通讯作者：
Christopher Just
通讯作者单位：
Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany
Highlights
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MAOM-C content was modeled for arable fields with different management.
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Organic fertilization, crop rotation, and soil texture define MAOM-C content.
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A POM-C/MAOM-C ratio indicator was developed and tested.
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This indicator contains information on MAOM-C saturation deficits.
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POM-C/MAOM-C ratio indicators might support climate mitigation strategies.
Abstract
Fig. 2. Mean OC, MAOM-C POM-C and the POM-C/MAOM-C ratio depicted for each experiment and treatment (no grassland, no Chernozems).
Fig. 3. Mean OC, MAOM-C, POM-C, and the POM-C/MAOM-C ratio depicted for each grassland and Chernozem.
Fig. 4. Boxplots depicting the distribution of OC, MAOM-C, POM-C, and the POM-C/MAOM-C ratio for control sites, organically fertilized sites, minerally fertilized sites, mixed fertilized sites, sites with multiple changes within the agronomic system, and grasslands in relation to soil texture. Each dot represents one treatment & site.
Fig. 5. Predicted vs. measured MAOM-C content of the calibration dataset for linear models with and without mixed effects using either two or three predictors as listed in Table 3.
Fig. 6. MAOM-C content in relation to the proportion of the fraction < 20 µm (%) of the respective soil. The left diagram contains all data, right diagram excludes grasslands and Chernozems. Dashed lines represent an estimated MAOM-C saturation area (Hassink and Whitmore, 1997, Six et al., 2002). Dot colors reflect the classification into the treatment categories control, control of grassland, grassland, organically fertilized, mineral or mixed fertilized experiments, and experiments with multiple systemic changes. Colored lines depict simple linear correlation of MAOM-C and the fraction < 20 µm (%) for the control soil (red), the managed soils (non-control) (green), and all soils using a 95th quantile regression model. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Measured POM-C vs. measured MAOM-C contribution for each experimental site in relation to POM-C/MAOM-C ratios of 0.1, 0.25, 0.5 and 1 (dashed lines). Each dot colour depicts a different experiment. Most experiments tend to have stable POM-C/MAOM-C ratios, others show distinct increase in the POM-C/MAOM-C ratio (e.g. red dots) indicating either MAOM-C saturation or hampered decomposition dynamics in the transfer of POM-C to MAOM-C. The dot size relate to amounts of organic fertilization (t C ha−1 a-1) where bigger dots indicate higher organic fertilization rates. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 8. MAOM-C sequestration potential (calculated with Six et al., 2002) vs. POM-C/MAOM-C ratio showing mostly logarithmic dependency. Exceptions (top left corner) meet the MAOM-C saturation potential with a low POM-C/MAOM-C ratio. The dashed line depicts a threshold at POM-C / MAOM-C ratio = 0.35 where data points above that ratio approximate the MAOM-C saturation line.
Conclusions
Based on a simple SOM fractionation method, we examined 25 long-term field experiments in Central Europe regarding POM-C and MAOM-C contents. We built cross-validated predictive MAOM-C models with decent goodness-of-fit using the soil texture (proportion of fraction < 20 µm), the total organic fertilization (t OC ha−1 a-1), and the below-ground OC input (t ha−1 a-1) derived by yields and carbon allocation coefficients. The model allows large-scale estimation of MAOM-C levels in commonly cropped farmlands. Thereby, we expect the difference in the intercept of linear regression of the control plots and the 95th quantile regression to be a rough approximation for management-induced MAOM-C differences. We estimate to have higher mean MAOM-C content of 4.1 mg g−1 due to the long-term adaption of improvements in organic fertilization and crop rotation management compared to not organically fertilized sites with the least diverse crop rotations. In a broader context, this corresponds to higher topsoil MAOM-C stocks of 1.38 – 1.84 t ha−1 in well-managed soils, which contributes to current climate change mitigation strategies. Therefore, it is important to identify poorly managed and, according to soil texture, inappropriately managed sites and to take action to reduce MAOM-C sequestration deficits of arable soils. In this context, we tested an indicator based on the POM-C/MAOM-C ratio. This indicator can be a valuable tool to investigate changes within the fractions respective to changes in the overall OC content of soils before and after management changes. Moreover, it might provide information on the MAOM-C saturation potentials of agricultural soils, where POM-C/MAOM-C ratios > 0.35 indicate approximation to MAOM-C saturated states. The POM-C / MAOM-C ratio indicator could be used as a guideline for agricultural management if its informative value can be verified in further studies and arable soils.
