A method for managing substances in a plant root zone, including the steps of providing a fluid distribution system, controlling the fluid distribution system, modeling the plant root zone, and distributing the substances thereto. The fluid distribution system is associated with an agricultural area. The fluid distribution system is controlled by way of a controller. The plant root zone is modeled for a plurality of locations in the agricultural area. The modeling step incorporates a desired three-dimensional distribution of the substances for each of the plurality of locations for a future time period. Substances are distributed to the plurality of locations by way of the fluid distribution system under control of the controller. The controller is dependent upon the desired three-dimensional distribution and the future time.