A description of how the DSS works is provided bellow
IRMA_SYS has been adapted for the plain of Arta (http://arta.irrigation-management.eu/). It is a regional, user-friendly computer/mobile-based, open and free modular software for estimating site specific crop water requirements and irrigation scheduling at multiple scales, from farm to water basin level, with high spatial resolution.
The system takes into account historical (from the system’s stations) and forecast agrometeorological data, along with crop and soil-water data to accomplish the above mentioned tasks. Also, it is fully customizable, allowing the users to add site specific information in order to customize the output of the system, taking advantage of additional information.
IRMA_SYS is addressed to irrigation professionals who have the background and the experience to interpret the information provided and use the system for setting up irrigation schedules, plan and record irrigation events as well as self-training regarding irrigation management.
The irrigation needs are estimated based on an approach that is called root zone soil water depletion, which is a simplified soil water balance based on an initial soil moisture condition and runs for a specified time period.
The basis for the calculations is the following formula (Allen et al., 1998):
where i is the current time period (i.e. the current day, or hour), Dr,i-1 is the root zone depletion at the end of the previous time period (mm), Pi is the precipitation (mm), ROi is the runoff (mm), IRn,i is the net irrigation depth (mm), CRi is the capillary rise (mm), ETc,i is the crop evapotranspiration (mm) and DPi is the water loss through deep percolation (mm).
The following limits were imposed on Dr,i:
Θs <= Dr,i <= TAW (2)
where Θs is the soil moisture at saturation (mm) and TAW is the total available soil water (mm), which is the difference between Field Capacity (FC) and Permanent Wilting Point (PWP), i.e.:
TAW = FC – PWP (3)
This approach is different than the one proposed by Allen et al., 1998 since according to them Dr,i is always positive.
ROi equals the amount of water that exceeds soil moisture at saturation after heavy rain, i.e.:
ROi = Pi + Θi–1 – Θs when (Pi + Θi–1 – Θs) > 0 (4)
where Θi–1 is the soil moisture at the previous time step. CRi and DPi are considered equal, since in the case of the Arta plain there is a shallow water table and equilibrium between them is considered.
So equation 1 becomes:
ETc,i is calculated using crop coefficient approach by multiplying reference evapotranspiration with the appropriate crop coefficient Kc (Allen et al., 1998).
Each time the user irrigates, the initial depletion derives from the provided irrigation water volume. Dr,i given, irrigation is triggered when the following condition is met:
Dr,i ≥ RAW (6)
where RAW is the readily available soil water calculated from TAW:
RAW = MAD × TAW (7)
depending on the maximum allowed depletion (MAD).
In this case, the net irrigation depth (IRn,i) is set equal to the corresponding root zone depletion from the previous time step, therefore:
The system takes into account historical (from the system’s stations), forecasts of the necessary agrometeorological data along with soil water information, in order to estimate the above mentioned soil water balance variables throughout the study area.
Potential Evapotranspiration (ET0 or PET) is estimated by implementing the FAO model (Allen et al., 1998) of the Penman-Monteith equation, in daily and hourly time steps.
The system takes into account daily aggregated historical data (from the system’s stations) and three hour forecasts, which are disaggregated to hourly values, of the necessary agrometeorological data to estimate potential evapotranspiration at the stations locations and then, through spatial interpolation, produces the corresponding ET0 maps of the study area.
The effects of characteristics that distinguish the cropped surface from the reference surface are integrated into the crop coefficient. By multiplying ET0 by the crop coefficient (Kc), ETc is determined:
ETc = Kc × ET0 (9)
IRMA_SYS incorporates crop coefficients for various crops adopted from literature but if appropriate information is available to the registered users, they are able to modify the Kc values, based on this information.
The effects of soil water stress on crop ET are described by reducing the value for the crop coefficient. This is accomplished by multiplying the crop coefficient by the water stress coefficient, Ks (Allen et al., 1998) that describes the effect of water stress on crop transpiration. Where the single crop coefficient is used, the effect of water stress is incorporated into Kc as:
ETc adj = KS × Kc × ET0 (10)
Ks = (TAW – Dr)/(TAW – RAW) (11)
For soil water limiting conditions, Ks < 1, while in the absence of soil water stress Ks = 1.
To express which percentage of irrigation water is used efficiently and which percentage is lost, the term: “irrigation efficiency” is used.
The water amount applied by the irrigation system and not being made available to be taken up by plant roots is wasted and reduces irrigation efficiency. The major causes for reduced irrigation efficiency are drainage of excess irrigation water to soil layers deeper than the depth of active roots and evaporation losses.
Registered users can provide custom information about irrigation efficiency to the system.
The following table presents the efficiencies of the different irrigation systems incorporated in the IRMA_SYS.
Table 1: Irrigation systems incorporated in the IRMA_SYS and their efficiencies
Subsurface drip irrigation
Irrigation frequency is an essential parameter for irrigation systems design and is defined as the frequency of applying water to a particular crop at a certain stage of growth and is expressed in days. The maximum irrigation frequency (MF), in days, is estimated as:
MF = RAW / ETc (12)
where RAW (mm) is the readily available soil water and ETc is the crop evapotranspiration (mm/day).
However, the number of days between two successive irrigation events depends also on:
a. The irrigation strategy and practices that each farmer follows
b. Water availability, especially in collective irrigation systems
c. The size of the irrigation equipment
d. Other farm and crop tasks that need to be carried out at the same time
Based on the above, the actual irrigation frequency is always less or equal than the maximum irrigation frequency and is hereby defined as the practical irrigation frequency (PF).
In this context, we introduced a factor named: “Irrigation Optimizer -IRT” defined as the ratio of practical to maximum irrigation frequency:
IRT = PF / MF, with 0.1 ≤ IRT ≤ 1 (13)
So, Eq. 8 now becomes:
IRn,i = IRT × Dr,i–1 (14)
IRT’s default value is set to 0.5, indicating that the next irrigation event should take place at the 50% of the maximum irrigation frequency and with the half of the calculated IRn,i.
By implementing IRT, the user can experiment with several alternative solutions in order to conclude to the best irrigation strategy, depending on the given conditions.
As a rule of thumb, small values of IRT result in frequent irrigations with smaller water amounts, while IRT values close to 1 result in infrequent irrigations with larger water amounts, close to RAW.
In IRMA_SYS when a user records an irrigation event with the corresponding volume of water in m3, the system calculates the mm of irrigation water by dividing the volume (m3) with the irrigated area (m2).
In this context, the IRMA_SYS term: “Irrigated Field Area (m2)” represents the actual wetted area that the irrigation water is distributed.
So when the irrigation system distributes water locally, not covering the total field area, which is the case for microirrigation or drip systems, it is of great importance that the users register in IRMA_SYS the actual wetted area and not the total field area.
Depending on the irrigation system layout, the wetted area may vary from 5% to 100% of the total field area.
Irrigated Field Area is always a fraction of total field area, and it can be estimated by multiplying the field area with factors like:
1. Percentage of wetted area - Pw (%)
2. Microirrigation ET reduction factor (r), that refers to the percentage of soil surface that is shaded by plants during midday/0.85, having 1 as maximum value
Following the guidelines of FAO for localized and sprinkler systems design:
the user can estimate the actual wetted area.
IRMA_SYS is located at: http://arta.irrigation-management.eu/.
The main feature is the map presentation of the different variables, in daily time scale, that are involved in the irrigation requirements methodology presented above, such as: Rainfall, Potential Evapotranspiration, Humidity, Temperature, Wind speed and Solar Radiation, with high spatial resolution of 70´70 m grid.
The maps are produced by implementing the Inverse Distance Weighting method for spatial interpolation, found in the GDAL library.
The system provides this information of the study area, through the WMS/WCS services provided by the Mapserver that was set for the purposes of the present project (http://arta.irrigation-management.eu/mapserver-historical).
Registration requires from potential users to provide a username, an e-mail and a password. If someone wishes not to register, a “Try” feature provides full access to the application features without the ability to store any changes to the already provided information.
Registered users can see their account information along with the irrigation advises based on the available historical and forecast data. Also, they can access the “Irrigation Events” page in order to manage the irrigation dates and irrigation water volume, the “Irrigation Report” pages for detailed information about the soil water balance and the “Irrigation Performance” graph to visualize and access information about the estimated water amount and the applied irrigation water.
Registered users can add their fields into the system using a map, in order to pinpoint the geographic location of each field, with the help of the Hellenic Cadaster orthophoto imagery basemap (http://gis.ktimanet.gr/wms/ktbasemap) that allows zoom in scales up to 1 m. The user should provide information regarding the field’s area, crop, irrigation type. Also, a list of the user’s already register fields is available at the bottom of the page.
If appropriate information is available to the registered users, they are able to modify the properties of every registered field, based on this information. This information consists of parameters grouped in three major categories:
· Irrigation Management
· Crop Parameters
· Soil Parameters
Irrigation Management includes information regarding irrigation efficiency and strategy. Crop includes information regarding the crop coefficient (Kc), the maximum allowed depletion factor (MAD), the estimated maximum and minimum root depth. Soil includes information regarding the FC, PWP and Θs. Appropriate ranges and the system’s default values, according to literature, are available to the user in order to provide guidance.
Registered users can add irrigation events and see a list of the already applied irrigations.
In the case of unknown irrigation water volume, the system assumes that enough water was applied in order for the soil moisture to reach FC, i.e. zero depletion. The corresponding irrigation water quantity (m3) appears at the “Irrigation Report” for user guidance and future reference.
The “Irrigation Report” page presents a summary of the information applied by the user, regarding the crop, the field, the irrigation system and the last irrigation, along with a tabulated presentation of the essential soil water balance variables, on an hourly time step, for the available forecast period, i.e. 72 hours.
If the user modifies the default properties of the field, in “Custom Parameters” section of the “Edit field” page, then the message: “using custom parameters” appears in the appropriate section.
The “Irrigation Performance” graph provides users means to visualize and access information about the estimated water amount, the applied irrigation water and the effective precipitation during the irrigation period that for Greece spans from 1st of April to 30th of September. Also, the data are for downloading as “comma separated values - csv” file for further processing.
Also, the quantities of Total Effective Precipitation (mm) together with the Total Estimated Irrigation Water Amount (mm) and the Total Applied Water Amount (mm) along with their Percentage difference (%) are available to the user, based on the registered irrigation events and the IRMA_SYS estimates, for the above specified period.
Registered users can change their personal information, set the notifications interval and choose their supervisor from the list of available supervisors.
Also, they can register themselves as potential supervisors. For further information about supervisors please refer to section: Irrigation supervisors.
The “Tools” page contains a set of useful tools for unit conversions, as:
· From mm to m3 of irrigation water and vice versa, since the corresponding field area is provided
· Irrigation duration in hours (h) according to mm of irrigation water and station flow rate (m3/h)
· Station flow rate (m3/h) according to mm of irrigation water and desired irrigation duration in hours (h)
A supervisor is assigned to another system user, by the user himself, in order to utilize the IRMA_SYS in his account.
Every user is able to declare himself as a supervisor, in his/hers “Account” menu, but in our perspective a supervisor is considered to be either:
1. An irrigation guru, which is a scientist in the field of Irrigation and Drainage
2. A certified professional that can supervise a number of irrigators as generic consultant or in the framework of an applied quality cultivation system (i.e. organic farming, integrated management etc.)
3. A user with great experience regarding irrigation and drainage issues
Through a list, available in his/hers Account menu, the user is able to choose one from the already declared supervisors and provide access to his fields to him.
A supervisor has no access to any other information apart from the registered fields in the IRMA_SYS.
The user, at his will, removes or changes the supervisor from his/hers Account menu also.
In this context, potential supervisors and certified professionals are encouraged to post their work contact details, along with their IRMA_SYS usernames, in order for the users to easily contact them at the Irrigation Management Forum: http://www.irrigation-management.eu/forumx/irrigation-system-gr.
The IRMA_SYS Forum - http://www.irrigation-management.eu/forumx/irrigation-system-gr, is an online discussion site where system users can hold conversations regarding topics of interest.
Users are encouraged to participate with questions, suggestions and comments about the IRMA_SYS.