Plants experience their greatest nutritional requirements when they begin filling fruit, a stage of growth that often coincides with the drier times of the year that can cause mineral availability in the soil to falter. The natural plant cycle has planned for this shortfall, though, and a healthy soil/plant ecosystem will create a reserve of plant available nutrition early in the growing season for the plant to utilize later.
The photosynthetic capacity of plants increases over the course of the growing season as the plants build frame and develop a larger leaf canopy. Before reproduction begins, this expanded photosynthetic capacity will produce more energy than the plants can use. This surplus energy is transmitted through the root system to build soil microbial communities, which results in the accumulation of stored energy and mineral nutrition in soil that plants can access later in the season.
During the framing stage of plant growth, when the plants are doubling or tripling their size in a very short amount of time, as much as 70% of the photosynthates being produced by the plant can be transmitted to the root system. As the fruit begin to fill, however, they become the primary destination of almost all photosynthates created by the plant. The energy reserves accumulated in the soil earlier in the year now become critical for the plant to be able to meet its nutritional needs, and continue to thrive.