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Soil microbial respiration as a tool to assess post mine

reclamationR. L. Haney a; L. R. Hossner b; E. B. Haney c

a USDA-ARS, Temple, Texas, USAb Texas A&M University, College Station, Texas, USAc Surface, Mining and Reclamation Division, Railroad Commission of Texas, Austin,

Texas, USA

First Published on: 06 July 2007To cite this Article: Haney, R. L., Hossner, L. R. and Haney, E. B. (2007) 'Soil

microbial respiration as a tool to assess post mine reclamation', International Journal

of Mining, Reclamation and Environment, 22:1, 48 - 59

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Soil microbial respiration as a tool to assesspost mine reclamation

R. L. HANEY*{, L. R. HOSSNER{ and E. B. HANEYx

{USDA-ARS, Temple, Texas 76502, USA{Texas A&M University, College Station, Texas, USA

xSurface, Mining and Reclamation Division, Railroad Commission of Texas,Austin, Texas 78711-2967, USA

An evaluation of soil quality, which integrates biological, chemical and physical

processes, would be beneficial to regulators as well as mining companies when

making reclamation decisions. Coal mining regulations require that industry

perform soil sampling and submit laboratory results in order to determine pre-

mine and reclaimed soil quality. A rapid and accurate biological soil quality

method, such as one-day CO2 (1-day CO2) analysis, can be used to determine soil

microbial activity which is related to the soils’ ability to sustain nutrient cycling.

Our objective in this study was to compare native and reclaimed soils from

surface-mine operations in order to assess the effectiveness of the 1-day CO2method as a tool for determining biological soil quality. Soil samples were taken

from sites that visually had poor and well-vegetated reclaimed areas of a surface-

mine operation as well as an undisturbed native site. Chemical, physical and

biological indicators were compared to 1-day CO2 analysis for microbial activity.

Results indicate that the biological soil quality indicators as summarized by

1-day CO2 analysis are a more sensitive indicator of soil health on the reclaimed

soils tested than chemical analysis alone. One-day CO2 analysis can be a useful

additional tool for regulators and mining companies when assessing the soils

ability to sustain plant growth and evaluate reclamation success.

Keywords: Soil; Microbial activity; Mineralization; Native; Reclamation

1. Introduction

Coal Mining Regulations require that industry perform soil sampling and submit laboratory

results in order to determine: (i) the quality of pre-mine soil (baseline); (ii) overburden quality for

selective handling of topsoil and subsoil substitution; (iii) initial post-mine soil quality after mining

and re-grade; and (iv) soil quality during the extended responsibility period (ERP). The ERP is a

period in which an area of land is monitored for successful re-vegetation after the last year of

*Corresponding author. Email: [email protected]

International Journal of Mining, Reclamation and EnvironmentVol. 22, No. 1, March 2008, 48 – 59

International Journal of Mining, Reclamation and EnvironmentISSN 1748-0930 print/ISSN 1748-0949 online 2008 Taylor & Francis

http://www.tandf.co.uk/journalsDOI: 10.1080/17480930701414584


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augmented seeding, fertilizing, irrigation, or other work, excluding the normal husbandry

practices followed in that county by persons with the same land use on land that was not mined.

Soil quality is determined during the ERP in order to confirm the soil’s capability of sustaining

vegetation and to meet the requirements for bond release after reclamation.

Good soil quality indicators should encompass ecosystem processes; integrate soil physical,chemical and biological properties; and be sensitive to variations in management and climate

(Franzluebbers et al . 2000). Soil quality has many factors that impact it; however, soil microbial

activity plays a large part in determining the potential of soil to sustain nutrient cycling, which is

critical to soil quality. Soil-testing parameters currently in use by mining companies may not

provide the most comprehensive data with which to make findings regarding soil quality and

reclamation success. The list of parameters currently used to estimate reclaimed soil quality is

extensive; including acid-base accounting (ABA), soil pH, metals, texture, and N, P and K; yet

fails to account for biogeochemical processes. In addition, the indicators currently used to assess

soil quality can be economically cumbersome, take extensive time to perform and be subject to

interferences in analysis and interpretation. Enumerating a few critical indicators of soil quality,

which integrate biological, chemical and physical processes, would be beneficial to the regulators

as well as mining companies when making reclamation decisions. A rapid and accurate biological

method will determine the microbial portion of soil quality and the soils’ ability to sustain nutrient

cycling.

Soil microbial biomass (SMB) and microbial activity are important biological properties in soil

quality assessment since they relate strongly with other biological, physical and chemical soil

properties such as aggregate stability, water retention, nutrient supply, pH buffering, and cation

and anion exchange capacity (Haney 1997). Microbial populations respond to changes in the soil-

chemical environment such as temperature, acidity, nutrient deficiencies, and water stress.

Measuring SMB and microbial activity serves as a useful indicator of the soils capability to sustain

plant growth.

Carbon dioxide evolution has been used as an indicator of the relative fertility of various soils for

about 80 years (Gainey 1919, Corbet 1934). Carbon dioxide is released by microbial respiration and

the amount of CO2 evolved is directly related to soil microbial activity. Several methods have been

proposed to measure SMB and microbial activity (CO2 evolution), including chloroform-

fumigation extraction, chloroform-fumigation incubation and substrate-induced respiration. The

disadvantages to these methods include expensive analytical equipment, variations in extraction

efficiency due to physical and chemical properties, and since they are chemical-based they do not

represent natural conditions. Incubation studies are more natural than chemical extractions, but

take 14 – 21 days to complete, which is too extensive (a.k.a. expensive) for routine soil testing.

Recent studies have shown that the evolution of CO2 in 1 day after rewetting dried soil was directlycorrelated with SMBC and N, 24-day C and N mineralization, basal soil respiration, microbial

activity under varying flora, and yield from agricultural soils of varying pH and type (Franzluebbers

et al . 2000). Laboratory drying and rewetting tends to produce a uniform release of C and N and

mimics drying/rewetting processes that occur under field conditions (Birch 1958, 1959, 1960).

Furthermore, short-term C mineralization (1 – 3 days) of soil after drying (408C or 608C) followed

by rewetting correlates strongly with longer-term (100-day) CO2 evolution and SMBC

(Franzluebbers et al . 1996, Haney et al . 1999). The method of CO2 evolution is simple, inexpensive,

rapid and accurate for assessing microbial activity. With refinement, the 1-day CO2 method may

prove to be a valuable tool for determining biological soil quality in native and reclaimed soils.

Our objective in this study was to analyse native and reclaimed soils from surface-mineoperations in order to assess the effectiveness of the 1-day CO2 method as a tool for determining

biological soil quality. Results of 1-day CO2 analysis were compared to tests commonly used by

Soil microbial respiration as a tool to assess post mine reclamation 49


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regulatory agencies to assess soil quality and other biological soil quality tests. These tests were

used to assess soil quality in reclaimed mine soils by comparing results to native soils and other

chemical/physical soil properties.

2. Materials and methods

Soil samples were taken from the Palafox and Rachal lignite mines. The mines are located in

Webb County, Texas. Webb County is located in south Texas adjacent to the Rio Grande in the

South Texas Plains major land resource area (figure 1). Temperatures range from an average high

Figure 1. Map displaying the Palafox and Rachal permit boundaries and soil series.

50 R. L. Haney et al.


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of 398C in July to an average low of 178C in January. Rainfall averages 20 inches per year, and the

growing season lasts for 314 days. Webb County’s scrub country is utilized primarily for cattle

ranching and wildlife habitat.

The Palafox clay loam comprises approximately 31% of the pre-mine soil at the Palafox Mine.

The Rachal Mine has about 12% of the Jimenez-Quemado complex (JQD), which is a shallow soilthat resides on side slopes of hills and ridges. The JQD soils are gravelly sandy clay loam on the

surface- nine inches, below which is a cemented caliche that extends to a depth of 64 cm. The

Catarina Clay composes 19% of the Rachal Mine. It is a saline soil that is in broad and narrow

valleys. The surface layer is comprised of clay about 35 cm thick, while the subsoil is saline clay

about 35 – 123 cm thick.

Mining has ceased at both mines. Sub-bituminous coal was mined using diesel and electric-

powered draglines. Topsoil was removed and stockpiled during mining, then redistributed over

mixed overburden. Fertilizer is applied and disked into the regraded topsoil after final re-grade.

Buffelgrass (Pennisetum ciliare) is planted at the rate of about 1.8 kg of pure live seed per acre.

Buffelgrass is commonly grown in South Texas and Northern Mexico due to its drought tolerance,

forage production, and adaptability to the semiarid region. It has a medium salinity tolerance and

is adapted to coarse, fine, and medium textured soils. Buffelgrass requires a pH between 6.0 and

8.5 for optimum growth. The post-mine land use at the Rachal and Palafox Mines is pastureland.

Soil sampling was conducted from reclaimed pastureland areas from the Palafox and Rachal

mines. The samples from the reclaimed areas were labelled as follows: Rachal-reclaimed with poor

vegetation is R1 P, R2 P, and good vegetation-R1 G R2 G, and R native is the undisturbed sample.

Palafox reclaimed but with poor vegetation P1 P, and good vegetation P1 G and P native is the

undisturbed sample. Soil samples taken from both mines were reclaimed roughly 20 years ago.

The reclaimed soil samples that were taken from poorly and well-vegetated areas were similar in

intended vegetation, slope, reclamation age and soil characteristics for comparison.

Approximately 20 soil samples were randomly taken from each site to a depth of 15 cm and

composited. The soil samples were dried at 408C and thoroughly mixed. Three replicates were

drawn from the composite samples. Samples were analysed for pH; electrical conductivity (EC);

plant-available N and P; soluble Na, Ca and Mg; sodium adsorption ratio (SAR); texture; soil

organic matter % (SOM); soil microbial biomass carbon (SMBC); 30-d N mineralization; and

microbial activity (30-d CO2 analysis).

One-day CO2 was determined by drying the soil in a forced draft oven at 408C. Samples were

dried for 24 hours, and sieved through a 5-mm sieve. Soil samples were thoroughly mixed and

weighed (40 g) into 50-ml plastic cups or glass beakers. Water content was adjusted to 50% water-

filled pore space. The wetted soil was placed into a 1-l canning jar with a vial containing 10 ml of

1 M KOH in the jar to trap evolved CO2, the jar sealed with an airtight lid, and placed in anincubator at 258C. Traps of KOH containing evolved CO2 were titrated with standardized 0.5 M

HCl after precipitation of carbonates with an excess of 3 N BaCl2 to the phenolphthalein endpoint

(Anderson and Domsch 1978).

The methods used for analysis are outlined in table 1. Statistical analysis was completed using a

SPSS statistical program (Systat 1994 – 1999).

3. Results and discussion

The pH values for all samples tested range from 8.5 to 8.7. The two native soil samples have pH

values of 8.5 and 8.6. Electrical conductivity values are below the suggested maximum of 4.0 mmhos/cm as outlined in the Surface Mining and Reclamation Division’s (SMRD) Technical

Release SA-2 (Railroad Commission of Texas 1988). Texas A&M University salinity



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recommendations, included in SA-2, show that there is a slight salinity hazard at EC values of

4.0 mmhos/cm. The native soil samples had EC values greater than the Rachal and Palafox

reclaimed soil samples, indicating that the reclaimed soils were not adversely affected by salt

content compared to native soils (figure 2).

Table 1. Methods used for the determination of soil quality in collected minesoils.

Analysis Method Reference

pH 1:1 soil-to-water ratio Black; 1965

Electrical Conductivity (EC) 1:1 soil-to-water ratio

Soluble Na, Ca, and Mg 1:1 soil-to-water ratio

Sodium Adsorption Ratio (SAR) 1:1 soil-to-water ratio USDA

Texture Hydrometer method EPA

Soil Microbial Biomass Carbon (SMBC) Fumigation-Incubation Voroney and Paul, 1984

Soil Organic Matter % (SOM) Modified Mebius Nelson and Sommers, 1982

N Mineralization Incubation Franzluebbers et al . 2000

C mineralization 30-d CO2 incubation Franzluebbers et al . 1996

Figure 2. Electrical conductivity (EC), pH, and sodium adsorption ratio (SAR) values for samplesfrom Rachal (R) and Palafox (P) mines. P, poor vegetation; G, good vegetation. Error bars

indicate one standard deviation.



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All samples have acceptable texture classes according to technical release SA-2. Texture classes

include loam, sandy loam and sandy clay loam. Sand values range from 43% to 72%, silt values

range from 12% to 37%, and clay values range from 16% to 28% (table 2). Three of the four

poorly vegetated sites have sand values greater than 55% and silt values less than 20%. There is no

general trend present concerning clay percent values for poorly- or well-vegetated areas.The results from the chemical tests used to test soil fertility indicate no trend between soils with

poor and good vegetation (figure 3). Nitrate-N, P, and NH4 levels for all samples, including the

native samples, were low, indicating that soil fertility is not the primary cause of the difference in

vegetation (figure 3). However, the biological tests (1-day CO2, SMBC, 30-day CO2, 30-day

N-min) reveal that there is a significant difference in biological soil quality between soil samples

from sparsely and densely vegetated areas (figures 4 – 6).

Table 2. Texture values for soil samples from the mine.

Sample ID % Sand % Silt % Clay Class

Rachal 1 P 68 14 18 SL

Rachal 2 P 56 16 28 SCL

Rachal 1 G 50 28 22 L

Rachal 2 G 47 35 18 L

Rachal native 52 32 16 SL

Palafox 1 P 63 19 18 SL

Palafox 1 G 72 12 16 SL

Palafox native 43 37 20 L

Figure 3. Inorganic N and P levels for reclaimed mine soils from the Rachal (R) and Palafox (P)

mines. P, poor vegetation; G, good vegetation. Error bars indicate one standard deviation.



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There is a significant difference between percent SOM in soils with poor and good vegetation

(figure 4). The reclaimed soils with good vegetation have higher SOM values than those that are

poorly vegetated or native soils. This indicates that increased organic matter content either

contributes to or is a result of increased vegetative biomass. The results also indicate that

reclaimed soil quality may be considered improved if compared to a native reference area. While

SOM is a good indicator of the amount of organic C present, it does not give an indication of thequality of the organic C present (resistant or readily mineralizable). The microbial activity (1-day

CO2) test is a better test for organic C quality. For example, if two soils have equal organic matter

Figure 4. Percent soil organic matter and 1-day CO2 from Rachal (R) and Palafox (P) mines. P,

poor vegetation; G, good vegetation. Error bars indicate one standard deviation.



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(organic C) but one has higher CO2 respiration, we can deduce that the quality of organic C is

more easily degraded with the soil with increased respiration.

Soil microbial biomass C (SMBC) is an estimate of carbon mass contained in microbial cells

(figure 5). Each of the poorly vegetated soil samples had a significantly lower SMBC content

when compared to soils that were well vegetated. The native soil samples have SMBC values

that are lower or not significantly different than the poorly-vegetated samples and the well-

vegetated sample from the Rachal 1 site. Soil microbial biomass C in the well-vegetated Rachal2 reclaimed soil was roughly twice as high as that of the native soil. This indicates that the

reclaimed soil exceeds the native soil values in biological soil quality. These results indicate that

Figure 5. Soil microbial biomass C and 30-day CO2 evolution from Rachal (R) and Palafox (P)mines. P, poor vegetation; G, good vegetation. Error bars indicate one standard deviation.



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the biological quality indicators were more sensitive in detecting soil differences in soil quality

than the physical and chemical analysis. Further, since biological systems (microbial activity) are

the driving force in nutrient cycling, it is logical to monitor these systems in addition to abiotic

systems (Doran and Parkin 1994). Many methods can be used to estimate of SMBC; however,

each method is either time consuming, requires the use of chloroform or uses a stimulant suchas glucose. In addition, many commercial soil testing laboratories are not equipped to perform

these analyses. When mining companies have soil samples sent to soil testing labs to evaluate

reclamation success, it would be useful if a biological method was available that was

inexpensive, simple and rapid. While SMBC is an excellent method for determining biological

soil quality as the data indicates, SMBC may not be appropriate in commercial soil testing

situations.

Microbial activity as described by 30-d CO2 evolution follows a similar trend as SMBC results

and is well correlated to SMBC (table 3). Thirty-day CO2 shows greater differences between poor

Figure 6. Nitrogen mineralized after 30-day incubation from Rachal (R) and Palafox (P) mines. P,

poor vegetation; G, good vegetation. Error bars indicate one standard deviation.

Table 3. Correlation matrix and significance values for biological soil quality indicators.

1-day CO2

Soil microbial

biomass C 30-day CO2

30-day N

mineralization

r P value r P value r P value r P value

Soil organic matter 0.79 0.01 0.87 0.002 0.73 0.02 0.82 0.006

1 day CO2 0.93 0.0002 0.95 0.0001 0.92 0.0004

Soil microbial biomass C 0.90 0.001 0.96 0.00003

30-day CO2 0.90 0.0008



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and good vegetation than SMBC and appears to be sensitive to differences in vegetation (figure 5).

However, analysis for 30-d CO2 evolution requires incubation for 30 days, making this test

impractical for use in a soil-testing laboratory, regardless of its potential use as a biological soil-

quality indicator.

Figure 7. Relationships between 1-day CO2 and 30-day nitrogen mineralization and 1-day CO2and soil microbial biomass C for soil samples from the reclaimed and native soils.



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All five biological soil quality indicators were highly correlated with each other (table 3) and

each demonstrated the ability to statistically separate good from poor vegetation (figures 4 – 6).

One-day CO2 is highly correlated with the other 4 biological methods (table 3), particularly SMBC

and 30-day N mineralization (figure 7). One-day CO2 analysis encompasses a natural system

(drying and rewetting soil), is well correlated with longer-term CO2 incubations (30-day) andSMBC. Treatment differences are clearly separated (figure 4) and the test is highly correlated to

nutrient cycling as determined by 30-day N mineralization (figure 7). Measuring biological soil

quality using 1-day CO2 is useful whenever speed of analysis is important or if resources are

limited. In addition, this method integrates physical and chemical indices since soil microbes are

essentially a product of their environment, have an effect on aggregate stability and nutrient

cycling, and are affected by properties such as soil pH, clay content and salt content (Haney 1997).

Overall, soil microbial activity as measured by 1-day CO2 after drying and rewetting soil could

become an excellent indicator of reclamation progress. This procedure, in combination with soil

chemical and physical parameters, will give mining managers a useful tool that is rapid, accurate

and inexpensive to assess their strategies for soil reclamation.

4. Conclusions

The biological indicators used in this study revealed differences in reclaimed soils with varying

degrees of vegetative productivity that were not visible using chemical and physical analysis alone.

Chemical and physical tests did not reveal a significant difference between any of the soils

sampled. It would be difficult to identify any differences between the poorly and well-vegetated

sites without the use of the biological tests used in this experiment. In addition, it would be difficult

to identify the improved nature of the reclaimed soils tested during this study when compared to

native soil samples using chemical and physical tests alone. A more accurate assessment of mine

soil could be established using chemical analyses in conjunction with biological tests. These results

also indicate that soils, which are higher in SOM, SMBC, N-mineralization capability and CO2evolution, appear to be more suitable for plant growth. The results of this study indicate that

the reclaimed soils analysed have equal or superior biological soil quality as compared to the

native soil.

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