MODELING LEAF CANOPY of EVENING PRIMROSE CROP (Oenothera spp.).

Modeling leaf area index (LAI) of crops is an important part for crop simulation. Models of LAI can be used for modeling crop photosynthesis and therefore growth. An experiment was designed in order to model LAI of a C₃ plant considering the effect of development and nitrogen fertilizations. Leaf area index (LAI) of a C₃ plant (evening primrose crop, Oenothera spp) was measured through all its life cycle. Evening primrose plants were sown in pots and it was applied three different nitrogen fertilizations (0, 80 & 160 Kg ha^-1). Mathematical models were built for the observed LAI for each nitrogen fertilization. These models considered the effect of plant development and nitrogen fertilizations. Evening primrose LAI al the first was low, minimum. After the growing point differentiated LAI had an exponential grow, which reached its maximum after at the flowering phase. This maximum was held just for around ten days. At the beginning of the fruit phase LAI decreased quickly, reaching zero at the middle of the maturation phase. LAI of this plant was composed by stem and spike LAI. Two quadratic equations were used to model this LAI behavior, as a function of degree-days; where nitrogen application determined the maximum LAI. using two single straight equations. The sum of both stem and spike LAI were the total LAI. Because at the rosette phase, LAI growth was so slow and cannot be explained by the former quadratic equations, another quadratic equation was used for modeling total LAI until the rosette phase (the first one) finished. LAI was controlled by the degree-days, and the N applications increased the manifestation of LAI due its positive effect over the leaf photosynthesis and the leaf growth respiration rates. This mathematical model of evening primrose LAI can be used for modeling growth of this crop.