Soil Water Distribution Research Articles

Using Apparent Electrical Conductivity as Indicator for Investigating Potential Spatial Variation of Soil Salinity across Seven Oases along Tarim River in Southern Xinjiang, China

Soil salinization is a major soil health issue globally. Over the past 40 years, extreme weather and increasing human activity have profoundly changed the spatial distribution of land use and water resources across seven oases in southern Xinjiang, China. However, knowledge of the spatial distribution of soil salinization in this region has not been updated since a land survey in the 1970s to 1980s (the harmonized world soil database, HWSD) due to scarce observational data. Now, given the uncertainty raised by near future climate change, it is important to develop quick, reliable and accurate estimates of soil salinity at larger scales for a better manage strategy to the local fragile ecosystem that with limited land and water resources. This study collected electromagnetic induction (EMI) readings near surface soil to update on the spatial distribution and changes of water and salt in the region and to map apparent electrical conductivity (ECa, mS·m−1), in four coil configurations: vertical dipole in 1.50 m (ECav01) and 0.75 m (ECav05), so as the horizontal dipole in 0.75 m (ECah01) and 0.37 m (ECah05), then all the ECa coil configurations were modeled with random forest algorithm. The validation results showed an R2 range of 0.77–0.84 and an RMSE range of 115.17–142.76 mS·m−1. The validation accuracy of deep ECa dipole (ECah01, ECav05, and ECav01) was greater than that of shallow ECa (ECah05), as the former integrated a thicker portion of the subsurface. The range of EC spatial variability that can be explained by ECa is 0.19–0.36 (farmland, mean value is 0.28), grassland is 0.16–0.49 (shrub/grassland, mean value is 0.34), and bare land is 0.28–0.70 (bare land, mean value is 0.56). Among them, ECav01 has the best predictive ability. As the depth increased, the influence of soil-related variables decreased, and the contribution of climate-related variables increased. The main factor affecting ECa variation was climate-related variables, followed by vegetation-related variables and soil-related variables. Scatter plot show ECa was significantly correlated with ECe_HWSD_030 (0–30 cm, r = 0.482, p < 0.01) and ECe_HWSD_30100 (30–100 cm, r = 0.556, p < 0.01). The predicted spatial ECa maps were similar to the ECe values from HWSD, but also implies that the distribution of soil water and salt has undergone tremendous changes since 1980s. The study demonstrates that EMI data provide a reliable and cost-effective tool for obtaining high-resolution soil maps that can be used for better land evaluation and soil improvement at larger scales.

Effects of alternate moistube-irrigation on soil water infiltration

Alternate moistube-irrigation is a new type of water-saving irrigation, and research on water infiltration with alternate moistube-irrigation is important for the design of irrigation schemes and helpful to understand and apply this technology. The effects of the pressure head (1.0 m and 1.5 m) and tube spacing (10 cm, 20 cm, and 30 cm between two moistubes respectively) on soil water infiltration in alternate moistube-irrigation were studied in laboratory experiments, and the cumulative infiltration, discharge of the moistube, and shape and water distribution of the cross-section of the wetting front were determined. The cumulative infiltration increased quickly and linearly with the infiltration time at 0-96 h (R2>0.99), and changed smoothly at 96-192 h with a basically steady infiltration rate. The discharge of the moistube increased rapidly at the beginning of irrigation, then decreased before stabilizing. The cumulative infiltrations and discharges of moistube under the 1.5 m pressure head were more than those under the 1.0 m pressure head. The shape of the cross-section of the wetting front for a single moistube was similar to a concentric circle. With the increase of tube spacing, the interaction between water infiltrations of two moistubes decreased. The soil water distributions around two moistubes were similar to each other under the 1.0 m pressure head and large tube spacing. When the tube spacing was 20 cm, the soil water distribution was more uniform around two moistubes. Keywords: alternate irrigation, moistube-irrigation, soil water infiltration, water use efficiency, water-saving irrigation DOI: 10.25165/j.ijabe.20201304.5297 Citation: Shen L X, Zhang Y M, Yang M, Liu R H. Effects of alternate moistube-irrigation on soil water infiltration. Int J Agric & Biol Eng, 2020; 13(4): 151–158.

Effect of vegetation patchiness on the subsurface water distribution in abandoned farmland of the Loess Plateau, China

Patchiness of grassland results in important effects on ecohydrological processes in arid and semiarid areas; however, the influences on subsurface water flow and soil water distribution remain poorly understood, particularly during vegetation succession on slopes. This study examined these effects by comparing the water flow behaviors and preferential infiltration between vegetation patches (VP) and interspace patches (IP) in three sites at different states of vegetation succession (grass, subshrub and shrub) in abandoned farmland of the Loess Plateau, China. Dye tracer infiltration showed that patchiness of vegetation increased spatial variations of soil water and preferential infiltration by increasing the densities of fine root length and fine root volume in the soil profile. Moreover, the more abundant and intricate roots following a lateral direction beneath VP likely contributed to lateral flow and infiltration variability. However, differences between VP and IP were not significant because considerable living fine roots and decayed roots of IP also provided preferential flow pathways. Our finding indicated that IP could compete with VP for access to soil water resources, which potentially increased hillslope-scale infiltration and reduced surface runoff and erosion risk. Under the different states of vegetation succession, subshrub patches showed significantly greater preferential infiltration volume (28.53 mm) and contribution of preferential infiltration to total infiltration (60.58%) than grass and shrub patches. Vegetation patch size made positive effects on improving preferential flow and water movement. Greater preferential flow in subshrub patches played a positive role in soil water storage and replenishment. Therefore, natural restoration of a slope area with small heterogeneity in preferential flow can be successfully applied in the Loess Plateau, particularly during the subshrub succession state.

Mass‐balance approach to quantify water distribution in soils based on X‐ray computed tomography images

AbstractX‐ray computed tomography (CT) is commonly used in soil science to quantify distributions of pores, water and solids within soil samples. Particularly promising for liquid visualization is dual‐energy scanning of samples with added dopant solutions. The approach uses solutions of heavy elements as a proxy for the soil water and utilizes the abrupt increase of the mass attenuation coefficient of heavy elements when crossing an X‐ray absorption edge, detectable by dual‐energy CT scanning. However, a key step in visualization of the added liquid is image segmentation. In partially saturated soils, the X‐ray CT images consist of voxels with the presence of solid, liquid and gaseous phases in different ratios. These ratios are generally ignored by the traditional image segmentation methods, which separate image voxels into groups with either zero or complete saturation by either prevailing phase. The objective of this study was to develop and test a new physically based segmentation approach that accounts for partial saturation of image voxels by liquids. We combined a theoretical equation for detected photon intensity with the mass conservation equation to compute saturation of image voxels by dopant solution applied to the soil. This approach was tested on soil micro‐columns with potassium iodide (KI) solutions. The proposed approach outperformed the traditional segmentation methods, particularly at low and intermediate water contents. Tests conducted for KI solutions in the concentration ranges from 2 to 20% revealed deterioration of the method accuracy with decreasing dopant concentration in the soil. Based on the results of this study we recommend 10 wt% KI solution for quantifying spatial distribution of liquids in soils using dual‐energy X‐ray microtomography.Highlights We developed a new approach to quantify soil water distribution based on X‐ray CT. This approach accounts for partial saturation of image voxels by liquids. This approach outperforms the standard image segmentation methods. Its application is limited to using dual energy monochromatic X‐ray beams.

Long-term simulation of potentially toxic elements (PTEs) accumulation and breakthrough in infiltration-based stormwater management practices (SMPs)

Stormwater management practices (SMPs) rely on infiltration and adsorption capabilities of soil and vegetative cover to mitigate the harmful impacts of contaminants in stormwater runoff, including potentially toxic elements (PTEs). Under chemical equilibrium conditions, the soil-water distribution coefficient (Kd) quantifies the relationship between the solid and aqueous phase PTE concentrations, and thus the PTE removal efficiency and mobility through the SMP soil layers during the infiltration process. The SMP loading ratio (LR), the ratio of the drainage area to the SMP infiltration area, combined with runoff concentration determines SMP mass loading and is also expected to impact PTE transport. In this study, a simulation model was developed to investigate PTE breakthrough and build-up in SMP media, considering the impacts of Kd and LR. Eight PTEs were simulated (Cl−, Cr, Fe, Zn, Cu, As, Cd, and Pb), and Cl− was the only PTE that showed high mobility and reached the groundwater table (e.g., ~ 1 year for breakthrough). Conversely, other PTEs were effectively immobilized in the top ~60 cm of soil for a simulated lifespan of 20 years. Soil and porewater contaminant indices, as indicators of SMP lifespan, were estimated based on the ratio of PTE porewater and soil concentrations after 20 years to published standards, suggesting the following order of environmental significance (most concern to least): Cl− > Cr > As > Pb > Fe > Cu > Cd > Zn. After 20 years of simulated use, only Cl− pore water concentrations at the groundwater table exceeded regulatory values, with porewater contamination index values of 4 to 7.5. Chloride also exceeded the surficial media soil contamination index, as did As and Cr, though these exceedences were largely associated with media background concentrations. Generally, higher LR and Kd contributed to higher accumulation of PTEs in top layers; however, simulations showed that the combination of low LR and high Kd may result in lower PTE accumulation in the media, such that the PTE concentration in soil may decrease in deeper layers. In these scenarios, a notable fraction of PTE load was adsorbed on top layers and considerably lower PTE concentrations reached the lower layers. Sensitivity analysis revealed that dispersion, infiltration rate, and kinetically-limited sorption did not impact the PTE accumulation and mobility to a practical extent. The results from this simulation may be adapted to various environmental conditions to enhance the design and maintenance of SMPs.

Modelling soil water distribution under Moistube irrigation for cowpea (VIGNA unguiculata (L.) Walp.) crop*

AbstractMoistube irrigation (MTI) is a type of technology which uses a semipermeable membrane to emit water continuously in response to soil water potential and applied pressure. Soil water dynamics under MTI incorporating plant water uptake have not been studied. Therefore, this study aimed at determining the soil water distribution under MTI, using cowpea as a reference crop. The effect of Moistube placement depth on the soil water dynamics under MTI was also determined. The experiment was carried out in tunnels with MTI and subsurface drip irrigation (SDI) as a control. The HYDRUS 2D/3D model was calibrated and thereafter used to simulate soil water dynamics for different placement depths. The soil water content above the Moistube/drip lateral was higher under SDI than MTI, while the lateral movement of water was similar for both irrigation types. The simulated soil water contents closely matched (coefficient of determination [R2] ≥ 0.57, root mean square error [RMSE] ≤ 0.029 cm3 cm−3, normalized root mean square error [NRMSE] ≤ 14.7% and efficiency [EF] ≥ 0.20) the observed values for both MTI and SDI. This showed that HYDRUS 2D/3D could be used to simulate water dynamics of irrigated cowpea. There was no significant difference (p > .05) between the root water uptake (RWU) in SDI and MTI. The Moistube placement depth did not significantly affect (p > .05) the RWU in loam soil but increased with increased placement depth in clay soil. The optimum placement depth of Moistube laterals for cowpea was 15 cm in loam and 20 cm in clay. This study forms the basis for design of MTI in terms of optimum placement depths for cowpea grown in loam and clay soils.

Parameterization of the water stress reduction function based on soil–plant water relations

Rational parameterization of the soil water stress reduction function in root water uptake model is crucial for accurate description of root water uptake and simulation of soil water dynamics in a soil–plant system. In this study, we propose three improvements to a popular transpiration-based approach to parameterize the water stress reduction function in a widely used macroscopic root water uptake model. The improvements are based on the interdependent relationships between soil and plant water status and consideration of effects of (1) relative distribution of soil water to roots on transpiration; (2) differences in growth levels of plants exposed to different levels of water stresses on potential transpiration; and (3) hysteresis of water stress on parameter optimization through identifying and discarding the data involved in the recovery periods when the discrepancy between soil and plant water availability is significant. Lysimetric experiments with winter wheat planted alternatively in greenhouse soil columns and in a field were conducted to test the proposed improvements. Through minimizing the residuals between the measured and estimated actual transpiration, the optimized parameterization was used to set up the root water uptake model. Thereupon, actual transpiration and relative transpiration were estimated and soil water content distributions were simulated. The estimated actual (RMSE ≤ 0.09 cm day−1) and relative (RMSE = 0.06) transpiration agreed well with the measurements. The simulated soil water content distributions also matched the measured values well for both experiments (RMSE ≤ 0.023 cm3 cm−3). Omitting any of the three proposed improvements reduced the estimation accuracy of relative transpiration, as the individual contribution ratio for each improvement was between 21.2 and 51.2%. The improvements should be reasonable in providing rational parameter estimation for the water stress reduction function, from which root water uptake models can be established to accurately evaluate plant transpiration and simulate soil water flow in a soil–plant system. The parameterization strategy for the water stress reduction function of root water uptake not only benefits accurate evaluation of plant transpiration under drought conditions but also contributes to further study and description regarding the apparent hysteresis of root water uptake after re-watering.

Influences of revegetation mode on soil water dynamic in gully slope of the Chinese Loess hilly–gully region

Gully slope is one of the most active areas of soil erosion in small watershed of the Chinese Loess hilly–gully region. Although its soil erosion has been effectively controlled with the implementation of the “Grain-for-Green Program” in this region, the soil water storage and distribution have been also impacted. In particular, unreasonable revegetation model has aggravated the water shortage, which may in turn threaten the health of ecosystems. However, yet little is known about the effect mechanism of vegetation on soil water in the gully slope. In this study, we examined the relationship between two revegetation modes, including afforestation (i.e. black locust forest) and natural revegetation (i.e. the grassland), and soil water in a depth of 0–120 cm of the gully slope, during the rainy season. The results showed that the effect of the vegetation to the soil water was smaller than that of the precipitation. Furthermore, the response of soil water to the environmental factors was higher in afforestation vegetation due to its lower soil water content, resulting in higher space dependence for soil water, compared to the natural revegetation. The lower soil water content of the black locust forest was mainly caused by its higher recession rate, not its supply. The soil water was deficient for a long time, caused by afforestation, with a shallower formation depth of the dried soil layer and stronger desiccation degree. However, this deficient could not be effectively relieved until in wet year. In comparison with the ridge slope, the effect of vegetation to soil water in gully slope was stronger, with greater water consumption in afforestation vegetation and the higher water storage in natural revegetation. From the aspect of water resources conservation on the water scale, the natural revegetation was the optimal revegetation mode in the gully slope of the loess hilly region.

Parameterization of Soil Hydraulic Parameters for HYDRUS-3D Simulation of Soil Water Dynamics in a Drip-Irrigated Orchard

Although surface drip irrigation allows an efficient use of water in agriculture, the heterogeneous distribution of soil water complicates its optimal usage. Mathematical models can be used to simulate the dynamics of water in the soil below a dripper and promote: a better understanding, and optimization, of the design of drip irrigation systems, their improved management and their monitoring with soil moisture sensors. The aim of this paper was to find the most appropriate configuration of HYDRUS-3D for simulating the soil water dynamics in a drip-irrigated orchard. Special emphasis was placed on the source of the soil hydraulic parameters. Simulations parameterized using the Rosetta approach were therefore compared with others parameterized using that of HYPROP + WP4C. The simulations were validated on a seasonal scale, against measurements made using a neutron probe, and on the time course of several days, against tensiometers. The results showed that the best agreement with soil moisture measurements was achieved with simulations parameterized from HYPROP + WP4C. It further improved when the shape parameter n was empirically calibrated from a subset of neutron probe measurements. The fit of the simulations with measurements was best at positions near the dripper and worsened at positions outside its wetting pattern and at depths of 80 cm or more.

Modeling Approaches for Determining Dripline Depth and Irrigation Frequency of Subsurface Drip Irrigated Rice on Different Soil Textures

Water saving techniques such as drip irrigation are important for rice (Oriza sativa L.) production in some areas. Subsurface drip irrigation (SDI) is a promising alternative for intensive cropping since surface drip irrigation (DI) requires a higher degree of labor to allow the use of machinery. However, the semi-aquatic nature of rice plants and their shallow root system could pose some limitations. A major design issue when using SDI is to select the dripline depth to create appropriate root wetting patterns as well as to reduce water losses by deep drainage and evaporation. Soil texture can greatly affect soil water dynamics and, consequently, optimal dripline depth and irrigation frequency needs. Since water balance components as deep percolation are difficult to estimate under field conditions, soil water models as HYDRUS-2D can be used for this purpose. In the present study, we performed a field experiment using SDI for rice production with Onice variety. Simulations using HYDRUS-2D software successfully validated soil water distribution and, therefore, were used to predict soil water contents, deep drainage, and plant water extraction for two different dripline depths, three soil textures, and three irrigation frequencies. Results of the simulations show that dripline depth of 0.15 m combined with one or two daily irrigation events maximized water extraction and reduced percolation. Moreover, simulations with HYDRUS-2D could be useful to determine the most appropriate location of soil water probes to efficiently manage the SDI in rice.

Effects of vegetation on the distribution of soil water in gully edges in a semi-arid region

Gully bank is an important part of the eroded gully and is an ecologically fragile zone. Vegetation and soil water play critical roles for regulating the hydrological process of gully banks and preventing the soil collapse of gully edge in arid and semi-arid areas. However, the effects of different vegetation on the distribution of soil water in the gully edge are still unknown in semi-arid areas. In this study, the variation in soil water content (SWC) was studied at distances of 0.5 m (D0.5), 2.0 m (D2.0), and 3.5 m (D3.5) from the gully edge in a shrubland (SL), bare land after removal of shrubs (SBL), grassland (GL), and bare land after removal of grasses (GBL). The results showed that SWC reduced with proximity to the gully edge in SBL and GBL. Soil water storage in both SL and GL was higher at D0.5 than at D2.0 and D3.5. In both dry and wet seasons, SWC in SL was significantly lower than that in GL at all locations (P < 0.05). Compared with SBL, the SWC in SL in the wet season significantly reduced 15.42%, 27.56%, and 27.73% at D0.5, D2.0, and D3.5, respectively (P < 0.05). Our findings suggest that grasses should be considered as a suitable choice for revegetation in gully banks to prevent excessive soil water depletion by shrubs and reduce the risk of soil collapse in the gully edge. These findings provide insights into the effects of different vegetation types on soil hydrological processes in gully edges.

Estimating Method of Maximum Infiltration Depth and Soil Water Supply

The maximum infiltration depth and soil water supply must be evaluated in order to estimate the soil water resource use limit by plants and soil water carrying capacity for vegetation, and realize the sustainable use of soil water resources. However, there is no non-destructive method to estimate maximum infiltration depth and soil water supply. We conducted a simulated infiltration experiment and a long-term fixed-position investigation in situ in artificial Caragana shrubland at the Guyuan Eco-experimental Station in the semiarid Loess Plateau. The results showed that infiltration depth for one rain event was equal to the distance from the surface to the crossover point between the two soil water distribution curves with soil depth before a rain event and after the rain event. The soil water supply for one rainfall event was the difference in the soil water resources in the soil layers from maximum infiltration depth that occurred after a long period, and could be estimated by a series of two-curve methods. A maximum infiltration depth of 2.9 m occurred in the artificial Caragana shrubland. The results provide a foundation for controlling soil degradation and sustainable use of soil water resources in water-limited regions.

Influence of Living and Dead Roots of Gansu Poplar on Water Infiltration and Distribution in Soil

During rapid urbanization, it is necessary to increase soil permeability and soil porosity for reducing urban runoff and waterlogging risk. Woody plants are known to increase soil porosity and preferential flow in soil via living roots growth and dead roots decay. However, the primary results of dead woody plant roots on soil porosity and permeability have been discussed based only on the hypotheses or assumptions of different researchers. In this study, living and dead roots (decayed under natural conditions for more than 5 years) of Gansu poplar trees (Populus gansuensis) were selected. They were selected to compare the influence between living and dead roots on water infiltration rate and soil porosity in a cylindrical container (diameter = 20 cm, height = 66 cm) under laboratory conditions. Results indicated that the steady-state water fluxes at the bottom of the containers without roots (control), with living roots, and with dead roots were 54.75 ± 0.80, 61.31 ± 0.61, and 55.97 ± 0.59 cm d−1, respectively. Both living roots and dead roots increased the water infiltration rates in soil and also increased the water storage capacity of soil. The water storage capacities of soil without roots, with living roots, and with dead roots were 0.279, 0.317, and 0.322 cm3 cm−3, respectively. The results from SEM indicated that smaller pores (30–50 μm) were in living roots and larger pores (100–1000 μm) were in dead roots. The soil permeability was increased by living roots possibly due to the larger channels generated on the surface of the roots; however, water absorbed into the dead roots resulted in greater water storage capacity.

Temporal and spatial distribution of soil water and nitrate content affected by surface irrigation and fertilizer rate in silage corn fields

Among surface irrigation systems, long border and furrow are more adaptive to mechanized farming but may cause a non-uniform distribution of water and nutrients. In this study, field experiments were carried out in a flat silage corn field in Hebei, China to investigate the uniformity along the length of border or furrow to understand the spatial and temporal distribution characteristics of soil water, electrical conductivity, and nitrate. This will guide irrigation and fertigation management recommendations, land consolidation, and high standard farmland construction. Border and furrow irrigation were tested using fertilizer rates of 750, 600, 450 and 300 kg/ha. Low quarter distribution uniformity (DUlq) and storage efficiency (E) were quantified to determine the distribution of soil water and soil nitrate content. The results indicate heterogeneity along the length of the border or furrow is weak for soil water content and is moderate for nitrate content, based on the uniformity coefficient (CV). The average low quarter distribution uniformity of soil water (DUlqW) was 96.34, there was a significant effect of irrigation type on DUlqW, and the DUlqW for border irrigation was 0.8% larger than that for furrow irrigation. The average low quarter distribution uniformity of nitrate content DUlqN was 79.04, and there was no significant influence of irrigation type and fertilizer rate on DUlqN. Spatial and temporal distribution analysis showed that the variation of soil water in the 0–60 cm soil layer was larger than that in 60–100 cm soil layer, and the electrical conductivity (EC) and nitrate content gradually decreased with increasing soil depth. There was a decreasing trend in soil EC and nitrate content with decreasing fertilizer rates. The storage efficiency of water (EW) for border irrigation was 56.63, and significantly lower than that for furrow irrigation over the whole growth duration. The nitrate storage efficiency (EN) was 65.47, and there was no significant effect of irrigation type or fertilizer rate on EN. Even with longer borders or furrows of 90 m, the uniformity of water and nitrate along the length of the border or furrow is weak or medium, which can create non-uniform conditions for crop growth. Furrow irrigation may store slightly more water in the top 60 cm of soil compared to border irrigation. Fertilizer rate had no significant effect on the uniformity and distribution of soil water or nitrate.

Characteristics of soil water and salt associated with Tamarix ramosissima communities during normal and dry periods in a semi-arid saline environment

Tamarisk (Tamarix ramosissima) plants are widely distributed in semi-arid regions with saline soils. In these environments, the survival and sustainability of the Tamarisk plants are critically related to the availability and distribution of soil water and salt. In this study, we analyzed the soil water content (SWC) and soil electrical conductivity (EC) to the depth of 60 cm in natural Tamarisk communities, located in a semi-arid saline region of northwestern China, in July 2016 (a normal period) and July 2017 (a dry period). The results showed that SWC varied from 1.91 to 7.82% and soil EC ranged from 9.65 to 25.38 mS/cm in the 0–60 cm soil layer. Despite the deficiency of precipitation in the study period of 2017, the SWC in all plots was higher at the 20–60 cm depth than that of the normal study period in 2016. Compared to 2016, the soil was also less saline in 2017, representatively by lower soil EC values at the 0–40 cm depth. Additionally, the SWC decreased with Tamarisk density, indicating that Tamarisk plants increase water consumption. The SWC and soil EC both revealed “island” distribution, with highest level found inside or underneath the Tamarisk plant canopies. Both the SWC and soil EC presented a strong or moderate spatial dependency, and the spatial dependency in soil EC were significantly affected by community composition. Correlations (Pearson’s r) showed that there were positive correlations between SWC and soil EC. The results above indicate that Tamarisk communities can ameliorate the semi-arid high saline soil environment, and that the growth and distribution of Tamarisk plants influence the spatiotemporal variability of SWC and soil EC. In addition, the results also demonstrate that the possible appropriate density in the process of constructing Tamarisk plants should be considered in order to achieve the optimal water condition. The study may provide a scientific basis for the ecological restoration and halophytes establishment in the semi-arid saline region of northwestern China and other areas with similar ecologies.

Soil water availability shapes species richness in mid‐latitude shrub steppe plant communities

AbstractQuestionsEcological communities are controlled by multiple, interacting abiotic and biotic factors that influence the distribution, abundance, and diversity of species. These processes jointly determine resource availability, resource competition, and ultimately species richness. For many terrestrial ecosystems in dryland climates, soil water availability is the most frequent limiting resource for plant species. We used field sampling coupled with process‐based soil water balance modeling to explore the relative importance of multiple macroclimatic, ecohydrological, and biotic variables on plant species and functional type richness at the landscape scale in dryland plant communities.LocationDryland plant communities dominated by big sagebrush (Artemisia tridentata) that span climatic and elevational gradients in Wyoming, USA.MethodsWe quantified species richness at 1,000 m2 and used multiple regression to determine whether mean climatic conditions, multiple metrics of soil moisture from a soil water balance model (SOILWAT2), soil physical and chemical properties, and shrub stand structure (biotic) variables were related to species and functional type richness.ResultsSpecies richness varied between 16 and 54 across sites. We found that species and functional type richness were related to both macroclimate and ecohydrology, but ecohydrology explained slightly more variation than climate. Biotic variables were always secondary to macroclimate and ecohydrology in our models. Variance partitioning revealed that large portions of variability in species (~54%), forb (~47%), and grass (~40%) richness were explained by ecohydrological variables.ConclusionsOur results highlight the importance of the spatial and temporal distribution of soil water for dryland plant species richness and suggest that documenting the ways in which climate, vegetation, and soil properties interact to determine soil water availability is critical for understanding biodiversity patterns in dryland plant communities. This work has relevance for other mid‐latitude, shrub‐dominated dryland plant communities where soil water availability strongly influences ecosystem structure and function.

Effect of Plastic Film Residue on Vertical Infiltration Under Different Initial Soil Moisture Contents and Dry Bulk Densities

In arid and semi-arid regions, plastic film mulching can effectively improve crop yield, but with the increase of service life, a lot of residual plastic film (RPF) remains in the soil. The application of a RPF to a soil will alter soil moisture processes, and thus, affect the soil water distribution and its effectiveness. A quadratic regression orthogonal design was used to study the effects of initial moisture content (IMC), dry bulk density (DBD), residual plastic film content (RPFC), and the burial depth of RPF on the migration time of wetting front (MF), moisture content (MC), and accumulative infiltration (AI) of a test soil. It was found that IMC, DBD, and RPFC were the main factors affecting MC, MF, and AI, while the burial depth of RPF had no significant influence. The order of influence for the factors affecting MF was IMC &gt; DBD &gt; RPFC, while the order of influence for the factors affecting MC and AI was DBD &gt; IMC &gt; RPFC. RPFC was parabolic in relation to MF, MC, and AI, when it was in the range of 50–100 kg/hm2, while within the same range MC and AI reached a maximum and MF reached a minimum. The analysis of the interactive responses revealed that when the DBD was greater than 1.29g/cm3, the MF initially decreased and then increased with the increase of RPFC. When the RPFC was more than 100 kg/hm2, the MF initially increased and then decreased with the increase of the DBD. When the DBD was larger than 1.31 g/cm3, the AI initially increased and then decreased with the increase of RPFC. It was apparent that the RPF not only had a blocking effect on the wetting front, but also affected the water flow. When the RPFC was between 50 and 100 kg/hm2, the soil MC was significantly increased. It was suggested that the RPF pollution area should increase the mechanical recovery of plastic film, standardize the use and recycling of agricultural RPF, optimize the planting model, and establish a recyclable model for the treatment of RPF pollution, and it was proposed that the RPFC remaining after recovery of the RPF should be less than 50 kg/hm2.This study can prove the law of soil water movement in the residue film pollution area and provide reference and solution ideas for the comprehensive treatment of residue film pollution in farmland.

Effect of mulching and subsurface drip irrigation on soil water status under arid environment

Aim of study: We investigated water evaporation of the soil surface and the soil water distribution under different mulching techniques using subsurface drip irrigation (SDI) system.Area of study: The experiment was conducted at the Agricultural Research and Experimental Farm in Dirab, Riyadh, Saudi Arabia, locating 24.4195° N, 46.65° E, and 552 m altitude.Material and methods: The two types of soil surface mulching were black plastic film (BPF) and palm tree waste (PTW), with no mulching (NM) as control. The two drip line depths from the soil surface (DL) were 15 cm and 25 cm, and surface drip irrigation (DI) was the control.Main results: In SDI, the use of BPF or PTW mulching resulted in enhanced water retention capacity of the soil and an approximately 6% water saving, compared with NM. The amounts of water saved at DL of 15 cm (19-24 mm) were greater than those at DL of 25 cm (15-20 mm), whereas the DI used the highest amount of applied water. The distribution of soil water content for BPF and PTW were found to be more uniform than NM.Research highlights: It is advised to mulch the soil with PTW due to lower costs and through a DL of 15 cm.

Interplay between Fingering Instabilities and Initial Soil Moisture in Solute Transport through the Vadose Zone

Modeling water flow and solute transport in the vadose zone is essential to understanding the fate of soil pollutants and their travel times towards groundwater bodies. It also helps design better irrigation strategies to control solute concentrations and fluxes in semiarid and arid regions. Heterogeneity, soil texture and wetting front instabilities determine the flow patterns and solute transport mechanisms in dry soils. When water is already present in the soil, the flow of an infiltration pulse depends on the spatial distribution of soil water and on its mobility. We present numerical simulations of passive solute transport during unstable infiltration of water into sandy soils that are prone to wetting front instability. We study the impact of the initial soil state, in terms of spatial distribution of water content, on the infiltration of a solute-rich water pulse. We generate random fields of initial moisture content with spatial structure, through multigaussian fields with prescribed correlation lengths. We characterize the patterns of water flow and solute transport, as well as the mass fluxes through the soil column. Our results indicate a strong interplay between preferential flow and channeling due to fingering and the spatial distribution of soil water at the beginning of infiltration. Fingering and initial water saturation fields have a strong effect on solute diffusion and dilution into the ambient water during infiltration, suggesting an effective separation between mobile and inmobile transport domains that are controlled by the preferential flow paths due to fingering.

Characterizing fast herbicide transport in a small agricultural catchment with conceptual models

Herbicide pollution in headwater streams due to agricultural practices is a major environmental concern and is characterized by episodic peak concentrations from fast transport paths. We rely on previous experimental studies in a small (1.2km2) agricultural catchment in the Swiss Plateau, to model dynamic diffuse herbicide pollution with emphasis on fast transport paths in a conceptual modelling framework at the catchment scale. We show how experimentalists’ understanding of the fate of herbicides (perceptual model) can be translated into conceptual models considering sorption, degradation, and fast transport of water and chemicals facilitated by impervious surfaces, tile drains and artificial shortcuts. Different types of experimental data (streamflow, high-frequency concentration measurements, and soil–water distribution coefficients) are used in a joint Bayesian inference of model parameters. We assess the ability of different spatial configurations of hydrological response units in explaining observed heterogeneity in transport behaviour of two corn herbicides. Thereby, we find that (1) relatively simple conceptual models can provide a realistic description of herbicide fate in small agricultural catchments, (2) accounting for spray drift onto hard surfaces is necessary to avoid a severe model bias during the first rainfall event after application, and (3) including catchment-specific experimentalist knowledge about important elements like artificial shortcuts and tile drains leads to a reduction in uncertainty of 30% compared to the more conventional conception of the proximity to the stream as the dominant risk factor.