A mathematical crop growth model for a mixed stand of Italian ryegrass (Lolium multiflorum L. and white clover (Trifolium repens L.).

Abstract

The main aim of this study was to develop a mathematical crop growth model for a mixed stand of ryegrass and clover. The modelling exercise consisted of an experimental component as well as the actual modelling component. The experimental part of the project was essential in terms of gaining a better understanding of the competitive Interactions between ryegrass and clover, as well as being essential for obtaining all the necessary parameters and variables for the model. The experimental results of the project revealed that a.':though the single leaf photosynthetic rates of clover were higher than those of the ryegrass, the clover was outcompeted by the ryegrass in mixed swards. This was due to the better eanopy structure and quantum yield efficiency of ryegrass relative to clover, It was also found that environmental temperature and increasing levels of interspecific competition strongly influenced the growth rates and carbon allocation coefficients of these crops. The interspecific competition experiment showed that ryegrass benefitted from its interactions with clover, while clover was detrimentally affected. This experiment also indicated that a transfer of nitrogen occurred from the clover to the ryegrass.

The model was based on the assumption that the canopy structures and quantum yield efficiencies of the respective crops would largely influence their competitive abilities. The model was unique in that it was a mixed crop growth model which accounted for the environmental effects of fluctuating temperature and irradiance on photosynthetic rates, the model was found to simulate the growth of ryegrass and clover, both in monoculture and in mixture, to satisfaction.