Computer simulation models of pasture production in Canterbury: description and user’s manual

Abstract

This report presents the detailed documentation of development, validation, application methodology, and computer coding of a set of dynamic simulation models of pasture production on the Canterbury Plains of New Zealand. The models were formulated and tested in the process of developing a relatively simple simulation model of perennial ryegrass / white clover pastures for use as a component of a whole farm model describing mixed cropping with irrigation in the Canterbury Plains. Three models of increasing complexity (CANPAS I, II, and III) were formulated and tested for that purpose. All three models simulate the passage of time in steps of one day and all estimate leaf area index, available soil water, and yield of green and dead herbage in the pasture. The CANPAS III model also predicts herbage digestibility parameters to facilitate model linkage to a sheep production module of the total farm model. Each version of CANPAS was designed to simulate various harvesting and irrigation managements, including no irrigation at all, and each version can be easily controlled by the main program of the whole farm : model to give simultaneous independent simulations of several paddocks of pasture on the same farm. The computer programs were written in the language CSMP73. The CANPAS III model was also converted to a subroutine in FORTRAN IV to facilitate application as a module of the whole farm model. Listings and a description of the conversion process are included in this report. Application of CANPAS III in optimisation studies is also demonstrated by linkage of the CSMP73 version to an optimisation subroutine.