Simulation modelling for orchard management

Abstract

The relative merits of the various management planning techniques are reviewed and discussed for application to long term planning and replacement programming in orchards. A simulation model is presented for a typical Australian pome orchard. It is tested using data from a 36ha., Orange, N.S.W., orchard for planning over a 100 year period. The main routine of the model calculated annual orchard profitability (both before and after tax) and sub-routines generate optimum tree replacement age and stochastic variability due to hail and drought. The flexibility of the model allowed principal dependent variables to be changes as required. Two replacement policies were tested. Trees were replaces with either the existing production system (270 trees/ha.) or the semi-intensive system (715 trees/ha.). The semi-intensive production system allowed the orchard to sustain wider cost, price and yield fluctuations. Under average price and yield conditions, converting the existing standard orchard to semi-intensive production gave an average annual improvement in after tax profit of approximately $13,000 in a 100 year simulation period. The existing trees were replaces at approximately 31 years of age and thereafter recycle at approximately 46 yearly intervals. The provision of irrigation with the semi-intensive system further improved profitability by $7,000 per annum. Replacement age varies inversely with price and yield levels, and the higher the interest rate used in the model calculations, the later should trees be replaced. Application of regression analysis to produces iso-performance curves revealed significant interactions between price, cost, yield and orchard profitability with price being the most sensitive parameter. The model has potential in investment appraisal and could easily be modified for other perennial crops. It provides a readily comprehendible and practical means of examining the effects of varying economic conditions and management strategies in horticultural businesses.