenarios derived from related research on climate characteristics of the study area, and the results showed that: 1) The effects of climate change in the future and different hydrological years on Robinia pseudopodia transpiration were greater than that in evaporation, while the opposite was true for Platycladus orientalis and Pinus tabuliformis. 2) Under all climate scenarios, the amount of transpiration for above tree species were distributed in 128.8-282.6, 99.3-200.3 and 140.5-220.5 mm, respectively, while the amount of evaporation were distributed in 94.6-135.4, 116.5-187.3 and 123.8-212.5 mm, respectively, and the transpiration and evaporation were both shown in the following aspect: the wet year > the normal year > the dry year. 3) As for transpiration, the response degree of three tree species to the climate characteristics of the future and different hydrological years was: Robinia pseudoacacia > Platycladus orientalis > Pinus tabuliformis, when it came to the evaporation, it was just the opposite. 4) In the same period of the future climate scenarios, the amount of transpiration in Robinia pseudoacacia plot was the largest among all tree species in wet and normal year, while in the dry year, the tree species with largest amount of transpiration was Pinus tabulaeformis. 5) The influence of precipitation on the transpiration and evaporation in growing season was stronger than that of temperature, and regression analysis indicated that the precipitation in growing season had a very significant linear function (P<0.01) with transpiration and evaporation for all 3 tree species. This study may provide valuable information for rational management of artificial afforestation tree species and restoration of the local ecological environment. [ABSTRACT FROM AUTHOR]

The Loess Plateau is the main rain-fed agricultural area in western China, and water shortage is a critical factor restricting vegetation establishment and growth in this region. Under the influence of global climate change in recent years, significant changes have taken place in climate characteristics of the Loess Plateau, which will have a far-reaching impact on evaporation and transpiration under different vegetation conditions. Therefore, there is need to make a in-depth research on the response of evaporation and transpiration to climate change for typical afforestation tree species, which has remarkable theoretical and practical significance in providing useful indications for tree species selection, water use efficiency improvement and ecosystem restoration. In order to evaluate the effects and mechanism of climate change on evaporation and transpiration of typical artificial afforestation tree species, a field experiment was carried out in the growing season of 2015-2016 (April 15th-October15th) at Nanxiaohegou basin (35°41′-35°44′N,107°30′-107°37′E), a typical small basin in gully region of the Loess Plateau selected by the Yellow River Water Conservancy Commission of China. In three sample plots of Robinia pseudoacacia, Platycladus orientalis and Pinus tabulaeformis, soil physical parameters of three soil depth (0-40 cm, >40-100 and >100-200 cm) and the distribution of root density were measured, and soil moisture content, leaf area index, evaporation, precipitation and meteorology data were observed during the study period, from which simulation models of transpiration and evaporation in three experimental plots were established by using Hydrus-1D software. The uncertainty of model parameters was analyzed through the Morris method, and the results showed that parameters of pore size distribution (40-100 cm) (n2), saturated water content (40-100cm) (θs2), field water capacity (θf), optimum threshold for root water absorption (h1), lower threshold for root water absorption (h2), soil water potential for permanent wilting (h3), extinction coefficient (μ), and parameter of vegetation interception model (a) had a great influence on transpiration, and the parameters related to the physiological characteristics of vegetation (h1, h2, h3, μ, and a) were the important reasons for the differences in transpiration of three tree species. The measured soil moisture content and evaporation data from 2015 were used to calibrate the model, and the data from 2016 were used to validate the model. Nash-sutcliffe efficiency coefficients were all above 0.700. The calibrated models were used to simulate evaporation and transpiration process under different presupposition scenarios derived from related research on climate characteristics of the study area, and the results showed that: 1) The effects of climate change in the future and different hydrological years on Robinia pseudopodia transpiration were greater than that in evaporation, while the opposite was true for Platycladus orientalis and Pinus tabuliformis. 2) Under all climate scenarios, the amount of transpiration for above tree species were distributed in 128.8-282.6, 99.3-200.3 and 140.5-220.5 mm, respectively, while the amount of evaporation were distributed in 94.6-135.4, 116.5-187.3 and 123.8-212.5 mm, respectively, and the transpiration and evaporation were both shown in the following aspect: the wet year > the normal year > the dry year. 3) As for transpiration, the response degree of three tree species to the climate characteristics of the future and different hydrological years was: Robinia pseudoacacia > Platycladus orientalis > Pinus tabuliformis, when it came to the evaporation, it was just the opposite. 4) In the same period of the future climate scenarios, the amount of transpiration in Robinia pseudoacacia plot was the largest among all tree species in wet and normal year, while in the dry year, the tree species with largest amount of transpiration was Pinus tabulaeformis. 5) The influence of precipitation on the transpiration and evaporation in growing season was stronger than that of temperature, and regression analysis indicated that the precipitation in growing season had a very significant linear function (P<0.01) with transpiration and evaporation for all 3 tree species. This study may provide valuable information for rational management of artificial afforestation tree species and restoration of the local ecological environment. [ABSTRACT FROM AUTHOR]

Soil salinization problems are widespread in the Hetao plain, Inner Mongolia, resulting from arid climate conditions, a shallow saline water table, poor irrigation water management, and insufficient drainage. This study follows previous research aimed at evaluating crop water use and controlling the salinity build-up in the region, namely using weighing and static water table lysimeters to parameterize a water balance model aimed at the development of appropriate irrigation scheduling. Two sets of five static water table lysimeters, which fixed depths ranged from 1.25 to 2.25 m, were used over two maize crop seasons. The mechanistic HYDRUS-1D model was further used to daily predict measured data on soil water contents, boundary fluxes in the interface between the saturated and unsaturated zones, the electrical conductivity of the soil saturation paste extract (EC e), and the actual crop evapotranspiration (ET c act). The soil water balance helped quantify the combined effect of water and salinity stresses on root water uptake as well as groundwater fluxes into the rootzone. The salt balance showed that the salinity build-up was much related to irrigation and capillary fluxes, and that the autumn irrigation carried out during the non-growing season was essential for controlling soil salinity. The efficiency of the autumn irrigation much depended on groundwater depth and the amount of water applied for salt leaching, with the best results found for the lysimeters with water table depths at 2.0 and 2.25 m (85–100%) for irrigation depths ≥ 220 mm. The lysimeters with shallower water tables never showed a leaching efficiency higher than 88%. This research shows that the sustainability of irrigation in Hetao depends on finding adequate solutions for controlling the depth of the saline groundwater, minimizing capillary fluxes to the rootzone, and developing consequent approaches for autumn irrigation leaching. • Soil water contents and fluxes, EC e , and ET c act were measured using water table lysimeters. • The HYDRUS-1D model successfully simulated lysimeter data during two seasons. • The water table depth influenced the effectiveness of autumn irrigation leaching. • The leaching efficiency only increased by improving soil drainage conditions. • Reducing autumn irrigation depth (<200 mm) promoted soil salinization. [ABSTRACT FROM AUTHOR]

Rational irrigation plays an important role in increasing crop yield and reducing water use. With a typical sand-layered farmland in the Hetao irrigation district as an example, field experiments were conducted during the growth period of maize, and a numerical model of soil water movement was applied to explore the field evapotranspiration, crop water consumption and soil water transport in the sand-layered soil. CropWat 8.0 software was applied to formulate the irrigation schedule under the fixed irrigation interval in each growth stage of maize. The soil water movement in sand-layered soil under different irrigation schedules was simulated by the HYDRUS-1D model. Results show that the HYDRUS-1D model could well simulate the soil water movement during the growth period of crops in the typical sand-layered farmland. In addition, the deep percolation loss of water could be reduced by approximately 20.4–37.6% with appropriate increase in the irrigation frequency and reduction in the irrigation quota. However, under the minimum irrigation interval, there were still 19.5% of irrigation water and rainfall lost by seepage through the deep sand layer. The water stress in the rhizosphere during the mid-stage of crop growth was only 13.9 mm with the irrigation frequency as every 10 days (I 10), while that was 107.97 mm with the irrigation frequency as every 25 days (I 25). The maximum ratio of actual transpiration rate of crops to actual evapotranspiration of the land was 73.6% with I 10 irrigation and the minimum was 63.4% with I 25 , indicating that increasing the irrigation frequency and reducing the irrigation quota each time are highly beneficial to increasing the water holding capacity for crop growth in the root zone in the sand-layered farmland. The study provides a basis for farmland water management in the arid and semi-arid areas. • Soil water movement in typical sand-layered farmland was simulated by calibrated HYDRUS-1D model. • Increase irrigation frequency and lower irrigation quota can reduce the deep percolation loss of water by 20–38%. • CropWat model contributed to achieve the goal of setting up different irrigation regime scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil desiccation in four planted forests with different tree ages was simulated under combined climate change scenarios. • Impacts of future climate on soil desiccation increased with tree ages in upper soil layers (0–40 cm), but decreased with them in lower soil layers (40–100 cm). • Precipitation and vapor pressure deficit were the dominant climatic factors influencing soil desiccation in upper and lower layers, respectively. • Tree age threshold for taking measures to control soil desiccation was unexpectedly delayed by 2a under future warming and drying climate. Investigating the impacts of climate change on soil desiccation in planted forests is of theoretical and practical importance for water resource management and ecological restoration in the Loess Plateau. In this study, field experiments were conducted in four planted forests (Platycladus orientalis plots) with tree ages of 5, 12, 25, and 35a (abbreviated as T5, T12, T25, and T35 plots, respectively). Based on which, Hydrus–1D models were calibrated and validated to simulate soil water dynamics under preset climate change scenarios. Then, the soil desiccation index (SDI) in different soil layers was calculated and evaluated. The results showed that under historical climate scenarios, soil desiccation levels were slight or medium in T5, T12, and T25 plots but were mainly medium or severe in T35 plots. Future warming and drying climate would greatly increase the SDI in all plots, and its impacts increased with tree ages in the upper soil layers (0–40 cm) but decreased with it in lower layers (40–100 cm). However, it only had limited influence on the responses of soil desiccation to the climate in different hydrological years. Precipitation and vapour pressure deficit dominated soil desiccation in the upper and lower layers, respectively, and both showed linear relationships (p < 0.05) with the SDI in corresponding soil layers. The SDI in the lower layers should be given full attention when controlling soil desiccation, and its rapid increase thresholds of tree ages were 20.3a under historical scenarios, but were unexpectedly delayed to 22.8a under future climate conditions. Our study not only improved the scientific understanding of the soil water conditions and their responses to climate change, but also provided valuable guidelines for the management of water resources and the restoration of the ecological environment in the semi-arid Loess Plateau. [ABSTRACT FROM AUTHOR]

In the present study Hydrus-1D software was used to simulate electrical conductivity, pH and sodium, potassium, calcium, magnesium, chloride and sulfate ions. Field experiments were performed at the Sugarcane Research Center located in south of Ahvaz on sugarcane varieties CP48-103 with four water treatments (one treatment was Karun river water and three treatments were diluted drainage water) and three replications. The samples were collected from 0-30, 30-60 and 60-90 cm soil depth before irrigation and electrical conductivity and anions and cations of soil were measured in the laboratory. Sensitivity analysis and calibration were first performed with the aim of verifying the Hydrus-1D software. The sensitivity analysis indicated that the software had maximum sensitivity to the saturated volumetric water content. Minimum sensitivity was for the inverse of the air-entry suction, tortuosity parameter, residual volumetric water contents and moderate sensitivity was for hydraulic conductivity at natural saturation. Also, the software did not show any sensitivity to empirical parameter related to the pore size distribution that is reflected in the slope of water retention curve. In calibration stage the amount of hydraulic conductivity at natural saturation, residual volumetric water contents, saturation volumetric water contents, the inverse of the air-entry suction, empirical parameter related to the pore size distribution and tortuosity were obtained as 18 (cm/day), 0.04 (cm3 /cm3 ), 0.63(cm3 /cm3 ), 0.012 (cm-1 ), 1.2 and 0.6 respectively. The results showed that the coefficient of determination of all parameters was more than 0.85 which confirms the appropriate capabilities of the model in simulation of electrical conductivity, pH, anions and cations. In the modeling carried out the amount of NRMSE was between 11 and 18 percent which indicates good performance of the model. The Nash-Sutcliffe efficiency criterion was obtained 0.72 to 0.8 that indicates a good match of the model with reality. The coefficient of residual mass in this paper was positive for electrical conductivity, pH and sodium, potassium, calcium, magnesium and negative for chloride and sulfate. The positive and negative coefficient of the residual mass shows less and over estimation of the model. [ABSTRACT FROM AUTHOR]

Groundwater provides an important source of water for maize cultivation where the water table is shallow in the semi-arid Hailiutu River catchment of the Maowusu Desert on the Erdos Plateau in Northwest China. A HYDRUS-1D model of the unsaturated flow beneath a maize (Zea mays L.) field was calibrated and validated with measured soil water contents at various depths during the maize growing period from 30 April to 1 October 2011, and from 23 May to 27 September 2012, respectively. The model computed the actual maize evapotranspiration (ETa) as 580 mm during the whole growing period from 30 April to 1 October 2011. The groundwater contribution to ETa was calculated to be 220 mm, accounting for 38% of maize water use during the growing season in 2011. When the groundwater level drops below a depth of 157 cm, maize can no longer use groundwater for transpiration. The irrigation water requirement increases with the increase of groundwater table depth. These results are very important for managing crop irrigation in the area. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR L. Ruiz [ABSTRACT FROM AUTHOR]

Quantification of groundwater recharge from precipitation in the huge sand dunes is an issue in accounting for regional water balance in the Badain Jaran Desert (BJD) where about 100 lakes exist between dunes. In this study, field observations were conducted on a sand dune near a large saline lake in the BJD to investigate soil water movement through a thick vadose zone for groundwater estimation. The hydraulic properties of the soils at the site were determined using in situ experiments and laboratory measurements. A HYDRUS-1D model was built up for simulating the coupling processes of vertical water–vapor movement and heat transport in the desert soil. The model was well calibrated and validated using the site measurements of the soil water and temperature at various depths. Then, the model was applied to simulate the vertical flow across a 3-m-depth soil during a 53-year period under variable climate conditions. The simulated flow rate at the depth is an approximate estimation of groundwater recharge from the precipitation in the desert. It was found that the annual groundwater recharge would be 11–30 mm during 1983–2012, while the annual precipitation varied from 68 to 172 mm in the same period. The recharge rates are significantly higher than those estimated from the previous studies using chemical information. The modeling results highlight the role of the local precipitation as an essential source of groundwater in the BJD. [ABSTRACT FROM AUTHOR]

HYDRUS-1D was combined with lysimeter experiments to study extinction depth and steady water storage in root zone (Ws) of groundwater evaporation (ETgw) under winter wheat and silt soil. The measured soil water contents and daily ETgw with various groundwater depths were used to calibrate and validate the parameters in HYDRUS-1D. In total, 13 groundwater depths ranging from 0.5 to 5.0 m were set up for scenario simulation to determine the extinction depth and Ws. The results showed that HYDRUS-1D had an acceptable performance in simulating the soil water storage in the 0-60 cm layer and the daily ETgw. Moreover, the ETgw decreased linearly with increasing groundwater depth from 0.5 to 2.5 m and decreased as a power function with increasing groundwater depth from 2.5 to 5.0 m. Under the condition of winter wheat and silt soil, the extinction depth of ETgw was about 5.0 m. Ws decreased linearly with increasing groundwater depth from 0.7 to 2.0 m, but was not influenced further by the groundwater at depths beyond 2.0 m. [ABSTRACT FROM AUTHOR]

Agricultural economy development and environment protection are often contradictory and closely linked in today’s world. For example, fertilizer application in some extent can increase crop production. On the other hand, it also may cause non-point source pollution and aggravate water pollution. In order to evaluate the environmental and economic benefits of agricultural activities objectively and scientifically, an integrated agricultural enviro-economic model was established in this study. The maximum of crop net profit calculated by agricultural input and output is the target function in this model, and the limit condition is the nitrogen loads released to the surface water body and/or groundwater. Thus how to calculate the crop yield and nitrogen leaching is the key issue. The Weishan irrigation district is the fifth irrigation district in China, which is irrigated by the Yellow River. More than 90% of the area is farmland, with rotation of winter wheat and summer maize. As a case study, the Weishan irrigation district was selected for model application because of its homogeneous planting and measurable irrigation. A calibrated and validated Hydrus-1D model was employed to simulate the nitrogen leaching, root uptake of nitrogen and crop yields in several scenarios with different irrigation and fertilization. And then the regression equations were reached between crop yield/nitrogen leaching and the amounts of irrigation and fertilization to get the values of coefficients in the integrated model. Finally, the integrated model was solved by using the optimization toolboxes in Matlab software, and optimal irrigation and fertilization schemes were obtained under different controls of nitrogen leaching. According to the scenario simulations by Hydrus-1D model, nitrogen leaching had a positive correlation with both irrigation and fertilization amounts. Crop yield had a peak value with some optimal irrigation, while no peak value appeared with the change of fertilization for the model’s inner deficiency. Based on the analysis and discussion, the economic benefit would increase as a result of the easing control of pollution (i.e., allowable nitrogen leaching increase), but the growth rate would slow down, that is, the marginal benefit of agricultural development was diminishing at the expense of environment benefit. In the study area, the net income of crops planting was reached the maximum when nitrogen leaching controlled under 500 kg/hm2 with irrigation of 240 mm and fertilization of 732 kg/hm2. If more strict control of nitrogen leaching is expected, fertilization should be decreased, which may reduce the farmer’s income. In this way, government can provide compensation to farmers for encouraging more environment-friendly agricultural production. By using the integrated enviro-economic model, the environmental compensation was about 913.5 Yuan/hm2 if cutting the allowable nitrogen leaching from 500 to 450 kg/hm2. Moreover, scientific guidance of irrigation and fertilization can offer best economic and environmental benefits. For example, if the local actual irrigation of 300 mm and fertilization of 610 kg/hm2 changed with irrigation of 240 mm and fertilization of 458 kg/hm2, the farmer’s income would increase 478 Yuan/hm2, and nitrogen leaching would decrease 123 kg/hm2 at the same time, which may reduce agricultural non-point source pollution remarkably. Although there are some uncertainties in the estimation, this model can be used to provide references for the policy making of agricultural environmental protection and compensation. [ABSTRACT FROM AUTHOR]

In this study, Hydrus-1D model was used to simulate the evaporation from the soil surface for different wetting intervals for northern region(sandy loam and clay loam) using input for climatic data , and data of class Apan evaporation.The results showed that data of pan evaporation class A can be relied on in simulating and calculation of evaporation from the soil surface, where the standards of statistics (IOA, R2) calculated on the basis of evaporation pan class A data are better for the wetting intervals (2,4, 8, 16 ) days compared with the values of those standards based on full climate data and both types of soil. The study also showed that the wetting intervals and their impact on evaporation from the soil surface and evaporation stages reasonably agree with the results of field experiments that have been made in this area. [ABSTRACT FROM AUTHOR]

Groundwater is regularly used for many purposes, such as drinking and agricultural irrigation systems. Still, it contains high levels of radionuclides (e.g., 238U, 232Th, and 226Ra) that are potentially hazardous to humans and the environment. In this study, activity concentrations of uranium isotopes were analyzed in 15 groundwater samples taken from 15 bored wells in Thu Duc district, Ho Chi Minh City, Vietnam. Environmental effects of the irrigation system with groundwater on agricultural soil in the study area were assessed by models. It was found that the activity concentrations of 238U and 234U in groundwater samples were in the ranges of (13.5–268.7) mBq l−1 and (20.2–438.3) mBq l−1, respectively. The ratio 234U/238U values were ranged from 1.12 to 2, with an average value of 1.44. Based on the model prediction, 25 years irrigation with the groundwater can inject 94.8 Bq both uranium isotopes in 1 kg topsoil. For investigated groundwater samples, the proposed removal method using K 2 FeO 4 removed 74.28% and 81.04% for 234U and 238U, respectively. • Method of groundwater preparation for alpha spectrometer. • Ratio of 234U/238U in groundwater samples in Ho Chi Minh City. • Long-term activity concentrations of uranium isotopes in soil based on model assessment. • Method for removal of uranium in groundwater using K 2 FeO 4. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the date palm water use under shallow saline groundwater condition. [•] We examine the effect of quality and management of irrigation on root water uptake. [•] The date palm will be affected by the low irrigation frequency in summer season. [•] Increasing the water table level during summer will increase the root water uptake. [ABSTRACT FROM AUTHOR]

Heihe River irrigation region is typical arid agricultural oasis. It is also important commodity grain, cotton and oil-producing areas. Water shortage is a key issue of limiting socio-economic development. Flood irrigation is still the main irrigation methods about agricultural production and they believe that a large number of farmland irrigation result in high crop yields. This approach not only reduces water use efficiency but also wastes a lot of valuable water resources. Therefore, investigating soil moisture movement laws has important theoretical significance and practical value for the agricultural water-saving irrigation. Although many related results for infiltration and drainage of soil moisture have been reported in previous literature, most of the studies have been focused on the Loess Plateau, red soil area of South China and karst area of Southwest China, few on arid oasis area. The double-ring infiltrometer is used to measure infiltration by the constant-head method, composed of inner-ring and outer-ring whose diameters are 80cm and 100cm, respectively. Representative position in the maize farmland and protection forestland was chose, and the Trime Tube depth of 275 cm and 265 cm was installed, respectively. The double-ring was embedded in soil and the water depth of the inner and outer-ring was 5 cm. Soil water content of infiltration and drainage processes was measured by Trime-IPH TDR and soil water movement was simulated accurately by Hydrus-1D model. Results of the simulations indicated that the soil textures significantly affected water infiltration and drainage. The finer grained layer was capillary barriers for water infiltration and drainage as well as had strong water holding capacity. The statistical analysis indicated that root mean square error (RMSE) and the relative error (RE) between the measured and estimated soil water content were below 0.02 and 0.68%, respectively. Root mean square error (RMSE) and the relative error (RE) between the measured and estimated soil water storage were below 0.908 and 0.9% respectively. HYDRUS-1D model had a high precision for the simulation of water transport of the oasis soil in vertical direction. The results can provide a scientific basis for water management and sustainable development of Heihe River Basin. [ABSTRACT FROM AUTHOR]

Large-scale agricultural activities cause deterioration of groundwater resources throughout the world. This study focuses on the irrigated agricultural district of Jinghuiqu in Shaanxi, China. The objectives are to identify the main sources and processes that control nitrate transport, and to assess the impact of long-term irrigation practices on nitrate leaching. The hydrogeochemistry of major solute constituents and stable isotope ratios of NO3−in groundwater were used to identify historical sources of contamination and transformation processes occurring in the shallow groundwater of the Jinghuiqu irrigation district. The N-NO3−concentrations in groundwater ranged from 0.0 to more than 100 mg L−1in April 1990, and from 0.47 to 42.0 mg L−1in December 2009. Our measurements of N-NO3−show that the main reasons for this dramatic decline in N-NO3−concentrations from 1990 to 2009 are denitrification, which controls nitrogen types, together with the sharp decline of the groundwater table. The isotope ratios in collected samples showed that the source of nitrate was mainly manure, a result that corresponds with historical data showing that manure was the main nitrate source before the 1980s, and that fertilizers became dominant thereafter. A numerical model was then used to evaluate future impacts of current irrigation practices on groundwater sources. The HYDRUS-1D model was employed first to evaluate the water movement and the N-NO3−solute transport for a single irrigation pulse experiment carried out under field conditions, and then in evaluating the long-term impact of irrigation on N-NO3−leaching. Simulations showed that, after introducing irrigation, the downward drainage fluxes of N-NO3−, and the N-NO3−and N-tot concentrations increased at all depths within the 2-m soil profile. This indicates that N concentrations below 1-m depth and in the groundwater could become even more elevated with increased future irrigation. [ABSTRACT FROM AUTHOR]

Abstract: Heavy rainfall and irrigations during the summer months in the North China Plain may cause losses of nitrogen because of nitrate leaching. The objectives of this study were to characterize the leaching of accumulated N in soil profiles, and to determine the usefulness of Br− as a tracer of surface-applied N fertilizer under heavy rainfall and high irrigation rates. A field experiment with bare plots was conducted near Beijing from 5 July to 6 September 2006. The experiment included three treatments: no irrigation (rainfall only, I0), farmers’ practice irrigation (rainfall plus 100mm irrigation, I100) and high-intensity irrigation (rainfall plus 500mm irrigation, I500), with three replicates. Transport of surface-applied Br− and NO3 − (assuming no initial NO3 − in the soil profile) and accumulated NO3 − in soil profiles were all simulated with the HYDRUS-1D model. The model simulation results showed that Br− leached through the soil profile faster than NO3 −. When Br− was used as a tracer for surface-applied N fertilizer to estimate nitrate leaching losses, the amount of N leaching may be overestimated by about 10%. Water drainage and nitrate leaching were dramatically increased as the irrigation rate was increased. The amounts of N leaching out of the 2.1-m soil profile under I0, I100 and I500 treatments were 195±84, 392±136 and 612±211kgNha−1, equivalent to about 20±5%, 40±6% and 62±7% of the accumulative N in the soil profile, respectively. N was leached more deeply as the irrigation rate increased. The larger amount of initial accumulated N was in soil profile, the higher percentage of N leaching was. N leaching was also simulated in summer under different weather conditions from 1986 to 2006. The results indicated that nitrate leaching in rainy years were significantly higher than those in dry and normal years. Increasing the irrigation times and decreasing the single irrigation rate after fertilizer application should be recommended. [Copyright &y& Elsevier]

Identifying the dominance of climate and land use in soil water balance (SWB) is critical for developing water resource management strategies in agriculture and in environment. The large soil water reservoir in the thick vadose zone of China's Loess Plateau has been depleting in recent years; however, the connection of climate and land use changes with SWB has rarely been differentiated. An experimental site from China's Loess Plateau with different land uses including farmland and apple trees of different ages (approximately 20 and 30 years old) were considered to partition the SWB components under the current (1957–2017) and future (2011–2040) climate using the HYDRUS-1D model. Simulated with three land use types and 20 climate change scenarios, 60 SWB scenarios were used to differentiate the role of climate and land use in SWB changes. For the climate change impacts, precipitation played an important role in SWB variability than temperature. Further, the variance of precipitation had greater effects than mean precipitation on SWB components. The changes in the actual evapotranspiration were dominated by precipitation and temperature, but the change in groundwater recharge was largely controlled by the conversion from farmland to apple trees. This study provides information to guide the implementation of the revegetation program on the Loess Plateau, and highlights the importance in differentiating the influences of climate and land use changes to sustain agriculture and water resources in the future. • Precipitation dominated soil water balance variability. • Precipitation variance had greater effects than precipitation average. • Changes in actual evapotranspiration was dominated by climate. • Changes in groundwater recharge was dominated by land use. [ABSTRACT FROM AUTHOR]

• FeII-AlIII LDH completely immobilized soil Cr(VI) at Cr(VI)/FeII (s) = 0.2 in a batch system. • In column system, soil saturated/unsaturated conditions and method of LDH application were highly determinative. • LDH injection into the unsaturated soil column immobilized 70% of leachable Cr(VI) • Cr(VI) immobilized in soil via its reduction to Cr(III) and subsequent precipitation. We synthesized nanoscale FeII-AlIII layered double hydroxide (LDH) and investigated its efficiency for reductive immobilization of Cr(VI) in a Cr-spiked alkaline loam soil using both batch and column experiments. Results of batch experiments indicated that addition of fresh LDH suspension to the soil at a mole ratio of Cr(VI) to structural FeII in LDH [FeII (s) ] = 0.2, completely immobilized Cr(VI). Column experiments, using same Cr(VI)/FeII (s) ratio, were conducted under four various modes of LDH suspension application to the soil. Addition of LDH suspension to the saturated and unsaturated packed soil columns at a pressure head of 2 cm was inefficient in reducing Cr(VI) to Cr(III) because of shallow penetration of LDH particles into the soil. Injection of LDH suspension into the soil columns greatly improved penetration of LDH particles into the soil. However, only 18.8% of leachable Cr(VI) was immobilized in the saturated soil column, while the same operation in the unsaturated column experiment increased Cr(VI) immobilization efficiency to 70.0%, a significant improvement in immobilization. In summary, nanoscale FeII-AlIII LDH was shown to be a fast and strong reductant, which successfully remediated a Cr(VI)- contaminated alkaline soil. [ABSTRACT FROM AUTHOR]

• Hydrus-1D was used to simulate T and E of three grasslands in the Loess Plateau. • The effects of climate change on T were greater than that on E. • Precipitation was the most dominant climatic factor affecting T and E. • Constructed grasslands had higher water use efficiency than natural one. • Constructed grasslands led to worse soil water conditions than natural one. Investigating the effects of climate change on transpiration (T) and evaporation (E) in natural and constructed grasslands is of theoretical and practical significance for vegetation restoration and water resource management in the Loess Plateau, China. In this study, a two-year field experiment was conducted in one natural (Imperata cylindrica plot) and two constructed grasslands (Pennisetum giganteum and Medicago sativa plots) in the semi-arid Loess Plateau. Hydrus-1D models were then established and validated to simulate T and E processes under scenarios combining climate characteristics in both future periods and different hydrological years. The results showed that under all climate scenarios, T in the natural grassland, and P. giganteum and M. sativa plots ranged from 63.7–179.3, 126.8–245.5, and 96.9–243.1 mm, respectively, while E ranged from 90.6–131.9, 68.7–92.8, and 70.4–92.4 mm, respectively. Both T and E showed a decreasing trend in the future periods, exhibiting the highest values in wet years and the lowest values in dry years. The effects of climate change on T were greater than that on E in all three grasslands. Of the studied grasslands, T of M. sativa plot exhibited the strongest response, followed by that in the natural grassland and P. giganteum plot. However, E of the natural grassland responded to the strongest degree, followed by that of the P. giganteum and M. sativa plots. Precipitation during the growing-season was the most dominant climatic factor affecting T and E , and was positively linearly related with T and E (P < 0.01) in all three grasslands. The conversion thresholds of precipitation for T - E dominance were 435.8, 149.4, and 253.3 mm for the natural grassland, and P. giganteum and M. sativa plots, respectively. In constructed grasslands, more water was lost through T than through E ; hence, the T / ET ratios were high (>0.55). In contrast, T was high in the natural grassland only in conditions of sufficient precipitation; hence, the T / ET ratio was relatively lower (around 0.5). Precipitation distribution strongly affected the soil water supply, and the natural grassland was more efficient in maintaining soil water than the constructed grasslands. Our study not only improves our understanding of the hydrological processes and water budget under different grass restoration measures, but also provides valuable guidelines for the management of water resources and the restoration of ecological environment in the Loess Plateau. [ABSTRACT FROM AUTHOR]

In topsoils, the activity concentrations of natural radionuclides (hereafter NRs) increase due to the addition of NRs from fertilizers, irrigation water, and air dust pollution. On the other hand, various physical-chemical and environmental processes such as radioactive decay, volatilization, leaching, erosion, and plant uptake were responsible for the decrease of the activity concentrations of NRs in the topsoils. In this study, behaviours of 40K, 210Pb, 226Ra, 238U, and 232Th in topsoils were modelled by the CEMC soil model and the HYDRUS-1D model. An exponential equation was proposed for estimating the accumulation rates of these radionuclides in the topsoils. Long-term accumulation of radionuclides was assessed for water spinach (Ipomoea Aquatica Forssk.) soil (hereafter VES) and rice (Oryza sativa L.) soil (hereafter RIS). We found that the current agricultural practices caused the increase of 40K activity concentration in the water spinach soil, and 40K, 210Pb, 226Ra, and 232Th activity concentrations in the rice soil. The accumulation rates of radionuclides were in the order 238U < 232Th < 226Ra <210Pb < 40K. 25 years of cultivation with water spinach can increase/decrease + (165 ± 6) Bq of 40K, – (8.2 ± 0.7) Bq of 210Pb, – (4.3 ± 0.2) Bq of 226Ra, – (7 0.3 ± 0.3) Bq of 238U, and – (1.8 ± 0.1) Bq of 232Th in 1 kg soil. For rice cultivation, these values are + (1004 ± 39), + (3.3 ± 0.2), + (3.0 ± 0.2), – (5.1 ± 0.3), (2.2 ± 0.1) Bq kg−1 for 40K, 210Pb, 226Ra, 238U, and 232Th, respectively. Image 1 • Behaviours of 40K, 210Pb, 226Ra, 238U, and 232Th in topsoils were modelled. • Equation for estimating accumulation rates of radionuclides in topsoils. • Long-term agricultural practices caused accumulation of radionuclides in topsoils. • Higher rates of accumulation were found in the rice (Oryza Sativa L.) soil. • Accumulation rates are in the order 238U < 232Th < 226Ra <210Pb < 40K. [ABSTRACT FROM AUTHOR]

• Long-term soil water dynamics was simulated under land-use change in the CLP. • Five phases of soil water dynamics were identified under land-use change. • Planting M. sativa and C. korshinskii intensified deep soil water decline. • Dry soil layer began to develop in 3–4 years of M. sativa or C. korshinskii growth. • A 4-m thick dry soil layer is recoverable in 7–8 years following land-use change. Soil water content (SWC) is critical for the health and sustainability of the ecosystem in water limited areas. Characterized by low precipitation and deep groundwater, the Chinese Loess Plateau (CLP) has experienced intensive agricultural and revegetation activities for a period long enough to alter the state of SWC to the extent that can affect plant growth and water cycle. Knowledge of long-term SWC dynamics under land-use change is therefore important for optimal water management and vegetation restoration in this water-scarce region. This study simulated and analyzed long-term (1970–2060) variations in SWC in the top 4-m soil layer in response to land-use change on CLP using the Hydrus-1D model. Soil and plant parameters required for the model were validated using in situ SWC data for different land-use types — exotic grass (M. sativa), exotic shrub (C. korshinskii), arable crop (S. italica or V. radiata) and natural grass (S. bungeana). Five phases of SWC dynamics driven by land-use change were identified: i) fluctuation of SWC with rainfall during arable cropping period; ii) rapid drop of SWC after exotic plant establishment; iii) period of no change for which SWC remained low and stable; iv) gradual recovery of SWC after conversion of exotic vegetation into natural grass; and v) fluctuation of SWC with rainfall under natural grass. Particularly, SWC decreased rapidly with the planting of M. sativa and C. korshinskii and water depletion depth increased with plant growth after revegetation. Dry soil layer (DSL) began to develop below 1-m after 3 years of growth of M. sativa or C. korshinskii. Also, SWC at depth below 1 m remained low and unavailable for plant growth. Compared with arable cropland, SWC in the 1–4 m soil layer decreased by 33% under both exotic grass and shrub during vegetation restoration period. However, it took 7–8 years for soil water to recover in the 0–4 m soil layer after 13-year (2004–2016) exotic grass or shrub was converted to natural grass. This suggested that DSL in the 4-m soil depth can fully recover by changing vegetation type. We concluded that planting M. sativa and C. korshinskii on arable cropland could enhance DSL formation in deep soil profile, but can gradually disappear upon land-use change. The results provided useful information for the prediction of long-term dynamics of soil water with land-use change. This is critical for the management of soil water in water limited areas. [ABSTRACT FROM AUTHOR]

• 10-m soil water profiles were continuously monitored for different land use types. • Apple orchards decrease subsurface water storage relative to farmlands. • Balance of economy versus environmental sustainability should be considered. Land use change (LUC) impacts on the soil water balance is important for effective water resources management and land use planning. The Loess Plateau of China has loess deposits up to 350-m depth and constitutes large reservoirs of soil water storage. In recent decades, areas within these reservoirs have been depleted of their water storage. LUC impacts on soil water storage have been previously investigated in this region; however, LUC impacts on other components of soil water balance such as evapotranspiration and deep drainage have received limited study because of difficulties in direct measurement of these components. Using continuously monitored 10-m soil water profiles under farmland and apple orchards converted from farmlands for 10, 20, and 30 years for the period 2011−2013, the HYDRUS-1D model was calibrated and then employed to evaluate long-term LUC impacts on different components of the soil water balance in a typical loess tableland based on climate data for the period 1960−2013. Compared with farmlands and young apple orchards (stand age <10 years), the measured soil water storage under mature apple orchards (stand age> 20 years) was significantly decreased over time. The simulated deep drainage was 12.1 mm year−1 under farmland and accounted for 2% of the annual average precipitation, but this value was reduced to near zero under mature apple orchards. The simulated average annual actual evapotranspiration was 565.8 mm and represented 98% of the average annual precipitation under farmlands, but the evapotranspiration was increased under mature apple orchards. The LUC-induced decrease in soil water storage and groundwater recharge threatens the sustainability of water resources and agriculture on the Loess Plateau. The balance between economic development and agriculture ecosystems and environmental sustainability are, therefore, important considerations in future land use planning. [ABSTRACT FROM AUTHOR]