Crop response of leek on fertilizer N from raw and composted chicken manure in organic horticulture

Organic chicken manure as a by-product of organic meat and egg production has to be destined to fields with a certified organic production. Chicken manure is a nutrient-rich, fast acting organic fertilizer. A high application rate may cause salt stress for a young crop. Stricter P-supply legislative standards will strongly limit the application rate in the near future. Involving chicken manure in a mixture for composting or just mixing it with compost results in a product with a different nature and nutrient composition. Fertilizer N availability was assessed for a set of raw and ‘composted’ chicken manure products and the resulting N dynamics in soil and crop N response were examined. The field trial had a completely randomized block design with four replicates and leek (Allium porrum) as a test crop. Mineral N stock in the soil profile and plant N uptake were assessed. N balances were calculated to express N release from soil organic matter. Low N availability was observed from pure compost products. High fertilizer N availability directly after application of raw chicken manure products clearly caused a priming effect, i.e. an additional N release from soil organic matter. Higher fertilizer N availability affected N uptake and crop quality. However, it did not result in a substantial yield increase. N release from soil organic matter clearly was a major source of plant available N in this organic cropping system. Differences in soil fertility between blocks highly affected crop N uptake and yield potential.