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A Modified Richard’s Equation for Assessing the Impact of Drought and Salinity in Arid and Semi-Arid Zones
... As the price of that pipeline is unaffordable, it needs a financial solidarity from all MENA countries which will put its water under exploitation. Arab water and the Peace water are examples (Hegazy, 2022b) . The water holds dissolved salts in a form of soil solution at a high state of energy or high osmotic potential. ...
... At equilibrium, the latter strains are balancing each other to make the biological system holds minimum free energy and maximum entropy . Silicon increases the water potential of the root's sap (Gong andChen, 2012 andAmin et al., 2014) and leaf area index (Hegazy, 2022b) which enables plants to uptake and transpirate more water for combating the stressed conditions. Therefore silica enhances the latter in vivo strains (Figs. 6 and 7). ...
... j: time (days). Equation(3)is the stress form of Richard's equation(Hegazy, 2022b) Where t, z: time and depth respectively (t, l), SSI: dimensionless soil stress index, c(h): soil water holding capacity (l -1 ), K: unsaturated hydraulic conductivity (l/t). β: soil hydraulic capacitance. ...
Ecosystem Services (ES) are increasingly being used by many countries around the world as a framework for addressing the United Nations (UN) Sustainable Development Goals (SDGs). This review article of the usability of Libyan soil databases for ES and SDGs is the first of its kind for North Africa. The objectives of the article are to: describe available the soil resources of Libya in relation to an ES framework; provide examples of the usability of Libyan soil databases for ES applications (e.g., provisioning, Healthy Eating Plate), and describe some of the typical disservices in the country. Desertification, salinization, and limited freshwater resources are the largest challenges (disservices) for agriculture and future development in Libya. Seawater intrusion in coastal areas due to rising sea levels has resulted in high concentrations of salts in irrigation waters, which can lead to low soil productivity. These challenges can be addressed by integrating Libyan soil resources into a market that transforms resources into goods and services to meet human demand in a sustainable manner, with non-market institutions mediating the interactions between humans and the environment. If Libyan soil resources are taken into account by both market and non-market institutions, it will lead to more efficient use of soil resources and also should enable the implementation of innovative strategies such as integrated farming systems, non-soil-based agricultural production (e.g., hydroponics), and alternative farming practices.
In plants, water deficiency can result from a deficit of water from the soil, an obstacle to the uptake of water or the excess water loss; in these cases, the similar consequence is the limitation of plant growth and crop yield. Silicon (Si) has been widely reported to alleviate the plant water status and water balance under variant stress conditions in both monocot and dicot plants, especially under drought and salt stresses. However, the underlying mechanism is unclear. In addition to the regulation of leaf transpiration, recently, Si application was found to be involved in the adjustment of root hydraulic conductance by up-regulating aquaporin gene expression and concentrating K in the xylem sap. Therefore, this review discusses the potential effects of Si on both leaf transpiration and root water absorption, especially focusing on how Si modulates the root hydraulic conductance. A growing number of studies support the conclusion that Si application improves plant water status by increasing root water uptake, rather than by decreasing their water loss under conditions of water deficiency. The enhancement of plant water uptake by Si is achievable through the activation of osmotic adjustment, improving aquaporin activity and increasing the root/shoot ratio. The underlying mechanisms of the Si on improving plant water uptake under water deficiency conditions are discussed.
Arid lands are a vital part of the earth’s human and physical environments. Human population is thin except in Indian arid zone, which is one of the most densely populated arid zones of the world. Arid land ecosystems play a major role in global biophysical processes by reflecting and absorbing solar radiation and maintaining the balance of atmospheric constituents. Water scarcity is the predominant feature of arid lands. In hyperarid, arid and semiarid regions, water is scarce most of the time, and human settlements may cluster around rare sources of water such as rivers, springs, wells and oases. These arid lands are also characterized by persistent water scarcity, frequent drought, high climatic variability and various forms of land degradation, including desertification and loss of biodiversity. These areas occupy 41% area of the earth’s land surface and are home to roughly 2.5 billion people who rely directly on arid land ecosystem services for their livelihoods and support 50% of the world’s livestock where 44% of the world’s food is grown. As per the aridity index, there are four categories of arid lands, hyperarid, arid, semiarid and dry subhumid regions. Livelihood sustainability in these regions is threatened by a complex and interrelated range of social, economic and environmental changes that present significant challenges to researchers, policymakers and, above all, rural land users. The present chapter provides an introductory overview of arid lands of the world, its distribution, causes of aridity, inhabitants and various types of land uses for livelihood.
Land covers in Saudi Arabia are generally described as salty soils with sand dunes and sand sheets. Waterlogging and higher soil salinity are major challenges to sustaining agricultural practices in Saudi Arabia principally within closed drainage basins. Agricultural practices in Saudi Arabia were flourishing in the last two decades. The newly reclaimed lands were added annually and distributed all over the country. Irrigation techniques are mostly modernized to fulfill water saving strategies. Nevertheless, water resources in Saudi Arabia are under stress and groundwater levels are depleted rapidly due to heavy abstraction that may exceed crop water requirements in most of the cases due to high evaporation rates. The excess use of irrigational water leads to severe soil salinity problems. Applications of remote sensing technique in agricultural practices became widely distinctive and cover multidisciplinary principal interests on both local and regional levels. The most important remote sensing applications in agricultural practices are vegetation indices which are related to vegetation and water especially in an arid environment. Soil salinity mapping in an arid ecosystem using remote sensing data is a demanding task. Several soil salinity indices were implemented and evaluated to detect soil salinity effectively and quantitatively. Thematic maps of soil salinity were satisfactorily produced and assessed.
The continuously increasing consumption and scarcity of natural freshwater resources impose threats on different aspects of human life. This study investigated the possible influences of meteorological factors, e.g., relative humidity, temperature, and wind speed, on net freshwater consumption (NFWC). Additionally, we determined the seasonal variations in these factors and forecasted the consumption rate over five years. We took Kuwait as an example and analyzed daily readings obtained from 2014 to 2018 by the Directorate General of Civil Aviation and Ministry of Electricity and Water. The results showed that the consumption rate was affected positively by temperature and negatively by relative humidity. In the seasonality results, two groups characterizing the summer (May to October) and winter (November to April) seasons were obtained regarding the corresponding meteorological factors and net freshwater production (NFWP) and NFWC. The summer season showed high temperature, NFWC, and NFWP and low relative humidity values. In contrast, the winter season revealed high relative humidity and low temperature, NFWC, and NFWP values. The forecasting model is highly accurate and estimated that NFWC will reach 171,919 million imperial gallons/year by 2024. Thus, the obtained results and performed analyses assist in the future management and performance of installed desalination processes.
Modeling water flow in the soil–plant–atmosphere continuum with the Richards equation requires a model for the sink term describing water uptake by plant roots. Despite recent progress in developing process-based models of water uptake by plant roots and water flow in above-ground parts of vegetation, effective models of root water uptake are widely applied and necessary for large-scale applications. Modeling root water uptake consists of three steps, (i) specification of the spatial distribution of potential uptake, (ii) reduction of uptake due to various stress sources, and (iii) enhancement of uptake in part of the simulation domain to describe compensation. We discuss the conceptual shortcomings of the frequently used root water uptake model of Feddes and suggest a simple but effective improvement of the model. The improved model parametrizes water stress in wet soil by a reduction scheme which is formulated as function of air content whereas water stress due to low soil water potential is described by the original approach of Feddes. The improved model is physically more consistent than Feddes’ model because water uptake in wet soil is limited by aeration which is a function of water content. The suggested modification is particularly relevant for simulations in heterogeneous soils, because stress parameters are uniquely defined for the entire simulation domain, irrespective of soil texture. Numerical simulations of water flow and root water uptake in homogeneous and stochastic heterogeneous soils illustrate the effect of the new model on root water uptake and actual transpiration. For homogeneous fine-textured soils, predicted root water uptake never achieves its potential rate. In stochastic heterogeneous soil, predicted water uptake is more pronounced at the interfaces between fine and coarse regions which has potential implications for plant growth, nutrient uptake and depletion.
Soil salinisation is one of the major soil degradation threats occurring in Europe. The effects of salinisation can be
observed in numerous vital ecological and non-ecological soil functions. Drivers of salinisation can be detected
both in the natural and man-made environment, with climate and the foreseen climate change also playing an
important role. This review outlines the state of the art concerning drivers and pressures, key indicators as
well as monitoring, modeling and mapping methods for soil salinity. Furthermore, an overview of the effect of
salinisation on soil functions and the respective mechanism is presented. Finally, the state of salinisation in Europe
is presented according to the most recent literature and a synthesis of consistent datasets. We conclude
that future research in the field of soil salinisation should be focused on among others carbon dynamics of saline
soil, further exploration of remote sensing of soil properties and the harmonization and enrichment of soil
salinity maps across Europe within a general context of a soil threat monitoring system to support policies and
strategies for the protection of European soils.
The title of this essay declares that silicon does have roles in plants and all participants in this conference know that that is so. This knowledge, however, is not shared by the general community of plant biologists, who largely ignore the element. This baffling contrast is based on two sets of experience. First, higher plants can grow to maturity in nutrient solutions formulated without silicon. That has led to the conventional wisdom that silicon is not an essential element, or nutrient, and thus can be disregarded. Second, the world's plants do not grow in the benign environment of solution culture in plant biological research establishments. They grow in the field, under conditions that are often anything but benign. It is there, in the real world with its manifold stressful features, that the silicon status of plants can make a huge difference in their performance. The stresses that silicon alleviates range all the way from biotic, including diseases and pests, to abiotic such as gravity and metal toxicities. Silicon performs its functions in two ways: by the polymerization of silicic acid leading to the formation of solid amorphous, hydrated silica, and by being instrumental in the formation of organic defence compounds through alteration of gene expression. The silicon nutrition of plants is not only scientifically intriguing but also important in a world where more food will have to be wrung from a finite area of land, for that will put crops under stress.
Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. In general, unsaturated models describe root uptake relatively simple. For example, root water uptake is mostly uncompensated and nutrient uptake is simulated assuming that all uptake is passive, through the water uptake pathway only. We present a new compensated root water and nutrient uptake model, implemented in HYDRUS. The so-called root adaptability factor represents a threshold value above which reduced root water or nutrient uptake in water- or nutrient-stressed parts of the root zone is fully compensated for by increased uptake in other soil regions that are less stressed. Using a critical value of the water stress index, water uptake compensation is proportional to the water stress response function. Total root nutrient uptake is determined from the total of active and passive nutrient uptake. The partitioning between passive and active uptake is controlled by the a priori defined concentration value cmax. Passive nutrient uptake is simulated by multiplying root water uptake with the dissolved nutrient concentration, for soil solution concentration values below cmax. Passive nutrient uptake is thus zero when cmax is equal to zero. As the active nutrient uptake is obtained from the difference between plant nutrient demand and passive nutrient uptake (using Michaelis–Menten kinetics), the presented model thus implies that reduced passive nutrient uptake is compensated for by active nutrient uptake. In addition, the proposed root uptake model includes compensation for active nutrient uptake, in a similar way as used for root water uptake. The proposed root water and nutrient uptake model is demonstrated by several hypothetical examples, for plants supplied by water due to capillary rise from groundwater and surface drip irrigation.
The macroscopic root water uptake approach was used in the numerical simulation model HYSWASOR to test four different pressure head-dependent reduction functions. The input parameter values were obtained from the literature and derived from extensive measurements under controlled conditions in the greenhouse. The simulation results indicated that the linear reduction function cannot fit the data satisfactorily. Most of the existing non-linear reduction functions can fit only half of the data range, while the best agreement is obtained with the non-linear two-threshold reduction function. The parameter values obtained by calibration differ only slightly from those of the experiments. Soil water pressure head heterogeneity over the root zone does not play an important role in water uptake. The roots appear to take up water from the relatively wetter parts of the root zone to compensate for the water deficit in the drier parts. While the simulated transpiration agrees closely with the experimental data, the main reason for the discrepancy between the simulated and actual water contents appears to be water uptake during the night.
Water has been labelled ‘blue gold’, and ‘blue gold’ is destined to be the critical issue of the 21st Century. Globally, irrigation is responsible for 80% of the world-wide spending of ‘blue gold’.Development of sustainable irrigation practices will require that we understand better the biophysical processes of root-water uptake in soil, and transpiration from plant canopies.Our review paper is divided into four parts: models, measurements, knowledge gaps and policy.First, we present a retrospective on what has been done with root-water uptake models since the pioneering scheme of Wilford R. Gardner in 1960. His solution for water movement to a plant root was analytical. Since then, nearly all the models calculate water flow using numerical solutions of the Richards’ equation. These schema include a water-uptake term specifically for the distributed uptake of water from soil by the root system. These models fall into two groups based on how the uptake term is handled. The most common formulations, called Type I, have evolved from the work of Gardner [Gardner, W.R., 1960. Dynamic aspects of water availability to plants. Soil Sci. 89, 63–73] and describe the microscale physics of water flow from the soil to, and through, the plant roots. The second form, Type II, comprises macroscopic, empirical functions that describe uptake based on responses to water potential. We discuss the merits and potential of these schemes. Yet, models are data hungry. Effective modeling requires apposite parameterisation to be effective. This can require substantive empiricism.Second, we present new data on the functioning of root-water uptake and transpiration by kiwifruit vines. We describe new observations in the root zone, obtained using arrays of time domain reflectometry (TDR) sensors. As well, we present results obtained with new methods of sap-flow measurement inside the kiwifruit vine's roots. These reveal the uptake dynamics during partial root zone drying (PRD), a technique oft-touted to reduce irrigation volumes.Next, we outline future research needs. This includes a requirement to infer better the matric potential at the soil–root boundary and its control on plant transpiration. We suggest that the role of reverse flow and specification of the root resistance also needs more researching. Further, linking the functioning of water uptake with the form of the root system will not be achievable until we know more about root resistance. Canopy area and architecture are critical for controlling transpiration, yet they are tiresome to measure. Improved measurement techniques, preferably remote, would enhance our ability to predict crop water-use and to assess more accurately the need for irrigation [Wesseling, J.G., Feddes, R.A., 2006. Assessing crop water productivity from field to regional scale. Agric. Water Manage. 86, 30–39].Finally, we demonstrate how our scientific knowledge can be used to develop sustainable irrigation practices.
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