Water harvesting and supplemental irrigation for improved water use efficiency in dry areas

Productivity / Water harvesting / Runoff / Water storage / Crop production / Water use efficiency / Arid lands / Water resources development / Rain-fed farming / Supplementary irrigation / Irrigation scheduling / Environmental effects / Research priorities / Case studies / West Asia / North Africa / India / Libya / Syria / Burkina Faso

An explicit hydrological algorithm for basic flow and transport equations and its application in agro-hydrological models for water and nitrogen dynamics

Hydrological simulation is a key component in argo-hydrological models for optimizing resources use and minimizing the environmental consequences in agriculture. In this study we extended a simple and explicit algorithm for solving the basic soil water flow equation by Yang et al. (J. Hydrol. 370, 177-190) to the solute transport equation. The key feature of the algorithm is to use a uniform soil layer thickness and a small time step in solving the soil water and solute transport equations, so that the calculations can be made on a layer basis. This drastically simplifies the procedure of modeling water and solute transport in soil using the basic equations. The proposed algorithm was tested against the complex finite element (FE) numerical scheme in simulating soil water and solute transport in different soils via numerical experiments. The results showed that the proposed algorithm with a uniform soil layer thickness of 5 cm and a small time step of 0.001d was able to achieve the identical accuracy as the FE method. Tests of the proposed algorithm in simulating water and nitrogen dynamics against data from a field experiment on wheat revealed that the predicted results with the simple algorithm were in good agreement with the time-course measurements of soil water and mineral N concentration at the various depths in the profile, suggesting that the proposed algorithm performed well and can be reliably applied in agro-hydrological models. The simplicity and accuracy of the algorithm will encourage scientists to use basic equations for soil water and solute transport more in the future for improving performance of agro-hydrological models

Infiltration from surface and buried point sources: The average wetting water content

The assumption in analytical solutions for flow from surface and buried point sources of an average water content, (θ) over bar, behind the wetting front is examined. Some recent work has shown that this assumption fitted some field data well. Here we calculated (θ) over bar using a steady state solution based on the work by Raats [1971] and an exponential dependence of the diffusivity upon the water content. This is compared with a constant value of (θ) over bar calculated from an assumption of a hydraulic conductivity at the wetting front of 1 mm day(-1) and the water content at saturation. This comparison was made for a wide range of soils. The constant (θ) over bar generally underestimated (θ) over bar at small wetted radii and overestimated (θ) over bar at large radii. The crossover point between under and overestimation changed with both soil properties and flow rate. The largest variance occurred for coarser texture soils at low-flow rates. At high-flow rates in finer-textured soils the use of a constant (θ) over bar results in underestimation of the time for the wetting front to reach a particular radius. The value of (θ) over bar is related to the time at which the wetting front reaches a given radius. In coarse-textured soils the use of a constant value of (θ) over bar can result in an error of the time when the wetting front reaches a particular radius, as large as 80% at low-flow rates and large radii

SWIM SWIM Paper System-Wide Initiative on Water Management ICARDA SWIM 7 Water Harvesting and Supplemental Irrigation for Improved Water Use Efficiency in Dry Areas Water Harvesting and Supplemental Irrigation for Improved Water Use Efficiency in Dry Area

SWIM Papers In an environment of growing scarcity and competition for water, increasing the productivity of water lies at the heart of the CGIAR goals of increasing agricultural productivity, protecting the environment, and alleviating poverty. TAC designated IWMI, the lead CGIAR institute for research on irrigation and water management, as the convening center for the System-Wide Initiative on Water Management (SWIM). Improving water management requires dealing with a range of policy, institutional, and technical issues. For many of these issues to be addressed, no single center has the range of expertise required. IIMI focuses on the management of water at the system or basin level while the commodity centers are concerned with water at the farm and field plot levels. IFPRI focuses on policy issues related to water. As the NARS are becoming increasingly involved in water management issues related to crop production, there is strong complementarity between their work and many of the CGIAR centers that encourages strong collaborative research ties among CGIAR centers, NARS, and NGOs. The initial publications in this series cover state-of-the-art and methodology papers that assisted the identification of the research and methodology gaps in the priority project areas of SWIM. The later papers will report on results of SWIM studies, including intersectoral water allocation in river basins, productivity of water, improved water utilization and on-farm water use efficiency, and multiple uses of water for agriculture. The papers are published and distributed both in hard copy and electronically. They may be copied freely and cited with due acknowledgment. Randolph Barke