A planter is provided with onboard seed treatment for treating seeds on the go during row-crop planting of an agricultural field. The seed treatment system of the planter allows for selective planting of specific zones of a field with treated seed, which may include planting different zones of the field with seeds having different treatments. The planter may store untreated seed in bulk and include a seed treatment system that selectively and precisely treat the untreated seeds during treatment events by way of an injection or spray nozzle system that applies liquid treatment to the seeds traveling along a tightly defined travel path, such as within pockets of a belt that carries the seeds through a seed tube.
