Since the advent of the Industrial Revolution modern agriculture has gravitated towards the use primarily of macronutrients such as nitrogen (N), phosphate (P2O5), potash (K2O), and lime for crop production, with an emphasis on micronutrients only when they became yield-limiting. The values of plant quality and soil conditions were minimized. The importance of soil organic matter and humic substances in crop growth were concurrently deemphasized. Yet, it is understood that nearly all soil processes tie closely to soil biological activities such as mineralization, immobilization, N-fixation, and nitrification. The organic fraction of soils, and the rhizosphere zone with its root exudates, contain organic substances in very low concentrations which can stimulate plant growth substantially. These substances include humic substances, growth regulators, vitamins, antibiotics, organic acids, and other materials. Certain added organic substances can also benefit plant growth in very low concentrations, sometimes with as little as 2×10−4kg/ha for triacontanol. The very important link between soil organic matter and active soil biological processes in aiding plant growth thus becomes even more important when it is understood that many organic substances present in very low concentrations can produce significant plant responses. Macronutrients, micronutrients and other common soil amendments cannot be considered exclusively when attempting to maximize soil fertility and plant growth.