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126 SOIL SCI. SOC. AM.
<br />Table 3- Average annual alfalfa yields (1976 -1979) as influenced
<br />by thickness of topsoil and subsoil over sodic spoils.t
<br />Topsoil thickness
<br />Subsoil
<br />thickness 0 cm
<br />cm
<br />10
<br />30
<br />50
<br />70
<br />90
<br />110
<br />130
<br />150
<br />170
<br />190
<br />0.70 eY
<br />1.18 cdY
<br />1.40 abY
<br />1.50 aY
<br />1.31 abcX
<br />1.12 cdY
<br />1.09 cdW
<br />1.06 dX
<br />1.11 cdY
<br />1.22 bcdY
<br />Mixed topsoil
<br />20 cm 60 cm and subsoil
<br />1.40 fZ
<br />� Z
<br />2.24 aZ ;
<br />2.16 abZ
<br />2.09 abZ
<br />2.15 abZ
<br />2.15 abZ
<br />1.82 cdZ
<br />1.57 efZ
<br />metric tons/ha
<br />1.42 dZ 0.48 fX
<br />1.77 bcZ 0.86 eX
<br />1.977ab - 1.31 dY
<br />2. 1 \ 1.58 bcY
<br />2.02 aZ 1.73 abY
<br />2.10 aZ 1.92 aZ
<br />1.94 abY 1,74 abX
<br />1.91 abY 1.88 aY
<br />1.77 bcZ 1.87 aZ
<br />1.61 cdZ 1.51 cZ
<br />t Within a column, same small letter indicates no significant difference
<br />(P = 0.05). Within a row, same capital letter indicates no significant
<br />difference (P = 0.05).
<br />Table 5- Average annual native grass yield (1976 -1979) as
<br />influenced by thickness of topsoil and subsoil
<br />over sodic spoils.t
<br />Subsoil
<br />thickness 0 cm
<br />Topsoil thickness
<br />cm metric tonslha
<br />10 0.09 dY 0.69 aZ
<br />30 0.44 cdXY 0.95 aZ
<br />50 0.68 bcY 1.05 aZ
<br />70 0.75 bcZ 1.08 aZ
<br />90 1.22 aZ 0.93 aYZ
<br />110 0.73 bcZ 0.96 aZ
<br />130 0.84 bZ 0.90 aZ
<br />150 0.72 bcZ 0.88 aZ
<br />170 0.69 bcZ 0.90 aZ
<br />190 0.80 bcZ 0.76 aZ
<br />Mixed topsoil
<br />20 cm 60 cm and subsoil
<br />0.58 bZ
<br />0.67 abYZ
<br />0.88 abYZ
<br />1.05 aZ
<br />1.01 aYZ
<br />0.93 abZ
<br />0.85 abZ
<br />0.94 abZ
<br />0.89 abZ
<br />0.70 abZ
<br />0.03 bY
<br />0.15 bX
<br />0.66 aY
<br />0.86 aZ
<br />0.82 aY
<br />0.97 aZ
<br />0.94 aZ
<br />0.90 aZ
<br />0.86 aZ
<br />0.98 aZ
<br />t Within a column, same small letter indicates no significant difference
<br />(P = 0.05). Within a row, same capital letter indicates no significant
<br />difference (P = 0.05).
<br />was observed in almost all crops studied. Part of this
<br />difference may have resulted from greater vehicle
<br />traffic across the upper end of the wedge than through
<br />the center during construction. In many instances,
<br />plant populations for the 190 -cm subsoil sampling
<br />site were poorer than further down the wedge, possibly
<br />due to more traffic. Also, since this was a south- facing
<br />slope, winter snow cover was often shallow near the
<br />top of the wedge (greatest subsoil thickness), with
<br />greatest snow cover midway down the slope. This
<br />pattern could affect soil water and temperature the
<br />next growing season.
<br />The 4 -year average crested wheatgrass yields are
<br />presented in Table 4. As with alfalfa, crested wheat -
<br />grass yields were highest in 1978 (over 5 metric tons/
<br />ha) and lowest in 1977. Greatest average yields ex-
<br />ceeded 2.5 metric tons /ha, a yield level that also sur-
<br />passes predicted grass yields for well- managed Temvik
<br />silt loam (USDA, 1978). ere a ain, fields increased
<br />with increased subsoil thickness to a out 70 cm, with
<br />si• t variation due to to •sot t m-st. Crested
<br />w eatg yiel. s or p ots in which subsoil and top -
<br />io were rt�l�ed rd d not differ significantly from these
<br />where either 20 or 60 cm of topsoil was spreadsepar-
<br />at over - tire subsoil. As with alfalfa, a yield reduc-
<br />tion occurred on most of the 190 -cm subsoil plots.
<br />Yield data for the native grass mixture are shown
<br />in Table 5. Results in general followed the same
<br />trends observed for alfalfa and crested wheatgrass:
<br />(i) yields tended to increase as subsoil thickness in-
<br />J., VOL. 45, 1981
<br />Table 4- Average annual crested wheatgrass yields (1976 -1979)
<br />as influenced by thickness of topsoil and subsoil
<br />over sodic spoils.t
<br />Subsoil
<br />thickness 0 cm
<br />Topsoil thickness
<br />cm metric tons/ha
<br />Mixed topsoil
<br />20 cm 60 cm and subsoil
<br />10 1.51 cXY 1.92 bYZ 2.16 cZ
<br />30 1.92 abcY 2.22 abYZ 2.55 abcZ
<br />50 2.02 abY 2,53 aZ 2.79 abZ
<br />70 2.19 aY 2.43 aYZ 2.85 aZ
<br />90 2.06 abY 2.68 aZ 2.82 abZ
<br />110 1.69 bcY 2.46 aZ 2.64 abcZ
<br />130 1.89 abcY 2.70 aZ 2.47 abcZ
<br />150 1.75 abcY 2.53 aZ 2.59 abcZ
<br />170 1.52 cY 2.36 abZ 2.53 abcZ
<br />190 1.62 bcY 2.32 abZ 2.32 bcZ
<br />Subsoil
<br />thickness
<br />Topsoil thickness
<br />cm kg/ha
<br />1.26 cX
<br />2.04 bY
<br />2.52 abZ
<br />2.61 abZ
<br />2.70 aZ
<br />2.45 abZ
<br />2.39 abZ
<br />2.48 abZ
<br />2.67 aZ
<br />2.71 aZ
<br />t Within a column, same small letter indicates no significant difference
<br />(P = 0.05). Within a row, same capital letter indicates no significant
<br />difference (P = 0.05).
<br />Table 6- Average annual spring wheat grain yield (1975 and
<br />1978) as influenced by thickness of topsoil and subsoil
<br />over sodic spoils.t
<br />Mixed topsoil
<br />0 cm 20 cm 60 cm and subsoil
<br />10 423 eX 1,465 dY 1,788 dZ 470 cX
<br />30 1,257 dY 1,976 cdZ 1,935 bcdZ 1,317 bY
<br />50 1,411 cdX 2,144 abcZ 2,124 abcZ 1,848 aY
<br />70 1,707 BY 2,137 abcZ 2,251 aZ 1,855 aY
<br />90 1,693 abY 2,271 abZ 2,083 abcZ 1,754 aY
<br />110 1,586 abcX 2,278 aZ 2,312 aZ 1,835 aY
<br />130 1,667 abX 2,312 aZ 2,144 abZ 1,828 aY
<br />150 1,579 abcX 2,231 abcZ 2,204 abZ 1,882 aY
<br />170 1,445 bcdX 2,244 abZ 2,144 abZ 1,882 aY
<br />190 1,532 bcdY 2,036 bcZ 1,929 bcdZ 1,922 aZ
<br />t Within a column, same small letter indicates no significant difference
<br />IP = 0.05). Within a row, same capital letter indicates no significant
<br />difference (P = 0.05).
<br />creased to at least 70 t (ii) lards from no topsoil or
<br />mixed treatments_were very low when less than 5 to
<br />70 c 1�1 of subsoil ti7 resent; (iii) maximum yields
<br />compare favorably with those expected of unmined
<br />Temvik silt loam; (iv) yields frequently (but not al-
<br />ways) decreased somewhat for the greatest soil thick-
<br />ness; and (v) yields were much larger in 1978 than
<br />in other years (yields as great as 2 metric tons /ha).
<br />Unlike the other forage crops, lowest native grass
<br />yields were obtained in 1976 instead of 1977, because
<br />of the slow rate of establishment, which is characteris-
<br />tic of warm - season grasses in the Northern Great
<br />Plains.
<br />Average spring wheat grain yields for 1975 and 1978
<br />are presented in Table 6. Maximum yields in 1978
<br />were 25% higher than those in 1975, with highest
<br />yield of 2,600 kg /ha. The responses of spring wheat
<br />to topsoil and subsoil thickness followed the same
<br />trends as for the other crops. Yields were near maxi-
<br />mum for all topsoil treatments, where at least 70 cm
<br />of subsoil was returned. Yields were highest where
<br />topsoil was not mixed with subsoil, were usually lower
<br />for the 190 -cm subsoil treatment than immediately
<br />downslope, and equaled or exceeded yields predicted
<br />for Temvik silt loam under good management (USDA,
<br />1978).
<br />The relative responses of these four crops of topsoil
<br />and subsoil thickness were calculated and are expressed
<br />as a percentage of the highest average yields measured
<br />
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