## 2 Materials and Methods
### Generating and Displaying IrrigWQ Output
In addition, four generic crops have been defined representing crops that are sensitive, moderately sensitive, moderately tolerant, or tolerant to crop yield and quality determining factors. Generic crops are used when it is necessary to obtain an indication of the effects of irrigation water constituents on crops for which no quantitative response data are available, but which are known to have the characteristics of a particular sensitivity category. While a steady-state Tier 1 assessment is executed instantaneously, Tier 2 assessments take longer, depending on the number of years selected for simulation. A minimum of 10 years is required but results more demonstrative of the variability associated with longer-term weather conditions can be obtained by running simulations for up to 45 years (although 50 years of weather data are captured for each weather station in the climate database, the first three years are used for a \"warm up\" simulation to establish a quasi-equilibrium between the various soil profile variables). The results of an FFU assessment are displayed on electronic output pages that summarise how the different suitability indicators are affected. The output can be printed or stored electronically. 1. The cover output page presents information on the user's description of the assessment that was conducted and the water analysis. For Tier 2 assessments, it also displays the  
Figure 3: Input screen for selection of site-specific characteristics, with shaded fields populated by IrrigWQ (being derived from the selected weather station and soil texture characteristics). site-specific characteristics on which the evaluation is based and a summary of the seasonal water balance components, as calculated during the simulation. 2. The second output page presents an overview of the FFU assessment of the four suitability indicators that characterise soil quality. 3. The third output page presents an overview of the FFU assessment of the five suitability indicators that characterise crop yield and quality. If a crop rotation was selected for the Tier 2 assessment, the overview of the five suitability indicators for the second crop is printed on a fourth page. 4. The fourth page (or the fifth page in the case where a two-crop rotation was selected) presents an overview of the FFU assessment of the two suitability indicators that characterise the effect of water constituents on the performance of irrigation infrastructure. The results for a WQR determination are similarly displayed on four or five pages. Tier 1 WQRs resemble current local and international guidelines. The Tier 2 threshold WQR values of irrigation water suitability indicators are back-calculated by interpolation as follows:  
1. Successive FFU assessments are conducted for specified periods of between 10 and 45 years using a number of pre-defined, hard-coded, model waters, having increasing constituent concentrations. 2. The 95 th percentile highest or lowest (as the case may be) annual or seasonal value of the suitability indicator is identified for each of the model water concentrations. 3. The threshold WQR concentrations corresponding to the criteria boundaries used for FFU categories are determined by interpolation from the 95 th percentile highest or lowest annual or seasonal values of the suitability indicator.