In Search for Biological Approaches to Mitigate Nitrate Leaching, Proximus Case.

Despite decades of efforts, reducing nitrate leaching while increasing/maintaining crop yield has remained a challenge. A great proportion of nitrate leaching occurs early growing season due to low N uptake, concomitant with excess nitrate concentration and soil moisture. Thus, from the environmental perspective, management of N fertilization is critical during this period. We hypothesized that enhanced N immobilization is the key mechanism through which Proximus® temporarily reduces soil/leachate nitrate concentration following addition of a N fertilizer. The field experiment was conducted in a completely randomized blocked design in Sheridan, IN. The field was maintained free of vegetation during the experiment. The treatments (4 replicates/treatment) included one-time surface application of Urea Ammonium Nitrate (UAN) (112 kg-N/ha), UAN (112 kg-N/ha) with Proximus® (23 L ha^-1), and UAN with Proximus® (37.5 L ha^-1). Soil sampling was conducted at weekly intervals, totally 8 sampling events from 0-4” and 4-8” depths. Soil nitrate concentration (both depths) and microbial biomass C (only 0-4” depth) were determined. In addition, nitrate concentration was measured in soil solution collected at 10” depth using tension lysimeters. Results (submitted by McCloughan et al., ASA 2017) suggested that Proximus® reduced nitrate leaching in both soil and soil leachate. The effect of Proximus® application of microbial biomass C was evident for three weeks post application. Application of Proximus® at higher rate resulted in a sharp increase (28%) in biomass (compared to UAN-only) that sustained only two weeks post application. The lower application rate of Proximus®, however, caused a more sustained increased in biomass 14% and 12% (compared to UAN-only), two and three weeks post application, respectively. The results suggest that potential of Proximus® in building microbial biomass and consequently N immobilization is rate sensitive. More experiments are being conducted in both field and greenhouse to better understand the interactions of fertilizer and application type on efficiency of Proximus®.