Nitrogen Losses: A Meta-analysis of 4R Nutrient Management in U.S. Corn-Based Systems

IPNI-2014-USA-4RM10

29 Apr 2016

2015 Annual Interpretive Summary


The specific aim of this meta‐analysis project was to determine the impact of 4R N management techniques on nitrous oxide (N2O) and nitrate (NO3) losses relative to corn yield. The team collected and synthesized field research data published prior to July 2014 that measured N losses as affected by 4R fertilizer N management (right rate, source, timing, and placement) in North American corn‐based cropping systems.

We identified 4,400 research papers that mention fertilizer, N, or nutrient management in agriculture, or fertilizer‐associated N2O or NO3 losses. After a review of titles and abstracts, the majority of studies were discarded because they were not about crop land, corn, or N losses, were outside North America, or addressed N losses and transport after the field. This triage found 237 studies suitable for further review; only 27 and 22 studies contained N2O and NO3 loss data and also reported corn yield. An additional nine N2O and five NO3 studies reported losses but not yield. The final database included 404 observations of N2O emissions and 396 observations of NO3 leaching losses. Data limitations made it difficult to identify possible trade‐offs between N2O and NO3 losses. Only one study reported losses of both N2O and NO3. Across all studies, the geographies for the N2O and NO3 data rarely overlap, and management practices for both types of field studies were diverse. For example, 60% of NO3 observations and only 1.6% of the N2O data were reportedly from tile‐drained fields. Thirty‐eight percent (38%) of the N2O observations, and only 8% of the NO3 observations, were from no‐till systems. Fertilizer N rate response curves showed crop yield increasing as a function of N rate to a maximum point; N2O emissions respond in an exponential fashion; and NO3 losses tend to be linear in relation to fertilizer application rate. Statistical models found that adding nitrification inhibitors with the N fertilizer significantly reduced yield‐scaled N2O emissions. Delaying fertilizer N application until the crop was growing (sidedress) had a similar effect of reducing N2O emissions. Nitrate leaching losses were lower in soils with more organic matter and in drier climates, but lack of data and high variability made it difficult to see any impact of fertilizer management.

To better determine management effects on losses, more data with broader regional coverage are needed. In the meantime, process‐based models calibrated to all available data may be the most reliable way to predict loss responses and to investigate relationships between losses of N2O and NO3.