Phosphor- und Kalium-Bilanzen über 35 Jahre DOK-Versuch & geschätzte K-Nachlieferungsraten auf einem Lössboden

Summary

We calculated a phosphorus (P) and potassium (K) balance for the DOK-trial (Therwil, Switzerland) for a 35-years cropping period. In the DOK-trial, three cropping systems (D: biodynamic, O: bioorganic and K: conventional) are maintained on both a full (2) and a halved (1) fertilization level. Additionally, a treatment with no fertilization (N) and mineral fertilization (M; since 1985) are included. Balance inputs included fertilization, deposition, nutrients inputs by seeds, while in the outputs removal of nutrients by harvested plant material and leaching was considered. For P, the balance was positive for treatment M and treatment O2, but negative for the other treatments. The K-balance was positive only for treatment M, while treatments D2, O2 and K2 showed a slightly negative K-balance. In general, extensively maintained treatments on the halved fertilization level as well as treatment N show a negative P and K-Balance. Due to relatively constant K-concentrations and K-removal by crops in treatment N for the last 3 cropping periods (7 years each) we estimated a supply potential of K from loess soil of approximately 50 kg/ha * yr.