A SIMULATION-MODEL FOR THE DYNAMICS OF RICE GROWTH AND DEVELOPMENT .2. THE COMPETITION WITH WEEDS FOR NITROGEN AND LIGHT

An age structured population model for the simulation of nitrogen and light competition between rice and weeds is reported. The weed flora is divided in to six groups based on differences in leaf shape, growth form, height and phenology. 1. (1) A common demographic model is used to describe the carbohydrate dynamics of rice and all weed groups. 2. (2) The potential nitrogen uptake of all plant groups is computed with a functional response model from predation theory. The ratio of current N in the plant to the theoretical maximum is used to scale photosynthesis and reduce plant growth rates. 3. (3) Competition for nitrogen among plant groups is based on the proportion of the root space explored by each group. 4. (4) Plant height and leaf area distribution are used to estimate the share of incident light absorbed by each plant group. The model predictions are compared to field data on growth and development of rice and weeds collected in irrigated paddies subjected to different weeding strategies. The effects of weed competition intensity and the timing of weeding on rice yield are examined. © 1990.