2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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8 COLORADO SCHOOL OF MINES RESEARCH INSTITUTE dried at 70 °C for 24 hr to obtain a wet -to -dry weight conversion factor. This factor was then applied to the wet weight field data to convert the individual strip and row weights to a dry weight basis. Cover Percentage cover of the perennial grasses was quantitatively determined in 1981 by measuring, with a tape measure, grass occupancy for each row within a strip. The measurements were made following harvesting and, in essence, measured the basal area coverage for each row of grass. In certain plots, sod formation by thickspike and western wheatgrass precluded quantification of cover by the above method; in such areas percentage basal cover was obtained by ocular esti- mate Rooting Depth A combination gamma- neutron probe was used to monitor moisture levels and, indirectly, rooting depth at four locations in each plot. Using the previously mentioned access holes, the probe was lowered down the hole and moisture data were collected at the 15, 30, 50, 70, 90, and 110 cm depths. According to Cable (1980), a neutron probe integrates soil water content in a sphere of soil ranging from 15 to 25 cm in radius around the source point. Density measurements were taken at the same time using the same probe. The moisture data were converted to percentage moisture by weight and graphed to show the extent of water removal. It was assumed that correlations exist between soil water depletion and the rela- tive quantity of roots present in the soil; a number of studies have shown that this assumption is valid for a variety of situations (Bohm, 1979). During most years, moisture data were collected in May, June, August, and October. Plant Establishment and Tillering Small subplots (0.09m were established in the spoil and soil buffer areas for the purpose of quantifying plant tillering and establishment. Using a wire hoop to mark the subplot boundary, sufficient soil or spoil was removed to cover the seeds with 2 cm of material. A counted number of seeds (30 pure live seed equivalent) was placed on the surface and the excavated material returned. Two such plots were established for each species planted, one in soil and one in spoil. At the end of the first growing season after planting, the number of live seedlings (plant establishment) and the number of tillers per established plant were recorded for each plot. Water Infiltration The rate of water infiltration for spoil and for soil (where soil depth was approximately 152 cm) was determined using an infiltrometer as described by Bertrand (1965) and Haise et al. (1956). A double -ring infiltrometer was used when there was sufficient room to accommodate both rings without damaging the established grasses. In many situations, there was sufficient room to accomo- date only the 30 -cm- diameter inner ring. To minimize lateral water movement when one ring was used, the ring was driven 10 to 18 cm into the ground. All infiltration tests were conducted for a 4 -hr period. Infiltration was measured at the time of plant harvesting, and ring locations were marked on a map to ensure that the same location was not used in subsequent years. Infiltration tests were initiated 2 years after plot establishment; the delay was to allow plot settling to be essentially complete prier to infiltration testing.