In the Darmstadt long-term fertilization trial, the application of composted cattle farmyard manure without (CM) and with (CMBD) biodynamic preparations was compared to mineral fertilization with straw return (MIN). The present study was conducted to investigate the effects of spatial variability, especially of soil pH in these three treatments, on soil organic matter and soil microbial biomass (C, N, P, S), activity (basal CO 2 production and O 2 consumption), and fungal colonization (ergosterol). Soil pH was significantly lower in the MIN treatments than in the organic fertilizer treatments. In the MIN treatments, the contents of soil organic C and total N were also significantly lower (13% and 16%, respectively) than those of the organic fertilizer treatments. In addition, the total S content increased significantly in the order MIN < CM < CMBD. The microbial biomass C content was significantly lower (9%) in the MIN treatments than in the organic fertilizer treatments. Microbial biomass N and biomass P followed microbial biomass C, with a mean C/N ratio of 7.9 and a mean C/P ratio of 23. Neither the microbial biomass C to soil organic C ratio, the metabolic quotient qCO 2 , nor the respiratory quotient (mol CO 2 / mol O 2 ) revealed any clear differences between the MIN and organic fertilizer treatments. The mean microbial biomass S content was 50% and the mean ergosterol content was 40% higher in the MIN treatments compared to the organic fertilizer treatments. The increased presence of saprotrophic fungi in the MIN treatments was indicated by significantly increased ratios of ergosterol-to-microbial biomass C and the microbial biomass C/S ratio. Our results showed that complex interactions between the effects of fertilizer treatments and natural heterogeneity of soil pH existed for the majority of microbial biomass and activity indices.

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-The study of sustainable land use is complex and long-term experiments are required for a better understanding of the processes of carbon stabilization. Objectives were (i) to describe for four long-term experiments the effects of fertilization and soil management on crop yields and the dynamics of soil organic carbon (SOC) and total N, and (ii) to discuss the usefulness of models for a better understanding of the underlying processes. Data of soil organic carbon and total N of four long-term experiments in Germany and China which studied the effect of fertilization (Bad Lauchstädt, Darmstadt) and tillage (Göttingen, Quzhou) were evaluated and soil organic carbon fractionation was carried out. The Rothamsted Carbon Model was used for a description and prediction of soil organic carbon dynamics as affected by fertilization and tillage in Bad Lauchstädt and Quzhou. The type of fertilizer added at common rates -either mineral N or farmyard manure -affected the crop yields only slightly, with slightly lower yields after manure application compared with mineral N fertilization. For both fertilization trials, manure applications at common rates had beneficial effects on soil organic carbon stocks in the labile pool (turnover time estimated as <10 years) and to a greater extent in the intermediate pool (turnover time estimated to be in the range of 10 to 100 years). A comparison of the effects of conventional tillage, reduced tillage and no-tillage carried out in Göttingen and Quzhou indicated only small differences in crop yields. Reduced tillage in Göttingen resulted in an increased C storage in the surface soil and C was mainly located in the mineral-associated organic matter fraction and in water-stable macro-aggregates (>0.25 mm). For Quzhou, no-tillage and conventional tillage had similar effects on total C stocks, with a greater spatial variability in soil organic carbon stocks in the no-tillage plots. Modeling required site-specific calibrations for the stock of inert organic matter for each of the sites, indicating that not all carbon stabilization processes are included in the model and that application of a model to a new site may also need site-specific adjustments before it can be used for predictions. After site-specific calibration, however, model predictions for the remaining treatments were generally accurate for the fertilization and tillage trials, which emphasizes the importance of temperature, moisture, soil cover and clay content on the decomposition dynamics of soil organic carbon and the significance of amounts and quality of carbon inputs in the soil for maintaining or increasing soil organic carbon stocks in arable soils.soil organic matter / C dynamics / Rothamsted carbon model / tillage / fertilization / soil organic carbon (SOC)

Type and rate of fertilizers influence the level of soil organic carbon (C org ) and total nitrogen (N t ) markedly, but the effect on partitioning of C and N into different pools is open to question. Objectives were to investigate the impact of fertilizer type and rate on labile, intermediate and passive C and N pools in a sandy Cambisol at Darmstadt, Germany, after 27 years of different fertilization treatments. The six treatments were: straw incorporation plus application of mineral fertilizer (MSI) and application of farmyard manure (FYM) each at high (140-150 kg N ha −1 year −1 ), medium (100 kg N ha −1 year −1 ) and low (50-60 kg N ha −1 year −1 ) rates. Soil microbial biomass C (C mic ) and N (N mic ) and C and net N mineralization (266 days incubation at 10°C and 50% waterfilled pore space) were determined. Soils (0-25 cm) of MSI treatments had significantly (p≤0.05) lower C mic stocks (308-361 kg ha −1 ) than soils of FYM treatments (404-520 kg ha −1 ). Differences in N mic stocks were less pronounced. After 266 days, mineralized C (1130-1820 kg ha −1 ) and N (90-125 kg ha −1 ) had significantly increased with fertilizer rate. The application of an exponential two-pool model showed that very labile pools (turnover times: 17 and 9 days for C and N, respectively) were small (1.3-1.8% of C org and 0.5-1.0% of N t ) and not influenced by type or rate of fertilizer. Stocks of the modeled labile C and N pools (turnover times: 462 and 153 days for C and N, respectively) were not influenced by the type of fertilizer but depended significantly on the application rate and ranged from 7 to 13% of C org and from 4 to 5% of N t . In contrast, the size of the calculated intermediate C pool was greater for the FYM treatments, and depended significantly on the interaction of fertilizer type and rate. The intermediate N pool was unaffected by fertilizer type or rate. Passive C and N pools, as experimentally revealed by oxidation with disodium peroxodisulfate (Na 2 S 2 O 8 ), were independent of the treatments. Overall, labile and intermediate pools were affected differently by the fertilizer type and the application rate.

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