Simulation of carbon assimilation and partitioning in maize

Crop simulation models offer a means of integrating scientific findings into a coherent description of crop adaptation to a complex environment. The detailed simulation of growth processes involved in carbon accumulation and partitioning is an essential prerequisite for modelling such adaptation. A procedure for simulating these processes in maize (Zea mays L.) was developed as part of a larger maize growth model. Hourly values for the gross photosynthetic rate of a maize canopy are accumulated into a pool from which hourly values of carbohydrate mobilized for both shoot and root growth are removed. Maintenance and growth respiration of both the shoot and root are then subtracted from the respective allocations of mobilized carbohydrate and the remainders accumulated into daily totals of dry matter growth. These daily totals are partitioned to and accumulated in the major plant organs depending upon growth stage. Growth partitioned to the leaves is converted to leaf area growth. Kernel number and maximum kernel mass are determined from growth functions during stages of ear formation and kernel set. Maturity is presumed to occur when maximum kernel mass is reached or when kernel growth is stopped due to inclement weather, Model output for partitioning, biomass, grain yield, kernel number, kernel mass, and leaf area index were compared with observed values at several sites across North America. Although many of the processes upon which the model is based require greater understanding, the model is able to provide estimates of these variables that are usually within 20% of recorded values. Greater accuracy in simulating maize growth will require further elucidation of the way in which environment influences basic growth processes as well as more detailed information regarding site-specific soil and meteorological characteristics.