2012-06-20_PERMIT FILE - C2010089 (59)

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and topsoil thickness ranging from zero to 60 cm, on mediums ranging from straight subsoil, various depths of subsoil covered by 30 and 60 cm of topsoil and a combined mixed topsoil. See Appendix 2.05.4(2)(d) -1 for this study entitled "Effects of Topsoil and Subsoil Thickness on Soil Water Content and Crop Production on a Disturbed Soil ". When averaged across all years, the highest production of Alfalfa was 2.24 metric tons/ha, which was associated with the 20 cm of topsoil over 70 cm of subsoil treatment. Overall average production of Alfalfa averaged 1.50 metric tons /ha, for the subsoil only treatment and 2.11 metric tons/ha for the 60 -cm topsoil over 70 cm of subsoil treatment. On the mixed topsoil /subsoil soil treatment production of Alfalfa was highest, 1.92 metric tons /ha at the 110 -cm depth. Statistically, there was no difference in Alfalfa production at thickness of respread subsoil up to 50 cm or for the mixed topsoil /subsoil soil treatment where Alfalfa production peaked at the 130 -cm depth and then declined at greater depths of respread soil material. These researchers concluded by stating that "at least 90 percent of maximum" yields could be obtained "with at least 90 cm of the mixed subsoil - topsoil spread over spoils." They also determined that "at least 90 % of maximum yield of all crops except wheat were obtained without separating topsoil and subsoil into discrete layers." In a followup study of the same plots performed in 2003, 28 and 29 years after plot establishment, Wick and others (2005) documented the long term effects of respread soil materials and plant community development on two wedge studies, started in 1974 and 1975, respectively. See Appendix 2.05.4.(2)(d) -3 for this study entitled "The Effects of Soil Depth and Other Soil Characteristics on Plant Community Development in North Dakota ". Findings of their study clearly revealed that forage production was significantly higher over time for both grasses and Alfalfa when the 1978 data were compared to the 2003 data. With respect to Smooth Bromegrass, they reported that after 28 years, highest production was found on the 60 to 120 cm total soils depths, but that the data were not statistically significant when compared to the 0 to 40 cm depths. For Alfalfa, highest production was associated with the mid slope plots where the depth of reapplied soil was 60 to 120 cm. Total depth of respread soil was found to have a statistically significant effect on plant growth after 28 years, but these authors concluded that "plant community production is no longer as dependent upon soil depth" and that other soil factors might Section 2.05.4(2) (d) Page 16 January 2012