Soil Water Distribution Research Articles

Paddy Field Water Movement Through Soil Profiles Under Different Water Management Practices: A HYDRUS 1D Model Study

Physical measurement of hydrological processes through soil profile is very complicated and timeconsuming. Complex and coupled physical processes like water movement with soil matric potential in puddled paddy field can be simulated using physical process-based model HYDRUS 1D. The model simulation was setup for the multilayered (different soil materials at 0-15 and 15-30 cm depth) paddy fields having continuous flooded irrigation (CFI) practice and water saving Alternate Wetting and Drying (AWD) practice. Measured soil physical properties of three Bangladesh Rice Research Institute (BRRI) regional station farms (Kushtia, Sirajganj, and Rangpur) were used as model input, initial and boundary conditions configuration. The model was calibrated and validated using the water data of a dry season field experiment in Kushtia. The calibrated (RMSE of 0.54 cm, d of 0.94, NSE of 0.89) water level data validated successfully with observed water level data of AWD practiced paddy field (d of 0.95, NSE of 0.92). Soil water content reached the threshold/critical level in AWD practice (-101 cm of water soil matric potential at 15 cm soil depth) earlier in light textured soil (loam or sandy loam) compared to heavy textured soil (clay). The physical properties of the layered soils (i.e., soil particle size distribution and soil water release curve, SWRC) did not affect much on water movement in CFI practice, but it had substantial impact on field water movement under AWD practice. The change in soil water storage followed the general trend for respective soil water holding and releasing capacity, clay soil was heavier and released water slowly than that of loam or sandy loam soils. The positive water flux above 15 cm of soil profile mainly drove the water flow due to evapotranspiration and soil water and pressure distribution along the soil profile while the negative fluxes below 15 cm of soil depth due to infiltration or percolation contributed as a secondary force. A basic understanding of HYDRUS simulated results would lead to realize the total physiohydrological environment in the paddy field. Bangladesh Rice J. 25 (2) : 57-67, 2021

Soil water distribution and dynamics across prescribed capillary barriers under evaporating surfaces

Soil water distribution and dynamics across prescribed capillary barriers under evaporating surfaces

Considering spatio-temporal dynamics of soil water with evapotranspiration partitioning helps to clarify water utilization characteristics of summer maize under deficit irrigation

Continuously increasing the utilization efficiency of agricultural water resources is vital to ensuring future water and food security. Deficit irrigation (DI) could provide a solution to optimize crop water productivity. Research on the spatio-temporal dynamics of soil water coupled with evapotranspiration partitioning is important for clarifying summer maize (Zea mays L.) water utilization characteristics and crop water productivity under different DI strategies, especially in semi-arid regions. Consequently, a three-year field experiment with full irrigation (CK) and eight DI treatments (T1–T8, comprised of combinations of 100 %, 80 %, and 60 % of crop evapotranspiration) was conducted. Data from large-scale weighing lysimeters, micro-lysimeters, and TDR sensors were combined to assess daily root water absorption at different soil depths, actual evapotranspiration (ETa) partitioning into plant transpiration (T) and soil water evaporation (E), and water use efficiency (WUE). Results showed that soil water consumption mainly occurred in the 0–40 cm, 0–60 cm, and 0–80 cm soil layers during the maize growth stages of planting–V6, V6–V12, and V12–R6, respectively. Water absorption above the 60-cm soil depth accounted for more than 92 % of the total water consumption. The appropriate irrigation wetting depth for summer maize could be controlled in the top 80-cm layer to avoid deep percolation. DI affected soil water distribution and availability, and thus decreased soil water consumption rate (WCR) and root water absorption amount. Under moderate water deficit conditions, WCR was rapidly restored to the non-water-stressed irrigation treatment level, and even exceeded that level in the deeper layers after a subsequent irrigation was applied, especially in the early maize growth stages. E/ETa was 31.0–32.5 % under full irrigation. DI decreased total soil water evaporation amount, but increased the E/ETa ratio. The threshold soil water value for defining when maize was subjected to water stress was 22.0 % (72 % of FC) during V3–V12, and 18.0 % (60 % of FC) during V12–R1. Our results suggest that less water was used in T1 (moderate DI) than with the full irrigation treatment. WUE increased by 5.5 %–7.5 % as irrigation amount decreased by 12.3–14.5 % and yield decreased by 3.3 %–8.0 %. These results improve our understanding of maize water consumption characteristics with regard to soil water absorption in different soil layers and evapotranspiration partitioning, and provide implications for efficient water management in arid areas of northwest China.

Numerical Simulation of Soil Water Dynamics in Automated Drip Irrigated Okra Field Under Plastic Mulch

Abstract In India, drip irrigation with plastic mulch is a common practise for irrigation that conserves water. For the design and administration of irrigation regimes, a thorough understanding of the distribution and flow of soil water in the root zone is required. It has been demonstrated that simulation models are effective tools for this purpose. In this work, an automated drip-irrigated Okra field with seven treatments namely T1- Soil moisture-based drip irrigation to 100% FC, T2- Soil moisture-based drip irrigation to 80% FC, T3- Soil moisture-based drip irrigation to 60% FC, T4- Timer based drip irrigation to 100% CWR, T5- Timer based drip irrigation to 80% CWR, T6- Timer based drip irrigation to 60% CWR and T7- Conventional drip irrigation at 100% CWR were utilised to mimic the temporal fluctuations in soil water content using the numerical model HYDRUS- 2D. With the help of the observed data, the inverse solution was used to optimise the soil hydraulic parameters. The model was used to forecast soil water content for seven field treatments at optimal conditions. Root mean square error (RMSE) and coefficient of determination (R2) were used to assess the congruences between the predictions and data. With RMSE ranging from 0.036 to 0.067 cm3 cm- 3, MAE ranging from 0.020 to 0.059, and R2 ranging from 0.848 to 0.959, the findings showed that the model fairly represented the differences in soil water content at all sites in seven treatments.

The effect of different biocrusts on soil hydraulic properties in the Tengger Desert, China

Water redistribution profoundly affects the dryland ecosystem’s function. Biological soil crusts (BSCs or biocrusts), which cover a large part of soil surface in arid land, significantly affect the water redistribution, but the results are conflicting at regional scale. In this study, the effects of different biocrusts on soil hydraulic properties, including soil water retention curve, soil water sorptivity, soil hydrophobicity and unsaturated hydraulic conductivity, were clarified in Tengger Desert. The results showed that the presence of BSCs significantly changed soil hydraulic properties. Compared to sand, BSCs increased water holding capacity and soil hydrophobicity, and decreased soil water sorptivity and unsaturated hydraulic conductivity. The enrichment of fine particles during the change from the less to the more developed BSCs contributed to the enhancement of water holding capacity, but this effect was mainly limited at 3-cm layer of soil underneath the ground surface. Soil hydrophobicity decreased with crust development, which contributed to the increase of soil water sorptivity. Unsaturated hydraulic conductivity decreased during the change from the less to the more developed BSCs, which exerted some negative effect on water infiltration. Our results highlight the important role of BSCs in hydraulic properties, and consideration of biocrusts and its hydrological behavior could help us better understand the distribution, movement and retention of soil water in this area.

A nuclear magnetic resonance based quantification of pore water distribution in unsaturated soils

This study presents a novel approach to quantify the distribution characteristics of pore water in unsaturated soil by using the nuclear magnetic resonance (NMR) technology. The SWCC and NMR T2 curves under different matric suction were measured during the drying process of soil specimen, and a conversion relationship between T2 and pore radius r of was determined. The method using capillary drainage model to simulate soil drying process was feasible, and pores of unsaturated soil were divided into saturated pore, unsaturated pore, and dry pore when the suction exceeded the air entry value. Pore water distribution curve based on T2 well described the distribution characteristics of pore water in unsaturated soil; the quantification of pore water distribution was realized through a defined index named pore water damage potential (Mcp), and a good mathematical relationship was observed between the relative damage degree and the matric suction. By introducing the Mcp, a modified VG model that reflected the characteristics of pore water distribution was in a good quantitative agreement with the experimental observations. The results achieved provided a valuable reference for revealing the internal mechanism of SWCC and establishing mechanical model of unsaturated soil based on pore water distribution.

Effects of Different Land Use Patterns on Soil Water in Loess Hilly and Gully Regions of China.

Soil water is a major barrier to ecological restoration and sustainable land use in China’s Loess Hilly Region. For the restoration of local vegetation and the optimal use of the region’s land resources, both theoretically and practically, it is essential to comprehend the soil water regimes under various land use types. The soil water content in the 0−160 cm soil profile of slope cropland, terraced field, jujube orchard, and grassland was continuously measured using EC-5 soil moisture sensors during the growing season (May−October) in the Yuanzegou catchment in the Loess Hilly Region to characterize the changes in soil water in these four typical land use types. The results showed that in both years of normal precipitation and drought, land use patterns varied in seasonal variability, water storage characteristics, and vertical distribution of soil water. In the dry year of 2015, the terraced field effectively held water. During the growing season, the 0−60 cm soil layer’s average soil water content was 2.6%, 4.2%, and 1.8% higher than the slope cropland, jujube orchard, and grassland, respectively (p < 0.05), and the 0−160 cm soil layer’s water storage was 43.90, 32.08, and 18.69 mm higher than the slope cropland, jujube orchard, and grassland, respectively. The average soil water content of the 0−60 cm soil layer in the jujube orchard was 2.9%, 3.8%, and 4.5% lower than that of slope cropland, terraced field, and grassland, respectively, during the normal precipitation year (2014) (p < 0.05). Only 35.0% of the total soil water storage was effectively stored in the 0−160 cm soil layer of the jujube orchard during the drought year. There was a significant difference in the grey relational grade between the soil water in the top layer (0−20 cm) and the soil water in the middle layer (20−100 cm) under different land use types, with the terraced field having the highest similarity degree of soil water variation trend, followed by grassland, slope cropland, and jujube orchard. Slope croplands in the study region may be converted into terraced fields to enhance the effective use of rainfall resources and encourage the expansion of ecological agriculture. Proper water management practices must be employed to reduce jujube tree water consumption and other wasteful water usage in order to guarantee the jujube orchard’s ability to expand sustainably. This would address the issue of the acute water deficit in the rain-fed jujube orchards in the Loess Hilly Region.

Electro-Magnetic Geophysical Dynamics under Conservation and Conventional Farming

In the context of global warming, agriculture faces severe challenges such as water scarcity and soil erosion. Key to achieving soil sustainability is the choice of farming practices, the consequences of which are generally site-specific. In this study, the ability of Electrical Resistivity Tomography (ERT) and Electro Magnetic Induction (EMI) methods were assessed for monitoring the effects of conventional (CONV) and conservation (CONS) agricultural practices. The aim is to highlight differences in soil water distribution caused by both short- and long-term effects of the two different practices. Results demonstrated that both ERT and EMI provided sufficient information to distinguish between the effects of CONV and CONS, while traditional direct measurements, being punctual techniques, lacked sufficient spatial resolution. The ERT transects showed that the soil was much more homogeneous as a result of CONS practices, resulting in a higher sensitivity to changes in the water content. Conversely, due to the heterogeneous soil structure under CONV, water distribution was more irregular and difficult to predict. Similar patterns were also observed with the EMI surveys, with a strong link to spatial variability. Finally, we conclude that for CONV soil, the accessible water for the plant is clearly controlled by the soil heterogeneities rather than by the forcing atmospheric conditions. This study is a first step towards paving the way for more refined hydrology models to identify which soil parameters are key to controlling spatial and temporal changes in soil water content.

In Situ Rainwater Collection and Infiltration System Alleviates the Negative Effects of Drought on Plant-Available Water, Fine Root Distribution and Plant Hydraulic Conductivity

Soil water status and fine-root characteristics are the foundation for implementing forest water-management strategies in semiarid forest plantations, where rainwater is always the sole source of water for plant growth. Rainwater management and utilization are effective strategies to alleviate water scarcity in semiarid areas as ground water is always inaccessible there. Through the implementation of an in situ rainwater collection and infiltration system (IRCIS), we investigated the effects of IRCIS on soil water and fine-root distributions in the 0–5 m soil profile in a wet (2015, 815 mm) and a dry year (2016, 468 mm) in rainfed Robinia pseudoacacia forests in the Loess Plateau region of China. The results showed drought significantly decreased plant water availability and hydraulic conductivity of roots and branches, but strongly increased soil moisture deficits and fine-root (&lt;2 mm diameter) biomass. With the implementation of IRCIS, soil profile available water and plant hydraulic conductivity can be significantly increased, but soil moisture deficits and fine-root (&lt;2 mm diameter) biomass can be significantly decreased. Drought also significantly influenced the root distribution of Robinia pseudoacacia. The maximum depth of Robinia pseudoacacia roots in the dry year was significantly greater than in the wet year. Therefore, Robinia pseudoacacia can absorb shallow (0–1.5 m) soil water in wet years, while utilizing deep (&gt;1.5 m) soil water in dry years to maintain normal growth and resist drought stress. The results of this study will contribute to the formulation of appropriate strategies for planning and managing rainwater resources in forest plantations.

One−Dimensional Seepage of Unsaturated Soil Based on Soil−Water Characteristic Curve

The uneven pore water distribution in unsaturated soil will cause water movement, change the hydraulic and mechanical characteristics of soil, and then cause soil damage. Therefore, it is important to study the hydraulic characteristics of unsaturated soil. In this paper, the law of conservation of mass and Darcy’s law were used to analyze the unit soil after seepage to obtain a continuous equation. Combined with the soil-water characteristic curve (SWCC), the effect of matric suction and permeability coefficient of unsaturated soil on infiltration rate is substituted into the equation. Through the analysis of pore water stress of the unit soil, the function of the unsaturated permeability coefficient with the effective saturation degree is obtained, and the theoretical formula of the one-dimensional infiltration rate of unsaturated soil is derived. Compared with other models, this formula has fewer parameters and is easy to use.

Approximate analytical solution to equation for two-dimensional soil-water movement in ponding infiltration based on numerical simulation

A simple analytical solution to two-dimensional (2D) ponding infiltration is essential for designing line-source or drip irrigation. We propose a new and simple approximate analytical method for calculating the 2D distribution of soil water with a 1-cm radius of ponding and uniform initial conditions and for estimating the horizontal and vertical distances of wetting fronts based on soil hydraulic parameters. The method assumes a semi-elliptical soil-wetting pattern and a one-dimensional profile of soil water at an arbitrary infiltration angle to solve the equation for the 2D movement of soil water and cumulative infiltration. We applied the numerical data simulated using HYDRUS-3D to validate the proposed method's parameters and evaluate the relationship between the wetting front and hydraulic parameters. The simulated results indicated that the assumptions were propitious to the fine-texture soils with air-entry suction larger than 10 cm. The ratio between the distances of the horizontal and vertical wetting fronts could be approximately predicted using the air-entry suction by analyzing the numerical results. The fitted results indicated that the parameters of the power function of the relationship between the distances of the horizontal and vertical wetting fronts and infiltration time could be described as polynomial and power functions of the diffusivity of saturated soil water. The approximate analytical solutions for the distance of the horizontal wetting front, depth of the vertical wetting front, and cumulative infiltration agreed well with other numerical simulations.

The Impacts of Bio-Based and Synthetic Hydrogels on Soil Hydraulic Properties: A Review.

Soil hydraulic properties are important for the movement and distribution of water in agricultural soils. The ability of plants to easily extract water from soil can be limited by the texture and structure of the soil, and types of soil amendments applied to the soil. Superabsorbent polymers (hydrogels) have been researched as potential soil amendments that could help improve soil hydraulic properties and make water more available to crops, especially in their critical growing stages. However, a lack of a comprehensive literature review on the impacts of hydrogels on soil hydraulic properties makes it difficult to recommend specific types of hydrogels that positively impact soil hydraulic properties. In addition, findings from previous research suggest contrasting effects of hydrogels on soil hydraulic properties. This review surveys the published literature from 2000 to 2020 and: (i) synthesizes the impacts of bio-based and synthetic hydrogels on soil hydraulic properties (i.e., water retention, soil hydraulic conductivity, soil water infiltration, and evaporation); (ii) critically discusses the link between the source of the bio-based and synthetic hydrogels and their impacts as soil amendments; and (iii) identifies potential research directions. Both synthetic and bio-based hydrogels increased water retention in soil compared to unamended soil with decreasing soil water pressure head. The application of bio-based and synthetic hydrogels both decreased saturated hydraulic conductivity, reduced infiltration, and decreased soil evaporation. Hybrid hydrogels (i.e., a blend of bio-based and synthetic backbone materials) may be needed to prolong the benefit of repeated water absorption in soil for the duration of the crop growing season.

Spatiotemporal dynamics of soil water-salt and its topographic gradient effects on Alpine area over the Northeastern Tibetan Plateau, China

Soil water–salt variations at different spatiotemporal scales and their influencing factors are essential for regional vegetation restoration and management. However, the study of soil water–salt of the alpine area has not taken into account the effect of topography, especially in the long time series. This work investigated the spatiotemporal characteristics of water and salt in topsoil from 2000 to 2021, using regression analysis of on-site data and MODIS products. The heterogeneity and trends of soil water–salt in various topographic factors (elevation, slope, and aspect) were also explored by selecting the maximum area of each gradient factor as the constrained condition with the help of ArcGIS software. The results revealed that 1) the models applied to SWC (soil water content), EC (electrical conductivity), and pH utilizing vegetation indices were suitable for estimating the spatiotemporal variations of soil water–salt. 2) Soil water–salt exhibited local aggregation characteristics with an upward trend in SWC and a downward trend in EC and pH as a whole. 3) Mean annual SWC peaked at 3,400–3,800 m with increasing elevation and trended downward with increasing slope. The aspect of mean annual SWC was characterized by lower values in the southwest and south and higher values in the north, while the results for pH were reversed. The slope had a greater influence on EC than on SWC and pH. 4) The trend change of SWC, EC, and pH fluctuated at 2000–2,400 m and &amp;gt;4,600 m with a clear inflection point at 4°–8° and 20°–24°, respectively. In summary, the effects of topography responded to the distribution and trends of soil water–salt. The results have significant implications for implementing ecological improvements in regions with complicated topography and can serve as a reference for formulating future ecological policies.

Spherical Interpretation of Infiltration from Trickle Irrigation

The hypothesis of this paper is that infiltration into drip irrigated soils can be described by simple spherical considerations as well as two dimensional (2D) numerical modeling. The major goal was to test a very simple model based on geometry of a sphere formulas, and compare it with elaborated numerical solutions and field experiments. Detailed analysis of soil–water infiltration under trickle regimes is shown to be pre-requisite in the search for the optimal design of system layout. Optimality and simplicity are sought by modeling a sphere for subsurface trickle/drip (SDI) and hemisphere (DI) pattern of moisture distributions during infiltration. Numerical simulations by MATLAB software were used to describe the distribution of soil water. The data produced by this simulation were successfully compared with analytical models and numerical results of Panoche clay loam. To simulate the four discharge rates (0.5, 1, 2, 3 Lh) under DI and SDI we used the input of Panoche soil properties, i.e., hydraulic conductivity function (Kθ) and soil water retention curve (ψθ). The resulting regression equation of numerical analysis (N) vs. spherical interpretation (S) was N = 0.97 × S − 19.1; r2 = 0.98. This result exposes the novelty of the approach by showing that infiltration from a drip/trickle source can be described by simple spherical radial symmetry in addition to analytical or numerical simulations. An example of a design parameter for 3000 cm3h suggested more emitters per meter laterals for SDI than for DI (100 vs. 77 unites, respectively) due to the shorter distance between SDI emitters that are required in order to maintain wetting continuity. At a discharge of around 500 cm3h of three different soils’ SDI, positive pressure was detected near the orifice and it caused discharge reduction. This is a self-compensating property of SDI that regulates individual emitters according to the soil hydraulic properties. In conclusion SDI is associated with larger capital investment compared to DI, but it can be compensated by improving the water use efficiency due to increased productivity while reducing losses of water through evaporation, but this option should be investigated as part of specific research.

Pore Water Distribution in Unsaturated Soil

Pore Water Distribution in Unsaturated Soil

Good harvests of winter wheat from stored soil water and improved temperature during fallow period by plastic film mulching

Plastic film mulching (FM) has been widely used to increase wheat yield in arid and semiarid regions. However, most researchers have focused on FM during the growth period of winter wheat; as such, a knowledge gap remains regarding FM in other periods. Accordingly, we established a long−term field experiment in 2002 that included four treatments on the Loess Plateau of China. These four treatments included the following: regular fertilization without film (NP), regular fertilization with FM in the fallow period (NPFF), regular fertilization with FM in the growth period (NPFG), regular fertilization with FM for the whole year (NPFW). In 2020 − 2021, we measured the soil water distribution and root distribution in the 0 − 200 cm profile; the soil temperature in 5, 15, 30, and 50 cm soil layers; the winter wheat grain yield; the water use efficiency (WUE); and rainfall use efficiency (RUE). Our results demonstrated that compared with NP, the winter wheat yield of NPFF, NPFG, and NPFW improved by 37.1%, 7.8%, and 21.3% (p < 0.05). The WUE of NPFF, NPFG, and NPFW was 29.5%, 14.3%, and 12.5% higher than NP. Additionally, the RUE of NPFF, NPFG, and NPFW was 37.8%, 8.9%, and 22.2% higher than NP. The profile’s annual average soil temperature of NPFF, NPFG, and NPFW were 0.6 °C, 1.0 °C, and 1.4 °C higher than NP. Further, the root mass of NPFF, NPFG, and NPFW were 16.7%, 41.7%, and 8.3% higher than NP, respectively, and the root mass percentage of NPFF, NPFG, and NPFW decreased significantly by 7.3%, 6.0%, and 24.8% less than NP, respectively, in the 0 − 40 cm soil layer (p < 0.05). In sum, FM during the fallow period was considered an appropriate yield increase measure on the Loess Plateau of China and similar regions because of its advantages in collecting precipitation during the fallow period, regulating wheat growth temperature, and obtaining high yields.

Modelling of Water and Nitrogen Flow in a Rain-Fed Ridge-Furrow Maize System with Plastic Mulch

Soil water and nitrogen are two important factors in the agro-ecosystem of the Loess Plateau, China. The ridge-furrow maize system with plastic mulch (RFPM) is a widely used measure to increase crop yield in the Loess Plateau area. The purpose of this study was to investigate the effect of the RFPM on soil water and inorganic nitrogen (N) distribution, especially with regard to the risk and dynamic of nitrogen losses, by using Hydrus-2D. The study was conducted over two consecutive years and consisted of two treatments: (i) the RFPM with the split application of nitrogen in 2013 (160 + 60 kg N ha−1, sowing and jointing stage) and (ii) the RFPM with a one-time fertilizer in 2014 (220 kg N ha−1, sowing stage). The results showed that the dynamic of soil water and nitrogen was clearly illustrated by Hydrus-2D, especially with regard to the nitrogen losses and utilization. The RFPM improved soil water consumption in both the ridge and the furrow; the soil water content was obviously fluctuating during the maize growing season, and the degree of fluctuation decreased as the depth increased. The soil NH4+-N concentration was mainly accumulated in the surface soil layer +15–10 cm; the highest NH4+-N concentrations were 69.12 and 104.62 mg·kg−1 in 2013 and 2014, respectively. The highest NO3−-N concentrations were 130.86 and 198.20 mg·kg−1 in 2013 and 2014, respectively. There was an exchange of NO3−-N between the ridge and the furrow when urea was applied in the furrow. The one-time fertilizer caused a high risk of NH3 volatilization; they were 20.40 and 27.41 kg N ha−1 in 2013 and 2014, respectively, which accounted for 9.27% and 12.46% of the N fertilizer inputs in 2013 and 2014, respectively. The rate of nitrite leaching was higher in the furrow than the ridge. However, a proper ratio of the split application of nitrogen would contribute to the NO3−-N leaching reduction; the NO3−-N leaching amounts were 18.13 and 31.26 kg N ha−1, which accounted for 8.24% and 14.21% of the N fertilizer inputs in 2013 and 2014, respectively. Our study indicates, therefore, that the RFPM with a split application of nitrogen would be more effective for the nitrogen losses; the RFPM is a suitable system for agriculture in the rain-fed area of the Loess Plateau, with the benefits of water-use efficiency and non-point source pollution reduction.

How much is enough in watering plants? State-of-the-art in irrigation control: Advances, challenges, and opportunities with respect to precision irrigation

With a rapidly expanding global population placing an ever growing demand on freshwater resources, an increased focus on irrigation techniques tailored to the specific needs of plant appears as one solution to minimize overall freshwater consumption. Precision irrigation methods seek to realize an acceptable compromise between yield and irrigation water consumption through control of the timing and quantity of water supplied to plants. The goal is to maintain the water content of the soil, achieve specific water use efficiency with regard to yield or maintain the physiological response of the plant to water stress within predetermined limits. Reliance on soil moisture measurements to establish irrigation water demand inadequately addresses heterogenous distribution of water in soil. Growing research interest is observed detailing the determination of plant water status directly from physiological responses. This paper reviews irrigation control approaches based on different plant water status assessment techniques. A distinct focus is made on application scale of the discussed control approaches, an aspect that has not been considered intensively enough in previous discussions of irrigation control approaches. A discussion of the observed strengths and shortcomings and technological advances supporting the various methods used to quantify plant water status extends the review. Emerging trends that are likely to have an impact on plant water status determination and optimal timing and quantification of irrigation water requirements are integrated to show latest results. A peek into the future of precision irrigation foresees greater reliance on plant-based signals, both in characterization of the control variable, namely the plant water status, and in generation of controller outputs in terms of quantity and timing.

Effects of plastic film mulching on the spatiotemporal distribution of soil water, temperature, and photosynthetic active radiation in a cotton field.

Plastic film mulching (PFM) affects the spatiotemporal distribution of soil moisture and temperature, which in turn affects cotton growth and the spatiotemporal distribution of canopy photosynthetically active radiation (PAR). Due to the spatial heterogeneity of soil moisture, temperature and limited monitoring methods, the issues such as relatively few sampling points and long sampling intervals in most existing studies prevent the accurate quantification of spatiotemporal changes in moisture and temperature along soil profile. To investigate the effects of PFM on spatiotemporal changes in soil moisture, temperature, and canopy PAR in cotton fields, two field trials of plastic film-mulched (M) and nonmulched (NM) cultivations were performed in 2018 and 2019. The grid method was used for the soil information continuous monitoring and multiple-time fixed-site canopy PAR monitoring during the duration of cotton growth. Two-year field trial data showed that, M cultivation increased soil moisture by approximately 13.6%–25% and increased temperature by 2–4 °C in the 0–50 cm soil layer before the first irrigation (June 20) and by 1–2 °C in the 70–110 cm soil layer, compared with NM cultivation. In addition, the temperature difference between the two treatments gradually decreased with the increase in irrigation and air temperature. The M treatment reached the peak PAR interception rate 10 days earlier than the NM treatment. In 2018 and 2019, the PAR peak value under the M treatment was 4.62% and 1.8% higher than that under the NM treatment, respectively, but the PAR interception rate was decreased rapidly in the late growth stage. Overall, PFM had an effect on soil moisture retention during the whole growth period and greatly increased the soil temperature before budding stage, thus promoted the early growth of cotton. Considering this, we suggest that the irrigation quota and frequency could be appropriately decreased in the case of plastic film mulching cultivation. For nonmulching cultivation, the irrigation quota and frequency should be increased, and it is necessary to take measures to improve the soil temperature before middle July.

Influence of Benggang slope cracks on soil water regimes: Comparison of model simulation and time‐domain reflectometry

AbstractCracks greatly influence the saturated hydraulic conductivity (Ks) of soil and are one of the most important factors for increasing Ks. Moreover, both cracks and Ks influence soil water distribution. This study aimed to investigate the consistency of the effects of cracks and Ks on the water distribution along slopes. Ks was measured in three soil layers along two typical Benggang (a severe gully erosion landform) slopes using a double‐ring infiltrometer. The Ks values show a gradual decrease with increasing distance from the gully head in the same soil layer, and this phenomenon is consistent with the distribution of cracks on the slope measured by the staining tracer method. This indicates that the distribution of cracks can be accurately predicted by measuring the spatial variation in Ks. The VADOSE/W model was employed to simulate soil water configurations and yielded inaccurate simulation results, typically in the lower slope. In addition, the simulation results were greatly improved through the inclusion of effective cracks by adjusting the material properties, but not solely by adjusting the Ks. Therefore, the influence of cracks on the water distribution is not well reflected by Ks, and cracks must be incorporated into the relevant models. The soil water content in the topsoil of the lower slope near the headwall with more cracks was than that of the upper slope, implying that cracks likely accelerate the downward movement of water and increase leakage. This process increases the water content and pore water pressure in deeper soil layers, thereby eventually increasing the likelihood of soil erosion. The results of this study can improve our understanding of the triggers of Benggang erosion and provide guidance on the prevention and control of soil erosion risks in areas with granitic soil.Highlights The influence of cracks on water distribution cannot be strongly reflected by Ks. Cracks must be considered when analysing the soil water content in a simulation mode. The distribution of cracks influences the timing and frequency of Benggang erosion. Soil cracks distribution is important in soil risk remediation and control such as Benggang erosion.