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Condujimos experimentos en invernadero para comparar las respuestas fotosintéticas y de crecimiento de dos zacates anuales invasores ( "Downy brome" = Bromus tectorum L. y"Medusahead" = Taeniatherum caput-medusae (L.) [Nevski]), 6 zacates cespitosos y 7 zacates rizomatosos a la aplicación del her bicida sulfosulfuron (1 -(2-ethylsulfonylimidazo [1,2 -a]pyridin -3 ylsulfonyl)-3-( 4, 6-dimethoxypyrimidin -2-yl)urea). Nuestros obje tivos fueron identificar patrones generales de respuesta de las especies y probar la hipótesis de que el sulfosulfuron indujo una reducción de la actividad fotosintética y que el crecimiento de los tallos sería mas pronunciado en plantas pequeñas en relación a plantas grandes. Las plantas pequeñas se trataron con sulfosul furon (70 g ai ha') en un experimento realizado en primavera las grandes en uno efectuado en verano. " Wildryes" y " Bromes" fueron consistentemente dañados, mientras que 5 de los "Wheatgrasses "no fueron susceptibles al sulfosulfuron. Los zacates rizomatosos generalmente experimentaron mas daño por el sulfosulfuron que los zacates cespitosos. Estos resultados sug ieren que el sulfosulfuron podría ser una herramienta útil de manejo de pastizales para controlar las especies invasoras no deseadas de zacates anuales sin afectar significativamente el crecimiento y fisiología de los zacates deseables del pastizal. r ange grasses AbstractWe conducted greenhouse experiments to compare photosynthetic and growth responses of 2 invasive annual grasses (downy brome = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) [Nevski]), 6 caespitose grasses, and 7 rhizomatous grasses to the herbicide sulfosulfuron (1-(2-ethylsul-idin-2-yl)urea). Our objectives were to identify general patterns of species responsiveness and test the hypothesis that sulfosulfuron induced reduction in photosynthetic activity and shoot growth would be more pronounced in small relative to larger plants. Small plants in a spring experiment and large plants in a summer experiment were treated with sulfosulfuron (70 g ai ha'). Wildryes and bromes were consistently injured; whereas, 5 of the 7 wheatgrasses were not susceptible to sulfosulfuron. Rhizomatous grasses generally experienced greater damage fromThese results suggest that sulfosulfuron would provide a useful rangeland management tool to control unwanted invasive annual grasses without significantly hindering growth and physiology of desirable rangeland grasses.

Farmers in the Zuni area of the semiarid American Southwest have successfully cultivated maize and other crops for over three millennia without using artificial fertilizers. Zuni agricultural fields are among the oldest, more or less continuously cultivated areas in the United States. Traditional Zuni agriculture is based on runoff farming, a system whereby runoff and organic‐rich sediment generated in small watersheds are captured and directed onto fields for crop use. We conducted a study to compare soil properties associated with paired and unpaired cultivated, abandoned, and uncultivated fields to evaluate the long‐term effects of cultivation on soil quality. Sampling and analytical methods of this research are especially applicable to geoarchaeological studies of anthropogenic effects on soil fertility and agricultural sustainability in ancient and traditional historical farming systems. Results of the Zuni soil study indicate that cultivation has altered some soil properties, including bulk density, organic carbon, total nitrogen, and C:N ratios in paired fields, but there is no indication that agricultural soils are degraded. This assessment supports the perception of Zuni farmers that long‐term cultivation has not caused a decline in agricultural productivity. © 2005 Wiley Periodicals, Inc.

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Research on soil fertility is presented in the context of runoff agriculture, a venerable farming system that has been used for millennia in arid to semiarid regions, where water is a major limiting resource for crop production. The agroecology of runoff farming was studied with the Zuni to evaluate nutrient and hydrologic processes, management, maize productivity, and soil quality in some of the oldest recognized fields in the United States. This ancient Southwest agriculture has functioned without conventional irrigation or fertilization by tapping into biogeochemical processes in natural watersheds connected to fields. Carefully placed fields are managed on alluvial fans and other valley margin landforms to intercept runoff and associated sediment and organic debris transported from adjoining forested uplands. We report on research to evaluate and link nitrogen and phosphorus, two key nutrients for crop production, in watershed, soil, and crop components of this agroecosystem. Nutrient data have been collected by observational and experimental methods for each component and the transport of nutrients from watershed to field to maize. The condition of Zuni agricultural soils suggests that their knowledge and management of soils contributed to effective conservation. This study and others indicate the need for further long‐term monitoring and experimental research on watersheds, runoff processes, field soils, and crops across a range of arid to semiarid ecosystems. © 2007 Wiley Periodicals, Inc.

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retention in alluvium-derived soils of headwater ephemeral streams. Zuni farmers of western New Mexico demonstrate knowledge Peterson et al. (2001) create a convincing case for about soil and hydrological processes that link upland watersheds to alluvium-derived soils that have crucial cultural, ecological, and conservation that maintains or restores the storage cahydrological functions. To define how hillslopes contribute to produc-pacity of headwater streams. Their data show that headtivity of soils derived from alluvium, we studied soil-vegetation-landwater streams play a key role in the physical and biologiform parameters in three headwater drainages on the Zuni Indian cal integrity of downstream waterways because of their Reservation. Analyses along eight summit to toeslope transects show great extent on the landscape and their proximity to that soil properties follow parabolic and linear trends with changes uplands that are source areas for runoff, sediments, and driven by elevation, lithology, and vegetation in the mesa-canyon nutrients. Properly functioning headwater systems repinyon-juniper-Gambel oak (Pinus edulis Engelm.-Juniperus spp.tain and recycle a large portion of the nutrients, particu-Quercus gambelii Nutt.) woodlands. Total organic C, N, and P concenlarly N, from uplands. This retention and recycling cretrations in surface horizons follow negative parabolic trends and are ates the richest soils and highest biological productivity highest on wooded backslopes and lowest on summits and toeslopes. Inorganic N and available P concentrations and total organic to inor-in many arid areas. Bull (1997) points out that many ganic N and P ratios increase linearly from summit to toeslope. Taken Native American farmers recognized the value of the together, soil, landform, and vegetation data suggest: (i) summit posisystem and their activities maintained these functions, tions are relatively stable with immobilizing microbial environments; while modern practices often have the opposite effect. (ii) inorganic nutrients increase progressively down steep and erodible Although many authors describe hillslope models that backslopes as inputs of forest litter are mixed with surface soil; (iii) link soil and nutrient-cycling processes from summits influx of mixed sediment and organic materials from backslopes mainto alluvial toeslopes (Ruhe and Walker, 1968; Conacher tains concentrations of inorganic nutrients on footslopes and toesand Dalrymple, 1977; Schimel et al., 1985; Aguilar and lopes. Entrenchment of drainage ways can circumvent these transloca-Heil, 1988), the unique terrain of the Colorado Plateau tion processes. Without the influx of organic materials, footslopes and creates lithologically segmented hillslopes different toeslopes may become nutrient-depleted as immobilization becomes the dominant microbial process. The results underscore the impor-from those described in accepted hillslope models. Our tance of functional connectivity between upland hillslopes and allu-objective was to develop a hillslop...