MODELING PEPPER SEEDLING GROWTH AND NUTRIENT-UPTAKE AS A FUNCTION OF CULTURAL CONDITIONS

A mechanistic model was developed to describe pepper seedling growth, and water, N, and P uptake as a function of N and P concentrations in the irrigation solution, growth medium volume per plant. planting density, and growth substrate characteristics. Such a model will help optimize irrigation and fertilization of transplants and elucidate some of the mechanisms involved in seedling production. The main assumptions in the model were that (i) the potential shoot and root growth rates depend on the N and P concentration in each organ; (ii) the actual growth rate of each organ is determined by the dry matter production rate, which is a function of plant leaf area, N and P concentration in the leaves, and assimilate partitioning between shoot and root, which itself depends on the ratio between potential growth rates of shoot and root; and (iii) the rates of N and P uptake per unit root weight are described by the Michaelis-Menten equation. Model parameters and functions were fitted from data on pepper seedlings grown in a solution culture. The model predicted satisfactorily the effects of steady and transient N and P supply, and growth substrate characteristics and volume per plant on dry matter production, and N and P uptake as a function of time. The parameters of major importance are those that relate the plant dry matter production rate and the nutrient uptake rate per root unit to the nutrient content in the shoot and root. Of secondary importance are the root radius, the growth medium water content, and the impedance factor to ion diffusion.