Charakterisierung und Eignung von organischen Handelsdüngemitteln für den Einsatz im ökologischen Landbau

One of the key issues in organic vegetable production in comparison to conventional production is the approach to soil and soil fertility, as is expressed in the regulations on permitted fertilizers and soil amendments. Vegetable crops are characterized by high nutrient contents and high production levels and consequently require high inputs of nutrients, mainly nitrogen and potassium. Furthermore, the cropping period of most vegetable crops is rather short in comparison to arable crops. The current fertilization strategy in practice is characterized by a base dressing of animal manure or compost, and top dressings that are applied throughout the growing season, using a variety of additional fertilizers like keratins (feather-, horn- and hair meal) or fertilizers from plant sources. This strategy can lead to high N and P surpluses and strong increase of soil P levels of fields. Vegetable crop growers can overcome the shortcomings either by expanding cropping of legume crops, or by reduction of base dressing of animal manures or composts simultaneously expanding the use of top dressings high in N and very low in P (e. g. keratins, vinasse), or by replacement of base dressings based on composted manures by approaches that keep N in the system (e. g. anaerobic digestion of N-rich feedstocks instead of composting)