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Maize has sustained the Zuni and other people in the arid American Southwest for many generations. In the traditional Zuni dryland agricultural system, fields are carefully placed on valley-edge landforms to tap into watershed hydrologic and ecosystem processes. In these geomorphic positions, field soils are managed to receive supplemental water and nutrients for crops by retaining storm runoff transported from adjoining uplands. Crop experiments were conducted to examine the effects of runoff on maize (Zea mays) productivity. Productivity of a Zuni maize cultivar and modern hybrid maize was evaluated with five treatment combinations of water and nutrient input sources in two traditional agricultural areas that have been cultivated for at least 1000 years. During the first year of the two-year experiment (1997-1998), one field received inputs from four runoff events, while the other field, with a larger watershed, received no runoff. In year two, the one remaining field (the other field was disrupted) had inputs from one runoff event. Growing season precipitation was above average for both years of the experiment. All treatments, including those receiving only precipitation, produced grain yields ranging from 852 to 3467 kg ha(-1) for Zuni maize. Grain and biomass productivity tended to be greater in the irrigation-plus-fertilizer control treatment. Productivity differences among treatments are attributed primarily to differences in water inputs rather than nutrient supply. Although the more densely populated hybrid maize out-yielded Zuni maize on a land area basis, Zuni maize produced greater yields per plant and more biomass than did the hybrid maize.