Recent evidence suggests abiotic reactions may rapidly convert inorganic nitrogen to organic forms, at rates comparable to microbial immobilization.  To date, this research has focused on forest soils; however, agroecosystems are more important sources of nitrogen pollution, especially nitrate loss.  Our study examined nitrate processing in four ecosystems at the Rodale Institute:  1) an organically managed agroecosystem fertilized with composted manure, 2) an organically managed agroecosystem using legumes for N fertilization, 3) a conventionally managed agroecosystem, and 4) a forest on a similar soil type near these agroecosystems.

We added K¹⁵NO₃ to sterile (gamma radiation) and live soils from all four systems and measured the quantity of ¹⁵N that became insoluble after minutes, days, and weeks.  In all cases, we found ¹⁵N in the insoluble soil pools, with as much as 60% of our original addition of ¹⁵N in the insoluble pool during the 3 week long sterile incubations.  However, preliminary analyses show no significant differences among the three agricultural systems.   In all the agricultural systems, there was no ¹⁵N found in the insoluble pool in either sterile or live incubations after 15 minutes, while in the forested systems there was about 3% of the labeled N in the insoluble pool in both  live and sterile samples.   Our data suggest abiotic reactions do play a role in transformation of nitrate into insoluble N; yet future studies examining transformation processes, composition and stability of insoluble N species are needed.