Information depth of elements affects accuracy of parallel pXRF in situ measurements of soils.

Though not litigable in most European countries, portable X-ray fluorescence spectrometers (pXRF) provide cost- and time-effective as well as prompt information about hot spots of inorganic soil contaminants. The quality of aqua regia analysis of contaminants can be approximated by a thorough sample preparation, i.e., homogenization, grinding, and sieving of the examined soil before pXRF measurement is carried out. However, elaborate sample preparation causes a trade-off in terms of the desired straightforwardness of the pXRF method. For a first assessment of the in situ accuracy of pXRF measurements, two equal pXRF devices were used in parallel to determine the contents of As, Cu, Fe, Mn, Pb, Rb, Sr, Zn, and Zr of 9 identical points of a riparian soil profile. Maximum measurement values were not restricted to one pXRF device, but changed from element to element. Pearson correlation coefficients of the parallel measurements varied between 0.07 (Cu) and 0.80 (Zn), reflecting small-scale heterogeneity of the soil constituents as well as element-specific interferences. For each element, overall deviations between measurement parallels were expressed as the root-mean-square error (RMSE) and contrasted against the element-specific information depth in soil, i.e., the depth interval, from which the received spectral signals originate. From this, a gradual relation could be derived: The greater the information depth, the more stable the measured element value turns out. This context should be taken into account, when interpreting contents of elements with small atomic numbers.

Carbon sequestration potential of soils in southeast Germany derived from stable soil organic carbon saturation.

Sequestration of atmospheric carbon (C) in soils through improved management of forest and agricultural land is considered to have high potential for global CO2 mitigation. However, the potential of soils to sequester soil organic carbon (SOC) in a stable form, which is limited by the stabilization of SOC against microbial mineralization, is largely unknown. In this study, we estimated the C sequestration potential of soils in southeast Germany by calculating the potential SOC saturation of silt and clay particles according to Hassink [Plant and Soil 191 (1997) 77] on the basis of 516 soil profiles. The determination of the current SOC content of silt and clay fractions for major soil units and land uses allowed an estimation of the C saturation deficit corresponding to the long-term C sequestration potential. The results showed that cropland soils have a low level of C saturation of around 50% and could store considerable amounts of additional SOC. A relatively high C sequestration potential was also determined for grassland soils. In contrast, forest soils had a low C sequestration potential as they were almost C saturated. A high proportion of sites with a high degree of apparent oversaturation revealed that in acidic, coarse-textured soils the relation to silt and clay is not suitable to estimate the stable C saturation. A strong correlation of the C saturation deficit with temperature and precipitation allowed a spatial estimation of the C sequestration potential for Bavaria. In total, about 395 Mt CO2 -equivalents could theoretically be stored in A horizons of cultivated soils - four times the annual emission of greenhouse gases in Bavaria. Although achieving the entire estimated C storage capacity is unrealistic, improved management of cultivated land could contribute significantly to CO2 mitigation. Moreover, increasing SOC stocks have additional benefits with respect to enhanced soil fertility and agricultural productivity.

Projected loss of soil organic carbon in temperate agricultural soils in the 21(st) century: effects of climate change and carbon input trends.

Climate change and stagnating crop yields may cause a decline of SOC stocks in agricultural soils leading to considerable CO2 emissions and reduced agricultural productivity. Regional model-based SOC projections are needed to evaluate these potential risks. In this study, we simulated the future SOC development in cropland and grassland soils of Bavaria in the 21(st) century. Soils from 51 study sites representing the most important soil classes of Central Europe were fractionated and derived SOC pools were used to initialize the RothC soil carbon model. For each site, long-term C inputs were determined using the C allocation method. Model runs were performed for three different C input scenarios as a realistic range of projected yield development. Our modelling approach revealed substantial SOC decreases of 11-16% under an expected mean temperature increase of 3.3 °C assuming unchanged C inputs. For the scenario of 20% reduced C inputs, agricultural SOC stocks are projected to decline by 19-24%. Remarkably, even the optimistic scenario of 20% increased C inputs led to SOC decreases of 3-8%. Projected SOC changes largely differed among investigated soil classes. Our results indicated that C inputs have to increase by 29% to maintain present SOC stocks in agricultural soils.