Soluble organic nitrogen in potentially mineralizable N assays: are we missing an important component?

We examined soluble organic nitrogen (SON) leached from long-term, sequentially leached, aerobic incubations. Leached SON, present in all depths (0-60 cm), ranged from 35% to 56% of total nitrogen (N). This unaccounted-for SON may have important implications in the estimation of plant available N and the potential for environmental N losses.