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  • Steffens, Markus  (6)
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  • 1
    Language: English
    In: Soil & Tillage Research, 2009, Vol.104(2), pp.299-310
    Description: Overgrazing has led to severe degradation and desertification of semi-arid grasslands in Northern China over the last decades. Despite the fact that vegetation is often heterogeneously distributed in semi-arid steppes, little attention has been drawn to the effect of grazing on the spatial distribution of soil properties. We determined the spatial pattern of soil organic carbon (SOC), total nitrogen (N ), total sulphur (S ), bulk density (BD), pH, Ah thickness, and carbon isotope ratios (δ C) at two continuously grazed (CG) and two ungrazed (UG79 = fenced and excluded from grazing in 1979) sites in and dominated steppe ecosystems in Inner Mongolia, Northern China. Topsoils (0–4 cm) were sampled at each site using a large grid (120 m × 150 m) with 100 sampling points and a small plot (2 m × 2 m) with 40 points. Geostatistics were applied to elucidate the spatial distribution both at field (120 m × 150 m grid) and plant (2 m × 2 m plot) scale. Concentrations and stocks of SOC, N , S were significantly lower and BD significantly higher at both CG sites. At the field scale, semivariograms of these parameters showed a heterogeneous distribution at UG79 sites and a more homogeneous distribution at CG sites, whereas nugget to sill ratios indicated a high small-scale variability. At the plant scale, semivariances of all investigated parameters were one order of magnitude higher at UG79 sites than at CG sites. The heterogeneous pattern of topsoil properties at UG79 sites can be attributed to a mosaic of vegetation patches separated by bare soil. Ranges of autocorrelation were almost congruent with spatial expansions of grass tussocks and shrubs at both steppe types. At CG sites, consumption of biomass by sheep and hoof action removed vegetation patches and led to a homogenization of chemical and physical soil properties. We propose that the spatial distribution of topsoil properties at the plant scale (〈2 m) could be used as an indicator for degradation in semi-arid grasslands. Our results further show that the maintenance of heterogeneous vegetation and associated topsoil structures is essential for the accumulation of SOM in semi-arid grassland ecosystems.
    Keywords: Semi-Arid Grassland ; Steppe Degradation ; Overgrazing ; Spatial Homogenization ; Soil Organic Matter ; Agriculture
    ISSN: 0167-1987
    E-ISSN: 1879-3444
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  • 2
    In: Global Change Biology, October 2015, Vol.21(10), pp.3836-3845
    Description: Organic carbon () sequestration in degraded semi‐arid environments by improved soil management is assumed to contribute substantially to climate change mitigation. However, information about the soil organic carbon () sequestration potential in steppe soils and their current saturation status remains unknown. In this study, we estimated the storage capacity of semi‐arid grassland soils on the basis of remote, natural steppe fragments in northern China. Based on the maximum saturation of silt and clay particles 〈20 μm, sequestration potentials of degraded steppe soils (grazing land, arable land, eroded areas) were estimated. The analysis of natural grassland soils revealed a strong linear regression between the proportion of the fine fraction and its content, confirming the importance of silt and clay particles for stabilization in steppe soils. This relationship was similar to derived regressions in temperate and tropical soils but on a lower level, probably due to a lower C input and different clay mineralogy. In relation to the estimated storage capacity, degraded steppe soils showed a high saturation of 78–85% despite massive losses due to unsustainable land use. As a result, the potential of degraded grassland soils to sequester additional was generally low. This can be related to a relatively high contribution of labile , which is preferentially lost in the course of soil degradation. Moreover, wind erosion leads to substantial loss of silt and clay particles and consequently results in a direct loss of the ability to stabilize additional . Our findings indicate that the loss in semi‐arid environments induced by intensive land use is largely irreversible. Observed increases after improved land management mainly result in an accumulation of labile prone to land use/climate changes and therefore cannot be regarded as contribution to long‐term sequestration.
    Keywords: Climate Change ; Fine Fraction ; Soil Organic Carbon ; Soil Texture ; Steppe Soils
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 3
    Language: English
    In: Plant and Soil, 2011, Vol.340(1), pp.35-58
    Description: Semiarid steppe ecosystems account for large terrestrial areas and are considered as large carbon (C) sinks. However, fundamental information on topsoil sensitivity to grazing is lacking across different spatial scales including the effects of topography. Our interdisciplinary approach considering soil chemical, physical, and vegetation properties included investigations on pit scale (square-metre scale), plot scale (hectare scale), and the scale of a landscape section (several hectares). Five different sites, representing a grazing intensity gradient, ranging from a long-term grazing exclosure to a heavily grazed site were used. On the pit scale, data about aggregate size distribution, quantity of different soil organic carbon (SOC) pools, SOC mineralisation, hydraulic conductivity and shear strength was available for topsoil samples from representative soil profiles. Spatial variability of topographical parameters, topsoil texture, bulk density, SOC, water repellency, and vegetation cover was analysed on the basis of regular, orthogonal grids in differently grazed treatments by using two different grid sizes on the plot scale and landscape section. On the pit scale, intensive grazing clearly decreased soil aggregation and the amount of fresh, litter-like particulate organic matter (POM). The weak aggregation in combination with animal trampling led to an enhanced mineralisation of SOC, higher topsoil bulk densities, lower infiltration rates, and subsequently to a higher risk of soil erosion. On the plot scale, the effects of soil structure disruption due to grazing are enhanced by the degradation of vegetation patches and resulted in a texture-controlled wettability of the soil surface. In contrast, topsoils of grazing exclosures were characterised by advantageous mechanical topsoil characteristics and SOC-controlled wettability due to higher POM contents. A combined geostatistical and General Linear Model approach identified topography as the fundamental factor creating the spatial distribution of texture fractions and related soil parameters on the scale of a landscape section. Grazing strongly interfered with the topography-controlled particle relocation processes in the landscape and showed strongest effects on the aboveground biomass production and biomass-related soil properties like SOC stocks. We conclude that interdisciplinary multi-scale analyses are essential (i) to differentiate between topography- and grazing-controlled spatial patterns of topsoil and vegetation properties, and (ii) to identify the main grazing-sensitive processes on small scales that are interacting with the spatial distribution and relocation processes on larger scales.
    Keywords: Steppe soils ; Soil organic matter fractions ; Organic carbon mineralisation ; Wind erosion ; Texture ; Vegetation cover ; Shear strength ; Hydraulic conductivity ; Water repellency ; Anisotropy
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    Language: English
    In: Biology and Fertility of Soils, 2012, Vol.48(3), pp.305-313
    Description: Soil labile organic carbon (C) oxidation drives the flux of carbon dioxide (CO 2 ) between soils and the atmosphere. However, the impact of grazing management and the contribution soil aggregate size classes (ASCs) to labile organic C from grassland soils is unclear. We evaluated the effects of grazing intensity and soil ASC on the soil labile organic C, including CO 2 production, microbial biomass C, and dissolved organic C and nitrogen (N) mineralization in topsoils (0–10 cm) in Inner Mongolia, Northern China. Soil samples were separated into ASCs of 0–630 μm [fine ASC (fASC)], 630–2000 μm [medium ASC (mASC)] and 〉2000 μm [coarse ASC (cASC)]. The results showed that heavy grazing (HG) and continuous grazing (CG) increased soil labile organic C significantly compared to an ungrazed site since 1999 (UG99) and an ungrazed site since 1979 (UG79). For winter grazing site (WG), no significant differences were found. CO 2 production was highest in cASC, while lowest in fASC. Microbial biomass C and dissolved organic C showed the highest values in mASC and were significantly lower in fASC. Grazing increased N mineralization in bulk soils, while it exhibited complex effects in the three ASCs. The results suggest that the rate of C mineralization was related to the rate of N accumulation. To reduce CO 2 emission and nutrient loss, and to improve soil quality and productivity, a grazing system with moderate intensity is suggested.
    Keywords: Soil organic carbon ; Microbial biomass carbon ; Dissolved organic carbon ; Semiarid grassland ; Inner Mongolia
    ISSN: 0178-2762
    E-ISSN: 1432-0789
    Source: Springer Science & Business Media B.V.
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  • 5
    Language: English
    In: Biology and Fertility of Soils, 4/2012, Vol.48(3), pp.305-313
    Description: Soil labile organic carbon (C) oxidation drives the flux of carbon dioxide (CO sub(2)) between soils and the atmosphere. However, the impact of grazing management and the contribution soil aggregate size classes (ASCs) to labile organic C from grassland soils is unclear. We evaluated the effects of grazing intensity and soil ASC on the soil labile organic C, including CO sub(2) production, microbial biomass C, and dissolved organic C and nitrogen (N) mineralization in topsoils (0-10 cm) in Inner Mongolia, Northern China. Soil samples were separated into ASCs of 0-630 mu m [fine ASC (fASC)], 630-2000 mu m [medium ASC (mASC)] and 〉2000 mu m [coarse ASC (cASC)]. The results showed that heavy grazing (HG) and continuous grazing (CG) increased soil labile organic C significantly compared to an ungrazed site since 1999 (UG99) and an ungrazed site since 1979 (UG79). For winter grazing site (WG), no significant differences were found. CO sub(2) production was highest in cASC, while lowest in fASC. Microbial biomass C and dissolved organic C showed the highest values in mASC and were significantly lower in fASC. Grazing increased N mineralization in bulk soils, while it exhibited complex effects in the three ASCs. The results suggest that the rate of C mineralization was related to the rate of N accumulation. To reduce CO sub(2) emission and nutrient loss, and to improve soil quality and productivity, a grazing system with moderate intensity is suggested.
    Keywords: Soil ; Grasslands ; Carbon ; Grazing ; Oxidation ; Soils (Organic) ; Biomass ; Mineralization ; Carbon Dioxide ; Atmosphere ; Nutrient Loss ; Nitrogen ; Ecosystem and Ecology Studies;
    ISSN: 0178-2762
    E-ISSN: 1432-0789
    Source: Springer (via CrossRef)
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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, June 2012, Vol.175(3), pp.434-442
    Description: The assessment of grassland degradation due to overgrazing is a global challenge in semiarid environments. In particular, investigations of beginning steppe degradation after a change or intensification of the land use are needed in order to detect and adjust detrimental land‐use management rapidly and thus prevent severe damages in these sensitive ecosystems. A controlled‐grazing experiment was established in Inner Mongolia (China) in 2005 that included ungrazed (UG) and heavily grazed plots with grazing intensities of 4.5 (HG4.5) and 7.5 (HG7.5) sheep per hectare. Several soil and vegetation parameters were investigated at all sites before the start of the experiment. Topsoil samples were analyzed for soil organic C (SOC), total N (N), total S (S), and bulk density (BD). As vegetation parameters, aboveground net primary productivity (ANPP), tiller density (TD), and leaf‐area index (LAI) were determined. After 3 y of the grazing experiment, BD increased and SOC, N, S, ANPP, and LAI significantly decreased with increasing grazing intensity. These sensitive parameters can be regarded as early‐warning indicators for degradation of semiarid grasslands. Vegetation parameters were, however, more sensitive not only to grazing but also to temporal variation of precipitation between 2006 and 2008. Contrary, soil parameters were primarily affected by grazing and resistant against climatic variations. The assessment of starting conditions in the study area and the application of defined grazing intensities is essential for the investigation of short‐term degradation in semiarid environments.
    Keywords: Steppe ; Desertification ; Soil Organic Carbon Soc ; Overgrazing ; Inner Mongolia
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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