What is DIDAS?
DIDAS is a software package aimed at assisting irrigators in the design of drip-irrigation systems and in irrigation scheduling. The program simulates drip irrigation of various annual crops and trees in various soils under different conditions of evaporation. It evaluates plant water-use efficiency, but not plant growth or yield. DIDAS is comprised of three modules:
- A drip-system design tool based on steady irrigation and water-uptake processes to assess the effect of geometrical attributes on water-use efficiency.
- A diurnal pattern module, based on steady irrigation and accounting for the diurnal patterns of plant-atmosphere resistance to water uptake and evaporation, serving for fine-tuning of the irrigation-system design and for preliminary evaluation of scheduling scenarios.
- An irrigation-scheduling optimization tool, based on the actual water application schedule and on the diurnal pattern of the plant-atmosphere resistance to water uptake.
Who should use DIDAS?
DIDAS is intended for both practitioners and scholars. Potential users include private growers and irrigators working for irrigation companies, extension services and growers' associations. It is also of benefit to researchers, lecturers and students interested in the processes of two and three-dimensional water flow and uptake in soils.
What is DIDAS good for?
Irrigators of annual and perennial crops can use DIDAS as a decision-support tool for assistance in selecting optimal
designs of drip-irrigation systems and optimal irrigation schedules, where water is a key limiting factor in crop production.
The program can serve as both a benchmarking tool for assessing and comparing existing system designs and irrigation
schedules and for developing new, water-use-efficient designs and schedules.
"Design" does not refer to the hydraulics of the irrigation system (pumps, valves, filters, pipe diameters, and the like), but to the geometrical attributes of the drip-irrigation system. These include: distances between emitters along drip lines and between drip lines, the depth of subsurface emitters, and the size and depth of root systems. DIDAS assesses the effects of these attributes on the plant's water-use efficiency under various environmental conditions (soil properties and atmospheric evaporative demand). DIDAS only refers directly to drip irrigation. Nevertheless, its three modules can also assist in understanding and assessing furrow irrigation, for example, by simulating irrigation with parallel line sources on a flat soil surface.
"Scheduling" refers to, and assists in optimizing drip-irrigation schedules for both 'every-few-days' irrigation and multiple daily irrigation pulses. DIDAS evaluates the effects of irrigation frequency, daily hours of water application and irrigation-pulse duration on water-use efficiency for a given scenario of: drip system design, soil properties, root system size and depth, and atmospheric evaporative demand. DIDAS cannot be used to assess plant water-use efficiency in rainfed crop production or when applying supplemental irrigation, i.e., it refers only to regular irrigation schedules.
Researchers, lecturers and students can use DIDAS as a research or training tool for studying the effects of various boundary (engineering and environmental) conditions on the processes of 2D and 3D water flow and uptake in variably saturated soils. Setting scenarios of coupled, on-surface or subsurface water sources and subsurface sinks, and utilizing the graphical outputs of the spatial distributions and temporal patterns of soil water potential enable methodological studies of the roles of gravity and capillarity in driving the soil water, and of the effects of soil, plant and atmospheric evaporative demand on water flow and uptake by plant roots. DIDAS also allows setting scenarios with just point or line water sources, which are relevant to other agronomic and environmental practices and to processes involving water application and leaks with no water uptake by plant roots.
What are DIDAS' concepts and principles?
DIDAS is designed to be user-friendly and to use a minimal number of readily available and intuitive parameters, while at the same time maintaining accuracy, robustness and relevance. The program performs computations based on analytical solutions of the relevant linearized water flow and uptake problems. Water flow is described by the superposition of solutions for positive sources (on-surface or subsurface emitters) and negative sinks (plant root systems). Steady water flow is assumed in the design module and unsteady flow is used in the irrigation-scheduling module. The design tool is based on a new, relative water-uptake rate (RWUR, ratio between water uptake rate and irrigation rate) criterion suggested for assessing the effect of the geometrical attributes on water use efficiency. The recommended RWUR criterion for design purposes is evaluated under the assumption of no plant-atmosphere resistance to water uptake. Namely, the plant roots apply maximum possible suction and the water uptake is determined only by the capability of the soil to conduct water from the sources (emitters) to the sinks (root zones). The computations of the RWUR require only three parameters describing soil texture, root-zone size, and potential evaporation in those few cases where it is important to account for evaporation from the soil surface. The irrigation-scheduling optimization tool is based on modeling unsteady water flow and on a relative water-uptake volume criterion (RWUV, ratio between daily water-uptake volume and daily irrigation volume). An alternative optimization criterion is maximization of the daily hours for which the evaluated (absolute) water-uptake rate is higher than a given threshold value. The computations of diurnal patterns of water-uptake rates and daily RWUV for a given irrigation scenario require additional information on the diurnal pattern of the plant-atmosphere resistance to water uptake and on the hydraulic conductivity of the soil.
How to use DIDAS?
DIDAS is written in DELPHI and runs under Microsoft Windows operating system (version XP and higher) with no
special supporting software requirements. The construction of the drip-irrigation scenario is performed via
a few GUI windows, which also contain a library of the required input parameters, and a best-fitting procedure
for the soil parameters. The computed RWURs and RWUVs are displayed graphically and the tabulated output
results can be exported to e.g. Windows Excel for further processing. DIDAS also includes an on-line help
feature that assists in setting up the irrigation scenario and choosing the desired output. An updated
version of the DIDAS package can be downloaded freely below.
DIDAS is comprised of three parallel, independently operating modules. Thus, the user can start running any one of them, and when moving to another module the relevant input parameters are saved for further use, if not altered by the user. The irrigation scenario is set up by filling in the input parameters of all relevant GUI windows, with possible back and forth, non-sequential navigation between the windows. When downloading DIDAS for the first time, it contains a set of default parameters; when it is run again, it remembers the irrigation scenarios defined during that last use in each module. It is also possible to save in an external file a defined irrigation scenario for future use.
The design tool computes the RWUR, and its output is the RWUR as a function of the radius of the root zone for different emitter or drip-line spacings, depending on the chosen scenario. We recommend assigning zero plant-atmosphere resistance to water uptake when assessing drip-system design issues.
The diurnal pattern module, accounting for the daily patterns of the plant-atmosphere resistance to water uptake and evaporation, serves as a mediator of the other two modules for fine-tuning of the design and for preliminary evaluation of water-uptake patterns, especially in moderate to fine-textured soils. Its output is the diurnal pattern of RWUR, as well as the relative (to irrigation) evaporation (RER) and deep percolation (RDPR) rates. This module also depicts the flow fields (equipotential and stream lines) for various emitter/root-zone configurations.
The irrigation-scheduling tool computes the diurnal (and every-few-days irrigation cycle) patterns of the RWUR and the daily and irrigation-cycle mean RWUV for a given irrigation scenario, accounting for the hourly plant-atmosphere resistance to water uptake. This module also depicts the temporal patterns of the water potential at specified locations. The simulated scenario of irrigation scheduling should include a sufficient number of irrigation cycles (larger for clayey as compared to sandy soils) to approach a quasi-steady, periodic pattern.