Resource Sharing in Intercropping Models and a Case Study with APSIM in Southern Australia

Various benefits of intercropping systems have been reported worldwide. However, fewer modeling studies of these systems have been undertaken. We present key intercropping features and processes in seven intercropping models, highlighting strengths and limitations. Representation of key processes such as resource sharing and plasticity are a challenge in modeling. Very few studies have investigated plasticity, focusing mainly on crop response to light. Therefore, further research is necessary to understand and incorporate these key processes in intercropping models. We selected APSIM to evaluate its ability to simulate the intercropping effects by 1) a theoretical combination of crops and crop densities and (2) a comparison against observed data in three locations in Victoria, Australia. Models for monocultures and intercrop combinations with varying crop density ratios for four crops (barley, canola, fababean and wheat) were calibrated and the model performance was evaluated. Simulated monoculture results were satisfactory but intercropping results were poor. The growth of intercrops was found to depend on interactions between the parameter KL (fraction of plant available water extracted daily) and soil water content whose dynamics in turn depended on the method and amount used to initialize soil water. The resource sharing ‘alternate day’ approach in the model may not be suitable in water-limited environments because it can lead to excessive advantage of one intercrop over the other. Incorporating intercrop-specific parameters, representation of plant density ratios and revising resource sharing algorithms in the model may improve results.