CAN SIMULATION-MODELS HELP DESIGN RICE CULTIVARS THAT ARE MORE COMPETITIVE AGAINST WEEDS

Differences in competitive ability between rice cultivars IR8 and Mahs uri, grown in well-fertilised irrigated conditions, were analysed by m eans of a mechanistic simulation model (INTERCOM) for crop-weed intera ction. The analysis revealed that the greater competitive ability of M ahsuri was due mainly to a greater relative leaf area growth rate earl y in the season and larger maximum plant height. Comparison of experim ental results and model outcomes indicated, however, that the present model is not entirely able to quantify the trade-off between competiti ve and yielding ability. The extent to which traits advantageous for c ompetition may lead to increased lodging or a larger number of unprodu ctive tillers is not quantified by the present model. This implies tha t use of INTERCOM for design of more competitive rice cultivars will r equire continuous interaction between modelling and experimentation. W ith those limitations in mind, the model was used to quantify the pote ntial contribution of various attributes to competitive ability. A sen sitivity analysis demonstrated that competition for light is mainly de termined by morphological characteristics of which early relative leaf area growth rate, early relative height growth rate and maximum plant height were found to be the most important. The ability of the model to identify key traits with respect to competitive ability makes it a useful tool for designing rice ideotypes.