Meta-Analysis of Enhanced Efficiency Fertilizers in Midwestern Corn Systems.

Enhanced efficiency fertilizers such as nitrification inhibitors, urease inhibitors, and polymer coated fertilizers may provide agronomic benefits in nitrogen fertilization of corn production systems. Their effectiveness, however, can be influenced by fertilizer application (source, rate, time, place), site management, and location due to climate and soil characteristics.  We performed a meta-analysis on the effect of enhanced efficiency fertilizers on corn yield in the Midwest.  We modeled corn yield data by the primary fertilizer sources (AA, UAN, urea).  In the model for Anhydrous ammonia (AA), the effect of nitrapyrin was non-significant (p = 0.16).  The model for Urea ammonium nitrate also showed a non-significant effect of enhanced efficiency fertilizers (NBPT, NBPT+DCD, Nitrapyrin, Calcium thiosulfate, or Nutrisphere; p = 0.84).  The factor of enhanced efficiency fertilizer in the model for urea was moderately significant (NBPT, Nitrapyrin, NBPT+DCD, Polymer-coated urea; p=0.05).  Other factors such as nitrogen rate, application time, seasonal water and temperature, and soil characteristics influenced corn yield to a greater extent than enhanced efficiency fertilizers.  Our understanding of the effects of enhanced efficiency fertilizers on corn yield under a variety of growing conditions in the Midwest would be much improved by 1) a greater number of published studies with more consistent reporting of means with variation, 2) finer scale in-season meteorological data, 3) more complete geographic coverage, 4) simultaneous measurement of environmental effects on water-quality and N₂O emissions with standardization of reporting in area- or yield-based units. Overall, this meta-analysis indicates a small, generally positive but variable and condition-specific impact of enhanced efficiency fertilizers on corn yields in the Midwest.  Additionally, the database created will be publicly available to help guide and inform future research efforts.