An integrated model for simulation of border-check irrigated dairy pasture production systems

Border-check irrigation is the predominant method of applying water to dairy pastures in Australia. Dairy pastures consume 40% of total irrigation water in Australia and, with irrigation water security in Australia under threat from climate variability/change and rising demands from other users, socio-economic pressure for water savings in the dairying sector are increasing. Currently, there are no simulation tools that successfully link factors controlling irrigation efficiency at the within-bay scale to management factors that drive economic water productivity (principally pasture growth, pasture consumption and animal production).A simulation framework was developed to connect a biophysical research model of weather–soil–plant animal interaction in dairy systems (‘DairyMod’) to a surface irrigation hydraulic model, SRFR (Simulation of basin, border and furrow irrigations). The connection enabled simulation of the effects of border-check irrigation scheduling and event management on irrigated pasture production systems. Modifications were made to DairyMod, in which the paddock surface was represented as a point, so that it could accommodate infiltration data in a one-dimensional form, from the surface irrigation model SRFR. Multiple simulations of DairyMod were run each representing different discrete spatial zones within an irrigation bay, and the SRFR routines connect each discrete spatial zone with information on the advance front water depth.Model integration and the workings of the integrated model are described, and the process used to verify the integrity of the data transferred between the two models is presented. Comparisons of data input and output parameters from the stand-alone models and the integrated model confirmed that the data transfer between the models within the integrated framework did not introduce new sources of errors.Preliminary output for a scenario involving three irrigation durations is also presented. The scenario represented a perennial ryegrass based pasture on a texture contrast clay loam soil over a period of 10 years using measured climate data. Model predictions agreed well with data reported in the literature for annual irrigation amounts and pasture growth. It was demonstrated that the integrated model could be used effectively to determine how pasture production varied with changes in irrigation management such as irrigation duration. A limitation of the integrated model was its dependence on two sets of infiltration models that were difficult to relate to each other.