Model of crop : weed competition applied to maize : Abutilon theophrasti interactions. I. Model description and evaluation

A complex set of interactions among crops, weeds and their environment dete rmines the impact of weed interference on crop productivity. These interact ions can be simulated with dynamic crop:weed competition models, such as AL MANAC. In this study, ALMANAC was modified to simulate maize:Abutilon theop hrasti competition. In the modified ALMANAC model, daily increases in leaf area index (LAI), height and rooting depth are attenuated on the basis of a ccumulated above-ground biomass and by environmental stress. Also, a simple , flexible method is adopted to partition radiation in a mixed canopy. A ma ize:A. theophrasti competition study conducted near Aurora, NY, in which a range of weed densities (0-16 plants m(-2)) were established in a maize cro p, was used to evaluate the model. The modified ALMANAC proved to be a usef ul tool for segregating the maize response to competition in 1991 (simulate d loss of 35% at the highest weed density) from those in 1992-94 (simulated losses not greater than 16%). Based on these findings, the modified ALMANA C model is judged to be capable of distinguishing between environmental con ditions that facilitate large yield losses and those that allow maize to ou tcompete A. theophrasti.