MODELING THE POPULATION-DYNAMICS OF AVENA-STERILIS UNDER DRY-LAND CEREAL CROPPING SYSTEMS

(1) A mathematical model for simulating the population dynamics of Avena sterilis ssp. ludoviciana (Dur.) Nyman has been constructed using previously reported data. The model considers the age structure of the population of seedlings as well as the effects of density on plant survivorship and reproduction. (2) The model is used to describe the behaviour of the population in the absence of control practices and to predict the effects of various control strategies. In the absence of control, and under continuous winter cereal cropping, the population grows hyperbolically, reaching equilibrium at a density of 535 plants m-2. Annual application of herbicides with < 85% control results in moderate reductions in the equilibrium level. To obtain a negative growth of the population it is necessary to apply herbicides annually with a control level of > 90%. Fallowing the land for 1 in every 2-3 years gave a practical method of containing the populations of A. sterilis. However, to eradicate this weed it was necessary to combine crop rotation with application of herbicides. (3) The effects of changing the values of the parameters on the output of the model were generally minor. The two processes most sensitive to parameter variation were dispersal and mortality of seeds after reproduction and the fecundity of the first cohort of plants. The contribution of late emerging plants to the overall dynamics of the population was rather small and could be disregarded. (4) The model was validated by comparing simulation results with those from long-term field studies. Model predictions closely matched experimental results from herbicide trials, but gave only a crude description of the population dynamics under various crop rotations.