Development and testing of a horticultural crop model within APSIM

Abstract

Ongoing uncertainty in irrigation water supply is a problem facing many of Australia's horticultural producers, whether it is due to drought, groundwater depletion, increased water regulation or community expectation for natural resource conservation. To respond to these pressures, improved irrigation management options are required. Simulation analyses provide the ability to explore the impacts of management options under these changing conditions but to date appropriate tools have not been available for horticulture. APSIM is a component-based modelling environment that has a long history of usage in crop, pasture and forestry systems analysis. Horticultural crop models are now being included into the suite of crop models available within APSIM. APSIM-Broccoli is one such model. APSIM-Broccoli calculates plant growth, development and water use on a daily time step. Predictions of phenological development emerge from calculations of various growth processes. For example, time to floral initiation is calculated from thermal time adjusted for accumulated vernalisation from germination or transplanting, and time to buttoning is dependant upon the thermal time required for the appearance of all leaves initiated prior to floral initiation. Photosynthesis is calculated using a light use efficiency which is affected by temperature, water and nitrogen stresses. A simple phytomer approach is used for canopy development where each successive leaf on the main stem is defined in terms of the length of its growth, lag and senescent phases. Assimilate is partitioned to individual leaves based upon daily growth rates determined by temperature-dependant leaf expansion processes. Canopy water demand is calculated using a Penman-Monteith formulation within the APSIM Micromet module (Snow and Huth, 2004). Extraction of soil moisture to satisfy this demand is calculated using the approach of Meinke et al. (1993). Testing of the model was carried out using two datasets chosen to highlight different areas within the model. The data of Tan et al (2000) includes leaf and phenological observations for several cultivars over a broad range of sowing dates for two locations in South East Queensland. APSIM-Broccoli was able to describe observed crop responses in canopy development and floral initiation to climatic conditions. Data for Broccoli growth and water use from the Gatton Research Station (27.55°S, 152.33°E) has been used to test the capability of the model in simulating biomass production and yield across different seasonal condition and irrigation strategies. Other horticultural crop models are currently under development. These include sweet corn, green bean, lettuce and potato. Once complete, these models will be used to explore management decisions at the field and farm level for landholders facing complex irrigation management decisions. © MODSIM 2009.All rights reserved.