Plant Available Soil Water Research Articles

Global Mapping of Potential and Climatic Plant‐Available Soil Water

AbstractThe estimation of plant‐available soil water (PASW) is essential to quantify transpiration fluxes, the onset of heatwaves, irrigation water management, land‐use decisions, vegetation ecology, and land surface memory in climate models. PASW is the amount of stored water available for plant use. It is broadly defined as the difference between soil water content at field capacity (FC) and wilting point (WP) in the root zone. The limiting states of FC and WP are linked to gravitational drainage and plant physiology and are often deduced from soil water characteristics at prescribed matric potentials (−3.3 and −150 m for FC and WP, respectively). Evidence suggests that static definition of FC at a constant matric potential ignores dynamic effects on FC attainment affected by soil and climate. Here, we revise the definition of PASW by considering (a) soil‐specific dynamic effects and (b) local climate effects of evaporation and rainfall frequency on PASW. The new global PASW maps benefit from state‐of‐the‐art soil maps, water characteristic parameterization, and incorporation of dynamic definition of FC. For completeness we provide static and dynamic PASW estimates. Globally, ice‐free soils store up to 19,941 km3 of water in the top 1 m (representing 18% of annual terrestrial precipitation). Adjusted for local climatic conditions, global PASW storage rarely exceeds 14,853 km3 per year highlighting the need for multiple refilling of soil profiles. Differences between potential and climatic PASW are manifested primarily in arid regions (where soil profiles are rarely filled to capacity) whereas in humid regions differences in PASW storage are minor.

Global maps of potential and climatic plant-available soil water

Global maps of potential and climatic plant-available soil water

Global maps of potential and climatic plant-available soil water

Global maps of potential and climatic plant-available soil water

Leaf trait modification in European beech trees in response to climatic and edaphic drought.

Leaf morphological and physiological traits control the carbon and water relations of mature trees and are determinants of drought tolerance, but it is not well understood how they are modified in response to water deficits. We analysed five sun-canopy leaf traits (mean leaf size (LS), specific leaf area (SLA), Huber value (HV), water potential at turgor loss point (Ψtlp ) and foliar carbon isotope signature (δ13 C)) in European beech (Fagus sylvatica L.) across three precipitation gradients sampled in moist (2010), dry (2019) and very dry (2018) summers, and tested their response to short-term water deficits (climatic water balance (CWB) preceding sample collection) and long-term water availability (mean annual precipitation (MAP), plant-available soil water capacity (AWC) and neighbourhood competition). Across the 34 sites, LS varied seven-fold (3.9-27.0 cm2 ), SLA four-fold (77.1-306.9 cm²·g-1 ) and HV six-fold (1.0-6.65 cm2 ·m-2 ). In the 2018 dataset, LS showed a negative and HV a positive relationship to MAP, which contradicts relations found in multi-species samples. Average Ψtlp ranged from -1.90 to -2.62 MPa and decreased across the sites with decreasing CWB in the month prior to measurement, as well as with decreasing MAP and AWC in 2019. Studied leaf traits varied considerably between years, suggesting that mast fruiting and the severe 2018 drought caused the formation of smaller leaves. We conclude that sun-canopy leaf traits of European beech exhibit considerable plasticity in response to climatic and edaphic aridity, and that osmotic adjustment may be an important element in the drought response strategy of this anisohydric tree species.

Regional variations in plant-available soil water storage and related driving factors in the middle reaches of the Yellow River Basin, China

Available soil water is considered the most important water resource for food production in agricultural ecosystems and sustainable vegetation restoration in arid and semi-arid regions. Compared to soil water content, plant-available soil water storage (ASWS) directly indicates the amount of soil water that can be used by plants. Understanding the spatial characteristics and controlling factors of ASWS can aid in improving the ability of the agricultural ecosystem to resist extreme natural disasters and stabilise grain production in China. In this study, ASWS in the 0–5.0 m profile was measured in an area of approximately 36.9 × 104 km2 in the middle reaches of the Yellow River Basin. The total ASWS in the 0–5.0 m profile of the study area was 113 × 1010 m3, 85% of which was stored in the > 450 mm rainfall zones. The spatial variation in ASWS was mainly controlled by climate and edaphic properties of the 0–1.0 m soil layer and < 450 mm rainfall zone. Regarding the 1.0–5.0 m soil layer and > 450 mm rainfall zone, edaphic properties were the dominant factors determining the spatial characteristics of ASWS. Based on the spatial characteristics of ASWS, the shallow soil water (0–1.0 m) in the middle region and deep soil moisture (1.0–5.0 m) in the southern region of the study area can support the rational use of soil water in agricultural and vegetation restoration activities. Large-scale revegetation activities using trees or shrubs might not be the optimal choice in regions with mean annual precipitation < 450 mm. Knowledge of the spatial characteristics and contributions of the ASWS controlling factors is indispensable for reasonable agricultural regionalisation and vegetation restoration, as well as for an invulnerable and stable grain output system.

Role of remotely sensed leaf area index assimilation in eco-hydrologic processes in different ecosystems over East Asia with Community Land Model version 4.5 – Biogeochemistry

The leaf area index (LAI) is a key variable for representing vegetation state, and it is closely related to simulating carbon and water exchanges between land and the overlying atmosphere in land surface and terrestrial ecosystem models. Model simulations are still limited in their representation of vegetation phenological processes and capturing the resulting LAI seasonality. Therefore, this study demonstrated how LAI assimilation into the model improved carbon and water fluxes in different ecosystems over East Asia. We assimilated LAI derived from Moderate Resolution Imaging Spectroradiometer data for seven years (2004–2010) over East Asia into the Community Land Model version 4.5 with a biogeochemistry module (CLM4.5-BGC) by employing the ensemble adjustment Kalman filter method. Results showed that LAI assimilation remarkably improved estimated gross primary production (GPP). In particular, the root mean square error decreased from 97.12 to 48.63 gC/m2/month across the region for June–August. Additionally, while evapotranspiration (ET) was less sensitive to LAI than GPP, the ET components of ground evaporation, canopy evaporation, and canopy transpiration significantly changed after assimilation. The analysis of plant-available soil water showed that LAI assimilation has unique effects on soil moisture depending on the soil layer, climate, and ecosystems. In general, the improvement in ecological prediction skill by LAI assimilation was particularly evident in temperate needleleaf forests where LAI was overestimated most distinctly. This study improves our understanding of the role of LAI assimilation in eco-hydrological processes in different ecosystems with CLM4.5-BGC, which allows for the improvement of model forecasting and more accurate simulation of the effects of LAI state evolution.

Sowing configuration affects competition and persistence of lucerne (

Spatial separation of species at sowing has been proposed as a means of managing interspecific competition in mixed swards. This study examined the effect of row configuration on persistence of lucerne (Medicago sativa L.) in pastures and pasture–cover crop mixtures at three sites in the Central West, and in pasture mixtures at three sites in the Riverina, New South Wales, Australia. Lucerne density, taproot diameter, groundcover, and spatial distribution relative to the original drill row were measured at all sites, and plant-available soil water and light interception during spring were assessed at some sites. Row configuration (alternate or mixed drill rows) did not affect lucerne persistence; however, where lucerne seed was concentrated in every third drill row, intraspecific competition led to increased lucerne mortality. This was estimated to occur at densities &gt;28 plants/m drill row. A lucerne density of ~55 plants/m2 in every or alternate drill rows (at row spacings of 250 mm) would likely achieve maximum lucerne production in the semi-arid environments tested, subject to the chance event of favourable conditions in the period after sowing that would maintain that density (e.g. cumulative summer rainfall &gt;100 mm and summer day degrees &lt;2160°C in 2 years at Cowra). The presence of a cover crop in the establishment year reduced lucerne density by 39% compared with pasture only, regardless of row configuration. Changed row configuration did not reduce competition for light under a cover crop, but there was a small increase in available soil water of up to 4.9 mm in the 0–1.15 m depth, mainly during the first summer, where pasture was sown in alternate compared with mixed drill rows with a cover crop. Soil was drier in pasture-only treatments than those with a cover crop, attributable to increased lucerne density and lower levels of litter cover on the soil surface. Pasture species remained largely confined to the original drill row, especially in drier environments, highlighting the importance of narrower row spacings for pasture establishment. In addition, we determined a mathematical relationship between lucerne density and the non-destructive measure of basal frequency; this relationship could be applied in mature lucerne stands with densities ≤80 plants/m2.

Evaluating optimal irrigation strategies for maize in Western Kansas

A calibrated and validated Decision Support System for Agro-technology Transfer – Cropping System Model (DSSAT-CSM), CERES-Maize, was used to (1) evaluate maize (Zea mays L.) yield and water productivities (WP) under various irrigation frequencies (IRF) triggered by different plant available soil water (PASW) on three soil types, and (2) assess the optimum IRF and PASW triggers for maximum yield and water productivity on three different soils (with a depth of 1.2 m) in Finney County, Western Kansas. The treatments were four IRF (2, 4, 7, and 9 days), four PASW (5%, 25%, 50% and 75%) irrigation trigger and three soil types with a total of 48 combinations. The model was set to automatically apply 25 mm irrigation at selected day intervals when certain irrigation triggering PASW conditions were met. This study showed that maintaining higher PASW up to 75% or above might result in too many irrigations per season, which could be costly. IRF-9 showed substantially lowest yield under most PASW tested in this study. The highest yield was simulated at irrigation amount of 400–450 mm and ET of 650–800 mm depending on soil types. The highest irrigation water productivity (IWP, 30–33 kg/ha/mm) was simulated when triggered by 25% and 50% PASW for Ulysses silt loams. Overall, IRF-4 under 50% PASW threshold provided the maximum maize yield and WP for all soil types.

Evaluating optimal irrigation for potential yield and economic performance of major crops in southwestern Kansas

The Decision Support System for Agrotechnology Transfer – Cropping System Model was used with an objective to evaluate maize (Zea mays L.), winter wheat (Triticum aestivum L.) and grain sorghum (Sorghum bicolor L. Moench) yield, crop water productivity (CWP) and return after variable cost (RAVC) under different combinations of irrigation interval/capacity and plant available soil water (PASW) thresholds on three soil types in southwestern Kansas. Maize, grain sorghum and winter wheat yields were maximized under irrigation capacity of 4.2–6.3, 3.1–4.2 and 2.5–3.1 mm/d, respectively. The lowest and highest values in the range corresponded to silt loam and fine sand soils, respectively. For maize, maximum RAVC ($630–710/ha) and CWP (25–27 kg/ha/mm) were achieved with a relatively shorter irrigation interval (25 mm/4–8 d). RAVC values for grain sorghum and winter wheat were not substantially affected by irrigation interval. The RAVC for grain sorghum and winter wheat ranged from $150 to $200/ha and $310 to $370/ha, respectively. The CWP of grain sorghum peaked at shorter irrigation interval (25 mm/6–8 d), whereas, high CWP of wheat was simulated even at longer irrigation interval (25 mm/26 d). Overall, for winter wheat and grain sorghum, irrigation strategy for attaining higher RAVC values is different from irrigation strategy for attaining higher yield. Whereas, for maize, irrigation strategy for higher yield is the same as that irrigation strategy for higher RAVC. This study guides producers to identify and prioritize the most suitable irrigation strategy for optimizing yield, CWP and/or income while enhancing sustainability of environment and management of ground water. The present work assumes all factors except water are optimal and findings are sensitive to dynamics of price changes, productivity levels and variations in crop management and climate.

Do earthworms (D. veneta) influence plant-available water in technogenic soil-like substrate from bricks and compost?

PurposeTopsoil and peat are often taken from intact rural ecosystems to supply the urban demand for fertile soils and soil-like substrates. One way of reducing this exploitation is to recycle suitable urban wastes to produce Technosols and technogenic soil-like substrates. In this study, we investigate the role earthworms can play in impacting the hydraulic properties of such a soil-like substrate.Materials and methodsIn a 4-month microcosm experiment, the influence of the earthworm species D. veneta on the hydraulic properties of brick-compost mixture was examined. Of the ten boxes filled with ca. 11 dm3 of ground bricks (0.7 cm3 cm−3) and green waste compost (0.3 cm3 cm−3), five contained earthworms (W-boxes) and the remaining five were used as controls (C-boxes). The substrate was periodically irrigated and the weight of the boxes and of the drained water was monitored. At the same time, images were taken from the front of the boxes to quantify the activity of the earthworms by image analysis and soil aggregation was studied with micrographs. Before and after the experiment, water retention curves were determined from disturbed samples of the substrate using the simplified evaporation method.Results and discussionAfter 6 weeks, differences between the C- and the W-boxes were evident. Micrographs showed brick-compost aggregates only for the substrates processed by earthworms. The earthworm activity leads to reduced evaporation and an increased water content in the respective microcosms. The effect persists even after disturbing the substrate. The proportion of plant-available soil water is about 0.02 cm3 cm−3 higher for the substrate processed by earthworms (0.250 ± 0.009 cm3 cm−3) compared with the control (0.230 ± 0.008 cm3 cm−3).ConclusionsThis study shows that earthworms are capable of ingesting and processing crushed bricks together with compost. The earthworms produced aggregates which persisted after disturbance and had a positive influence on the water retention capacity of such a soil-like substrate constructed from waste.

Advancing simulations of water fluxes, soil moisture and drought stress by using the LWF-Brook90 hydrological model in R

Soil vegetation atmosphere transport (SVAT) models are important for the quantification of water fluxes, soil water availability, drought stress and their uncertainties under climate change. We present LWFBrook90R, an enhanced implementation of the well-established, process-based SVAT model LWF-Brook90 for the R environment for statistical computing. The package provides new functions and sub-models for model parameterization, and facilitates parallel computing, sensitivity analysis and inverse calibration of the model. A case study comprising i) basic forward water balance simulations for temperate grassland vegetation, deciduous and evergreen forest, ii) a parallelized sensitivity analysis, and iii) Bayesian calibrations based on soil water storage observed in a poplar (Populus nigra × P. maximowiczii) Short Rotation Forest (SRF) demonstrates the utility of the R package. The sensitivity analysis revealed parameters affecting plant-available soil water storage capacity and the vegetation's timing and level of water demand to be most important for the annual course of simulated soil water storage, with seasonal and interannual differences in parameter importance rankings. The subsequent calibration yielded a very high agreement between daily simulated and observed soil water storage (0-200 cm soil depth) for the calibration and validation datasets, with Nash-Sutcliffe efficiencies of 0.97 and 0.95, respectively. The final model predicted high though realistic rates of annual evapotranspiration (2011: 844 ± 3.8 mm y-1, 2012: 733 ± 4.5 mm y-1) for the poplar SRF, regularly exceeding grass reference evaporation (ET0) by 20-47% during the months of the growing season. However, basing calibrations solely on observed soil water storage probably resulted in biased partitioning of evapotranspiration towards interception losses. The integration of the LWF-Brook90 hydrological model into R with its wide variety of extensions was successfully tested and may provide efficient, reliable and reproducible water balance predictions by facilitating complex statistical analyses and large-scale applications of the model.

A 3-dimensional model of Pinus edulis and Juniperus monosperma root distributions in New Mexico: implications for soil water dynamics

(1) To develop a 3D root distribution model for pinon-juniper woodland using only tree species, sizes and locations as input. (2) To interpret a two-year time series of soil moisture relative to root distributions. The study was conducted in a pinon (Pinus edulis (Englem.)) -juniper (Juniperus monosperma (Englem.) Sarg.) woodland in New Mexico. We extracted roots from 720 soil blocks (30 cm × 10 cm × 10 cm) cut from the walls of three 10-m long and 1.5-m deep trenches. Roots were sorted by species and diameter class. Distribution models were developed for the dry weight of roots ≤5 mm in diameter. Soil water content and water potentials were measured in soil profiles under tree cluster and canopy gaps for 2 years, including a protracted dry-down period. Pinon had twice the root dry mass of juniper, similar to the ratio of canopy projection areas. Root densities were ca. 50% lower in soils under canopy gaps compared to tree clusters and the species ratio did not significantly differ between clusters and gaps. Pinon root density declined faster with soil depth and distance from the stem compared to juniper. A hard caliche layer at 60–80 cm soil depth had no apparent effect on the already low root density at that depth. Overall, the models explained 66% (pinon) and 54% (juniper) of the spatial variation in root density at the scale of sampled soil blocks. During an 8-month dry period, soil moisture declined faster in regions of higher root density: in shallow soil and under tree clusters. This left a reserve of plant-available soil water in the deep soil under canopy gaps. Horizontal variation in root density in these open woodlands is predictable and an important component of the dynamic interactions between plant and soil. Under wet and dry conditions, soil water content is substantially different under tree clusters and canopy gaps.

Characterizing Sugarcane Production Areas Using Actual Yield and Edaphoclimatic Condition Data for the State of Goiás, Brazil

Sugarcane (Saccharum officinarum L.) yield is affected by climate, soil and management. The main approach used in Brazil defines the suitable area for growth considering soil and climate data, without considering the capacity of local management in reducing yield-limiting factors. Thus, the aim of this study is to characterize homogenous areas using sugarcane actual yield, climate, total plant-available soil water capacity (TASW), and production intensity data. The study was conducted in the Goias state, totalizing 246 counties. The first step was to group areas based on actual yield obtained from 1973 to 2016. The groups were characterized considering climate (rainfall and air temperature), soil (TASW), and sugarcane production data. Actual sugarcane yield formed eight homogenous groups, numbered 1–8, containing 12 and 50 counties each group. The counties groups with a higher yield have a higher production intensity. They are near mills, have a higher TASW, and are divided in traditional and recent expansion areas. The counties groups with a lower yield have a lower TASW and a higher air temperature. Hotter regions are in the western and northern state border. New areas of expansion were available near current sugarcane mills within areas with a higher TASW. Thus, preferential regions were defined by associating edaphoclimatic conditions with high yield. These areas can receive support to improve sugarcane production.

Traditional dry soil layer index method overestimates soil desiccation severity following conversion of cropland into forest and grassland on China’s Loess Plateau

Due to severe soil erosion and low crop yield, sloping croplands have been converted into forests and grasslands during the past decades on China’s Loess Plateau (CLP). The introduced exotic high-water consumption plants cause soil water deficit that leads to the formation of dry soil layer (DSL). The traditional index method used to determine the existence of DSL considers only soil hydraulic property of “stable field capacity” and fails to fully reflect the interactions between soil water and vegetation. A new index method that considers physiological response of vegetation to drought is needed for DSL research. Here, we proposed a new method to identify and quantify the severity of DSL and compared the proposed method with the traditional method using field data for the 5 m soil depth in typical tree (R. pseudoacacia, n = 85) and grass (M. sativa, n = 20) plantations on CLP. The number of sites detected with DSL through the new method was less than the traditional method for both species. Based on the traditional method, the level of DSL was even more severe; with mean DSL thickness of 3.2 for R. pseudoacacia and 3.9 m for M. sativa. Then for the new index method, it was only 2.4 m for both plantations. DSL formation depth was much deeper under the new method than the traditional method. Also mean plant available soil water (PASW) stored in the identified DSL by the traditional method was ∼44.1 and 37.8 mm; accounting for 37.2 and 88.9% of total PASW in the 1–5 m soil profile under R. pseudoacacia and M. sativa, respectively. Thus, the traditional DSL index method overestimated DSL severity as it fails to account for plant soil water availability, especially in areas with coarser soil texture. The proposed new index method that is based on soil water potential is more suitable for characterization of DSL conditions under different soil types. This is critical for application in reclamation of DSLs and optimization of vegetation cover in the study area and beyond.

Limiting factors of aspen radial growth along a climatic and soil water budget gradient in south-western Siberia

Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in south-western Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall.We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.

Historical changes in the stomatal limitation of photosynthesis: empirical support for an optimality principle.

The ratio of leaf internal (ci ) to ambient (ca ) partial pressure of CO2 , defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation model uncertainties for predicting terrestrial carbon uptake and water use. We test a theory based on the least-cost optimality hypothesis for modelling historical changes in χ over the 1951-2014 period, across different tree species and environmental conditions, as reconstructed from stable carbon isotopic measurements across a global network of 103 absolutely dated tree-ring chronologies. The theory predicts optimal χ as a function of air temperature, vapour pressure deficit, ca and atmospheric pressure. The theoretical model predicts 39% of the variance in χ values across sites and years, but underestimates the intersite variability in the reconstructed χ trends, resulting in only 8% of the variance in χ trends across years explained by the model. Overall, our results support theoretical predictions that variations in χ are tightly regulated by the four environmental drivers. They also suggest that explicitly accounting for the effects of plant-available soil water and other site-specific characteristics might improve the predictions.

Changes in some bioactive compounds of red cabbage (Brassica oleracea L.var.Rubra) under water stress

A two-year study was performed on red cabbage (Brassica oleracea L.var.Rubra) to assess the effect of different irrigation levels on yield, sugar and organic acid contents. The study was conducted using drip irrigation system on a clay loam soil. The volume of irrigation water applied with 4-day intervals to each treatment was based on Class-A pan evaporation (Ep). In the full irrigation treatment (I1.0), a pan evaporation using screen covered Class-A pan was measured with 4-day intervals and all amount of evaporation was applied in the normal (1.00xEp) treatment, and deficit amounts were imposed on three irrigation treatments as I0.7 (0.7xEp), I0.3 (0.3xEp), and I0.0 (0.0xEp). The plant-available soil water at maturity and yield of red cabbage was significantly related to irrigation amounts. Imposition of deficit irrigation resulted in yield reduction, especially in the severe stress treatments I0.3 and I0.0. Therefore, yields were related linearly to irrigation. That’s why, if there is no water scarcity full water demand of red cabbage need to be compensated for the whole growing season. However, in the deficit treatment, total sugar and especially ascorbic, oxalic, tartaric and malic acid contents increased, and only lactic acid decreased, on the other hand there was no significant effect of different water levels on the content of citric acid.

An evaluation of a methodology for seasonal soil water forecasting for Australian dry land cropping systems

Soil water is a critical resource in many rain-fed agricultural systems. Climate variability represents a significant risk in these systems, which has been addressed in the past through seasonal weather outlooks. This study undertakes a pilot assessment of the potential to extend seasonal weather outlooks to plant available soil water (PASW). We analyse 20 sites in the southeast Australian wheat belt using seasonal weather outlooks from the Predictive Ocean-Atmosphere Model for Australia (POAMA; (the operational seasonal model of the Australian Bureau of Meteorology), which were downscaled and used in conjunction with the Agricultural Production Simulator (APSIM). Hindcast rainfall, potential evapotranspiration (PET) and PASW outlooks were produced on a monthly basis for 33 years at a point scale. The outlooks were assessed using a range of ensemble verification tools. The results showed hit rates that outperformed climatology for rainfall and PET in the short-term (0–2 months), and for PASW with longer lead times (2–5 months). Continuous rank probability skill scores (CRPSS) were generally statistically worse than climatology for rainfall and PET and statistically better than climatology for PASW over 1–3 months. The influence of initial soil water is seasonally dependent, with longer dependence in low evapotranspiration periods. Improved weather model downscaling approaches would transition to climatology and could improve both weather and PASW outlooks. PASW outlooks were strongly reliant on initial conditions, indicating the importance of understanding current soil water status, which needs to be interpreted in a seasonal context as its influence varies over the year. Expanded operational soil water monitoring would be important if PASW outlooks are to become routine.

More Recent Wheat Cultivars Extract More Water from Greater Soil Profile Depths to Increase Yield in the Texas High Plains

Core Ideas We investigated the depth and amount of soil‐water extraction in TAM wheat cultivars. Yield was largely related to soil‐water extraction under dryland conditions. Relatively newer cultivars were able to extract more water from deeper soil profile. Drought is the most important factor limiting wheat (Triticum aestivum L.) yield in the U.S. southern High Plains (SHP). Adoption of suitable cultivars and crop management practices are crucial to reducing yield loss from drought in the area. We conducted a 5‐yr study to investigate the depth and amount of net soil water extraction (SWE) in four wheat cultivars at different growth stages. Plants were grown under dryland conditions and volumetric soil water content (SWC) was measured in 0.2‐m increments to the depth of 2.4 m at planting, jointing, anthesis, and maturity. There were large variations in grain yields (474–3685 kg ha−1) in dryland wheat across years and cultivars. Yield was largely determined by plant available soil water (PASW) at planting and seasonal precipitation. In a season with high yield (3548 kg ha−1 in 2016), net SWE occurred in the whole 0.0‐ to 2.4‐m profile. In contrast, in a season with very low yield (650 kg ha−1 in 2011), net SWE was limited to the upper 1.2 m. More recent cultivars (TAM 110, TAM 111, and TAM 112) were able to extract more water from deeper in the soil profile (particularly between jointing and maturity), and had higher evapotranspiration (ET), biomass, and yield than the legacy wheat cultivar (TAM 105), especially during the dry seasons of 2011 and 2012. This study demonstrated that effective use of soil water from greater soil depths is important for greater ET and yield under dryland conditions in a semiarid environment.

Trends in Plant Available Soil Water on Producer Fields of Western Kansas

Abstract. Residual soil water after harvest and prior to planting was measured to a depth of 2.4 m with neutron attenuation techniques for approximately 45 irrigated corn and 45 dryland wheat fields annually from 2010 through 2012 in the western one-third of Kansas. The sampling locations were in three-county transects in northwest, west central and southwest Kansas with generally five fields for each crop type for each county. Residual plant available soil water (PASW) in corn fields was generally much greater than in wheat fields (150%-160% greater) for any given sampling period illustrating the residual influence of irrigation. Although weather conditions varied between regions and years there was not a strong effect on PASW in irrigated corn fields but there was an effect in dryland wheat fields. Annual differences in fall irrigated corn PASW for the 21 individual fields that were available for sampling in all three years varied less than 50 mm/2.4 m soil profile implying considerable stability in an individual producer’s response (irrigation management and irrigation system capacity) to changing weather conditions as evidenced by the similar year-to-year PASW values. Drought conditions existed for much of the total period (fall 2010 through fall 2012) in southwest Kansas, yet the irrigated corn PASW was still relatively high (PASW value at approximately 62% of water stored at field capacity in a 2.4 m profile). So, the presence of drought may not be a good indicator of the amounts of residual soil water producers are leaving after irrigated corn harvest. Although differences in irrigated corn PASW varied greatly among producers (183% to 722% within a region), there were much smaller differences between regions and years with a variation from 8% to 22%. Irrigation system capacity (flowrate/area) had very little effect on residual fall PASW in the corn fields possibly indicating that producers with deficit capacity are pumping earlier and later into the season to help mitigate their lower irrigation capacity. Irrigated corn grain yields began to plateau when PASW reached a value of approximately 200 mm/2.4 m profile which would represent a water storage of approximately 56% of field capacity. The residual PASW in irrigated corn fields decreased about 1 mm for each 2 mm decrease in irrigation and cropping season precipitation illustrating the difficulties that can arise in managing for a target residual PASW. These results suggest that producers should be scheduling irrigation with science-based methods, rather than habits and previous experiences. Keywords: Corn, Field capacity, Soil moisture content, Soil water, Volumetric water content, Wheat.