Soil Water Dynamics Research Articles

A novel framework to study the effect of tree architectural traits on stemflow yield and its consequences for soil-water dynamics

A novel experimental approach and numerical framework are proposed to study the effect of tree architectural traits on stemflow yield and its effects on soil-water dynamics. The framework includes a data mining workflow employing information from two experimental steps: (i) evaluation of the effect of tree aboveground architecture on stemflow yield and (ii) quantification of specific parameters for soil-water dynamics with and without stemflow. We studied double-funnelling (stemflow and root-induced preferential flow) under three sycamore (Acer pseudoplatanus L.) trees growing on a slope in Scotland during the summer season and measured architectural traits. Stemflow yield ranged from 1.3 to 3.8% of the incident rainfall, with funnelling ratios of between 2.2 ± 2.1 and 5.2 ± 3.9. Double-funnelling to a depth of up to 400 mm beneath the soil surface occurred as matrix flow and was significantly and positively correlated with the vertical root distribution. Soil-water dynamics were distinctly different with and without stemflow. Our framework revealed that the number of tree branches, their insertion angle, leaf number, and stem basal diameter influenced stemflow yield within rainfall thresholds of 1.1 and 3.5 mm d-1. The framework also showed that stemflow yield had a negative impact on soil matric suction, while air temperature was the most influential covariate affecting soil-water dynamics, likely due to its strong correlation to evapotranspiration during the summer season. In spite of the study limitations, such as small sample size and differences between individuals, we show that the proposed framework and experimental approach can contribute to our knowledge of how stemflow generated aboveground triggers major responses in soil-water dynamics belowground.

Simulating the effects of conventional versus conservation tillage on soil water, nitrogen dynamics, and yield of winter wheat with RZWQM2

The movement and distribution of the soil water and nitrogen are significantly influenced by tillage management. However, the dynamics of soil water and nitrogen due to changes in tillage and surface residue cover can be difficult to characterize due to limitations in field experimentation. The objective of this study was to quantify the differences in the soil water and nitrogen balance in the 0–100 cm soil profile, winter wheat (Triticum aestivum L.) yield, water productivity (WP) and nitrogen use efficiency (NUE) that occur when conventional tillage (CT) was changed to four types of conservation tillage treatments (no-tillage [NT], subsoiling tillage [ST], no-tillage with straw [NS] and subsoiling tillage with straw [SS]). Experimental data from 2011 to 2016 collected in Henan province, China on a sandy loam soil was used to calibrate and validate the Root Zone Water Quality Model (RZWQM2). Then the model was used to simulate four tillage systems (NT, NS, ST, SS) that were then compared with CT. The agreement index (d) between simulated and measured soil water content, soil nitrate concentration, and grain yield ranged between 0.71 and 0.93. The root means square error (RMSE) of the soil water content and nitrate concentration was in the range 0.02–0.03 cm cm−1and 5.5–10.3 mg kg−1, respectively. When CT was converted to NT from 2011 to 2016, the model simulated a 9.1 % reduction in annual water loss and a 55.6 % decrease in nitrogen leaching loss and simulated significant increase in average grain yield, WP and NUE. Replacing CT with NT appears to be the best of the four alternative conservation tillage conversion strategies in Henan Province of China.

Effective alleviation of rural poverty depends on the interplay between productivity, nutrients, water and soil quality

Most of the world's poorest people come from rural areas and depend on their local ecosystems for food production. Recent research has highlighted the importance of self-reinforcing dynamics between low soil quality and persistent poverty but little is known on how they affect poverty alleviation. We investigate how the intertwined dynamics of household assets, nutrients (especially phosphorus), water and soil quality influence food production and determine the conditions for escape from poverty for the rural poor. We have developed a suite of dynamic, multidimensional poverty trap models of households that combine economic aspects of growth with ecological dynamics of soil quality, water and nutrient flows to analyze the effectiveness of common poverty alleviation strategies such as intensification through agrochemical inputs, diversification of energy sources and conservation tillage. Our results show that (i) agrochemical inputs can reinforce poverty by degrading soil quality, (ii) diversification of household energy sources can create possibilities for effective application of other strategies, and (iii) sequencing of interventions can improve effectiveness of conservation tillage. Our model-based approach demonstrates the interdependence of economic and ecological dynamics which preclude blanket solution for poverty alleviation. Stylized models as developed here can be used for testing effectiveness of different strategies given biophysical and economic settings in the target region.

Assessing field-scale variability of soil hydraulic conductivity at and near saturation

Saturated hydraulic conductivity (Ks) is a crucial hydraulic property for assessing soil water dynamics. Understanding the spatial variability of Ks in a field is important for site-specific resource management. However, direct measurement of hydraulic conductivity K as a function of soil water pressure head h [K(h)] is time consuming and laborious. Alternatively, pedotransfer functions (PTFs) have been developed to predict Ks indirectly based on more easily measurable soil properties. Although PTFs have been used for decades, their validity for estimating the field-scale spatial variability of Ks remains unclear. The objectives of this study were to characterize the spatial pattern of K(h) at and near saturation in an agricultural field by a coregionalization technique, and in comparison, to evaluate the performance of ROSETTA PTF in characterizing the spatial variability of K(h) at the field scale. Surface soil (7–13 cm) K(h) in the vertical direction was measured at 48 locations in a 71-m by 71-m grid within a no-till farmland. Apparent electrical conductivity was densely measured using a contact sensor Veris 3150 and used as ancillary variable in a coregionalization approach. Experimental semivariograms and cross semivariograms were derived and applied in cokriging to generate K(h) maps. Geostatistical analysis presented similarities in maps of measured K(h) with ROSETTA-predicted K(h) data for a matric potential of −10 cm. However, the strong spatial heterogeneity of measured Ks, which was caused by macropores, observed in the field was not captured by ROSETTA estimates. The results indicated that texture dominated PTFs like ROSETTA, in which soil structure is not considered, might be useful in characterizing the spatial pattern of unsaturated hydraulic conductivity rather than Ks. Field scale Ks maps based on PTF estimates should be evaluated carefully and handled with caution.

Bivariate analysis of drought duration and severity for irrigation planning

In this study, the effectiveness of a bivariate analysis of agricultural drought characteristics for irrigation planning was evaluated. The case study was conducted in locations in central Italy and was based on olive crops which are widely grown in that area under rainfed or deficit irrigation regimes. For each locality, the available time series of daily precipitation and maximum and minimum temperatures were used to simulate the daily soil water dynamics (SWt) for olive crops. The simulation was performed assuming 10 irrigation strategies, different for both the volume and date of the interventions. By applying the Theory of Runs to SWt, with a threshold corresponding to the readily available water, the agricultural drought events in the time series were identified and characterised by their duration D (days) and severity S (i.e. the cumulative evapotranspiration deficit in mm) for each locality and strategy.A 2-parameter Gamma distribution was fitted to both D and S, whilst their dependence structure was modelled by a Gumbel copula. The evaluation of the best irrigation strategy in each locality was obtained by comparing the contour lines of the pairs (d,s) having a 10-year return period for the condition D ≥ d AND S ≥ s. Results showed a great influence of both climate and irrigation strategy on the joint distribution of D and S. Some strategies, despite a very similar behaviour in the severity, differed a lot in terms of the associated values of duration, thus denoting different dynamics of water stress (more or less intense). Among the single-irrigation strategies, the optimal one was usually represented by an application at the end of June. Among the double-irrigation strategies, the optimal one involved two interventions, one at the end of June and one at the end of July. These results were also discussed taking into account the corresponding probability of consecutive severe drought events.

A New Principle for Measuring the Average Relative Humidity in Large Volumes of Non-Homogenous Gas.

Due to the current extent of arid regions, the pressure on available water resources is increasing. A suitable measure for water availability and dynamics in dry soil is the relative humidity of the soil air. Due to the heterogeneity of soil, water inputs, and root water uptake, the humidity of soil air will vary in space. Therefore, area-representative measurement methods are needed to find a representative measure of the soil water status. Existing sensors for the direct determination of relative humidity only represent a single location with a spatial extent of up to several cm. We introduce a new measuring principle that averages over a spatially heterogeneously distributed relative humidity. It is based on the selective diffusion of water vapor pressure through a tubular semipermeable membrane to/from a closed measurement chamber. A measured pressure change is sensitive to the water vapor pressure and enables, without any external calibration, to estimate an average of the relative humidity. The comparison of our first laboratory prototype of the new sensor with calibrated reference sensors for relative humidity in a range of approx. 4 to 100% proves the linearity of the measuring method and its high accuracy. For further optimization improved reference measurement techniques are necessary. A potential application is the improvement of water use efficiency in irrigated agriculture.

Soil rock fragment is stronger driver of spatio-temporal soil water dynamics and efficiency of water use than cultural management in holm oak plantations

Water is the main component in the conservation and functioning of Mediterranean ecosystems. There is a trade-off between plant water use during establishment and soil water conservation. Rock fragments and cultural management are two key factors affecting soil water dynamics on forest establishment. In this work, we studied the interactions of different cultural management techniques (tillage, herbicide and mulching) with soil rock fragment content (soil gravel) and their effects on the spatio-temporal water dynamics and efficiency of water use in Mediterranean forest plantations. Soil water content (SWC, l/m3), soil water depletion rate (k) and water use efficiency (WUE, μmol CO2/mol H2O) were monitored along a two-year period in a holm oak reforestation. The results show that SWC and its spatio-temporal dynamics were defined by a significant interaction between the cultural management techniques and the rock fragment content. Cultural management techniques had weak effects on SWC when compared to the control treatment, although significant differences were found. The soil rock fragment content accounted for most of the variability in SWC; and soils with a content below 5% had higher water contents. The cultural treatments showed some influence on water behaviour under SWC more limited conditions, that is, when rock fragment contents was higher than 15% and/or in summer periods. Finally, SWC was also a limiting factor for the WUE of holm oak seedlings, being the WUE values higher when the soil water supply was more restricted. The maximum WUE was reached at a rock fragment content in the soil profile of 17%, combined with mulch treatment, during dry summer conditions. Thus, the interaction between the rock fragment content and cultural management is a key element in trade-offs between water conservation and plant water-use objectives in Mediterranean forest restoration strategies.

Extent of Bollworm and Sucking Pest Damage on Modern and Traditional Cotton Species and Potential for Breeding in Organic Cotton

Resistance against cotton bollworm is one of the main arguments for the use of genetically modified (GM) Bt cotton around the globe. The use of GM is prohibited in organic systems and thus the remunerative value of organic cotton cultivation depends on effective bollworm control. In this study, we investigated the extent of bollworm and sucking pest damage in 68 different hybrid and varietal lines of Gossypium hirsutum and varietal lines of G. arboreum at two different locations with contrasting soil fertility and water dynamics. The damage potential of bollworms was assessed from open capsules at two time points. Sucking pests were assessed at three time points using a scoring method. G. arboreum varietal lines and G. hirsutum hybrids were on average significantly more tolerant than G. hirsutum varietal lines to bollworm under fertile and irrigated situations. For sucking pests, the G. arboreum varietal lines were clearly more tolerant than G. hirsutum hybrids and varietal lines. Since, recently, pink bollworm (Pectinophora gossypiella) became resistant against Bt cotton and pressure of sucking pests severely increased, screening of genetic resources and systems-based cotton breeding for bollworm and sucking pest tolerance will improve sustainability of organic and conventional cotton production.

Influence of vegetation type and soil properties on soil water dynamics in the Šumava Mountains (Southern Bohemia)

This study focuses on the description of soil water dynamics at four sites with different land cover types, namely beech forest, conifer forest, meadow and clipped grass. The analysis was based on soil tensiometer measurements from five consecutive vegetation seasons (comprising both wet and dry years). We investigated both column average pressure heads and also their vertical distribution. The soil water balance was studied by the HYDRUS-1D model.The highest pressure heads were observed at the grassland site, followed by the meadow site. The forested sites were generally reaching lower pressure head values, which was a result of higher evapotranspiration and different soil properties. The differences between the spruce forest (Picea abies (L.)) and beech forest (Fagus sylvatica L.) were evident namely in dry periods, when the beech site was experiencing lower pressure heads. Contrarily, the spruce site was drier (with recorded lower pressure heads) in wet periods and at the beginning of each season. Compared to the conifer forest, lower pressure heads were observed in beech forest, namely at the bottom of the inspected soil column (down to 100 cm). The inspection of the soil water balance revealed different rates of evapotranspiration and drainage at all sites. The evapotranspiration was highest in the beech canopy followed by spruce and both grass covered sites. The differences between spruce and beech forest were based namely on the water consumption efficiency and differences in interception rates, vertical distribution of the roots, and soil hydraulic properties.

“Responsiveness of mature oak trees (Quercus robur L.) to soil water dynamics and meteorological constraints in urban environments”

Urban trees contribute to the regulation of microclimates of cities through transpirational cooling. The main environmental factors determining transpiration are evaporative demand and soil water availability. However, growth conditions in urban areas are often unfavorable and may promote drought stress. The responses of trees to these conditions may vary between species and age classes, and in addition, can be modified by their environment. For a better understanding of water use patterns of urban tree species, these responses were investigated as a function of different meteorological and soil conditions of their urban environments. To identify physiological responses of mature oaks (Quercus robur L.) to contrasting site conditions, sap flow measurements were carried out in two consecutive growing seasons (2013 and 2014) in urban and suburban areas of Hamburg, Germany. Even considering the varying and sometimes challenging local soil and meteorological conditions, the oaks showed predominantly uniform response patterns. At all study sites, sap flow dynamics were characterized by saturation responses to increasing vapor pressure deficits during both daytime and nighttime conditions, reflecting stomatal responsiveness and hence, a stomatal down-regulation of water loss at demanding atmospheric conditions. Accordingly, the water use of oak trees was characterized by an isohydric strategy, which can help to avoid the risk of cavitation. Moreover, the maximum values of nighttime sap flow exceeded 20% of the daily total at all sites, indicating high rates of nocturnal transpiration and thus a relevant cooling effect during the night. Actual sap flow followed potential sap flow at all sites despite decreasing soil water potentials in the upper soil layers. This suggests actual sap flow during both growing seasons was only limited by atmospheric water demand. Accordingly, the studied mature oak trees maintained high rates of transpiration even in times of reduced soil water availability and thus could provide cooling under challenging site conditions. In contrast to suburban areas, however, oaks in the urban site showed reduced absolute sap flow rates, indicating transpiration sensitivity to different situations of water demand and supply. Due to its water use strategy and its ability to cope with moderate drought, Q. robur can be considered a suitable urban tree species in view of current and future demanding urban growth conditions.

Effect of Cover Crop Termination Timing on Pools and Fluxes of Inorganic Nitrogen in No‐Till Corn

Cover crops are increasingly used around the world to enhance N cycling and provide a suite of agroecosystem benefits. The N scavenging capacity of cover crops during winter months is well recognized. Our research characterized spring management effects (e.g., early vs. late termination) on cover crop biomass, decomposition and N release rates, inorganic soil N, soil water dynamics, and corn (Zea mays L.) performance. Cereal rye (Secale cereale L.) was established in Beltsville, MD, to evaluate three management scenarios: no cover crop; early termination (∼40 d before corn planting); late termination (∼7 d before corn planting). Cereal rye biomass was quantified before termination, and decomposition was tracked over a 24‐wk period to assess loss. Soil N content to 100 cm, soil volumetric water content, and corn performance were evaluated over the corn growing season. Low spring precipitation in 2016 led to similar amounts of cereal rye biomass for early and late termination; however, late‐terminated cereal rye had lower quality biomass (higher C/N) in both years, leading to slower decomposition and N release rates. Over the corn growing season, late‐terminated cereal rye consistently had smaller soil N pools, suggesting more efficient N cycling (better synchrony of N release from cover crop residues with corn N demand) than early‐terminated cover crops. Corn yields were smallest following late‐terminated cereal rye in 2016, but there was no difference in yields among cover crop treatments in 2017. Overall, we conclude that planting cereal rye cover crops and delaying termination until later in the season will help retain and efficiently cycle N while maintaining high corn yields.Core Ideas We tested the effect of cover crop termination timing on N dynamics before corn. Late‐terminated cereal rye had slower rates of biomass loss and N release. Larger soil N pools in 2017 than 2016 resulted from lower corn yields. Cover crop biomass and corn performance were influenced by precipitation levels. Nitrogen was more efficiently cycled in systems with cover crops than systems without cover crops.

Temporal trends in soil physical properties under cropping with intensive till and no-till management

ABSTRACT Improved process understanding of temporal change in soil hydraulic, water retention, and soil physical properties is required to improve modelling of soil-water dynamics. This study reports on temporal trends in soil physical properties for intensive till and no till irrigated wheat, from autumn sowing to summer harvest. There were significant temporal trends for bulk density, readily available water capacity, and unsaturated hydraulic conductivity (at three matric potentials). Using a simple two-parameter exponential model for unsaturated hydraulic conductivity, the model coefficients appeared to increase over the first 10 weeks, followed by a decrease and later increase, but the temporal effect when using this model was not significant given the parameter uncertainty. Daily rainfall, irrigation, and evapotranspiration were evaluated as possible explanatory variables, but these were not generally significant in explaining temporal trends of soil properties. An implication is the need to provide temporal data to parameterise hydrological models for more accurate modelling, including irrigation scheduling.

Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model

Abstract. We propose an alternative model concept to represent rainfall-driven soil water dynamics and especially preferential water flow and solute transport in the vadose zone. Our LAST-Model (Lagrangian Soil Water and Solute Transport) is based on a Lagrangian perspective of the movement of water particles (Zehe and Jackisch, 2016) carrying a solute mass through the subsurface which is separated into a soil matrix domain and a preferential flow domain. The preferential flow domain relies on observable field data like the average number of macropores of a given diameter, their hydraulic properties and their vertical length distribution. These data may be derived either from field observations or by inverse modelling using tracer data. Parameterization of the soil matrix domain requires soil hydraulic functions which determine the parameters of the water particle movement and particularly the distribution of flow velocities in different pore sizes. Infiltration into the matrix and the macropores depends on their respective moisture state, and subsequently macropores are gradually filled. Macropores and matrix interact through diffusive mixing of water and solutes between the two flow domains, which again depends on their water content and matric potential at the considered depths. The LAST-Model is evaluated using tracer profiles and macropore data obtained at four different study sites in the Weiherbach catchment in southern Germany and additionally compared against simulations using HYDRUS 1-D as a benchmark model. While both models show qual performance at two matrix-flow-dominated sites, simulations with LAST are in better accordance with the fingerprints of preferential flow at the two other sites compared to HYDRUS 1-D. These findings generally corroborate the feasibility of the model concept and particularly the implemented representation of macropore flow and macropore–matrix exchange. We thus conclude that the LAST-Model approach provides a useful and alternative framework for (a) simulating rainfall-driven soil water and solute dynamics and fingerprints of preferential flow as well as (b) linking model approaches and field experiments. We also suggest that the Lagrangian perspective offers promising opportunities to quantify water ages and to evaluate travel and residence times of water and solutes by a simple age tagging of particles entering and leaving the model domain.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees. It comes with advantages such as water saving, water retention and drought resistance. A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method. In this study, a mathematical model (WSPI-WR model) for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions. Moreover, this model also considers the soil evaporation, pit wall evaporation and water level variation in the pit. The finite element method was used to solve the model, and the law of mass conservation was used to analyse the water level variation. The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard. Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions. The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation. The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution. The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit. Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil. Keywords: root water uptake, soil water dynamics, numerical simulation, water storage pit irrigation, apple tree DOI: 10.25165/j.ijabe.20191205.4005 Citation: Guo X H, Lei T, Sun X H, Ma J J, Zheng L J, Zhang S W, et al. Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation. Int J Agric & Biol Eng, 2019; 12(5): 126–134.

Soil water response to rainfall in a dune-interdune landscape in Horqin Sand Land, northern China

Soil water dynamic is considered an important process for water resource and plantation management in Horqin Sand Land, northern China. In this study, soil water content simulated by the SWMS-2D model was used to systematically analyse soil water dynamics and explore the relationship between soil water and rainfall among micro-landforms (i.e., top, upslope, midslope, toeslope, and bottomland) and 0–200 cm soil depths during the growing season of 2013 and 2015. The results showed that soil water dynamics in 0–20 cm depths were closely linked to rainfall patterns, whereas soil water content in 20–80 cm depths illustrated a slight decline in addition to fluctuations caused by rainfall. At the top position, the soil water content in different ranges of depths (20–40 and 80–200 cm) was near the wilting point, and hence some branches, and even entire plants exhibited diebacks. At the upslope or midslope positions, the soil water content in 20–80 or 80–200 cm depths was higher than at the top position. Soil water content was higher at the toeslope and bottomland positions than at other micro-landforms, and deep caliche layers had a positive feedback effect on shrub establishment. Soil water recharge by rainfall was closely related to rainfall intensity and micro-landforms. Only rainfalls > 20 mm significantly increased water content in > 40 cm soil depths, but deeper water recharge occurred at the toeslope position. A linear equation was fitted to the relationship between soil water and antecedent rainfall, and the slopes and R<sup>2</sup> of the equations were different among micro-landforms and soil depths. The linear equations generally fitted well in 0–20 and 20–40 cm depths at the top, upslope, midslope, and toeslope positions (R<sup>2</sup> value of about 0.60), with soil water in 0–20 cm depths showing greater responses to rainfall (average slope of 0.189). In 20–40 cm depths, the response was larger at the toeslope position, with a slope of 0.137. In 40–80 cm depths, a good linear fit with a slope of 0.041 was only recorded at the toeslope position. This study provides a soil water basis for ecological restoration in similar regions.

Evaluating the effects of biodegradable film mulching on soil water dynamics in a drip-irrigated field

Drip irrigation with plastic film mulching (PM) is an important agricultural practice used to conserve soil water and produce higher crop yields worldwide. However, the plastic film is usually made from non-degradable polyethylene materials, which may lead to the incorporation of plastic into soils and cause a series of negative environmental effects. As such, biodegradable film mulching (BM) can represent a valuable alternative to PM. A two-year experiment was carried out during the 2014 and 2015 seasons to evaluate the effects of PM, BM, and no film mulching (NM) on the soil water balance in the corn field. The two-dimensional numerical HYDRUS-2D model was calibrated and validated using experimental data collected in 2014 and 2015, respectively, under BM, PM, and NM and then used to evaluate soil water contents (SWC), water fluxes, and soil water balances in two-dimensional soil profiles. The results of numerical simulations were in good agreement with measurements, with the mean relative errors for the calibration and validation periods for BM, PM and NM of 11.2%, 10.7%, and 11.7%, respectively. The results showed that SWCs were similar in the BM and PM scenarios during early and middle crop growth periods. Significant differences in SWCs were observed only after the average fraction of the disintegrated area of the biodegradable film was equal or higher than about 40% (during the late crop growth period). The results also showed that mulching mainly affects SWCs in the top 0–20 cm soil layer. There were significant differences in cumulative evaporation and water fluxes between different treatments, but an insignificant difference in root water uptake between PM and BM. Cumulative evaporation for BM increased by 30.5% compared to PM and decreased by 41.9% compared to NM. Corresponding cumulative water fluxes at the 80 cm depth increased and decreased by 6.6% and 48.8%, respectively. Two-dimensional simulations of soil water content distributions revealed that the “water stress” area in the soil profile (with SWCs lower than readily available water) before irrigation was 1.79 and 0.75 times larger for BM than for PM and NM, respectively. SWCs in the surface soil layer of BM also increased after rainfall during the late crop growth period, which improved the rainwater use efficiency by 8.2% compared to PM. Both experiments and simulations revealed that BM has more comparable soil moisture dynamics to PM than to NM.

Similarity of soil freezing characteristic and soil water characteristic: Application in saline frozen soil hydraulic properties prediction

Accurate prediction of hydraulic properties in frozen soils is of importance for the role of frozen soil water dynamics in cold region water cycles. Furthermore, the existence of solute is known to complicate the water, heat and solute transport in frozen soils. To predict hydraulic properties in saline frozen soils more accurately, experiments on soil water characteristic curves (SWCCs) and soil freezing characteristic curves (SFCCs) were conducted under five solute types combined with five solute content levels. Results showed that, under low salinity conditions (e.g., no higher than 1.0% g/g dry soil), the conversion of SFCCs to SWCCs (or SWCCs to SFCCs) was possible by using generalized Clausius-Clapeyron equation (GCCE). The combination of these two curves could predict more reliable hydraulic parameters for the compensation in experimental data ranges. Comparison of the combining method with other direct or indirect experimental results indicated that accurate and integral θl − h relationships could result in accurate estimation in hydraulic parameters in frozen saline soils. This study has proposed an improved method for predicting hydraulic parameters in saline frozen soils, and more validation work with experiments under various soil and solute conditions is needed before incorporating it into frozen soil properties predicting frameworks.

Cover Crop Effects on Corn Plant Sap Flow Rates and Soil Water Dynamics

Cover crops (CC) are used for soil quality improvement. However, the effects of CC on soil water availability for cash crop is yet inconclusive. Plant sap flow measurement techniques are among the most reliable methods to evaluate water stress and water consumption by measuring the whole‐plant transpiration. The objective of the study was to quantify plant sap flow dynamics in corn (Zea mays L.), soil water dynamics, and corn yields in response to CC and no cover crop (NCC) management. The study was conducted at Bradford Research Center, University of Missouri, Columbia, in 2017 and 2018. A Dynamax Flow32‐1K sap flow measurement system and a CR1000 data logger with Dynagage sensors were used to measure sap flow rates. Volumetric soil moisture (VSM) content was estimated at 15‐min intervals by Campbell CS‐616 sensors installed at 10‐, 20‐, and 30‐cm soil depths in 2018. The NCC corn plants had greater daily average sap flow rates early and lower sap flow rates later in the season compared with CC. The CC treatment showed significantly greater VSM than NCC, with 14, 12, and 4% greater values at 10‐, 20‐, and 30‐cm depths, respectively. Corn yield in 2017 was significantly greater in NCC treatment than in the CC treatment, with values of 8.07 Mg ha−1 in CC and 9.41 Mg ha−1 in NCC. This study revealed that soils of CC treatment maintained greater soil moisture conditions and provided more water to corn plants for a longer period.

Soil Water Dynamics and Winter Wheat Performance under Precipitation Change in the Loess Tableland Region, China

The responses of soil water and winter wheat (Triticum aestivum L.) to changes in precipitation are crucial for stability of wheat yield and soil water conservation in the Chinese Loess Tableland Region (LTR). A 2‐yr (2014‐2016) experiment was conducted in the LTR to investigate soil water dynamics and winter wheat performance under three precipitation levels: Rc (normal), R+ (increased by one‐third of normal), and R− (decreased by one‐third of normal) by a real‐time precipitation allocation system. Soil water storage (SWS) at a depth of 0–3.8 m showed positive (R+) or negative (R−) responses to precipitation. The mean SWS in different soil layers followed an order of R+ > Rc > R−. During the experiment, the 0–3.8 m SWS decreased by 34.5 mm (R+), 183.8 mm (Rc), and 218.9 mm (R−). The shoot biomass and grain yield varied little among three precipitation levels in 2014–2015, but was reduced by 50% in R− compared with Rc in 2015–2016. The R− and Rc treatments had higher water use efficiency (WUE) than R+ in 2014–2015, and Rc was the highest in 2015–2016. The proportions of soil water to water consumption in R+ and Rc increased from 22.5% in 2014–2015 to 42.5% in 2015–2016 on average, and for R− was stable over 2‐yr (average 44.5%). Soil water plays a critical role in winter wheat performance under changes in precipitation, which should guide winter wheat production and soil water management in the future.Core Ideas Precipitation changes soil water storage but does not change the regime of soil water changing with time. Response of winter wheat yield to precipitation change has hysteresis effect. Supplementary effect of soil water compensates for the negative effect of decreased precipitation. Performance of supplementary effect is determined by precipitation pattern.

Soil Water Dynamics with Spring Camelina in a Three‐Year Rotation in Washington's Winter Wheat–Fallow Region

Core Ideas The soil water dynamics of 3‐yr winter wheat–camelina–summer fallow and 2‐yr winter wheat–summer fallow rotations were measured for 8 yr. At harvest, there was less soil water after camelina than after winter wheat in the 2‐yr rotation. The water deficit persisted through the 13‐mo fallow period and decreased the yield of 3‐yr vs. 2‐yr winter wheat. Increased cropping intensity may increase risk and variability in dry environments. Camelina [Camelina sativa (L.) Crantz] of the Brassicaceae family is a short‐season drought‐ and frost‐tolerant oilseed. Camelina has been promoted as an alternative crop for the low‐precipitation (<350 mm annually) Mediterranean‐like climate region of the US inland Pacific Northwest, where a monoculture 2‐yr winter wheat (Triticum aestivum L.) (WW)–summer fallow (SF) rotation is widely practiced. An 8‐yr experiment was conducted to compare a 3‐yr WW–camelina–SF rotation with the typical 2‐yr WW–SF rotation to analyze the soil water dynamics of these two crop rotations. Growing spring‐planted camelina reduced soil water content at the beginning of the fallow; this reduction resulted in an average of 21 mm less water at WW planting and a 170 kg ha‐1 reduction in grain yield compared with WW–SF. We show that (i) the deep‐rooted broadleaf weed Russian thistle (Salsola tragus L.) present in camelina most years was the most likely reason for greater in‐crop soil water use than with WW–SF, and (ii) the limited camelina residue was probably responsible for greater evaporative loss during the spring to late summer segment of the fallow. We report the first findings from the Pacific Northwest drylands of greater water use by a cool‐season spring crop versus WW and greater evaporative loss during the summer caused by lack of residue in a minimum‐tillage SF comparison. Here, extending the crop rotation to include camelina was costly in terms of water use, surface soil residue cover, soil water storage during the fallow, and WW grain yield.