A MODEL OF BEAN (PHASEOLUS-VULGARIS L) GROWTH TYPES I-III - FACTORS AFFECTING YIELD

A per capita, supply-demand regulated, age-structured population dynam ics model of the growth and development of the common bean (phaseoulus vulgaris L.) is used to simulate three growth types in Brazil. The mo del assumes that the crop canopy is composed of age-structured subpopu lations of leaf, stem and root masses, and of fruit numbers and associ ated masses. The dynamics of each subpopulation is modelled using an a ge-structured distributed-maturation time model with attrition. The in teraction of photosynthate supply to demand regulates the rudiments of bean physiology. The daily rate of photosynthate production is estima ted using the Gutierrez-Baumgartner functional response model, with th e genetic demand for carbon as modified by nitrogen and water availabi lity being the major controlling variable in the model. The ratio of t he realized photosynthate production rate (i.e. the supply) to the max imum assimilation rate for drymatter (i.e. the demand) controls all dr ymatter allocation rates, the initiation rates of new subunits (i.e. f ruits) and their associated masses, and the shedding rates of differen t aged buds and fruits. given initial conditions, the physiology and p opulation dynamics of the crop model are driven by observed weather (i .e. solar radiation, maximum and minimum temperatures, rainfall, wind relative humidity) and soil water dynamics. Nitrogen is considered non -limiting in the model. The role of plant density to bean yield in gro wth types I to III was assessed using field data and simulation.