Soil development on loess substrate in central Germany — results of a long‐term trial on soil formation§

In 1948, a model soil formation trial was started in Halle/Saale by Schmalfuß. Loess nearly free of soil organic matter (SOM) was used as substrate and the soil formation has been studied in dependence on the level of mineral P and N fertilization. The trial consists of 48 glazed clay cylinders (∅︁ 40 cm × 100 cm), which are open at the bottom. The cylinders are embedded in the ground and stand on a layer of gravel. The trial is divided in a section with constant P and graduated N application and a section with constant N and graduated P application respectively. In the first 30 years, yields increased strongest in the highest NP fertilizer treatment compared with the no‐N or no‐P fertilizer treatment. Afterwards yields in the different fertilization treatments remained nearly constant on the reached levels. Actually the mean shoot dry matter per year is 2.5 times higher in the highest fertilizer treatment as compared to the no‐N fertilizer treatment. The C_org content in the topsoil increased over 49 years in the highest fertilized treatment from 0.18% at the beginning of the trial to 1.94%. Compared to the treatments without N or P fertilization this corresponded, however, only to a 1.2 fold increase. With higher levels of fertilizer application, humus accumulation and biological activity increased relatively faster than the C_org content in the topsoil. Soil organic matter improved the nutrient availability (increase of cation exchange capacity, mobile P fractions). It is assumed that decalcification and the decrease in the C/N ratio will continue. The lower C_org and N_org contents and the lower cation exchange capacity in comparison with soils developed in‐situ near to the parent loess material suggest a still ongoing soil formation process in the trial.