A plant growth model for integrated weed management in direct-seeded rice: I. Development and sensitivity analyses of monoculture growth

Abstract

A new model, DSRICE1, was developed to analyze weed management strategies in direct-seeded rice ( Oryza sativa) systems. Previous rice models have not accounted for important cultural and weed management factors in direct-seeded systems, such as growth from seeds and water-depth effects on plant growth. Here we describe the development and sensitivity analysis of DSRICE1 for monoculture rice growth under water-seeded conditions. DSRICE1 is largely process-based and includes all standard weed management practices except fertility. Simulation inputs include latitude, daily solar radiation, daily maximum and minimum temperatures, water depth, and seed rate. Phenology depends on thermal units. Growth begins with seed storage mobilization to seedlings, and photosynthesis starts when the first leaf is extended. Canopy light dynamics depend on leaf and stem area distributions for both live and dead dry mass, and on water depth when submerged. Water-depth effects were explicitly simulated as reflection and attenuation of light. Model analyses revealed that parameter sensitivities varied over time. Some parameters were always important, while the effects of others were limited to particular parts of the season. Judged over the whole season, the most important parameters were for photosynthesis and light capture. Unlike in most monoculture simulations, early height gain rate was important in DSRICE1 because it determined when plants emerged from the water into full light. Analyses of model structure and specifications revealed that predictions were significantly affected by the use of skewed live leaf area distributions and the non-rectangular hyperbola for the light response curve, and the inclusion of water-depth and dead canopy dry mass effects on canopy light dynamics. The cropping system and management processes simulated in DSRICE1 had important effects on model predictions of rice growth. Explicit consideration of these factors distinguishes DSRICE1 from other rice growth models, and may lead to better simulation analyses of system interactions with plant growth and weed management strategies.