Modelling Monto Vetiver Growth and Nutrient Uptake for Effluent Irrigation Schemes

摘要

The MEDLI model (Model for Effluent Irrigation by Land Irrigation) is used throughout Aus tralia to design and test the sustainability of effluent irrigation schemes. MEDLI models the partitioning of water, nutrients and salt from the waste stream as it passes through pond treatment, is irrigated onto land growing crops or pastures, and percolates to groundwater. It presently has a limited library of crop and pasture species parameter values and due to the enormous potential demonstrated by vetiver for effluent irrigation schemes, this library was extended to include Monto vetiver. This paper presents the methodology used to determine the growth and nutrient uptake model parameters needed to add Monto vetiver to the dynamic, daily time-step pasture growth model used in MEDLI. The parameters for Monto vetiver were drawn from the literature and determined from a purpose-designed field trial conducted at GELITA APA, Beaudesert, Queensland. The modelling predictions of biomass growth and nutrient uptake using these parameter values were then validated against data collected at an independent field site, at Beenleigh, Queensland. Monto vetiver demonstrated exceptional growth rates. This can be attributed to radiation use efficiencies comparable with those of other C4 grasses of 18 kg/ha per MJ/m~2 and its tolerance to a wide range of conditions that would slow the growth of many species. As a consequence, modelling demonstrated that vetiver exhibits a greater potential to take up nutrients than many other grass species under similar conditions. However, before applying the parameters in other regions or other cultivars of vetiver, it is recommended that model predictions be checked against local knowledge of shoot dry matter yields and nutrient concentrations.