The applicator comprises a relatively thin, streamlined knife blade adapted to be positioned with its longitudinal axis inclined upwardly and rearwardly during use with a leading edge of the applicator slicing through the subsoil and a lowermost and forwardmost point thereof penetrating the subsoil for the progressive entry of a wedge immediately behind the point which firms up and smooths the lowermost portion of the slice being created by the knife. Upwardly and rearwardly inclined, streamlined wings at the bottom of the blade but above the wedge project beyond the rear of the wedge to define a pocket into which anhydrous ammonia or other substances can be deposited. In one embodiment, the wings commence at the point and diverge rearwardly therefrom at a faster rate than the wedge to provide increased surface area for lifting and fracturing the soil as the knife moves therethrough, providing particular relief in root-bound subsoils. In a second embodiment especially suited for soils which are not self-closing, a pair of outwardly projecting closing fins are provided above and generally rearwardly of the wings to cause the rearwardly flowing soil to be directed downwardly and rearwardly into the slit and around and behind the knife, thus promoting closing of the slit and retention of the deposited substance.