Nutrient Management Research Database

http://ucanr.edu/sites/Nutrient_Management_Solutions/files/212718.pdf

Limited soil nitrogen (N) availability is a common problem in organic vegetable production that often necessitates in-season fertilization. The rate of net nitrogen mineralization (N_min) from four organic fertilizers (seabird guano, hydrolyzed fish powder, feather meal, and blood meal) containing between 11.7% and 15.8% N was compared in a laboratory incubation. The fertilizers were mixed with soil from a field under organic management and incubated aerobically at constant moisture at 10, 15, 20, and 25 °C. N_min was determined on samples extracted after 1, 2, 4, and 8 weeks. Rapid N_min was observed from all fertilizers at all temperatures; within 2 weeks between 47% and 60% of organic N had been mineralized. Temperature had only modest effects, with 8-week N_min averaging 56% and 66% across fertilizers at 10 and 25 °C, respectively. Across temperatures, 8-week N_min averaged 60%, 61%, 62%, and 66% for feather meal, seabird guano, fish powder, and blood meal, respectively. Cost per unit of available N (mineralized N + initial inorganic N) varied widely among fertilizers, with feather meal the least and fish powder the most expensive.

The objective of this work was to assess the rate of N mineralization from commonly used high-N organic fertilizers over a range of soil temperatures.  To achieve this, a laboratory incubation experiment was conducted, using samples of blood meal, feather meal, pelletized seabird guano and hydrolyzed fish powder mixed with soil that had been under organic vegetable production.  Soil temperatures were chosen to represent the range of temperatures typically in the coastal valleys of central California.  Samples were analyzed after 1,2,4, and 8 weeks of incubation for mineral N concentration, with any increase representing N mineralized from the organic fertilizers.  

The organic fertilizers assessed had total N concentrations ranging between 11.7% and 15.8%.  Fish powder showed rapid N mineralization after just 1 week at all temperatures, while the other fertilizers showed similar N mineralization at higher temperatures, but had significantly lower N mineralization at lower temperatures.  The authors conclude that high-N organic fertilizers can effectively supply in-season N, as shown by the rapid mineralization of all fertilizers tested with the first 2 weeks of incubation.  However, while N availability was similar among all fertilizers tested, cost was generally higher than mined sources of N, and varied considerably, making high-organic fertilizers an option that would likely be used sparingly.