Meta-analysis of Enhanced Efficiency Fertilizers in Corn Systems in the Midwest
Enhanced efficiency fertilizers can be an effective means of managing nitrogen to prevent losses to the environment, both to protect natural resources and improve crop yields. However, the range of environmental and management factors that can influence their success can be difficult to put into context. This meta-analysis will help growers, industry, and academics by compiling the most up-to-date information and move the concept of 4R nutrient stewardship and sustainable agriculture forward.
IPNI-2014-USA-4RM06
24 Mar 2015
2014 Annual Interpretive Summary
Enhanced efficiency fertilizers (EEF) such as nitrification inhibitors, urease inhibitors, and polymer-coated fertilizers may provide environmental and agronomic benefits in nitrogen fertilization of corn. Their effectiveness, however, can be influenced by fertilizer source, rate, application time, and placement and can vary by location due to climate and soil characteristics. In this study we performed a systematic review and, where possible, a meta-analysis on published data from the Midwest region to address the effectiveness of EEF on corn yield, nitrous oxide emissions, and nitrate leaching.
We identified 29 studies comprising 690 observations that were amenable to meta-analyses describing corn yield response for the years 1994-2014. We modeled corn yield data by primary fertilizer sources. The model for anhydrous ammonia (AA) vs. AA+nitrapyrin was moderately significant, but had a significant interaction of AA+nitrapyrin at low temperatures. There was a significant model for UAN vs. UAN with inhibitors (NBPT, NBPT+DCD, thiosulfate, or nitrapyrin) showing a significant interaction with a combination of application timing and placement. There was also a significant effect of EEF in the model of yield with urea-based sources. Urea+NBPT, urea+nitrapyrin, and SuperU(R) all yielded greater than urea alone. In addition urea+NPBT and urea+nitrapyrin yielded more than polymer-coated fertilizers. In all of these models, climate and soil characteristics were highly significant and only by taking into account this variation were we able to detect differences in EEF. The ability to predict EEF effectiveness was restricted because of a lack of appropriate reporting in the literature of means and variation for use in meta-analysis. Data on N2O emissions are variously reported as area-based or yield-based emissions due to fertilizer inputs and are collected over different time periods, which limits comprehensive comparisons among studies. Initial results show that AA has greater fertilizer-induced emissions than other sources, but more in-depth modeling will be required to determine efficacy of EEF. In the review of nitrate leaching studies, only two out of six studies in the region reported variation, making a meta-analysis infeasible.
The review of the literature demonstrates a great need for more published studies pertaining to water quality throughout the Midwest, and also for standardization of reporting in area or yield-based results and for the consistent reporting of summary statistics. Overall, this systematic review and meta-analysis has demonstrated the potential of EEF to positively affect yields in certain circumstances and also highlights the complexity involved with environmental and management interactions. The data summarized provide a rich baseline from which to project future study needs and for posing hypotheses regarding improved effectiveness of nitrogen utilization.