This invention provides a method of enhancing plant growth involving the steps of: providing an application of nitrogen-15 isotope to a plant to obtain a concentration of nitrogen-15 isotope at least 10 percent greater than the concentration occurring in an untreated plant. A plant growing in a treated area exhibits at least one of: increased plant yield measured in terms of increased root length and increased leaf area compared to a plant growing in a portion of untreated soil. Furthermore, the step of providing the application of nitrogen-15 isotope to a plant includes treating a foliar portion of a plant with a synergistic concentration of a nitrogen-15 isotope, wherein a treated plant exhibits at least one of: increased plant yield measured in terms of increased root length and increased leaf area, compared to a plant growing without a treatment of a synergistic concentration of the nitrogen-15 isotope.
