Abstract

LUDWIG, B., GEISSELER, D., MICHEL, K., JOERGENSEN, R.G., SCHULZ, E., MERBACH, I., RAUPP, J., RAUBER, R., HU, K., NIU, L., LIU, X.

Agron. Sust. Dev., 31:361-372 (2011)

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 Lauchstadt, Darmstadt) and tillage (Gottingen, 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 Lauchstadt 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 Gottingen and Quzhou indicated only small differences in crop yields. Reduced tillage in Gottingen 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.