Soil water repellency can significantly degrade its agricultural utility and bring aboutnegative environmental consequences (i.e., reduced infiltration capacity, enhanced overland flow,increased ...erosion rates, and water infiltration occurred in irregular patterns). The presented studyaimed to establish whether excluding albic Podzols from agricultural production and theirspontaneous inhabitation by a pine tree stand affected their hydrophysical properties. Studies withthe application of the water drop penetration time (WDPT) test showed that a change in the landuse increased the potential water repellency of the surface layer (horizon A) and caused itschangeover from strongly repellent class (Class 2) to extremely repellent (Class 5). The relationshipbetween soil moisture content and wettability made it possible to determine the critical soil moisturecontent (CSMC) for the occurrence of the phenomenon of water repellency. It was confirmed thatthe CSMC value increased along with a change in use. For the site under arable use, it was 9–10vol.%, whereas for the site formerly under arable use and currently covered predominantly by apine tree stand, a value in the range of 14–16 vol.% was reached. A laboratory experiment on surfacerunoff of the soil formerly under arable use showed that over half of the rainfall may be transformedinto surface runoff as a result of occurring water repellency. This means that exceeding the criticalsoil moisture content makes the recharge of soil retention difficult and may significantly influencethe water balance of soil, as well as increasing its susceptibility to drought.
Key Points
A sequential water use model with scarcity, inefficiency and saline return
Marginal value of water is computed according to scarcity, salinity and loss
Water management benefits increase ...with salinity level and evaporative losses
In arid and semiarid regions, irrigation water is scarce and often contains high concentrations of salts. To reduce negative effects on crop yields, the irrigated amounts must include water for leaching and therefore exceed evapotranspiration. The leachate (drainage) water returns to water sources such as rivers or groundwater aquifers and increases their level of salinity and the leaching requirement for irrigation water of any sequential user. We develop a conceptual sequential (upstream‐downstream) model of irrigation that predicts crop yields and water consumption and tracks the water flow and level of salinity along a river dependent on irrigation management decisions. The model incorporates an agro‐physical model of plant response to environmental conditions including feedbacks. For a system with limited water resources, the model examines the impacts of water scarcity, salinity and technically inefficient application on yields for specific crop, soil, and climate conditions. Moving beyond the formulation of a conceptual frame, we apply the model to the irrigation of Capsicum annum on Arava Sandy Loam soil. We show for this case how water application could be distributed between upstream and downstream plots or farms. We identify those situations where it is beneficial to trade water from upstream to downstream farms (assuming that the upstream farm holds the water rights). We find that water trade will improve efficiency except when loss levels are low. We compute the marginal value of water, i.e., the price water would command on a market, for different levels of water scarcity, salinity and levels of water loss.
Hillslope response has traditionally been studied by means of the hydraulic groundwater theory. Subsurface flow from a one-dimensional hillslope with a sloping aquifer can be described by the ...Boussinesq equation Mem. Acad. Sci. Inst. Fr. 23 (1) (1877) 252–260. Analytical solutions to Boussinesq's equation are very useful to understand the dynamics of subsurface flow processes along a hillslope. In order to extend our understanding of hillslope functioning, however, simple models that nonetheless account for the three-dimensional soil mantle in which the flow processes take place are needed. This three-dimensional soil mantle can be described by its plan shape and by the profile curvatures of terrain and bedrock. This plan shape and profile curvature are dominant topographic controls on flow processes along hillslopes. Fan and Bras Water Resour. Res. 34 (4) (1998) 921–927 proposed a method to map the three-dimensional soil mantle into a one-dimensional storage capacity function. Continuity and a kinematic form of Darcy's law lead to quasi-linear wave equations for subsurface flow solvable with the method of characteristics. Adopting a power function of the form proposed by Stefano et al. Water Resour. Res. 36 (2) (2000) 607–617 to describe the bedrock slope, we derive more general solutions to the hillslope-storage kinematic wave equation for subsurface flow, applicable to a wide range of complex hillslopes. Characteristic drainage response functions for nine distinct hillslope types are computed. These nine hillslope types are obtained by combining three plan curvatures (converging, uniform, diverging) with three bedrock profile curvatures (concave, straight, convex). We demonstrate that these nine hillslopes show quite different dynamic behaviour during free drainage and rainfall recharge events.
The agro-hydrological model SWAP was used in a distributed manner to quantify irrigation water management effects on the water and salt balances of the Voshmgir Network of North Iran during the ...agricultural year 2006–2007. Field experiments, satellite images and geographical data were processed into input data for 10 uniform simulation areas. As simulated mean annual drainage water (312 mm) of the entire area was only 14% smaller than measured (356 mm), its distribution over the drainage units was well reproduced, and simulated and measured groundwater levels agreed well. Currently, water management leads to excessive irrigation (621–1436 mm year-1), and leaching as well as high salinity of shallow groundwater are responsible for large amounts of drainage water (25–59%) and salts (44–752 mg cm-2). Focused water management can decrease mean drainage water (22–48%) and salts (30–49%), compared with current water management without adverse effects on relative transpiration and root zone salinity
With prolonged rainfall, infiltrating wetting fronts in water repellent soils may become unstable, leading to the formation of high‐velocity flow paths, the so‐called fingers. Finger formation is ...generally regarded as a potential cause for the rapid transport of water and contaminants through the unsaturated zone of soils. For the first time, field evidence of the process of finger formation and finger recurrence is given for a water repellent sandy soil. Theoretical analysis and model simulations indicate that finger formation results from hysteresis in the water retention function, and the character of the formation depends on the shape of the main wetting and main drainage branches of that function. Once fingers are established, hysteresis causes fingers to recur along the same pathways during following rain events. Leaching of hydrophobic substances from these fingered pathways makes the soil within the pathways more wettable than the surrounding soil. Thus, in the long‐term, instability‐driven fingers might become heterogeneity‐driven fingers.
Irrigation has been used for thousands of years to maximize the performance, efficiency and profitability of crops and it is a science that is constantly evolving. This potential for improved crop ...yields has never been more important as population levels and demand for food continue to grow. Recognising the need for a coherent and accessible review of international irrigation research, this book examines the factors influencing water productivity in individual crops. It focuses on nine key plantation/industrial crops on which millions of people in the tropics and subtropics depend for their livelihoods (banana, cocoa, coconut, coffee, oil palm, rubber, sisal, sugar cane and tea). Linking crop physiology, agronomy and irrigation practices, this is a valuable resource for planners, irrigation engineers, agronomists and producers concerned with the international need to improve water productivity in agriculture in the face of increased pressure on water resources.
As global pressure on water resources intensifies, it is essential that scientists understand the role that water plays in the development of crops and how such knowledge can be applied to improve ...water productivity. Linking crop physiology, agronomy and irrigation practices, this book focuses on eleven key fruit crops upon which millions of people in the tropics and subtropics depend for their livelihoods (avocado, cashew, Citrus spp., date palm, lychee, macadamia, mango, olive, papaya, passion fruit and pineapple). Each chapter reviews international irrigation research on an individual fruit crop, identifying opportunities for improving the effectiveness of water allocation and encouraging readers to link scientific knowledge with practical applications. Clearly written and well illustrated, this is an ideal resource for engineers, agronomists and researchers concerned with how the productivity of irrigated agriculture can be improved, in the context of climate change, and the need for growers to demonstrate good irrigation practices.
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