VADOSE ZONE HYDROLOGIC PROCESSES AND TRADITIONAL DRYLAND FARMING TECHNOLOGY ON THE HOPI INDIAN RESERVATION, ARIZONA

Due to extreme aridity, it is necessary for Hopi farmers to minimize moisture losses in non-irrigated fields. New data indicate that the traditional Hopi farmer reduces moisture loss by controlling processes that affect vadose zone hydrology. Fields are located on naturally stratified soils that comprise barriers to vertical drainage and bare soil evaporation. All cultivation activities serve to preserve or enhance the soil profile. Field clearing and weed removal eliminate competitors for water without disturbing natural soil profiles, and reduce transpiration loss. Windbreaks control eolian transport and improve soils of nearby areas, therefore, allowing field expansion. Planting techniques place seeds into zone of optimal moisture, while protecting sand mulch. Planting in widely spaced clumps provides each clump with water from a large, discrete volume of soil.

This study characterized the 2002 seasonal hydrology of two Hopi agricultural fields, comprised of mixed eolian, fluvial, and pedogenic deposits overlying Mancos Shale bedrock, using gypsum block, temperature, rainfall, wind, solar radiation, and relative humidity sensors recorded on a thirty-minute interval, and supplementary rain gauges recorded on a five-minute interval. Given the 2002 severe drought year in northeast Arizona, the correlation of layered soil profiles with crop survival is striking. Results of unsaturated zone simulations of moisture input, redistribution, drainage, and bare soil evaporation for soil profiles recorded in agricultural fields contrasted with simulations for soils of non-cultivated areas indicate the effectiveness of layered soils in retention of soil moisture. An accurate conceptual model using integrated systems analysis was imperative for successful mathematical model simulations of the two Hopi fields.