An apparatus for delivering a beneficial agent to a subterranean location is disclosed in one embodiment of the invention as including a water collection chamber having a substantially open end. A water-transporting membrane is provided to communicate with the water collection chamber. An extraction chamber receives water through the water-transporting membrane, expanding the extraction chamber. A dispensing chamber, containing a beneficial agent such as fertilizer, is configured to contract upon expanding the extraction chamber. This causes the dispensing chamber to expel the beneficial agent through a subterranean delivery channel, such as a rigid hollow spike. In certain embodiments, a rate adjustment mechanism may control the rate that water is received through the water-transporting membrane, thereby controlling the rate the beneficial agent is expelled from the subterranean delivery channel.