The objective of tbis research was to determine the effects of selected vegetation, soil, rock, and slope variables on lnflltration of semiarid rangelands with slope gradients ranghtg from g-70%. Analyses were made on 2 sets of data collected a year apart in the Guadalupe Mountains of New Mexico and consisted of Pearson and partial correlation analysis of the dependent infiltration variables and independent site variables. In addition, htfiltratioa was regressed against uncorreiated factors produced by factor analysis. Vegetal cover and biomass strongly ifiuenced infiltration. The relative importance of grasses, shrubs or litter was dependent on their respective abundance, especially grass. Soil depth also limited infiltration especially as soil water storage became satisfied. Infiltrability was negatively correlated with rock cover and the smallest rock size fragments were the most negatively related. When the effects of vegetal cover and slope were removed (using partial correiation analysis) however, the median sized rock fragments (26-150 mm) were positively related to infiltrabiiity, and the smailest rock fragements (2-12 mm) were negatively related. Partial correl8tion analysis also suggested 8 positive correlation between htfiltrabigty and slope gradient. Key Wordsz soil water, htfihration, rangeland hydrology An understanding of basic hydrologic processes on rangeland is critical for effective range watershed management. The infiltration process fundamentally influences rangeland hydrology; thus, knowledge of factors that influence infiltration is important. Many studies have assessed the influence of soil and vegetation factors on rangeland infiltration. Few, however, have evaluated semiarid rangelands and none to our knowledge have included very steep slopes in their study. Results of these studies have been variable depending on the characteristics of the study area (Branson et al. 1981).

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Water infiltration rates into soils after 30 min in shrub canopy areas and in shortgrass interspaces on the Rolling Plains were similar across grazing treatments of heavy and moderate stocking, continuous grazing; rested and grazed deferred-rotation; rested and grazed high intensity, low frequency (HILF); and two livestock exclosures which had been grazed for 20 years. The mid-grass interspace infiltration rates for the deferred-rotation treatments approached rates in the exclosures and exceeded rates in the heavily stocked, continuously grazed, and grazed HILF pastures. Infiltration rates in the HILF grazing treatments were similar to those of the heavily stocked, continuously and moderately stocked continuously grazed pastures. Infiltration rates in the rested HILF pasture were similar to those of the deferred-rotation pastures; however, the grazed HILF pasture had rates lower than the deferred-rotation pasture rates or rates of the exclosures. Aggregate stability, organic matter content, mulch, standing crop, bulk density, and ground cover significantly influenced infiltration rates.

The objective of this study was to develop a smaii plot (1 m*) rainfall simulator operational on steep terrain in the Guadalupe Mountains of New Mexico. The simuiator developed is bandportable and consists of a spray head assembly mounted on 3 adjustable legs. A 946-liter tank equipped with a gasoline powered pump was connected to the spray head assembly via rubber garden hoses. On steep slopes gravity provided sufficient pressure to operate the simulator. Site selection was limited to areas where the water tank could be located in a suitable upsiope position. The simuiator has been used for 2 years on 170 plots and has proved durable. Advantages of this device are the low cost of construction and operation, and the flexibility in plot-site selection it provides. The principal disadvantages are associated with the single stationary nozzle, such as uneven application of water at small drop sizes and low kinetic energies. An ideal rainfall simulator has yet to be developed. Those that most closely reproduce rainfall patterns and intensity are expensive and require large expenditures of manpower for setup and operation (Foster et al. 1979). However, rainfall simulators, even though imperfect, are essential tools for investigating hydrologic processes on arid and semiarid rangeland where rainfall events are sporadic. Simulator experiments can be used to estimate infiltration, interrili erosion runoff rates, and chemical water quality for given storm events. Impacts of range management practices (grazing strategy, brush control, reseeding) on the watershed can also be evaluated using rainfall simulators. Rainfall simulators can be used to collect data in a relatively short period, rather than the 10 to 20 years needed to collect sufficient information from natural rainfall events. Rainfall simulators also provide maximum control over plot conditions and rainfall characteristics. Rainfall simulators in common use by range watershed scientists are the mobile drop-forming (Blackburn et al. 1974), Rocky Mountain infiltrometer (Dortignac 1951) and versions of the Purdue type (Bertrand and Parr 1961). Ail the above provide mobility, but use of each is restricted to relatively flat terrain. Hand-portable infiltrometers have been developed (Adams et al. 1957, McQueen 1963, Seiby 1970, Munn and Huntington 1976, Malekuti and Gifford 1978) and are more suitable for rugged terrain. Munn and Huntington (1976) report the Tahoe Basin infiltrometer to be functional on slopes to 60%. Hand-portable infiltrometers, however, have not been widely used, perhaps because many are bulky, heavy, require pumps or motors, or have a limited water supply. This paper presents the construction, operation, rainfall characteristics, and limitations of a hand-portable small rainfall simulator developed for use on steep slopes in the Guadalupe Mountains of New Mexico. Materials and Methods The simulator employs a single stationary nozzle. Various full cone nozzles can be used depending on the desired drop size and velocity, area to be covered, and appli...

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