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a Carbon Management and Sequestration Center, The Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210-1085
b School of Natural Resources, FAES, The Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210-1085
c Los Alamos National Lab., Los Alamos, NM 87545
* Corresponding author (shukla.9{at}osu.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b) for Vinton, no significant differences were observed in b, electrical conductivity (EC), pH, saturated hydraulic conductivity and water infiltration for the 0- to 10-cm depth among fertility treatments in RMS and UMS for both Jackson and Vinton County sites. Average soil organic C (SOC) 5 yr after reclamation in 1981 was 14.2 Mg ha–1 for Jackson and 15.1 Mg ha–1 for Vinton site for the 0- to 10-cm depth. In 2001, average SOC was 28.7 Mg ha–1 for Jackson and 30.24 Mg ha–1 for Vinton site. A two-fold increase in SOC was obtained at both sites between 1981 and 2001. Soil pH was >6.4 and was favorable for root development and biomass production at both reclaimed sites. No significant differences in several soil properties between UMS and RMS showed that fertility treatments improved the soil quality of RMS.
Abbreviations: EC, electrical conductivity • e.c.d., equivalent cylindrical diameter • FC, field capacity water content • FL1, no fertilizer or (0-0-0) • FL2, 112-25-46 kg NPK ha–1 • FL3, 224-49-92 kg NPK ha–1 • I, cumulative infiltration in 2.5 h • ic, water infiltration rate at 2.5 h • i5, water infiltration rate at 5 min • JCS, Jackson County Experimental site • Ks, saturated hydraulic conductivity • LSD, least significant differences • MWD, mean weight diameter of aggregate • RMS, reclaimed minesoil • SMCC, soil moisture characteristic curves • StP, storage pore • SOC, soil organic carbon • TC, total carbon concentration • TrP, transmission pore • UMS, undisturbed soil (unmined) • VCS, Vinton County Experimental site • WSA, water-stable aggregation • b, bulk density • 
0, antecedent soil water content
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Mining and related activities lead to severe loss of SOC mainly because of the topsoil loss, mechanical mixing of A horizon with B and C horizons during removal or material handling and increased rate of mineralization, erosion, and leaching from exposed topsoil. Restoration of disturbed mine soil can improve soil quality, enhance biomass productivity and increase SOC concentration (Lal et al., 1998a). Relatively large organic matter returns along with fertilizer additions and application of lime to raise soil pH above 5.5, can stimulate soil biological activities, enhance aeration, increase macroporosity, and improve aggregation (Schjønning et al., 1994; Haynes and Naidu, 1998; Shukla et al., 2003).
Soil structure and water storage and transmission characteristics are influenced by morphological and physical properties of soils (Barnhisel and Hower, 1997). Compacted reclaimed soil and spoil lack a continuous macropore network, which impedes root development and aeration, and decreases water retention and transmission (Indorante et al., 1981). Earlier studies on soil water transmission properties include measurement of soil moisture characteristic curves (SMCC) and unsaturated hydraulic conductivity and Ks on loose soils; and short duration water infiltration tests in field and long duration on repacked columns (Smith et al., 1971; Pedersen et al., 1980). Some of these studies were conducted on reclaimed soil alone (Chong et al., 1986; Underwood and Smeck, 2002), others compared soil development in reclaimed and unmined sites for b, Ks, soil water retention, and water infiltration rate (Pedersen et al., 1980; Gorman and Sencindiver, 1999; Barnhisel and Gray, 2000; Thomas et al., 2001). Some studies also assessed physical characteristics and water movement through spoil profiles (Rogowski and Jacoby, 1979; Ward et al., 1983; Skousen et al., 1998).
A slow water infiltration rate is reported from newly RMSs mainly due to the compaction and sorting during the reclamation process (Chong and Cowsert, 1997; Harms and Chanasyk, 2000; Guebert and Gardner, 2001). Data on water infiltration, sorptivity, movement, redistribution, and storage within the soil profile are important (Chong et al., 1986) to identifying the best management practices for forage, grain, and/or timber production on RMSs. Therefore, there is a need to evaluate effects of reclamation on water transmission properties of RMSs.
Soils are complex and dynamic systems, the rooting depth and nutrient requirements are often site-specific functions of climate, land use, and management options. The goal is to reconstruct the reclaimed site in a manner that maximizes the rate of soil improvement over time (Jansen, 1981). Such goals warrant site-specific investigations designed to study temporal changes in soil properties after reclamation (Barnhisel and Hower, 1997). Few studies have compared physical properties of the RMS with those of the undisturbed state (Smith et al., 1971; Potter et al., 1988). Further, there are not enough data on aggregation and water transmission properties (e.g., infiltration rate, water retention and redistribution, Ks).
This study was conducted at two unique Ohio surface mine sites that: (i) are among the oldest reclaimed to modern standards, (ii) allow for study of the effect of post reclamation fertility management on mine soil redevelopment, and (iii) permit comparisons with nearby native soils typical of those at sites before mining. The objectives of this study were to: (i) determine the soil quality improvement in RMS and compare it with the UMS, and (ii) assess the sink capacity of RMS to sequester SOC. Soil sampling and analyses were based on the hypothesis that reclamation activities and subsequent fertilization management lead to (i) soil development and formation of an A horizon, and (ii) improvement in soil structural and water transmission characteristics through increases in SOC.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The mine soil was classified as Fairpoint (loamy-skeletal, mixed, active, nonacid, mesic Typic Udorthents) in JCS and as Bethesda (loamy-skeletal, mixed, active, acid, mesic Typic Udorthents) in VCS. Development of a CB horizon between 1981 and 2001 in the RMS at JCS resulted in the soil being reclassified as a Typic Eutrudep. Since development of a Bw horizon (1981–2001) in the RMS at VCS, the soil has been reclassified as a Dystric Eutrudept (Underwood and Smeck, 2002). A nearby UMS at the JCS is classified as Omulga silt loam (fine-silty, mixed, mesic Typic Fragiudalfs), and a similar UMS at the VCS as Wharton silt loam (fine-silty, mixed, mesic Ultic Hapludalfs). Both typify the UMSs at minesites before disturbance (Kerr, 1985).
Average annual precipitation for the study area is 1090 mm with 530 to 580 mm occurring during the growing season between May and September. The average annual temperature is 11°C and the number of frost-free days ranges from 160 to 180. Underwood and Sutton (1992) established forage fertility plots in the spring of 1979 to assess the potential for forage and hay production at these two locations (Fig. 1). Soil fertility experiments were superimposed on existing forage stands at both sites in 1979 with four replications and nine N-P-K treatment combinations. The experiments at both JCS and VCS were continued for 16 yr from 1979 to 1994. After 1994, no fertilizer was applied to these plots. For this study, soil measurements were made in October 2001 in the RMS plots where three N-P-K treatment combinations were applied annually between 1979 and 1994: (i) no fertilizer or 0-0-0 kg ha–1 NPK or FL1, (ii) 112-25-46 kg ha–1 NPK or FL2, and 224-50-92 kg ha–1 NPK or FL3. Four locations were identified in the Year 2001, in each of the nearby UMS and three fertility plots in the RMS (RMSFL1, RMSFL2, and RMSFL3) in both counties, for measuring soil physical and water transmission properties and obtaining bulk and core soil samples (Fig. 1).
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b was measured by the core method (Blake and Hartge, 1986) and corrected for gravel content (Lal, 1979). Bulk soil samples were air-dried, and 50 g of aggregates between 5 and 8 mm were separated for determining water-stable aggregates (WSAs) and MWD by the wet sieving technique (Yoder, 1936; Youker and McGuinness, 1957). Remaining soil was sieved through a 2-mm sieve, and 50 g of the sieved soil was used for particle-size analysis by the hydrometer method (Gee and Bauder, 1986).
About 10 g of sieved soil (<2 mm) was very finely ground, passed through a 0.5-mm sieve, and about 1 g of the fine sample was used for determination of total C (TC) concentrations by the dry combustion method (Nelson and Sommers, 1986). The method was calibrated using atropine (C17H23NO3; 70.56% C and 4.84% N). Soil pH was close to 7 for both sites, and SOC for a specific layer of thickness (d) was calculated as the product of b, d, and TC (Lal et al., 1998b).
Water infiltration rate was measured at each of the sampling locations at JCS and VCS on the soil surface using a double ring infiltrometer with a 27-cm diameter outer ring and a 15-cm diameter inner ring (Bouwer, 1986). Grass at each location was trimmed and infiltration tests were conducted for 2.5 h for both JCS and VCS. The test site was covered with a plastic sheet after these tests to minimize evaporation losses. Soil moisture content was determined gravimetrically before the start (0) and 24 h after the infiltration test (field capacity water content [FC]). Infiltration rate after 5 min (i5), equilibrium infiltration rate after 2.5 h (ic), and cumulative infiltration after 2.5 h (I) were calculated from recorded infiltration-time data. The Ks was measured on soil cores by the constant head method (Klute and Dirkson, 1986). The SMCC were determined on intact soil cores for 1-, 3-, and 6-kPa suctions using the tension table (Leamer and Shaw, 1941), and for 10-, 30-, 100-, and 300-kPa suctions using the pressure plate apparatus (Klute, 1986). In terms of their functions in relation to plant growth, pores of equivalent cylindrical diameter (e.c.d.) >50 µm are described as transmission pore (TrP), those between 0.5 and 50 µm as storage pore (StP), and those <0.5 µm as residual pore (Greenland, 1977). Since we did not measure moisture content at 0.5-µm e.c.d., we assumed that all pores between 0.2- and 50-µm diameter are StPs. The EC and pH were measured on soil pastes (1:1) (<2 mm) using a hand held conductivity meter and pH electrode (Mclean, 1982; Rhoades, 1982).
Statistical Analysis
The ANOVA was computed using the randomized block design of the Statistical Analysis System (SAS Institute, 1989) for tests of all soil physical, chemical, and water transmission parameters for the 0- to 10-cm depth from four treatments (UMS, RMSFL1, RMSFL2, RMSFL3) and the 10- to 20-cm depth for three treatments in RMS (FL1, FL2, FL3) separately for both sites. Significant interactions (P 
0.05) and the least significant differences (LSD) for mean separation were calculated by comparing reclamation activities within site (treatment x replicate), fertility treatment within site (treatment x replicate).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b also did not differ among three soil fertility treatments in the JCS for either depth but was in the order RMSFL3 = RMSFL1 < RMSFL2 for the 0- to 10-cm depth in VCS (P < 0.05).
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b, WSA, MWD, EC, and pH were low (<14%) and infiltration rates, and Ks were high (31–155%) (Tables 1 and 3). The SMCCs showed that CV for moisture content at a given matric potential was in the order RMSFL2 > RMSFL1 > RMSFL3 (from 23–18%) for JCS and RMSFL2 > RMSFL3 > RMSFL1 for VCS (from 31–10%) (Fig. 2 and 3). The total dry biomass from the fertility plots in RMS for Year 2002 was also statistically similar for both sites (1.37–1.42 Mg ha–1 for RMSFL3 and FL1 for JCS, and 0.86–1.42 Mg ha–1 for RMSFL1 and FL3, respectively; P < 0.05), which was due to the substantial growth of legumes in RMSFL1 and RMSFL2. No significant differences in soil physical properties observed within fertility treatments RMS were probably due to (i) growth of good pasture cover across all fertility treatments, which aided in WSA by altering freeze-thaw and/or dry-wet cycles, (ii) increase in water holding capacity and water infiltration into the soil via root channels, and (iii) discontinuation of soil fertility treatments after 1994, during the 8 yr before these studies.
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b and SOC determined in 1981 and 2001 showed b declined by 9% for the JCS and 5% for the VCS, and SOC increased two-fold for both sites over a 20-yr period (Tables 5 and 6). Soil organic C from the 0- to 10-cm layer for RMS increased from 14.2 Mg ha–1 in 1981 to 28.7 Mg ha–1 in 2001 for the JCS, and from 15.1 to 30.2 Mg ha–1 for the VCS (Tables 5 and 6), slightly more than a two-fold increase over a 20-yr period. Akala and Lal (2001) reported a three-fold increase in SOC from 10.2 to 29.6 Mg ha–1 for the 0- to 10-cm depth over a 25-yr period in the southeastern Ohio for age chronosequence of RMSs under continuous grass. The rate of SOC sequestration is reported to be a function of time, climate, antecedent soil properties, and vegetation and post mining management (Schulze and Stitt, 1995; Merrill et al., 1998). Since the JCS and VCS were under similar climatic, vegetation, and management conditions, SOC has not yet reached the equilibrium level for either of the two sites. The highest SOC of 65.9 Mg ha–1 was obtained for the UMS at the VCS, which was in continuous grass but now has tree-bush cover since 1978 (Table 5).
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Clay concentration decreased over the 20-yr period (1981–2001) for both depths for RMS at the JCS and for the 0- to 10-cm depth for the VCS (Table 6; Underwood and Smeck, 2002). For the VCS, mean clay concentration decreased over the past 20-yr period for the 0- to 10-cm depth only (Tables 2 and 6). A recognizable A horizon can develop in a relatively short period of time in RMS (Daniels and Amos, 1981; Haering et al., 1993). For JCS, soil structure evolved from weak medium subangular blocky to weak very fine subangular blocky in the 0- to 10-cm layer. For VCS, soil structure was from strong medium platy to medium fine granular in the 0- to 10-cm layer. The consistence of Ap horizon improved from firm to friable for both sites. Underwood and Smeck (2002) also reported increases in root density in the Ap horizon. These changes along with the decrease in soil b, increase in SOC and aggregation are in agreement to our hypothesis that reclamation activities lead to soil development and the formation of an A horizon.
Soil Properties for Reclaimed Minesoils and Unmined Soils
According to USDA classification, soil texture was silt loam for UMS at both sites. For JCS, sand and clay concentrations were similar between UMS and the RMS (P < 0.05; Table 1). Bulk density was similar in both UMS and RMS (P < 0.05; Tables 1). The WSA and MWD were higher for UMS than RMS (P < 0.05; Table 1). More aggregation in UMS was largely because it was undisturbed and under continuous grass cover. However, i5, ic, and I were similar for UMS and RMS (P < 0.05; Table 1). Similar values of i5, ic, and I were due to the higher antecedent water content in UMS than RMS before the infiltration tests. Soil moisture characteristic curves also showed that CV for water release at a given matric potential was smallest or soil was relatively homogeneous for UMS at both sites (Fig. 2 and 3). Water lost by StPs was also higher for UMS than RMS (P < 0.05) and was in accord with the higher WSA and FC for UMS. Total soil C concentrations were similar between UMS and RMS, indicative of the likely effect of fertilization on increases in TC concentration (P < 0.05; Tables 1). The EC did not differ between UMS and RMS but pH was lower in UMS than RMS (P < 0.05; Table 1). The higher pH for the RMS than UMS was due to the application of lime during reclamation. The pH for the RMS and UMS was >6 and was favorable for the growth and sustenance of grass cover. Overall, soil properties have improved in the last 25 yr since reclamation, which is evident from the now similar b, I, and SOC concentrations between UMS and RMS.
For VCS, mean sand concentrations did not differ between the UMS and RMS but the clay concentrations did (P < 0.05; Table 3). The b varied in the order RMSFL2 > RMSFL1 = RMSFL3 = UMS (P < 0.05). The WSA and MWD were in the order UMS > RMS (P < 0.05). The i5, ic, and I were higher for the UMS than RMSFL1 and RMSFL2 (P < 0.05). The average volume of TrP varied as UMS > RMSFL3 (P < 0.05; Table 4), however, the Ks, FC, and volume of StP were similar among the UMS and RMS (P < 0.05; Table 1 and 4). Significant differences were observed for 0 between UMS and RMSFL1 and RMSFL3 (P < 0.05; Table 3). The EC was in the order UMS > RMSFL2 = RMSFL1 (P < 0.05; Tables 2) but pH remained similar (P < 0.05). The TC concentrations were the highest for the UMS (P < 0.05; Table 3) and were in the order UMS > RMSFL2 = RMSFL1 = RMSFL3 (Table 5). The similar values of volumes of StPs, Ks, and pH for UMS and RMS are indicative of soil quality improvement in reclaimed site. However, in terms of water storage within the soil pores, soil quality in reclaimed plots has the possibility of further improvements in the form of increases in water-stable aggregation, which was identified as the most dominant soil quality indicator for both the sites by Shukla et al. (2004).
A comparison between RMS and UMS for JCS showed that the silt plus clay concentrations and TC concentrations were lower and sand concentration higher in the RMS, which showed less particle cohesion for aggregation in RMS than UMS (Shaver et al., 2002; Shukla et al., 2003). The UMS had the highest potential for particle cohesion, and consequently the highest WSA (Solomon et al., 2002). The TC concentration for UMS was higher in the VCS than in the JCS probably because the experimental plots for UMS treatment in the VCS were under continuous grass and tree-bush cover.
Soil organic C was highest for UMS at the VCS (65.9 Mg ha–1), and was about twice as much as that for RMS at JCS or VCS (<37 Mg ha–1 for both sites). The values of ic and I in the UMS and RMS for VCS are consistent with the changes in soil structure, reduction in b, and increase in the WSA, MWD, and SOC concentration (Shaver et al., 2002; Shukla et al., 2003). The high moisture content in the transmission and StPs for both RMS sites for the 0- to 10-cm depth is indicative of improvement in soil structure, pore continuity and porosity by fertilizer application (Schjønning et al., 1994). The increase in total biomass by fertilizer application improved soil structure, decreased b, and increased WSA and water infiltration at both JCS and VCS. Our second hypothesis that reclamation improves soil structure and water transmission properties was thus proven correct.
Even 25 yr after reclamation, mean WSA and MWD were slightly higher for the UMS than the RMS for both JCS and VCS. Potter et al. (1988) also reported substantial differences in soil physical and hydraulic properties of RMS and UMS in North Dakota 11 yr after reclamation. However, infiltration rate, TC concentrations, and volumes of TrP were similar between UMS and RMS, which clearly indicated that reclamation with topsoil and subsequent fertilizer application over time improved soil structure and water transmission properties. The success of these sites to provide practical information and advance scientific knowledge of mine soil development is attributed to: (i) continuity in site maintenance for more than 25 yr, (ii) availability of baseline data on soil properties and forage biomass, and (iii) availability of undisturbed reference sites for comparative assessment of temporal change in soil quality.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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b and increase in SOC concentration, WSA and infiltration in the RMS are indicative of the positive effects of fertilizer application on improvement in soil aggregation, structure, and water transmission properties. Reclamation with topsoil and fertilizer application doubled the SOC concentration in the 0- to 10-cm layer for both sites between 1981 and 2001, and there still remains unfilled C sink capacity in both RMSs. Improvement in quality of RMS has implication to economic welfare because of the impact on production of crops and pasture, and environment quality because of increase in C sequestration in soil and biota. The study also advances scientific knowledge with regard to the processes of soil quality enhancement in general, but SOC accretion and soil aggregation in particular. |
ACKNOWLEDGMENTS |
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Received for publication April 11, 2003.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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