Amount, Distribution and Driving Factors of Soil Organic Carbon and Nitrogen in Cropland and Grassland Soils of Southeast Germany (Bavaria). Wiesmeier, M., Hübner, R., Barthold, F., Spörlein, P., Geuß, U., Hangen, E., Reischl, A., Schilling, B., von Lützow, M., & Kögel-Knabner, I. 176:39–52.
Amount, Distribution and Driving Factors of Soil Organic Carbon and Nitrogen in Cropland and Grassland Soils of Southeast Germany (Bavaria) [link]Paper  doi  abstract   bibtex   
[Highlights] [::] Drivers and distribution of agricultural SOC and N stocks of Bavaria were analyzed. [::] SOC differences between cropland and grassland are related to subsoil C. [::] Soil moisture controls SOC and N, temperature/precipitation are of minor importance. [::] Cropland and grassland soils in Bavaria store 242 and 134 Mt SOC and 19 and 12 Mt N. [::] For C sequestration soil types and topography are more important than land use. [Abstract] Agricultural soils have a high potential for sequestration of atmospheric carbon due to their volume and several promising management options. However, there is a remarkable lack of information about the status quo of organic carbon in agricultural soils. In this study a comprehensive data set of 384 cropland soils and 333 grassland soils within the state of Bavaria in southeast Germany was analyzed in order to provide representative information on total amount, regional distribution and driving parameters of soil organic carbon (SOC) and nitrogen (N) in agricultural soils of central Europe. The results showed that grassland soils stored higher amounts of SOC (11.8 kg m-2) and N (0.92 kg m-2) than cropland soils (9.0 and 0.66 kg m-2, respectively) due to moisture-induced accumulation of soil organic matter (SOM) in B horizons. Surprisingly, no distinct differences were found for the A horizons since tillage led to a relocation of SOM with depth in cropland soils. Statistical analyses of driving factors for SOM storage revealed soil moisture, represented by the topographic wetness index (TWI), as the most important parameter for both cropland and grassland soils. Climate effects (mean annual temperature and precipitation) were of minor importance in agricultural soils because management options counteracted them to a certain extent, particularly in cropland soils. The distribution of SOC and N stocks within Bavaria based on agricultural regions confirmed the importance of soil moisture since the highest cropland SOC and N stocks were found for tertiary hills and loess regions, which exhibited large areas with potentially high soil moisture content in extant floodplains. Grassland soils showed the highest accumulation of SOC and N in the Alps and Pre-Alps as a result of low temperatures, high amounts of precipitation and high soil moisture content in areas of glacial denudation. Soil class was identified as a further driving parameter for SOC and N storage in cropland soils. In total, cropland and grassland soils in Bavaria store 242 and 134 Mt SOC as well as 19 and 12 Mt N down to a soil depth of 1 m or the parent material, respectively. [Excerpt: SOC and N stocks as driven by environmental parameters] The storage of total SOC and N in both cropland as well as grassland soils was primarily associated with soil moisture, indicated by a strong positive correlation with the TWI [...]. Large TWI values are usually found at lower areas of a landscape with large contributing areas and indicate increased likelihood of saturated conditions (Sorensen et al., 2006 and Grabs et al., 2009). The reduced mineralization of OM in groundwater soils in these areas is the most important factor for the accumulation of SOC and N stocks in agricultural soils of Bavaria. Total storage of SOC in agricultural soils of Baden-Württemberg was also mainly linked with reduced mineralization in soils with high soil moisture regimes (Neufeldt, 2005). This effect is not restricted to subsoils because SOC and N stocks from A horizons of cropland and grassland soils were also strongly controlled by TWI. One has to bear in mind that the TWI is not comparable to measured soil moisture but only indicates locations with potentially high water content in the soil due to the topographical position. Thus, extensive data for soil moisture derived from in situ measurements or microwave remote sensing ( Mulder et al., 2011) might considerably enhance the explained variance of the regression models. [...] [] [...] [] A further important parameter controlling the accumulation of SOC and N was climate. Remarkably, from the three climate-related parameters (mean annual temperature, annual precipitation, elevation) derived from the PCA, elevation accounted for higher variance than temperature and precipitation. This is probably related to the coarser spatial resolution of temperature and precipitation (1 km) compared with the accurate measurement of elevation at the sampling locations. [...] [] [...] [] Besides soil moisture and climate, the factor 'soil class' was identified for cropland soils to have a certain impact on SOC and N stocks. The question arises, if there is an inherent effect of soil class(es) on the accumulation of SOC and N or if the relationship between soil class and SOM is subject to intercorrelations with other environmental parameters that were not detected by the PCA. [...] [] [...] [Conclusions] Soil moisture was determined to be the most important driving factor for SOC and N storage for both cropland and grassland soils. Climate effects are less important in agricultural soils because they are balanced by management options to at least a certain amount. The regional distribution of agricultural SOC and N stocks within Bavaria highlights the importance of regions with large contributing areas such as floodplains, depressions and glacial basins for soil moisture-induced SOC storage. These areas are concentrated mainly in the tertiary hills and loess regions and to a lower amount in the region of Jurassic sediments and the northern Bavaria hill area where prevailing cropland soils store high amounts of SOC and N. We propose that these agricultural regions should be preferentially considered for maintaining substantial cropland SOC stocks in Bavaria. The (pre-)mountainous grassland areas, particularly the Alps and Pre-Alps, are also favourable for the storage of large amounts of SOM. A change of land use in these regions would strongly reduce SOC storage and should be prevented. For further improvement of the regression models for total SOM storage, high-resolution data for soil moisture derived from remote sensing as well as data on long-term C input, historical land use and soil texture should be incorporated. Since soil moisture as a decisive driving factor for SOM storage in agricultural soils varies at small spatial scales, a regionalization of SOC stocks using a digital soil mapping approach would substantially improve the detection of local hot spots of SOC and elucidate its controlling factors. We propose focusing on pedogenetic and topographical features of the landscape that are related to high soil moisture content for approaches to increase SOC stocks in agricultural soils of central Europe. The findings of this study indicate that higher SOC and N stocks in grassland soils compared with cropland soils are not primarily related to land use but can be mainly attributed to a soil moisture-induced accumulation of SOM in the subsoil. A detrimental effect of soil cultivation on SOM storage in the topsoil was detected only to a minor degree in cropland soils because a certain proportion of SOM was apparently relocated to depth in the course of tillage. We conclude that subsoils are of great importance for SOC storage in agricultural soils and recommend the inclusion of subsoils in agricultural SOC studies.
@article{wiesmeierAmountDistributionDriving2013,
  title = {Amount, Distribution and Driving Factors of Soil Organic Carbon and Nitrogen in Cropland and Grassland Soils of Southeast {{Germany}} ({{Bavaria}})},
  author = {Wiesmeier, Martin and Hübner, Rico and Barthold, Frauke and Spörlein, Peter and Geuß, Uwe and Hangen, Edzard and Reischl, Arthur and Schilling, Bernd and von Lützow, Margit and Kögel-Knabner, Ingrid},
  date = {2013-08},
  journaltitle = {Agriculture, Ecosystems \& Environment},
  volume = {176},
  pages = {39--52},
  issn = {0167-8809},
  doi = {10.1016/j.agee.2013.05.012},
  url = {https://doi.org/10.1016/j.agee.2013.05.012},
  abstract = {[Highlights]

[::] Drivers and distribution of agricultural SOC and N stocks of Bavaria were analyzed. [::] SOC differences between cropland and grassland are related to subsoil C. [::] Soil moisture controls SOC and N, temperature/precipitation are of minor importance. [::] Cropland and grassland soils in Bavaria store 242 and 134 Mt SOC and 19 and 12 Mt N. [::] For C sequestration soil types and topography are more important than land use.

[Abstract]

Agricultural soils have a high potential for sequestration of atmospheric carbon due to their volume and several promising management options. However, there is a remarkable lack of information about the status quo of organic carbon in agricultural soils. In this study a comprehensive data set of 384 cropland soils and 333 grassland soils within the state of Bavaria in southeast Germany was analyzed in order to provide representative information on total amount, regional distribution and driving parameters of soil organic carbon (SOC) and nitrogen (N) in agricultural soils of central Europe. The results showed that grassland soils stored higher amounts of SOC (11.8 kg m-2) and N (0.92 kg m-2) than cropland soils (9.0 and 0.66 kg m-2, respectively) due to moisture-induced accumulation of soil organic matter (SOM) in B horizons. Surprisingly, no distinct differences were found for the A horizons since tillage led to a relocation of SOM with depth in cropland soils. Statistical analyses of driving factors for SOM storage revealed soil moisture, represented by the topographic wetness index (TWI), as the most important parameter for both cropland and grassland soils. Climate effects (mean annual temperature and precipitation) were of minor importance in agricultural soils because management options counteracted them to a certain extent, particularly in cropland soils. The distribution of SOC and N stocks within Bavaria based on agricultural regions confirmed the importance of soil moisture since the highest cropland SOC and N stocks were found for tertiary hills and loess regions, which exhibited large areas with potentially high soil moisture content in extant floodplains. Grassland soils showed the highest accumulation of SOC and N in the Alps and Pre-Alps as a result of low temperatures, high amounts of precipitation and high soil moisture content in areas of glacial denudation. Soil class was identified as a further driving parameter for SOC and N storage in cropland soils. In total, cropland and grassland soils in Bavaria store 242 and 134 Mt SOC as well as 19 and 12 Mt N down to a soil depth of 1 m or the parent material, respectively.

[Excerpt: SOC and N stocks as driven by environmental parameters]

The storage of total SOC and N in both cropland as well as grassland soils was primarily associated with soil moisture, indicated by a strong positive correlation with the TWI [...]. Large TWI values are usually found at lower areas of a landscape with large contributing areas and indicate increased likelihood of saturated conditions (Sorensen et al., 2006 and Grabs et al., 2009). The reduced mineralization of OM in groundwater soils in these areas is the most important factor for the accumulation of SOC and N stocks in agricultural soils of Bavaria. Total storage of SOC in agricultural soils of Baden-Württemberg was also mainly linked with reduced mineralization in soils with high soil moisture regimes (Neufeldt, 2005). This effect is not restricted to subsoils because SOC and N stocks from A horizons of cropland and grassland soils were also strongly controlled by TWI. One has to bear in mind that the TWI is not comparable to measured soil moisture but only indicates locations with potentially high water content in the soil due to the topographical position. Thus, extensive data for soil moisture derived from in situ measurements or microwave remote sensing ( Mulder et al., 2011) might considerably enhance the explained variance of the regression models. [...]

[] [...]

[] A further important parameter controlling the accumulation of SOC and N was climate. Remarkably, from the three climate-related parameters (mean annual temperature, annual precipitation, elevation) derived from the PCA, elevation accounted for higher variance than temperature and precipitation. This is probably related to the coarser spatial resolution of temperature and precipitation (1 km) compared with the accurate measurement of elevation at the sampling locations. [...]

[] [...]

[] Besides soil moisture and climate, the factor 'soil class' was identified for cropland soils to have a certain impact on SOC and N stocks. The question arises, if there is an inherent effect of soil class(es) on the accumulation of SOC and N or if the relationship between soil class and SOM is subject to intercorrelations with other environmental parameters that were not detected by the PCA. [...]

[] [...]

[Conclusions]

Soil moisture was determined to be the most important driving factor for SOC and N storage for both cropland and grassland soils. Climate effects are less important in agricultural soils because they are balanced by management options to at least a certain amount. The regional distribution of agricultural SOC and N stocks within Bavaria highlights the importance of regions with large contributing areas such as floodplains, depressions and glacial basins for soil moisture-induced SOC storage. These areas are concentrated mainly in the tertiary hills and loess regions and to a lower amount in the region of Jurassic sediments and the northern Bavaria hill area where prevailing cropland soils store high amounts of SOC and N. We propose that these agricultural regions should be preferentially considered for maintaining substantial cropland SOC stocks in Bavaria. The (pre-)mountainous grassland areas, particularly the Alps and Pre-Alps, are also favourable for the storage of large amounts of SOM. A change of land use in these regions would strongly reduce SOC storage and should be prevented. For further improvement of the regression models for total SOM storage, high-resolution data for soil moisture derived from remote sensing as well as data on long-term C input, historical land use and soil texture should be incorporated. Since soil moisture as a decisive driving factor for SOM storage in agricultural soils varies at small spatial scales, a regionalization of SOC stocks using a digital soil mapping approach would substantially improve the detection of local hot spots of SOC and elucidate its controlling factors. We propose focusing on pedogenetic and topographical features of the landscape that are related to high soil moisture content for approaches to increase SOC stocks in agricultural soils of central Europe. The findings of this study indicate that higher SOC and N stocks in grassland soils compared with cropland soils are not primarily related to land use but can be mainly attributed to a soil moisture-induced accumulation of SOM in the subsoil. A detrimental effect of soil cultivation on SOM storage in the topsoil was detected only to a minor degree in cropland soils because a certain proportion of SOM was apparently relocated to depth in the course of tillage. We conclude that subsoils are of great importance for SOC storage in agricultural soils and recommend the inclusion of subsoils in agricultural SOC studies.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13930718,~to-add-doi-URL,agricultural-resources,crops,germany,grasslands,nitrogen,organic-carbon,soil-carbon,soil-resources,topographic-wetness-index,vegetation},
  options = {useprefix=true}
}
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