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