Nitrification Rate Depends on Nitrogen Fertilizer Source in Root-Zones for Bioregenerative Life-Support

Salt Lake Community College Westpointe Campus, Salt Lake City, UT

Nitrification helps recycle nitrogen (N) in closed root-zones with multiple N inputs. We studied nitrification rates in peat moss soilless media adjusted to pH 6.5 to 7 and watered with nutrient solutions containing 9 mM N from ammonium nitrate, ammonium, nitrate, urea, or microbial biomass (lysed cells of the N-fixing bacteria Azotobacter vinelandii). We leached the media with nutrient solution every week for 150 days and measured the pH, electrical conductivity, and nitrate concentration. We measured ammonium in the peat moss at the end of the study using a potassium chloride extraction and quantified total N by combustion. Nitrification had a lag time of two to three weeks followed by rapid conversion in the succeeding weeks. The mass balance recovery of N as nitrate was highest in the nitrate treatment (89% ± 9%) and lowest in the urea treatment (73% ± 13%). Nitrification is beneficial in soilless media and can help recycle N in bioregenerative life-support systems.