The small subsistence farmer has been the numerically dominant element of the rural equatorial Andes. Farmers frequently use fungicides and other pesticides, especially on potatoes and irrigated crops, where sale helps repay the purchase costs. Pesticide use is often dependent on rainfall, with low use during dry periods and high use during wet periods when infestations are greater. Enrique Mayer has written of Andean "production zones" as delimited "bounded ecosystems" with "precise boundaries" which can be readily mapped, and have "a characteristic type of field" which exhibit a "specific form of social organization." Such a characterization could be applied to Ecuador only with the cautions that since group controls outside irrigation are relatively weak, the visible production zones are epiphenomena of adaptive processes operating largely at the level of the individual farms. The volcanic ash soils permit other strategies than terracing to permit irrigation; it has already been demonstrated that fertilization can take place without terracing.