Modelling the competition for light and nitrogen between rice and Echinochloa crus-galli

The competition for light and nitrogen between rice (Oryza sativa L.) and barnyardgrass (BYG; Echinochloa crus-galli (L.) Beauv. ssp. hispidula) in an irrigated paddy is described by means of simulation. (1) Growth and development of both rice and BYG are simulated with the same plants model which accounts for tiller production and for mass growth of leaf, culm, root, and grain on each tiller. (2) Competition for light depends on the plant height and the vertical leaf area distribution, and is expressed as the share of incident light absorbed by rice and BYG, respectively. (3) Competition for nitrogen is based on the proportion of root space explored by rice and BYG and is estimated from the respective root mass. (4) The model, originally developed for rice, is validated here for BYG planted in monoculture at different densities. (5) The model predictions on biomass growth of competing rice and BYG are compared to field data collected in a replacement experiment. (6) The effect of BYG competition on rice yield is demonstrated for various rice and BYG planting densities.