Laboratory column studies were used to quantify the nitrogen and phosphorus leaching dynamics from a biofilter soil, fertilizer amendments, and experimental controls throughout four years of simulated runoff application.
The results showed that the biofilter soil starting materials were a significant source of nutrients, particularly for nitrogen. Compost was identified as the ideal nitrogen amendment, leaching only 7% of the mass initially added to the test column. This minimal washout response was attributed to the slow mineralization of humic materials. Lecithin and Nitroform® leached the lowest amount of phosphorus amongst the tested soil amendments, whereas the inclusion of polymerized tung oil with these nutrient sources (oleophilic fertilizer) only expedited phosphorus release. In contrast, the oleophilic fertilizer demonstrated a more controlled nitrogen release than the Lecithin and Nitroform® and this inconsistency was attributed to greater microbial nitrogen immobilization over phosphorus upon carbon based biostimulation.