The impact of soil water distribution on root development and root water uptake of winter wheat

Root water uptake (RWU) is a key process in the root zone that determines water movement from the soil into roots and transport to the atmosphere via plant leaves. Different RWU models were developed with different assumptions and parameters but the description of this process and its parameterization remain challenging in soil hydrology. Due to the difficulty to obtain root development and soil states in undisturbed soils, dynamic root distributions and a physically based concept to describe water uptake from soil profiles with vertical variations in soil water availability are often not taken into consideration. The simulated RWU is rarely evaluated by measured transpiration for field conditions. This study aims at 1) introducing two minirhizotron (MR) facilities that were installed in two types of soils with different water treatments for monitoring dynamics of root and soil moisture in situ, 2) parameterizing RWU models that use different concepts and investigating the difference in RWU patterns and possible links, 3) exploring the effect of soil water availability on root development and RWU that were estimated by different RWU models, and evaluating the estimated RWU by measured transpiration. Winter wheat was considered in this study. Two MR facilities were constructed in two different soils (stony vs. silty) to monitor root growth and root zone processes. Each facility was established with three subplots: sheltered, rainfed, and irrigated. Root dynamics were observed in 7-m-long rhizotubes that were installed horizontally at 10, 20, 40, 60, 80, and 120 cm depth. Time domain reflectometer (TDR) probes, tensiometers, and matrix potential sensors were installed at those six depths to measure soil water content and water potential. The measurements served as input for inversely estimating soil and root-system related parameters of three RWU models: Feddes (without compensation), Feddes-Jarvis (with compensation, FJ), and Couvreur (physically based model with compensation that have been implemented in Hydrus-1D, C). Sap flow was monitored in each plot of the two soils. Measurements in the rhizotron facilities demonstrated that soil water content, root density, and crop biomass of winter wheat were higher in the silty than in the stony soil, in which plant and root growth were obviously affected by water treatments and soil types. Using the data from the sheltered plot of the stony soil, the three models predicted soil moisture equally well and the soil hydraulic parameters optimized by the models with compensation were comparable. The obtained RWU parameters of the FJ model and root hydraulic parameters for winter wheat were consistent with data reported in the literature. The FJ and C models simulated similar root-system scale stress functions that link total RWU to the effective root zone water potential. The root-system related parameters of the C model could be constrained but not those of the FJ model. When broadening the model parameterization and simulations to different soils and water treatments, the soil hydraulic parameters could be well identified by the FJ and C models. Patterns of crop and root development differed in the plots of the two soils, which resulted in different RWU due to different soil water availability. The FJ and C models simulated similar RWU which was the lowest in the sheltered plot of the stony soil where RWU was also lower than the potential RWU. In the silty soil, RWU was equal to the potential uptake for all treatments. The C model predicted the ratios of the transpiration fluxes in the two soils slightly better than the FJ model. The variation of simulated RWU between the different plots agreed well with measured sap flow but with a constant offset which needs further study.Der Einfluss der Bodenwasserverteilung auf die Entwicklung und die Wasseraufnahme der Wurzeln von Winterweizen Die Wurzelwasseraufnahme (WWA) kontrolliert den Wassertransport vom Boden über die Pflanze in die Atmosphäre. Verschiedene mathematische Modelle, die sich in ihrer Komplexität und ihren Parameter unterscheiden, erklären die WWA; doch nach wie vor ist die Beschreibung dieses Prozesses eine Herausforderung in der Bodenhydrologie. Die Messung der Wurzelentwicklung im ungestörten Boden ist kompliziert, daher wird die dynamische Verteilung von Wurzeln und deren Wasseraufnahme häufig nicht beachtet. Ferner werden simulierte WWA selten mit Transpirationsmessungen verglichen. Die vorliegende Studie hat zum Ziel 1) zwei Minirhizotron Anlagen (MR) zu beschreiben, welche zur in-situ-Erfassung der dynamischen Wurzelentwicklung in zwei verschiedenen Böden installiert wurden, 2) drei verschiedene Modelle zur WWA zu parametrisieren, um Unterschiede in den Mustern der Wasseraufnahme herauszufinden, 3) den Effekt von Bodenwasserverfügbarkeit auf die Wurzelentwicklung zu untersuchen und die abgeschätzte WWA mit Xylemflussmesswerten zu bewerten. Die Modellansätze und Methoden sind allgemeingültig; in dieser Studie wurde Winterweizen betrachtet. Die MR Anlagen wurden auf zwei Böden (steinig vs. schluffig) zur Betrachtung des Wurzelwachstums und anderer Prozesse der Wurzelzone konstruiert. Beide Anlagen wurden dreigeteilt: überdacht, beregnet und bewässert. Betrachtungen der Wurzeldynamiken erfolgten in sieben Meter langen Plexiglasröhren, horizontal installiert in 10, 20, 40, 60, 80 und 120 cm Tiefe. In diesen Tiefen wurden auch mittels Sensoren Wasserpotential, Bodenfeuchte und -temperatur gemessen. Diese Daten waren Input für die Schätzung der von Boden- und Wurzelsystem abhängigen Parameter von drei Modellen zur WWA: Feddes (F), Feddes-Jarvis (FJ) und Couvreur (C), implementiert in Hydrus-1D. Die Simulationen wurden mit lokalen Xylemflussmessungen verglichen. Die MR Messungen zeigten, dass Bodenwassergehalt, Wurzeldichte und Pflanzenbiomasse von Winterweizen auf dem schluffigen Boden höher waren als auf dem steinigen. Für den abgedeckten Bereich in der steinigen Anlage prognostizieren die Modelle F, FJ und C die Bodenfeuchte gleich gut und die Modell-optimierten Parameter waren vergleichbar. Die Parameter für die WWA des FJ Models und die wurzelhydrologischen Parameter für den Winterweizen waren übereinstimmend mit Literaturdaten. Mit den Modellen FJ und C konnten vergleichbare Stressfunktionen auf Skala des Wurzelsystems simuliert werden. Die Wurzelsystem-abhängigen Parameter des C Modells wurden belegt, die von FJ nicht. Wenn Modellparametrisierung und Simulationen auf alle Böden und Bewässerungstechniken ausgeweitet wurden, konnten die bodenhydrologischen Parameter gut mit dem FJ und dem C Modell identifiziert werden. Die Muster in der Pflanzen- und Wurzelentwicklung unterschieden sich zwischen den Plots beider Böden, was zu unterschiedlichen WWA Raten bedingt durch verschiedene Bodenwasserverfügbarkeiten führte. Das FJ und das C Modell simulierten ähnliche WWA Raten, welche am niedrigsten für den bedachten Plot im steinigen Boden war, wo die WWA niedriger war als die potentielle WWA. In dem schluffigen Boden waren die WWA Raten gleich der potentiellen WWA in allen drei Plots mit unterschiedlicher Bewässerungstechnik. Das C Modell prognostizierte die Transpirationsflussraten für beide Böden besser als das FJ Modell. Die Variationen der simulierten WWA zwischen den unterschiedlichen Plots stimmten mit den Xylemflussmessungen überein, jedoch benötigt der konstante Zeitabstand zwischen simulierten WWA Raten und Xylemfluss weitere Untersuchungen

Assessing the drought risk of oilseed rape to target future improvements to root systems

The yield of UK’s commercial oilseed rape (Brassica napus) crops has not increased over the last three decades, while a significant increase in yield has been found in trials that test new varieties before they enter the market. It has been suggested that oilseed rape is susceptible to drought and that this may contribute to the poor yield of some commercial crops. A thorough literature review revealed that there is little information on the water relations of oilseed rape crops and in particular on root growth and function and thus no strong evidence to support the above hypothesis. The aim of this thesis was to investigate root function and water relations of oilseed rape to determine whether it is more sensitive to drought than wheat, a crop species grown in rotation with oilseed rape. The water relations of wheat (Triticum aestivum L. cv. Tybalt) and oilseed rape (Brassica napus L. cv. SW Landmark) were compared in a lysimeter experiment conducted in an open sided glass house to test the hypothesis that oilseed rape was more sensitive to drying soil than wheat. Plants were grown with or without irrigation at a population density equivalent to that of commercial field crops. Irrigated oilseed rape crops transpired more water than wheat crops and oilseed rape showed a greater reduction in growth when water was withheld. The onset of drought also occurred slightly earlier in oilseed rape. In a separate experiment the root hydraulic conductance of oilseed rape, measured on a root surface area basis, was about twice that of wheat (113.1 ± 20.0 mlNm-2Nh-1NMPa-1 for oilseed rape and 53. 5 ± 10.6 for wheat). These results suggest that oilseed rape needs a less dense root system for water extraction than wheat. In the above experiment plants were grown in relatively loose soil repacked into the lysimeters. It has been suggested that oilseed rape is particularly sensitive to soil compaction, which may be a common occurrence in commercial fields. Therefore the sensitivity of oilseed rape and wheat growth to compaction was compared in an experiment under well-watered conditions. Plants were grown in a controlled environment chamber in pots packed with soil at four different bulk densities. Although the root length, shoot mass, leaf area and stomatal conductance of oilseed rape were all reduced by soil compaction, oilseed rape was no more sensitive to soil compaction than wheat under these well-watered conditions. When soil dries it also hardens and high soil strength is known to impede root growth and alter plant-water relations. The hypothesis that oilseed rape is more sensitive to increasing soil strength than wheat was tested in an experiment in which soil bulk density and soil water content were varied to create a range of soil strengths. At low soil strength oilseed rape had a greater stomatal conductance than wheat, but as soil strength increased, stomatal conductance decreased to a greater extent in oilseed rape, indicating a more sensitive response. In dense or strong soil, plants often rely on pores created by earthworms or roots of the previous crop to explore the soil volume. The ability of oilseed rape and wheat to exploit soil pores to penetrate hard soil layers was compared in a pot experiment. A hard layer, comparable to a hard–pan in a cultivated field, was created at twelve centimetre depth of each pot by packing the soil to a bulk density of 1.5 g·cm-3 relatively loose soil at a bulk density of 1.1 g·cm-3 was present above and below the layer. In one treatment seven pores were drilled through the hard layer; controls had none. Presence of pores in the hard layer led to a significant increase in number of roots in the deeper soil, of 29% for wheat and 54% for oilseed rape. This project has shown that the physiological response to drought occurred earlier in oilseed rape than in wheat and that stomatal conductance and biomass production of oilseed rape reacted more sensitively to soil drying. However, water use by oilseed rape does not seem to be limited by the ability of its roots to explore the soil and transport water compared to wheat. The growth and distribution of roots under a range of soil conditions was as good as, if not better than, that of wheat. The implications of these findings for the commercial production of oilseed rape in the UK are discussed

Study of Atmospheric Pollution Scavenging: Twentieth Progress Report

published or submitted for publicationis peer reviewedOpe

Snowmelt energy balance in a burned forest stand, Crowsnest Pass, Alberta

xii, 129 leaves : ill,, map ; 29 cmForested watersheds in western North America are subject to significant change from natural and anthropogenic disturbance, including wildfire. Forest canopy changes have subsequent impacts on sub-canopy snow processes. A simple, process-based point energy balance model was developed to quantify differences in energy balance characteristics between a burned and a healthy forest stand. Potential model uncertainties were identified using sensitivity analyses. Simulated snowmelt accurately recreated measured snowmelt, providing confidence in the model’s ability to simulate energy balance processes in subcanopy environments where wind redistribution and sublimation are not major drivers of the local snowmelt energy balance. In the burned stand, sub-canopy snow accumulation was greater but melted more rapidly than in the healthy stand. The removal of forest canopy resulted in more energy available for snowmelt, including higher short-wave and lower long-wave radiation, and increased turbulent fluxes. Burned stands should be considered a separate land cover type in larger scale watershed models

Modelling and Management of Irrigation System

Irrigation is becoming an activity of precision, where combining information collected from various sources is necessary to optimally manage resources. New management strategies, such as big data techniques, sensors, artificial intelligence, unmanned aerial vehicles (UAV), and new technologies in general, are becoming more relevant every day. As such, modeling techniques, both at the water distribution network and the farm levels, will be essential to gather information from various sources and offer useful recommendations for decision-making processes. In this book, 10 high quality papers were selected that cover a wide range of issues that are relevant to the different aspects related to irrigation management: water source and distribution network, plot irrigation systems, and crop water management

Agricultural Water Conservation: Tools, Strategies, and Practices

Water scarcity is a critical issue for agriculture, and, hence, efficient management and conservation practices for agricultural water use are essential for adapting to and mitigating the impacts of current and future discrepancy between water supplies and water demands. This Special Issue focuses on “Agricultural Water Conservation: Tools, Strategies, and Practices”, which aims to bring together a collection of recent cutting-edge research and advancements in agricultural water conservation. The Special Issue intends to give a broad overview focusing on on-farm water conservation practices, advanced irrigation tools and water technologies, and the best management practices and strategies for efficient water use in agriculture

Addressing Data Resolution in Precision Agriculture

Irrigated agriculture constitutes the greatest consumptive water use globally, so that irrigation efficiency measures are an important part of global efforts to best utilize this limited resource. However, greater irrigation efficiency must be achieved while simultaneously maintaining or increasing crop yields and farming profitability. Incremental water use decisions are made at the local level by farmers under many real world constraints; consequently they face significant risks in operating large and complex irrigation systems. These decisions should be supported by reliable information upon which to base operational plans and irrigation scheduling. Implementing precision irrigation effectively depends upon highly resolved estimates of crop water demand so that application rates match demand precisely both in location and timing. A fundamental challenge in mapping the irrigation requirement is addressing the heterogeneity of soil, biophysical, and atmospheric processes which mediate water demand. However, existing methods to determine the irrigation requirement assume that field conditions are homogeneous. Precision irrigation systems may enable more specific water distribution than traditional irrigation equipment, but allocating the correct amount of water requires crop water estimates that accurately reflect the variability of the irrigation requirement and consider the scale and timing at which irrigation can be delivered. This dissertation synthesizes the results from field studies which analyzed spatial patterns of irrigation performance and crop water demand under real field conditions. The first experiment quantified the performance of a precision irrigation system and determined the data resolution required for effective utilization of the system’s capability (Chapter 2). Field trials were conducted with a variable rate center pivot sprinkler (VRI) under normal farming conditions to determine this spatial resolution. The result was the definition of a performance coefficient and characteristic length scale associated with the irrigation system. The characteristic length scale describes the highest resolution prescription possible with VRI. Following on these findings, a second study compares an electromagnetic (EM) soil mapping method using extensive laboratory soil characterization as a basis for comparison (Chapter 3). The motivation of the study was to validate the EM method’s capability to detect small scale variations in soil water holding capacity, and to determine under which conditions the EM method can obtain reliable and robust soil maps. The findings reinforce earlier work on the importance of instrument calibration, and also show that specific soil characteristics may preclude using EM methods to map soil in some regions. Following the soil mapping study, further studies investigated methods to measure crop evapotranspiration (ET). A literature review was conducted to establish a catalog of contemporary methods to monitor ET, focusing on those commonly used in agriculture (Chapter 4). From this review, the surface renewal method (SR) emerged as potentially able to map ET feasibly and cost-effectively. Four field experiments were conducted over two years under a range of field conditions to establish a robust protocol for the determination of surface fluxes with SR (Chapter 5). Three of these experiments specifically investigated the potential for SR to be implemented from a moving sensor platform, such as an unmanned aerial vehicle. Experiments showed SR could estimate sensible heat flux as accurately as eddy covariance during moving trials. However, analysis of the minimum flux averaging period demonstrated that SR cannot resolve fluxes at the requisite spatial scales for precision irrigation. Nonetheless, SR remains promising for other practical applications in measuring surface fluxes. Future research questions and potential applications are explored in Chapters 5 and 6. The methods described here are directly relevant to water managers at the levels of farms and irrigation districts. Efficient irrigation planning depends on timely, reliable, and site-specific information in order to anticipate crop water demand, irrigate adequately to prevent drought stress, and maximize yield from the available resource. Growers and irrigation specialists currently have many resources at their disposal, including regional and satellite based ET estimates, state and local soil mapping, and scientific irrigation planning software. However, these methods do not provide site-specific and real time measurements of actual crop water demand, and farmers do not have any reliable means by which to validate the accuracy and precision of these estimates. For this information to be directly useful in irrigation planning, it should be validated by on site measurements. Reliable, local, and real time information is required to realize the full potential of precision agriculture

Quality assurance plan for a project entitled : earthern liners : a study of transit time

Cover title."Date: 4/18/86"--P. 1."USEPA cooperative agreement no. CR-812650-01."Includes bibliographical references (p. 76-81)

Chemical Indicators of Surface Water Pollution

High quality surface water is critical for maintaining healthy ecosystems and ensuring safe drinking water, yet is often compromised by point and non-point contamination sources. Failed septic systems, an example of non-point source pollution, may generate pools of untreated or minimally treated wastewater that can runoff into nearby streams. There are currently no means of quickly determining the impact of this pollution on surface water. Representative emerging contaminants (caffeine and triclosan) were targeted as indicators from failed septic systems and chlorination disinfection byproducts (haloacetic acids) for the effluent from conventional municipal wastewater treatment plants. Methods for the analysis of these compounds in various matrices were developed and applied to both effluent types and surrounding surface waters. Typical caffeine and triclosan concentrations in conventional municipal wastewater treatment plant effluents were 0.23μg/L and 0.3μg/L, respectively, as compared to 22μg/L and 7μg/L from septic tank effluents. Excitation-emission fluorescence spectrophotometry was also investigated as a tool for characterizing pollution from wastewater sources