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ROWCROP RESPONSE TO TOPSOIL REPLACEMENT ON HIGH
TRAFFIC VS LOW TRAFFIC SOIL RECONSTRUCTION SYSTEMS1
R. E. Dunker and R. G. Darmody2
Abstract. Poor soil physical condition is identified as the most limiting factor to
successful row crop production on mined land in Illinois. Compacted mine soils
lack a continuous macropore network to provide for water movement, aeration
and root system extension. Critical to reclamation success are i) selection of the
best available soil materials used in soil reconstruction and ii) reclamation
methods which will minimize compaction during soil reconstruction. In Illinois,
topsoil replacement has generally enhanced seedbed preparation, stand
establishment, and early season growth when compared to graded spoil materials.
Yield response to topsoil replacement has ranged from strongly positive to
strongly negative. Excellent corn and soybean yields have been achieved when
reclamation methods result in low strength soils. Total crop failures have
commonly occurred when high traffic soil replacement methods result in mine
soils with high soil strength.
Additional Key Words: topsoil, minesoil, prime farmland reclamation, compaction
_____________________
1 Paper was presented at the 2005 National Meeting of the American Society of Mining and
Reclamation, Breckenridge CO, June, 19-23 2005. Published by ASMR, 3134
Montavesta Rd., Lexington, KY 40502.
2 Robert E. Dunker is an Agronomist, Department of Crop Sciences, University of Illinois,
Urbana, IL 61801 email:r-dunker@uiuc. Robert G. Darmody is a Professor of Pedology,
Department of Natural Resources and Environmental Sciences, University of Illinois,
Urbana, IL 61801 email: rdarmody@uiuc.edu
Proceedings America Society of Mining and Reclamation, 2005 pp 302-327
DOI: 10.21000/JASMR05010302
303
Introduction
This paper will report and summarize research done by the University of Illinois concerning
rowcrop response to various reclamation practices. Discussion of results will focus on yield
responses, observations, and summary of the Illinois research. There will be little attempt to
distinguish between prime and non-prime farmland, even though prime farmland is addressed
separately in federal legislation. The principles of reclamation for row crops, and to a large
degree, the potential for success are quite similar for prime and non-prime farmland. Most prime
farmland must by law be reclaimed to row crop capability, but not all row crop reclamation is on
prime farmland.
Selection of Soil Materials
Segregation and replacement of horizons from the premine soils is a practice that is required
by Public Law 95-87 (1977). Early reclamation research focused on the evaluation and
characterization of selected soil materials to be used for soil horizon replacement or substitution,
if the substituted soil material could be shown to be as productive as the natural soil horizon it
replaced. Construction of minesoils with good quality soil materials and desirable physical
properties is essential to attain productivity levels necessary for bond release.
Greenhouse evaluation revealed that replacement or alteration of the claypan subsoils of
southern Illinois would increase crop growth by enhancing the chemical and physical properties
of mined land (Dancer and Jansen, 1981; McSweeney et. al., 1981). Topsoil materials generally
produced somewhat greater plant growth than did mixtures of B and C horizons, but the B and C
horizon mixtures were commonly equal to or better than the B horizon materials alone. The
natural subsoils of this region are quite strongly weathered and acid, or are natric and alkaline
(Snarski et al., 1981). Alternative material was generally much higher in bases than the acid
soils and lower in sodium than the natric soils. Liming and fertilizing of the soil horizon material
produced good yield response and reduced the need for material substitution. McSweeney et al.
(1981) also got favorable greenhouse response to blending of substratum materials with B
horizon materials from the high quality Sable soils (Typic Haplaquolls) in western Illinois. This
response to blending was less pronounced than that observed with materials from southern
Illinois.
Most of the Illinois research has centered around field experiments to evaluate row crop
response to soil replacement and various reclamation practices. Premine soils ranged from the
highly productive deep loess soils developed under prairie vegetation (Mollisols) at the western
Illinois sites to the lighter colored, more strongly developed Alfisols at the southern Illinois sites.
Corn (Zea mays L.) and soybeans (Glycine max (L.) Merr) were grown on these newly
constructed soils to evaluate productivity. Most of the early field studies addressed the issue of
topsoil and subsoil horizon replacement.
Topsoil replacement has generally been beneficial for seedbed preparation, stand
establishment, and early season growth when compared to graded spoil materials (Jansen and
Dancer, 1981). Yield response to topsoil replacement has ranged from strongly positive to
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strongly negative. At the Norris mine in western Illinois, scraper placement of 18 in of dark
prairie topsoil resulted in a significant positive corn yield response in three of four years when
irrigated and two of four when not irrigated (Table 1). Soybeans responded favorably to topsoil
in one of the two years studied (Dunker and Jansen, 1987a). Significant negative yield responses
to topsoil occurred in years of weather stress. Year to year variation in corn yield was
considerably greater on the unirrigated topsoil than the unirrigated wheel spoil. Compaction
caused by the use of scrapers to replace topsoil is assumed to be the reason for low topsoil yields
in years of weather stress. The zone directly below the topsoil has a bulk density of 1.7 to 1.9
g/cm3 and very low hydraulic conductivity..
Table 1. Corn yields in response to irrigation and topsoiling at Norris Mine in western
Illinois.
Treatment
1979
1980
1981
1983
Mean
bu/ac
bu/ac
bu/ac
bu/ac
bu/ac
Irrigated Topsoil/Wheel Spoil
191 a
166 a
175 a
193 a
181 a
Unirrigated Topsoil/Wheel Spoil
155 b
70 d
165 a
20 c
102 c
Irrigated Wheel Spoil
142 b
144 b
105 b
169 a
140 b
Unirrigated Wheel Spoil
100 c
89 c
109 b
70 b
92 d
Undisturbed Sable soil
156 b
124 b
173 a
70 b
131 b
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
At the Norris topsoil wedge experiment, A horizon material was replaced over wheel spoil by
scrapers in thickness ranging from 0 to 24 in. There was a significant positive yield response to
increasing topsoil thickness for corn, but not for soybeans . Year by year results showed positive
relationships to topsoil thickness in years of favorable weather, but negative responses in years
of moisture and temperature stress (Jansen et al., 1985).
At Sunspot mine, in western Illinois, topsoil and B horizon materials replaced over dragline
spoil was evaluated over an eight-year period. Soil treatments consisted of 15 in of topsoil
replaced over replaced B horizon; 15 in of topsoil replaced directly over dragline spoil; 36 in of
B horizon replaced directly over dragline spoil; and dragline spoil only. Bulldozers pushed the
soil materials onto the plot areas and it is important to note that scrapers were never allowed
directly on the plots at any time during construction (Figure 1).
An undisturbed tract of Clarksdale soil (Udollic Ochraqualf) was used as an unmined
comparison. Topsoil replacement resulted in significantly higher corn yields in four out of eight
years when replaced over B horizon materials and six of eight years when topsoil was replaced
directly over dragline spoil (Dunker and Jansen, 1987b). Corn grown on the topsoil replaced
treatments had a higher percent stand at harvest, had fewer barren stalks, and a higher ratio of
shelled grain per total ear weight than corn on the non-topsoil treatments. Soybean yields were
significantly higher on the topsoil replaced treatments in six of seven years whether or not B
horizon materials were replaced. The topsoil/B horizon treatment produced corn yields
comparable to the undisturbed Clarksdale in five of seven years while the B horizon treatment
without topsoil produced corn yields comparable to the undisturbed in only one year. The
305
dragline spoil was unable to produce corn yields equal to the Clarksdale in any of the years
studied whether topsoil was replaced or not (Table 2). Fehrenbacher et al., (1982) found that
corn roots penetrated significantly deeper in the B horizon materials than the dragline spoil and
that bulk densities were significantly higher in the graded dragline spoil than the replaced B
horizon at a depth of 22 in and deeper. Bulk densities between the B horizon material and the
undisturbed Clarksdale were similar. It is not possible to determine whether the favorable
response to the B horizon treatment was due to the B horizon material, or to the lower soil
strength which resulted from the careful handling.
Figure 1. Placing B horizon material at Sunspot mine
Table 2. 1981-86 average corn and soybean yields in response to topsoil and subsoil
replacement at Sunspot Mine in western Illinois.
Treatment
Soybeans
Corn
bu/ac
bu/ac
Topsoil/B Horizon
36 b
130 a
Topsoil/Dragline Spoil
31 c
110 b
B Horizon only
27 d
86 c
Dragline Spoil only
17 e
65 d
Undisturbed Clarksdale soil
40 a
135 a
Values followed by the same letter within a column are not significantly different at the P< 0.05 level.
Soil strength data taken with a continuous recording cone penetromter showed low soil
strength values for Topsoil/B Horizon and B Horizon only compared to those plots constructed
with dragline spoil (Fig. 2). Average soil strength ( 9-44” Average Penetrometer Resistance) was
significantly correlated with corn yields averaged over the seven-year study (Fig. 3).
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1986 Sunspot Mine Penetrometer Data
Penetrometer Resistance, PSI
0200 400 600 800 1000
Soil Depth,inches
0
5
10
15
20
25
30
35
40
45
Topsoil/ Dragline Spoil
Topsoil/ B Horizon
Dragline Spoil Only
B Horizon Only
Figure 2. Soil strength profiles of Sunspot treatments
Positive crop yield response to soil horizon replacement in southern Illinois has been less
dramatic than has been observed at the western Illinois sites (Table 3). This is understandable
considering that A horizons are more highly weathered and average 8-9 inches in depth
compared to 15-18 inches in the highly productive western Illinois soils. At River King, in
southern Illinois, 9 inches of topsoil replaced by scrapers over wheel spoil significantly increased
corn yields in only one of eight years and soybeans in three of six . The River King site has good
quality spoil and rather mediocre topsoil. A nearby plot of topsoil and root media replaced
entirely by scrapers was included as a comparison to the wheel spoil treatments. Crop
performance on all three mine soils can be characterized as poor. Extensive grading and traffic
zones between the topsoil and wheel spoil negatively affected the ability of rowcrops to develop
root systems to adequately take up nutrients and water.
307
1980-86 Sunspot Mine
Individual Plot Mean Yields
9-44 in Average Penetrometer Resistance, PSI
200 400 600 800
Yield, bu/ac
40
60
80
100
120
140
160
R=0.87
Figure 3. Relationship of soil strength and corn yields on Sunspot plots
Table 3. 1978-85 average corn and soybean yields in response to topsoil and subsoil
replacement at River King Mine in southern Illinois.
Treatment
Soybeans
Corn
bu/ac
bu/ac
Scraper Placed Topsoil/Wheel Spoil
18 a
54 a
Wheel Spoil only
13 b
52 a
Scraper Placed Topsoil & Root Media
13 b
33 b
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
Soil horizon replacement and thickness of soil materials from southern Illinois was studied at
the Captain mine in Perry County, Illinois. The Captain wedge experiment evaluated corn and
soybean yield response to thickness of scraper (Fig. 4) placed rooting medium (0 to 48 in thick)
over graded cast overburden, with and without 9 inches of replaced topsoil.
Yields of both corn and soybeans increased with increasing thickness of hauled material to
about the 24-30 in depth (Fig. 5). Meyer (1983) found very few roots below the 24 in depth and
found that roots in the subsoil were largely confined to desiccation cracks. The physical
condition of the scraper placed rooting medium is best characterized as compact and massive
with very high bulk density and poor water infiltration. Soil strength profiles taken at the 48” soil
depth end of the Captain wedge indicated high soil strength values throughout the entire profile
(Fig. 6) These scraper built soils lack the macropore network needed to conduct water and to
provide avenues for root growth. Soybean yields on the scraper placed root medium were
significantly lower than a nearby undisturbed tract in all seven years of the study, whether topsoil
308
was replaced or not. Corn yields were comparable to the undisturbed site in three of the years
which can be characterized as low stress years (Table 4).
Figure 4. Scraper haul system replacing soil materials with
high axle load on rubber tires results in high strength soils
Table 4. 1979-86 average corn and soybean yields in response to scraper placed topsoil and
root media replacement at Captain Mine in southern Illinois.
Treatment
Soybeans
Corn
bu/ac
bu/ac
Scraper Topsoil/Scraper Placed Root Media
13 b
33 b
Scraper Placed Root Media only
12 b
38 b
Undisturbed Cisne/Stoy soil
27 a
70 a
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
Poor soil physical condition has proven to be the most severe and difficult factor limiting
reclamation of many prime farmland soils. Indorante et al. (1981), in a comparison of mined and
unmined land in southern Illinois reported that reconstructed mine soils studied had higher bulk
densities and they lacked any notable soil structure. Natural improvement in compacted mine
soils is a slow process. Thomas and Jansen (1985) studied soil development in eight mine spoils
ranging in age from 5 to 64 years by evaluating physical, chemical and micromorphological
properties. All eight minesoils showed some evidence of soil development, but depth of structure
development ranged from only 1.5 in at the 5 yr old site and 14 in at a 55 yr old site. No
evidence of clay translocation attributable to soil development was found. Color and texture
309
pattern changes were determined to be a result of the mixing of materials rather than
developmental processes.
y = 17.34x^.24 r = .92
20
40
60
80
100
010 20 30 40 50
Rooting Media Depth, in
y = 17.34x^.24 r = .92
20
40
60
80
100
010 20 30 40 50
Rooting Media Depth, in
1979-90 Captain Wedge Corn
Yield, Bu/a
Figure 5. Relationship of scraper placed rooting media wedge and
1979-90 average crop yields
1988 Captain Scraper Placed Wedge Plots
Penetrometer Resistance, PSI
0100 200 300 400 500 600
Soil Depth, In
0
5
10
15
20
25
30
35
40
45
Scraper Topsoil/
Root Media (48")
Scraper Root Media (48")
Figure 6. Soil strength profiles of Captain wedge plot treatments
Illinois has an abundance of high quality soil materials for use in soil construction. Row crop
success on mine land has been as dependent upon the method by which soil horizons have been
replaced as the quality of soil materials selected. Excellent corn and soybean yields have been
achieved on low strength soils in high stress as well as low stress years. Soil horizon segregation
and replacement in Illinois has generally shown a moderate positive yield response. In most
y = 5.27x^.21 r = .98
5
10
15
20
25
30
35
010 20 30 40 50
y = 5.27x^.21 r = .98
5
10
15
20
25
30
35
010 20 30 40 50
1979-90 Captain Wedge Soybeans
Yield, Bu/a
Rooting Media Depth, in
310
cases , however, the soil physical condition that is established during soil construction is clearly
a more significant concern than whether or not materials from the natural soil horizons are
replaced (Jansen and Dancer, 1981).
McSweeney and Jansen (1984) studied the soil structure patterns and rooting behavior of
corn in constructed soils. On a site that received extensive subsoil grading, the subsoil was
severely compacted and massive. Root penetration into these subsoils was primarily horizontal
instead of vertical. Cross sections of the roots were noticeably flattened and compressed. The
researchers described a "fritted" soil structure they defined as an artificial soil structure
consisting of rounded loose aggregates formed by rolling along the soil conveyor, resulting in
soil of low strength and high in macropores. Although subject to compaction at the upper
surface, the extensive void spaces between aggregates allow for excellent root penetration. Four-
year average corn and soybean yields on these plots with well developed fritted structure were
equal to or better than yields obtained on nearby natural soils (McSweeney et al., 1987). By
contrast, corn and soybean yields from a nearby set of plots with root media replaced entirely by
scrapers were unable to produce comparable yields to the undisturbed soil in any of these four
years. The rooting materials for both experiments were similar with major differences associated
with method of soil replacement
The Captain Mix Plots created using the wheel-conveyor-spreader (Fig. 7) were designed to
follow a series of greenhouse experiments which began in 1977. Greenhouse evaluation
revealed that alteration of the claypan soils in southern Illinois increased crop growth by
enhancing the chemical and physical properties of the reclaimed land. The Captain Mix Plots
consist of several treatments that are composed of differents depth mixes of the original soil
profile replaced by the conveyor-spreader.
Figure 7. Captain wheel-conveyor- spreader system resulting in low strength soils
Excellent corn and soybean yields have resulted on these low strength soils in high stress as
well as low stress years. Penetrometer data from the Mix Plots reflect the excellent physical
condition resulting from placing rooting materials with the wheel-conveyor system (Table 5 and
Fig. 8). Rowcrop yields comparable to those obtained on nearby undisturbed soils were achieved
311
in all eleven years of this study (Dunker et al., 1992). Topsoil replaced with the soil spreader
infrequently produced any significant yield response (Table 6).
Table 5. Mean penetrometer resistance values for soil treatments constructed with wheel-
conveyor-spreader on the Captain Mix Plots.
Treatment
9-18”
Depth
18-27”
Depth
27-36”
Depth
36-44”
Depth
PSI
PSI
PSI
PSI
Topsoil/3’ Mix
179 abc
97 d
77 b
98 b
Topsoil/10’ Mix
183 ab
136 bc
91 b
96 b
Topsoil/15’ Mix
210 a
161 ab
125 a
111 ab
Topsoil/20’ Mix
219 a
176 a
117 a
108 ab
10’ Mix
135 c
103 b
100 ab
170 a
20’ Mix
121 c
110 cd
101 ab
112 ab
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
1989 Captain Wheel Conveyor Plots
Penetrometer Resistance, PSI
0100 200 300 400 500 600
Soil Depth, In
0
5
10
15
20
25
30
35
40
45
A/3 ft Mix
A/10 ft Mix
A/15 ft Mix
A/20 ft Mix
10 ft Mix
20 ft Mix
Figure 8. Soil strength profiles of Captain wheel-conveyor mix plots
Although the mining wheel-conveyor-spreader system proved successful in constructing
productive soils after surface mining, it does not offer a generally applicable solution to the
problem of restoring land to agricultural productivity after mining. The method is an inflexible
system and cannot be used at most mines. Evident options are to develop a method by which
excessively compacted soils can be ameliorated to a significant depth or to develop other
312
material handling options which will produce soils with good physical characteristics. Natural
soil improvement processes are slow, especially at greater depths, as is evident from the 10-year
corn and soybean yields observed on the wedge and mix plots (Fig. 9). Year to year variation is
associated more with weather stress and management factors than from any measurable natural
soil improvement.
Table 6. 1981-91 average corn and soybean yields in response to soil treatments
constructed with wheel-conveyor-spreader at Captain Mine in southern Illinois.
Treatment
Soybeans
Corn
bu/ac
bu/ac
Topsoil/3’ Mix
29 a
113 a
Topsoil/10’ Mix
27 ab
109 a
Topsoil/15’ Mix
27 ab
111 a
Topsoil/20’ Mix
27 ab
98 b
10’ Mix
24 b
100 b
20’ Mix
25 ab
102 b
Undisturbed Cisne/Stoy soil
27 ab
112 a
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
79 80 81 82 83 84 85 86 86 88 89 90
0
40
80
120
160
Corn
Yield, bu/a
79 80 81 82 83 84 85 88 89 90
0
10
20
30
40
50
Scraper Wheel-conveyor
Soybean
Yield, bu/a
79 80 81 82 83 84 85 86 86 88 89 90
0
40
80
120
160
Corn
Yield, bu/a
79 80 81 82 83 84 85 88 89 90
0
10
20
30
40
50
Scraper Wheel-conveyor
Soybean
Yield, bu/a
Figure 9. Comparison of corn and soybean yields on root media placed by wheel- conveyor
system (TS/3’ Mix) and nearby scraper placed root media
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As an alternative to the wheel-conveyor system, corn and soybean response to mine soil
construction with rear-dump trucks and scraper pans were studied from 1985-91 at Denmark
Mine in southern Illinois (Hooks et al., 1992). Two truck-hauled treatments, one which limited
truck traffic to the spoil base only(TNT), and one which allowed truck traffic on the rooting
media as it was placed (TWT), were evaluated (Fig. 10).
Figure 10. Rear dump trucks replacing root media with traffic on media (TWT)
A third treatment consisted of scraper hauled rooting media (SCR). The rooting media was
comprised primarily of the B horizon of the natural unmined soil and all treatments had 8" of
topsoil replaced on the rooting media using dozers to prevent wheel traffic compaction.
Significant differences in soil strength, a measure of soil compaction, and rowcrop yields were
observed among treatments over the five-year period. The lowest soil strength and highest
rowcrop yields occurred on the treatment without truck traffic. Soil strength and yield response
were similar for the truck with surface traffic and the scraper treatment (Table 7 and Table 8).
Soil strength profiles are shown in Fig. 11. Aerial photo of corn and soybean plots show effects
of each treatment on vegetative growth (Fig. 12).
Table 7. Mean penetrometer resistance values for soil treatments on the Denmark Plots.
Treatment
9-18”
Depth
18-27”
Depth
27-36”
Depth
36-44”
Depth
PSI
PSI
PSI
PSI
Truck Placed Root Media w/o Traffic
182 b
189 b
161 b
172 b
Truck Placed Root Media with Traffic
223 ab
227 ab
213 ab
217 ab
Scraper Placed Root Media
272 a
275 a
258 a
258 a
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
314
Table 8. 1985-91 average corn and soybean yields in response to rear-dump truck placed
and scraper placed root media at Denmark Mine in southern Illinois.
Treatment
Soybeans
Corn
bu/ac
bu/ac
Truck Placed Root Media w/o Traffic
20 b
99 a
Truck Placed Root Media with Traffic
16 c
71 b
Scraper Placed Root Media
16 c
63 b
Undisturbed Cisne/Stoy soil
26 a
103 a
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
Denmark Penetrometer Data
Penetrometer Resistance, PSI
050 100 150 200 250 300 350 400
Soil Depth, Inches
0
5
10
15
20
25
30
35
40
45
SCR
TNT
TWT
Figure 11. Soil strength profiles of Denmark treatments
Severe compaction and compacted interfaces between soil layers have proven to be major
problems which limit productivity of most reclaimed soils. A truck handling system which
handles both topsoil and subsoil in one operation was evaluated at Cedar Creek Mine in western
Illinois from 1992-94. During plot construction, each rear-dump truck was loaded with the
equivalent of 36 in of subsoil and 12 in of topsoil on top of the load (Fig. 13). Subsoil and
topsoil were dumped by the trucks in one operation eliminating the need for topsoil replacement
by scapers. Some mixing of the topsoil and subsoil occurred but the majority of topsoil
remained at the soil surface. Thin lenses of topsoil extended into the subsoil material. These
lenses could actually encourage root exploration into the subsoil below.
315
Figure 12. Aerial photo of Denmark plots showing vegetative growth
differences of corn and soybean among treatments.
Figure 13. Rear-dump truck loaded and placing the equivalent of 36 in of
subsoil and 12 in of topsoil on top of the load in one operation
Two other treatments, one being rear-dump truck placed subsoil with scraper placed topsoil
and the other rear-dump truck placed subsoil without topsoil were included in the evaluation.
Penetrometer resistance data collected in 1994 (Fig. 14) indicated that wheel traffic from the use
of scrapers to replace topsoil had a negative impact on the underlying placed subsoil. Soil
strength values increased due to scraper traffic by 82% over that of the rear-dump system. 1992-
94 mean yields indicate the system using rear-dump trucks to simultaneously replace both
rooting media and topsoil is superior to using scrapers to replace topsoil over hauled rooting
media. Results also show a significant response to topsoil replacement using this system
(Table 9). On a nearby tract a mixture of the topsoil and root media combined was included in
the comparisons.
316
0
6
12
18
24
30
36
42
48
050 100 150 200 250 300
SCR
TRK
MIX
Penetrometer Resistance, PSI
Cedar Creek, May 1994
Soil
Depth,
inches
Figure 14. Soil strength profiles of Cedar Creek truck plot treatments
Table 9. 1992-94 average corn yields in response to rear-dump truck placed root media and
topsoil and scraper placed topsoil at Cedar Creek Mine in western Illinois.
Treatment
Corn
bu/ac
Truck Placed Root Media with Topsoil
159 a
Scraper Placed Topsoil over Truck Placed Root Media
131 b
Truck Placed Root Media w/o Topsoil
130 b
Values followed by the same letter within a column are not significantly different at the P<0.05 level.
Thompson et al. (1987) used root length and root length densities to evaluate bulk densities
and soil strength values as indicators of root system performance. Because root restriction is
generally the factor most important in limiting crop performance in mine soils, determining the
suitability of soils for root system development could be a useful method of evaluating reclaimed
soils. Soil strength was evaluated with the use of a constant rate recording cone penetrometer
developed by Hooks and Jansen (1986). Results indicate that both penetrometer resistance and
bulk density are useful methods to predict root system performance in soils. They are especially
317
useful in predicting root extension into deeper depths of the root zone. Penetrometer resistance
and bulk density were highly correlated in the lower root zone, but poorly correlated nearer the
soil surface.
Penetrometer data have proven useful for evaluating the soil strength effects of several
reconstruction methods, of high traffic lanes on reclaimed areas and of tillage methods for
alleviating compaction (Vance et al., 1992). Soil strength values decreased with decreasing
traffic. Scraper soil material handling methods produced the highest soil strengths, soils from
truck-haul systems were intermediate, and soils built by a wheel-conveyor-spreader system had
the lowest soil strength. Penetrometer measurements have resulted in wide ranging values
between reclamation treatments and corresponding wide ranging values in crop yield.
Correlation of penetrometer resistance with crop yield has been good. Average soil strength over
the 9-44 inch profile depth was highly correlated with five-year mean yields across reclamation
treatments (Table 10).
Table 10. Linear correlations between logarithmic transformation of six-year mean yields
and penetrometer resistance values from four reclamation treatments in Illinois
(Vance et al., 1992).
Soil Crop
Depth Segment Corn Soybeans
Correlation Coefficient (r2)
9-18 in -0.97* -0.91†
18-27 in -0.96* -0.99**
27-36 in -0.96* -0.99**
36-44 in -0.96* -0.99**
Avg 9-44 -0.98* -0.99**
†, *, **, Statistically significant at the 0.10, 0.05, and 0.01 levels of
probability respectively.
Soil strength measurement with the deep profile penetrometer is a viable method for
assessing long term yield potential of mined land when chemical and plant nutritional variables
are not yield limiting factors. While yield variation among years is associated more closely to
weather variables than soil factors, soil strength appears to be closely correlated to mean yields
averaged over multiple years (Fig. 15).
318
Avg. 9-44 inch Penetrometer Resistance
0100 200 300 400 500
Yield, bu/ac
20
40
60
80
100
120
140
160
R = 0.79
Figure 15. Relationship of 9-44” average soil strength and corn yield of mine soils Data set
consist of data from topsoil replaced treatments of five mine sites with a
minimum of five years of yield data..
The penetrometer can also be an important management tool for the mine operator to assess
levels of soil compaction so it can be determined if deep tillage will be needed as well as to
evaluate the effectiveness of such deep tillage operations (Dunker et al., 1994). An example of
differences in soil strength as a result of moving topsoil with a cross-pit wheel to create topsoil
stockpiles on the graded rooting media is illustrated in Fig. 16. This mine had previously used a
scraper haul system to transport and replace topsoil, but unacceptable compaction resulted. This
new approach eliminated the wheel traffic from scrapers by allowing use of low-ground-pressure
dozers to push topsoil from the stockpiles created by the cross-pit wheel. The operator
concerned about the effects of the size of the topsoil stockpliles on the graded rooting media
used the cone penetrometer with a gridded sampling pattern to assess soil strength with depth to
evaluate the effect of this reclamation method. Penetrometer data provided the operator
information to determine where compaction problems occurred and to make decisions on the
number and size of topsoil stockpiles to be placed in the reclaimed area.
From an engineering or physical approach, soil strength is a parameter that could be
predicted based on density, texture and moisture conditions of the soil. In the reclamation
studies reported by Illinois researchers, soil strength is considered as a relative composite value.
Moisture content is a major factor controlling penetromter values when soils are drier than field
capacity. Data collected in the spring, when soils are uniformly moist, and when minor
differences in soil moisture occur between adjacent treatments are more likely to be correlated
with yield. Such measurements under the same cropping system are considered to be a
reflection of the soil x environment interaction and a valid part of the composite-value soil
strength. Penetrometer data are also reproducible over time, as reported by Dunker et al. (1994).
Fig. 17 shows the effects of two different deep-tillage treatments, TLG (32 in) and DM1 (48 in),
319
over a five-year sampling period. These curves demonstrate both the repeatability of
penetromter data and the ability to assess effective depth of tillage operations.
0100 200 300 400 500
0
100
200
300
Distance, feet
134.2
178.9
178.9
178.9
178.9
223.7
223.7
223.7
268.4
268.4
268.4
268.4
313.2
313.2
313.2
357.9
357.9
357.9
402.6
402.6
402.6
447.4
447.4
447.4
447.4
492.1
492.1
492.1
536.8
536.8
536.8
581.6
581.6
581.6
626.3
626.3
626.3
626.3
671.1
671.1
671.1
671.1
715.8
760.5
805.3
850.0
Topsoil Berms
Penetrometer Resistance, PSI 27" Depth
Berm
Berm
Berm
Topsoil Berms
27" Soil Depth
Figure 16. Gridded contour plots (two dimensional and three dimensional contour)
showing effects of topsoil berms on soil strength (PSI) at 18 to 27 inch soil depth
0
6
12
18
24
30
36
42
480200 400 600 800
1988
1989
1991
1993
0
6
12
18
24
30
36
42
48 0200 400 600 800
1988
1989
1991
1993
DMI
Penetrometer Resistance, PSI
Penetrometer Resistance, PSI
TLG-12
Soil
Depth,
inches
Soil
Depth,
inches
Figure 17. Results of penetrometer data taken over a 5-year period evaluating tillage
effects. The TLG-12 is a tillage tool that works to a 32 in depth, DMI deep plow
works to a depth of 48 in.
320
Ameiliorating Compaction with Tillage
The effect of using a deep soil loosener (Kaeble-Gmeinder TLG-12) on corn grown on wheel
spoil was evaluated over a two-year (1985-86) period at Norris Mine in western Illinois (Dunker
et al., 1989). The TLG-12 has an effective tillage depth of approximately 32 in and was
successful in significantly lowering penetrometer resistance in both the 9-18 in and 18-27 in
depth segments when compared to the unripped wheel spoil treatments. Corn yields increased
significantly with the TLG-12 treatment in both years, although the magnitude of response was
greater in 1985, a year of greater climatic stress. Significant differences for pollination dates,
percent barren stalks, shelling percentage, and soil moisture potential levels at certain depths
were observed between the ripped and non-ripped treatments. Two-year average corn yields for
both topsoil/wheel spoil and wheel spoil without topsoil were comparable to corn yields from a
nearby undisturbed Sable (fine-silty, mixed, mesic Typic Haplaquolls) soil while two-year non-
ripped mine soil yields were not (Figure 18).
175
146
161
150
179
0
50
100
150
200
250
Y
i
e
l
d
,
B
u
/
A
TS TLG TS CON SP TLG SP CON SABLE
Figure 18. Two-year corn yield means for TLG (32 in Tillage) and conventional (9 in
tillage) for topsoil and non-topsoiled wheel spoil plots at Norris Mine.
The effects of seven tillage treatments (Fig. 19) ranging in depth from 9 to 48 in) were
evaluated on a reclaimed mine soil over a 6-year period in southern Illinois (Dunker et al., 1995).
The mine soil consisted of 8 in of topsoil replaced over 42 in of scraper-placed rooting media.
The pre-tillage physical condition of this mine soil was compact and massive. A nearby tract of
Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualfs) was used as an unmined
comparison. Crop yields for both corn and soybeans significantly increased with tillage depth.
Average soil strength decreased and net water extraction by the growing crop increased with
increasing depth of tillage. The 42 in deep tillage treatments with the DMI deep plow
significantly reduced soil strength (9-44 in avg.) from 2.8 to 0.93 Mpa. Significant correlation
(alpha=0.01) occurred between 9-44 in mean soil strength and 6-year mean corn (-0.92) and 4-
year mean soybean (-0.92) yields.
321
Figure 19. Burning Star deep tillage treatments
322
Fig. 20 shows regression equations of penetrometer levels and mean yields for tillage
treatments. Deep tillage successfully restored productivity. However, the depth of tillage
required to meet productivity levels was influenced by initial level of soil strength. Tillage
significantly affected crop yield and measured agronomic variables, such as barren plants,
shelling percentage, average ear weight, and average test weight in grain. Corn and soybean
yields increased with increasing tillage depth within and across the six-year period (Fig. 21).
Crop yields comparable to the undisturbed Cisne soil were achieved on the deepest tilled
treatments (48 in depth) in 5 of the 6 years that corn was tested and 4 of the 4 years that
soybeans were tested. Post-tillage penetrometer data indicate that amelioration effects of tillage
persisted, and significant positive yield effects of deep tillage were observed after 7 years, the
conclusion of the study (Fig. 22). However, because deep-tilled soils may be subject to
mechanical recompaction, management plans must include compaction-avoidance techniques.
y = 1320.46x^-0.49 r = -0.97
0
30
60
90
120
100 200 300 400 500
Average
Corn
Yield,
bu/ac
9-44" Average Penetrometer
Resistance, PSI
1991-1997 Burning Star Deep Tillage Plots
Relationship of Tillage Deep Treatments and Yield
Figure 20. Relationship of 1991-97 mean corn yields and soil strength at
Burning Star 2 deep tillage plots
323
81
78
90
95
99
119
117
123
-10
10
30
50
70
90
110
130
Yield. bu/ac
CHS 9"TG2 16" TLG
32" RM1
32" DM3
38" DM1
48" DM2
52" Cisne
1991-97 Average Corn Yields
Figure 21. 1991-1997 average corn yields on Burning Star 2 deep tillage plots
1993 BS#2 Penetrometer Data
7 Years after Tillage Applied
Penetrometer Resistance, PSI
050 100 150 200 250 300 350 400 450 500 550 600
Soil Depth, Inches
0
5
10
15
20
25
30
35
40
45
50
CHS 9"
TG2 15"
TLG 36"
RM1 36"
DM3 38"
DMI 48"
DM2 48"
Figure 22. Soil strength profiles of Burning Star 2 tillage
treatments seven years after application
324
Summary- Constructing Productive Post-Mine Cropland Soils
In summary, results from the Illinois work shows that achieving mine land productivity is
attainable if reclamation plans are designed to minimize compaction, use good quality soil
materials and use high management levels (herbicides, fertility, adapted crop varieties) in
rowcrop production. Illinois has an abundance of high quality materials to use for soil
construction and row crop success on mined land has been dependent upon the method by which
soil horizons have been replaced and the quality of the materials selected. Excellent corn and
soybean yields have been achieved on low strength soils in high stress as well as low stress years.
However crop failures have occurred when reclamation methods result in mine soils with high
soil strength. Truck handling of rooting media with limited surface traffic has resulted in a more
productive and less compacted soil compared to a high traffic scraper haul system for replacing
root media.
Building productive and useful postmine cropland requires planning, innovation, and
commitment to succeed. Jansen and Hooks (1988) discuss the following concepts for successful
cropland soil reclamation.
Design.
Construction of productive post-mine soils should be done by developing and following a
definite design. The design could be patterned after the premine soils on the site to be mined,
and in many instances that is appropriate. A better practice, however, is to develop an ideal
design patterned after the best natural soils for the crops to be grown. It will not be possible to
duplicate any natural soil (McCormack, 1974). Though the ideal soil cannot be matched, it will
serve as a useful guide for selecting materials, for placing them in the new soil, and for
evaluating the finished product.
Selecting Suitable Materials.
The A and B horizons of the premine soil will often be the best available material with which
to construct a new soil. There will be, however, locations where material from some horizons in
the premine soil is less favorable for construction of a new soil than is material from a deeper
strata in the geologic column. The various layers in the geologic column at each site should be
evaluated to determine which are best for soil construction. Some sites have a surplus of
excellent quality soil building materials available, whereas the quantity of good material will be
inadequate at other sites.
The top 5 ft of the new soils should be constructed of medium textured materials (silt loams,
loams, or light silty-clay loams). Coarse fragments (gravel and rock) should be absent or make
up only a small portion of the total soil volume. Medium textured soils that are low in coarse
fragments generally have the highest capacity to store available water for plants. High water
storage capacity is most crucial in climates where dry periods during the growing season are
common. Clays are active in storage and release of plant nutrients and hence important, but
soils that are too high in clay commonly have poor tilth, low hydraulic conductivity, and poor
aeration.
325
The soil pH should be near neutral or slightly acid for most crops (midwest). Base saturation
should be high, and monovalent ions such as sodium should be low enough in relation to calcium
or magnesium on the exchange complex so that clays will flocculate. The soil should be rich in
weatherable minerals. Elements essential to plant and animal life should be present in adequate
quantities. Materials that are toxic to plant or animal life, or that release toxic materials upon
weathering, should be absent.
Soil organic matter stabilizes soil structure, improves tilth, and is active in storing and
releasing plant nutrients. It is particularly important in the plow layer because that is where the
seedbed must be prepared and where many of the plant nutrients will be stored. Soils that are
low in organic matter are more prone to sealing, and crusting than similar soils high in organic
matter. The infiltration rate is lower on low organic matter soils causing high runoff and high
erodibility.
Microbial life in the soil plays an important role in plant growth. Generally an abundance of
desirable microbes can be obtained only from the premine soils. Deeper geologic strata are not a
good source. A desirable microbial population can be established quite rapidly, however, if the
chemical and physical environment is favorable.
Soil structure is important for soil tilth, aeration, water movement, and water storage. Only
the material from the premine soil will have desirable soil structure. Soil structure should be
considered when selecting materials for the new soil only if the material can be moved without
destroying that structure. Soil structure will very slowly develop in the new soil, even if absent
immediately after soil construction.
Moving Materials and Constructing the Soil.
The means used to move overburden must be capable of segregating the selected materials
and placing them at the appropriate level in a new soil while preserving soil structure or
establishing a favorable density or soil strength. The only alternative to intensive grading is to
have control over material placement by equipment used to move overburden, so that only
minimal grading will be needed. Another option is to use deep tillage after final grading to
alleviate compaction and create a favorable structure. Deep tillage has been shown to be
effective in returning productivity of compacted mine soils.
There is no simple formula for reconstructing soils that can be applied to all lands to be
mined. Soils are complex entities and soil needs vary with climate, land use, and management
systems. Each site will have a unique set of materials available with which to construct a soil.
Characteristics that are usually desirable in cropland soils can be described, but the final detailed
planning will need to be done separately for each site. Technology has been developed to insure
that cropland, both prime and non-prime, can be successfully reclaimed.
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