2012-06-20_PERMIT FILE - C2010089 (62)

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Soil samples were collected in mid- to late -July with a truck mounted rotating soil probe. Soil was collected in 30 cm increments to a depth of 120 cm or to the subsoil -spoil contact and separated in predetermined increments and by natural breaks. A total of 144 soil samples were taken at the ZSW and 36 at the SSW in the center of randomly chosen production plots in each slope position. Samples were dried at 32 °C for four days, put into a soil de- aggregation machine and then passed through a 2 -mm sieve. Topsoil and subsoil depths were determined in the field, EC1 was determined with an Orion Model 550A EC meter and pH was determined from a 1:1 paste with a glass electrode (Orion Model 550A). Soil texture was determined on a subset of samples (206 samples) with the hydrometer method (Day, 1965). Data were analyzed with one -way analysis of variance and multiple correlation analysis using Jmp, Version 4.0.4 (2001). Past vs. present data and 2003 production data were analyzed with one -way analysis of variance. Multiple correlation analysis was used to determine the strength of the relationship among production, total soil depth, EC and pH. A collinear relationship between slope position and total soil depth (as a result of wedge design) allowed for depth ranges to be determined for each slope position. Results and Discussion Climate data was obtained from the Beulah, ND NOAA station. This station is 8 km to the east of the ZSW and 37 km to the west of the SSW and has the most complete records in the area. Precipitation was highly variable between the sampling years (1976 -1981, 2003). Precipitation timing and amounts in 2003 was most similar to 1978. Spring and summer precipitation values in 2003 and 1978 were 13.7 and 10.2 cm, respectively, in the spring and 13.1 and 14.2 cm, respectively, in the summer (Table 1). Mean air temperatures were also similar between 2003 and 1978 with average monthly temperatures approximately 13.7 and 16.9 °C in May and June, respectively (Table 2). Table 1. Total precipitation in centimeters at the Beulah, ND NOAA station. 1976 1977 1978 1979 1980 1981 2003 Jan. -Mar. 4.4 3.8 1.6 4.3 2.8 1.1 4.4 Apr. 7.3 0.4 4.4 4.5 1.9 1.0 2.6 May 1.7 8.1 5.8 2.0 0.5 3.0 11.1 June 13.3 7.9 6.4 6.1 9.0 11.3 7.5 July 1.3 6.1 7.8 11.4 2.2 5.5 5.6 Apr. -July 23.6 22.4 24.3 24.0 13.6 20.8 26.8 Aug. -Dec. 8.3 24.8 12.2 7.1 21.2 17.3 12.2 Annual 36.2 51.0 38.1 35.3 37.6 39.2 43.4 Comparison of Past and Present Data Crested wheatgrass plot production values were significantly higher (F <0.01) in 1978 compared to 2003 for the ZSW and SSW (Table 3). This was due to invasion of other weedy plant species into the crested wheatgrass plots as a result of years of grazing. In the previous study by Merrill et al. (1998), the crested wheatgrass plots consisted of a monoculture of crested wheatgrass. This grass is a non - native, aggressive cool season grass with higher productivity 1237 CM