2013 ASHS Annual Conference

Variable rate (VR) fertilization is most effective in orchards with high spatial variability because the technology is designed to exploit variability. Perfectly uniform orchards with no gaps between canopies would not benefit from VR technology. If the location and size of tree canopies in the orchard can be determined, then the next logical step is to apply nutrients (inorganic or organic sources) only where they will be used and only in appropriate doses to match requirements. Roots, which are the primary targets for fertilizer applications, approximately follow the footprint of tree canopies. The highest concentrations of roots are found at the canopy edge and around the trunk, due to enhanced rainwater deposition from canopy drip and trunk flow, respectively. Large regions of an orchard receiving banded fertilizer would waste nutrients without VR fertilization. Widely-spaced orchards are more susceptible to off-target fertilizer wastage, and hence benefit the most from VR technology. Precision fertigation using computerized open hydroponics is another precision agriculture technology used in modern citrus orchards to maximize yields, and minimize water and fertilizer consumption. Daily drip fertigation can drastically alter the feeder root mass distribution under a citrus tree canopy, whereby most of the active fibrous roots are concentrated around the drip emitters. These and other selected examples will be discussed in the context of potential impacts of precision agriculture on roots and root functions.