Reducing Nitrate Leaching with Proximus®, a New Tool for Nitrogen Management.

Our objective was to explore the effect of Proximus® on soil nitrate leaching, and to compare its performance to standard nitrogen (N) management products. The research was conducted on fallow corn ground across three locations in the Midwest. Urea ammonium nitrate was applied at 112 kg N / ha with and without Proximus® application. Other N management treatments included N-(n-butyl) thiophosphoric triamide (NBPT) + dicyandiamide (DCD) and Nitrapyrin. After application, soils were monitored for up to 11 weeks for changes in soil nitrate (NO₃-N) and ammonium (NH₄⁺-N) concentrations. Also during this time, soil solution sampled from suction lysimeters was analyzed for nitrate concentrations. This was an approximation of nitrate concentration in leachate. The data showed soil nitrate concentrations were reduced when Proximus® was applied. Nitrate concentrations in soil solution were also observed to be reduced. The combination of NBPT + DCD was observed to reduce nitrate concentrations as well as to sustain a pool of soil ammonium. The effect of Proximus® on NH₃ and NO_x gas release from the soil surface were also measured, but the effects were minimal and no different than the N control. Overall, Proximus® reduced nitrate concentrations in both the bulk soil and soil solution across multiple Midwest soils. This research demonstrated that the effect occurs in soil without the presence of a crop. The data did not support the idea that the effect was related to urease inhibition, nitrification inhibition or denitrification. Therefore, we hypothesized that the mechanism for this was related to the assimilation of mineral nitrogen into soil microbial biomass. Evidence for this, as well as the effects of Proximus® in corn, is discussed elsewhere.