Die Bodenkultur - Journal for Land Management, Food and Environment
K.-U. HEYLAND and H.-P. KAUL:
A model of weed population dynamics used for the determination of optimal weed control strategies with regard to crop management of winter wheat and sugar beet
The aim of this study is the quantitative estimation of the influence of crop management factors (herbicide application, nitrogen fertilization, crop density) on weed population dynamics in a rotation with sugar beet and winter wheat. The parameters of a deterministic difference equation model are estimated.
After verification of the model simulation experiments are conducted to optimize the crop management strategies with regard to minimum herbicide input.
The data base for parameter estimation and model verification are results of a long time field experiment (since 1983) with corresponding management systems for all crops within the rotation. Specific data were taken in 1987 to 1989, thus testing the management systems on different weed densities that had been evolved until then. This was completed with a two year experiment in winter wheat testing reduced herbicide doses.
The results could be summarized:
1. Herbicides show different influences in reducing weed populations depending on date and dose of application as well as weather conditions of the specific year.
2. Weed emergence rate depends on herbicides, fertilization and crop density, while the development rate is only influenced by the date and dose of herbicide application. Finally the seed production per weed plant can hardly be changed by the checked crop management.
3. A simple model of population dynamics explains quite well the weed abundance over years for the tested range of management systems and initial low weed densities.
4. Among the tested management systems only early post emergence herbicide application guarantees substantial low weed seed banks, while one year without spraying herbicides leads to a dramatic population increase.
5. In using simulation experiments a new weed control strategy is developed that, in contrast to economic thresholds, is based on every year spraying of reduced herbicide doses.
6. Crop management factors, e. g. fertilization and crop density, could favourably be used to support weed suppression of less effective herbicide applications in integrated crop management systems.
Key-words: mathematical model, weed population dynamics, herbicide application, winter wheat, sugar beet.