Environmental sustainability of future fertilizers: tradeoffs between ammonia volatilization and nitrate leaching for 11 enhanced efficiency fertilizers

Nitrogen (N) fertilizers are critical to modern society and human well-being. However, these benefits have tradeoffs, as N fertilizer in excess of plant demand can lead to environmental impacts. New fertilizer technologies reduce losses to the environment, but many studies evaluate few technologies, and most field studies are difficult to cross-compare due to site and/or environmental effects. The objective of this study was to evaluate several enhanced efficiency fertilizers (EEFs) under common greenhouse conditions to isolate the effect of the EEF from the environmental effects in the field. Here we “stress tested” 11 EEFs under greenhouse conditions using two different soil types (clay loam from Iowa, USA, sandy loam from Minnesota, USA) for performance in two key areas – NH3 volatilization and N leaching. Our study included three nitrification inhibitors (DMPSA, Pronitridine, Nitrapyrin), one urease inhibitor (NBPT), two dual inhibitors (DCD+NBPT+Urea, DCD+NBPT+UAN), five polymer coated fertilizers, and two conventional fertilizers (UAN and urea). We found strong performance tradeoffs among EEFs. Considering both tests, there were six EEFs that performed well: two inhibitors (DMPSA, DCD+NBPT+Urea), and four polymer coated fertilizers (all three polyurethane-coated and the PLA/PBS-coated fertilizers). We also found the same class of EEF (e.g. nitrification inhibitor) could perform very differently based on substrate (e.g. Urea vs. UAN). Given that the polymer coated fertilizers all likely biodegrade very slowly (years) under field conditions and could accumulate microplastics in the environment, the two inhibitor-class EEFs (DMPSA, DCD+NBPT+Urea) may be promising candidates for additional field tests until more biodegradable polymers are developed.