Environ Monit Assess DOI 10.1007/s10661-014-3658-0
Changes in soil microbial biomass and aggregate stability under different land uses in the northeastern Turkey O. Kara & M. Baykara
Received: 30 April 2013 / Accepted: 21 January 2014 # Springer International Publishing Switzerland 2014
Abstract The characteristics of three neighboring soils from the NE of Turkey were evaluated in order to elucidate the effect of different land-use management on the soil aggregate stability and microbial biomass in Galyan-Atasu dam watershed. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard (agriculture), the second site is a forest dominated by mature coniferous trees, and the third site is grassland. Soil aggregate stability values for the 1–2-mm aggregates increased from forest (lowest) to agriculture (highest) in the current study. The percentage of clay was highest in agriculture soils with 33.57 %, and overall stability values increased according to soil clay content. The lower aggregate stability in the forest soils probably reflects the highly silty texture soils with 11.95 % compared to agriculture and grassland. However, in our study, there were no significant correlations between aggregate stability and organic C concentrations either in cultivated or forested soils. Aggregate stability depended more on the organic matter content when the organic matter content was greater than 50 or 60 mg g−1. Below that threshold, aggregate stability may be mainly related to clay content. Furthermore, the results confirmed that higher percentages of Cmic/Corg in agricultural soils are the result of more labile organic substrates maintained in the soil, allowing O. Kara (*) : M. Baykara Department of Forest Engineering, Faculty of Forestry, Karadeniz Technical University, 61080 Trabzon, Turkey e-mail: [email protected]
a higher microbial biomass C per unit of soil organic C. This work gives a better understanding of the relationships between land-use type and soil aggregation and allows to know the soil response to different types of management in humid environments. Keywords Aggregate stability . Land use . Microbial biomass . Soil texture
Introduction Understanding how land use influences soil aggregate stability and microbial ecology is important for the sustainable forestry and agricultural practices. Environmental degradation caused by inappropriate land-use management is a problem that has attracted attention in Turkey (Ozden et al. 2000). Almost 86 % of the land is suffering from some degree of erosion (Kara et al. 2010). Land-use patterns, specifically conversion of forest to agriculture, affect soil aggregation directly by destruction of the macro-aggregates and indirectly through changing chemical, physical, and biological factors, such as organic matter, soil moisture, pH, microbial biomass, etc. (Barto et al. 2010). Soils support critical processes such as hydrological and biochemical cycling, contain a wide array of organisms, and also provide a nutrient and hydrological reservoir, crucial both for below- and above-ground organism survival (Neary et al. 1999). Soil management affects the quantity and quality of soil nutrients as well as microbial biomass and respiration in soil (Yang et al. 2008; Dube
Environ Monit Assess
et al. 2009). Land-use change can modify soil C contents because of the interactions mediated by soil microorganisms (Dube et al. 2009). The microbial community includes a wide range of individual species that may respond very heterogeneously to changes in the environment. Microorganisms can lose their resilience to ecosystem disturbances and become no longer able to perform their normal processes of nutrient cycling and maintaining soil structure (Brady and Weil 1999). Many studies have found a significant correlation between microbial biomass and aggregate stability (Tisdall and Oades 1982; Sparling et al. 1992; Kandeler and Murer 1993). Soil microorganisms excrete enzymes responsible for mineralizing high molecular weight compounds and also release extra-cellular polysaccharides (Chenu 1993; Amézketa 1999; Baldrian et al. 2008) which bind soil particles, stabilizing the soil aggregates. Production of extra-cellular polysaccharides and other cellular debris by microorganisms helps in maintaining soil structure as well as soil health. No previous attempt has been made to examine relationships between soil aggregate stability and soil microbial biomass under different land-use patterns in northeastern Turkey, Trabzon. Therefore, the objective of this study was to assess the effects of microbial biomass and physicochemical characteristics of the soil on soil aggregation in relation to land use in GalyanAtasu dam watershed, located in northeastern Turkey, which is the main drinking water supply of Trabzon.
Materials and methods Study site The study site was located near the city of Trabzon in northeastern Turkey. Elevation is approximately 450 m, westerly aspect. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard which is an important commercially successful agricultural product of Turkey, the second site is a forest dominated by mature coniferous trees and oriental spruce (Picea orientalis L.), native to northeastern provinces in Turkey, and the third site is grassland which has been used for livestock grazing for over 50 years. These three study sites are located close to Atasu-Galyan Dam, under same ecological condition, such as climate, topography, soil type, bedrock, etc. The climate of this region is humid mesothermal, characterized by warm summers. Based on
climatological data from the past 35 years, the annual mean temperature of this province is 11.5 °C. The mean temperature of the hottest month, August, is 20.3 °C. The annual mean precipitation of this region is 1,111.7 mm, and the annual relative humidity is 72 %. The principal geological formation of the research area is basalt and dacite. Forest and agriculture soils were shallow, while grassland soil was moderately deep. The general characteristics of soils in all study areas were slightly acid and slightly alkaline, well drained, and have very strong soil horizons. Soil sampling This study was conducted with a completely randomized design. Soil samples were taken from 30 different points in each site (forest, agricultural, grassland) on 16 July 2012. The litter layer was removed before soil samples for microbial analyses were taken at a depth of 10 cm. All visible roots and coarse fragments (>2 mm) were removed. Soil samples were sieved with 2-mm sieves and stored at 4 °C until microbial analysis. Also, at each site, 30 soil cores (10×8 cm) were collected to determine the physical and chemical properties of the soil. A total of 180 soil samples were collected for physical, chemical, and microbial analyses. Physical and chemical properties of soils Soil cores were collected from the top soil (0–10-cm depth) of each site, total of 90 samples, oven dried at 105 °C for 24 h, and weighed to determine bulk density. Bulk density was calculated from mass and volume. Pore space was calculated from the bulk and particle density. The additional larger samples were collected from each soil profile to be used in the determination of particle size distribution, pH, CaCO3 content, particle density, soil moisture, and organic carbon. The following selected soil physical and chemical properties were determined by means of appropriate methods: soil particle size distribution by the hydrometer method, particle density by the pycnometer method, soil moisture content by the gravimetric method, pH in 1:2.5 (w/v) of soil/water suspension by pH-meter, soil organic matter by the Walkley-Black wet oxidation method, and CaCO3 content by the Scheibler calcimeter method (Rowell 1994). Samples for aggregate stability analysis were sieved using 1- and 2-mm sieves, of which the 1–2 mm aggregate fractions were used in the wet sieve method
Environ Monit Assess
Data analyses
(Eijkelkamp 2008). Aggregate stability was determined by the breakdown rate of the aggregates in water. A total of 4.0-g aggregates were moistened on 0.25-mm sieves. After 8 min of moistening, aggregates were sieved for 3 min in cups with distilled water. Subsequently, sieves were lifted, water percolated, and cups with dispersing solution (containing 2-g sodium hexametaphosphate L−1) replaced the distilled water. Aggregates were sieved for a second time in the dispersing solution until all material finer than the sieve diameter was being dissolved and only stones and organic material remained. The cups with distilled water and dispersing solution with dissolved soil were placed in an oven at 110 °C, as long as required to evaporate all the water.
This study was conducted with a completely randomized design. The effects of different land-use patterns on physical, chemical, and microbial characteristics of soil were analyzed by ANOVA, and mean separations were computed using Duncan’s multiple range test. Bivariate analysis was also performed with Pearson’s linear correlation between soil variables. Discriminant analysis (DA) is used to analyze the differences between two or more groups of multivariate data using one or more discriminant functions in order to maximally separate the identified groups. Therefore, DA was employed to find the difference between the land uses along with the soil variables.
Microbial biomass C (Cmic) Soil microbial biomass C (Cmic) was estimated by extracting 30-g oven-dried equivalents of field-moist mineral soil samples in 0.5 M K2SO4 (1:4 w/v) by the chloroform-fumigation-extraction method described by Brookes et al. (1985) and Vance et al. (1987). The organic C content of K2SO4 extract was determined after oxidation with 0.4 N K2Cr2O7 at 150 °C for 30 min, followed by back-titration with ferrous ammonium sulfate. Cmic was calculated from the difference in extractable organic C between fumigated and unfumigated soil samples as follows: biomass C=2.64 EC, where EC refers to the difference in extractable organic C between the fumigated and unfumigated treatments; 2.64 is the proportionality factor for biomass C released by fumigation extraction (Vance et al. 1987).
Table 1 Comparison of soil physical and chemical characteristics under different land-use patterns
Results and discussion Soil physical and chemical properties Similarities and differences in soil properties between forest, agriculture, and grassland land-use types are summarized in Table 1. Significant differences (P
Changes in soil microbial biomass and aggregate stability under different land uses in the northeastern Turkey O. Kara & M. Baykara
Received: 30 April 2013 / Accepted: 21 January 2014 # Springer International Publishing Switzerland 2014
Abstract The characteristics of three neighboring soils from the NE of Turkey were evaluated in order to elucidate the effect of different land-use management on the soil aggregate stability and microbial biomass in Galyan-Atasu dam watershed. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard (agriculture), the second site is a forest dominated by mature coniferous trees, and the third site is grassland. Soil aggregate stability values for the 1–2-mm aggregates increased from forest (lowest) to agriculture (highest) in the current study. The percentage of clay was highest in agriculture soils with 33.57 %, and overall stability values increased according to soil clay content. The lower aggregate stability in the forest soils probably reflects the highly silty texture soils with 11.95 % compared to agriculture and grassland. However, in our study, there were no significant correlations between aggregate stability and organic C concentrations either in cultivated or forested soils. Aggregate stability depended more on the organic matter content when the organic matter content was greater than 50 or 60 mg g−1. Below that threshold, aggregate stability may be mainly related to clay content. Furthermore, the results confirmed that higher percentages of Cmic/Corg in agricultural soils are the result of more labile organic substrates maintained in the soil, allowing O. Kara (*) : M. Baykara Department of Forest Engineering, Faculty of Forestry, Karadeniz Technical University, 61080 Trabzon, Turkey e-mail: [email protected]
a higher microbial biomass C per unit of soil organic C. This work gives a better understanding of the relationships between land-use type and soil aggregation and allows to know the soil response to different types of management in humid environments. Keywords Aggregate stability . Land use . Microbial biomass . Soil texture
Introduction Understanding how land use influences soil aggregate stability and microbial ecology is important for the sustainable forestry and agricultural practices. Environmental degradation caused by inappropriate land-use management is a problem that has attracted attention in Turkey (Ozden et al. 2000). Almost 86 % of the land is suffering from some degree of erosion (Kara et al. 2010). Land-use patterns, specifically conversion of forest to agriculture, affect soil aggregation directly by destruction of the macro-aggregates and indirectly through changing chemical, physical, and biological factors, such as organic matter, soil moisture, pH, microbial biomass, etc. (Barto et al. 2010). Soils support critical processes such as hydrological and biochemical cycling, contain a wide array of organisms, and also provide a nutrient and hydrological reservoir, crucial both for below- and above-ground organism survival (Neary et al. 1999). Soil management affects the quantity and quality of soil nutrients as well as microbial biomass and respiration in soil (Yang et al. 2008; Dube
Environ Monit Assess
et al. 2009). Land-use change can modify soil C contents because of the interactions mediated by soil microorganisms (Dube et al. 2009). The microbial community includes a wide range of individual species that may respond very heterogeneously to changes in the environment. Microorganisms can lose their resilience to ecosystem disturbances and become no longer able to perform their normal processes of nutrient cycling and maintaining soil structure (Brady and Weil 1999). Many studies have found a significant correlation between microbial biomass and aggregate stability (Tisdall and Oades 1982; Sparling et al. 1992; Kandeler and Murer 1993). Soil microorganisms excrete enzymes responsible for mineralizing high molecular weight compounds and also release extra-cellular polysaccharides (Chenu 1993; Amézketa 1999; Baldrian et al. 2008) which bind soil particles, stabilizing the soil aggregates. Production of extra-cellular polysaccharides and other cellular debris by microorganisms helps in maintaining soil structure as well as soil health. No previous attempt has been made to examine relationships between soil aggregate stability and soil microbial biomass under different land-use patterns in northeastern Turkey, Trabzon. Therefore, the objective of this study was to assess the effects of microbial biomass and physicochemical characteristics of the soil on soil aggregation in relation to land use in GalyanAtasu dam watershed, located in northeastern Turkey, which is the main drinking water supply of Trabzon.
Materials and methods Study site The study site was located near the city of Trabzon in northeastern Turkey. Elevation is approximately 450 m, westerly aspect. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard which is an important commercially successful agricultural product of Turkey, the second site is a forest dominated by mature coniferous trees and oriental spruce (Picea orientalis L.), native to northeastern provinces in Turkey, and the third site is grassland which has been used for livestock grazing for over 50 years. These three study sites are located close to Atasu-Galyan Dam, under same ecological condition, such as climate, topography, soil type, bedrock, etc. The climate of this region is humid mesothermal, characterized by warm summers. Based on
climatological data from the past 35 years, the annual mean temperature of this province is 11.5 °C. The mean temperature of the hottest month, August, is 20.3 °C. The annual mean precipitation of this region is 1,111.7 mm, and the annual relative humidity is 72 %. The principal geological formation of the research area is basalt and dacite. Forest and agriculture soils were shallow, while grassland soil was moderately deep. The general characteristics of soils in all study areas were slightly acid and slightly alkaline, well drained, and have very strong soil horizons. Soil sampling This study was conducted with a completely randomized design. Soil samples were taken from 30 different points in each site (forest, agricultural, grassland) on 16 July 2012. The litter layer was removed before soil samples for microbial analyses were taken at a depth of 10 cm. All visible roots and coarse fragments (>2 mm) were removed. Soil samples were sieved with 2-mm sieves and stored at 4 °C until microbial analysis. Also, at each site, 30 soil cores (10×8 cm) were collected to determine the physical and chemical properties of the soil. A total of 180 soil samples were collected for physical, chemical, and microbial analyses. Physical and chemical properties of soils Soil cores were collected from the top soil (0–10-cm depth) of each site, total of 90 samples, oven dried at 105 °C for 24 h, and weighed to determine bulk density. Bulk density was calculated from mass and volume. Pore space was calculated from the bulk and particle density. The additional larger samples were collected from each soil profile to be used in the determination of particle size distribution, pH, CaCO3 content, particle density, soil moisture, and organic carbon. The following selected soil physical and chemical properties were determined by means of appropriate methods: soil particle size distribution by the hydrometer method, particle density by the pycnometer method, soil moisture content by the gravimetric method, pH in 1:2.5 (w/v) of soil/water suspension by pH-meter, soil organic matter by the Walkley-Black wet oxidation method, and CaCO3 content by the Scheibler calcimeter method (Rowell 1994). Samples for aggregate stability analysis were sieved using 1- and 2-mm sieves, of which the 1–2 mm aggregate fractions were used in the wet sieve method
Environ Monit Assess
Data analyses
(Eijkelkamp 2008). Aggregate stability was determined by the breakdown rate of the aggregates in water. A total of 4.0-g aggregates were moistened on 0.25-mm sieves. After 8 min of moistening, aggregates were sieved for 3 min in cups with distilled water. Subsequently, sieves were lifted, water percolated, and cups with dispersing solution (containing 2-g sodium hexametaphosphate L−1) replaced the distilled water. Aggregates were sieved for a second time in the dispersing solution until all material finer than the sieve diameter was being dissolved and only stones and organic material remained. The cups with distilled water and dispersing solution with dissolved soil were placed in an oven at 110 °C, as long as required to evaporate all the water.
This study was conducted with a completely randomized design. The effects of different land-use patterns on physical, chemical, and microbial characteristics of soil were analyzed by ANOVA, and mean separations were computed using Duncan’s multiple range test. Bivariate analysis was also performed with Pearson’s linear correlation between soil variables. Discriminant analysis (DA) is used to analyze the differences between two or more groups of multivariate data using one or more discriminant functions in order to maximally separate the identified groups. Therefore, DA was employed to find the difference between the land uses along with the soil variables.
Microbial biomass C (Cmic) Soil microbial biomass C (Cmic) was estimated by extracting 30-g oven-dried equivalents of field-moist mineral soil samples in 0.5 M K2SO4 (1:4 w/v) by the chloroform-fumigation-extraction method described by Brookes et al. (1985) and Vance et al. (1987). The organic C content of K2SO4 extract was determined after oxidation with 0.4 N K2Cr2O7 at 150 °C for 30 min, followed by back-titration with ferrous ammonium sulfate. Cmic was calculated from the difference in extractable organic C between fumigated and unfumigated soil samples as follows: biomass C=2.64 EC, where EC refers to the difference in extractable organic C between the fumigated and unfumigated treatments; 2.64 is the proportionality factor for biomass C released by fumigation extraction (Vance et al. 1987).
Table 1 Comparison of soil physical and chemical characteristics under different land-use patterns
Results and discussion Soil physical and chemical properties Similarities and differences in soil properties between forest, agriculture, and grassland land-use types are summarized in Table 1. Significant differences (P
