Organic vegetable farmers use a wide variety of nitrogen (N) fertilizers from commercial products (made from animal and seed meals) to manures and composts. These organic N sources must undergo mineralization and nitrification to become plant available inorganic N (microbial processes). How much and when nitrogen becomes available can be highly variable dependent on product characteristics and local weather conditions, and this subsequent N availability can greatly impact yield. The objective of this study was to determine nitrogen mineralization, head timing, and overall yield from seven different organic fertilizer treatments on fall broccoli (Brassica oleracea ‘Castle Dome’). Studies were conducted over two years at the UGA Durham Horticulture Farm on certified organic land and organic fertilizers (with the exception of the control) were applied to provide a rate of 134 kg N ha-1. Fertilizers ranged from processed animal meals to composts and fresh poultry litter. Nitrogen mineralization was measured using in-situ soil cores and ranged from 0 (immobilization) to 100% of the N applied. Significant N was observed from the soil only treatment which provided on average 100 kg N ha-1 over the growing season. In both years, overall higher yields were observed with blood meal and lowest yields were observed with compost/control treatments. Fertilizer type impacted the timing of heading and overall harvest windows.
