1. Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, University of Kassel, Steinstraße 19, 37213 Witzenhausen, Germany
2. Royal Gardens and Farms, Royal Court Affairs, Sultanate Oman
3. Soil Biology and Plant Nutrition, University of Kassel, Nordbahnhofstraße 1a, 37213 Witzenhausen, Germany