Enhanced‐efficiency fertilizers are not a panacea for resolving the nitrogen problem

Abstract

Improving nitrogen (N) management for greater agricultural output while minimizing unintended environmental consequences is critical in the endeavor of feeding the growing population sustainably amid climate change. Enhanced-efficiency fertilizers (EEFs) have been developed to better synchronize fertilizer N release with crop uptake, offering the potential for enhanced N use efficiency (NUE) and reduced losses. Can EEFs play a significant role in helping address the N management challenge? Here we present a comprehensive analysis of worldwide studies published in 1980-2016 evaluating four major types of EEFs (polymer-coated fertilizers PCF, nitrification inhibitors NI, urease inhibitors UI, and double inhibitors DI, i.e. urease and nitrification inhibitors combined) regarding their effectiveness in increasing yield and NUE and reducing N losses. Overall productivity and environmental efficacy depended on the combination of EEF type and cropping systems, further affected by biophysical conditions. Best scenarios include: (i) DI used in grassland (n = 133), averaging 11% yield increase, 33% NUE improvement, and 47% decrease in aggregated N loss (sum of NO , NH , and N O, totaling 84 kg N/ha); (ii) UI in rice-paddy systems (n = 100), with 9% yield increase, 29% NUE improvement, and 41% N-loss reduction (16 kg N/ha). EEF efficacies in wheat and maize systems were more complicated and generally less effective. In-depth analysis indicated that the potential benefits of EEFs might be best achieved when a need is created, for example, by downward adjusting N application from conventional rate. We conclude that EEFs can play a significant role in sustainable agricultural production but their prudent use requires firstly eliminating any fertilizer mismanagement plus the implementation of knowledge-based N management practices.

Effect of urease and nitrification inhibitors on ammonia volatilization and abundance of N‐cycling genes in an agricultural soil

“…In contrast, other authors have shown a reduction of NH 3 emissions by double inhibition with urea compared with urea alone [see Li et al. () and Kanter and Searchinger () for reviews].…”

“…Globally, urea is the N‐fertilizer most widely applied in modern agriculture, and its use has increased 100‐fold in the last 50 years mainly due to its low cost ( Thompson and Meisinger , ; Glibert et al., ; Heffer and Prud'homme , ). Among the management strategies to improve the N use efficiency of fertilizers and to mitigate gas emissions, urease and nitrification inhibitors could be used to reduce NH 3 and N 2 O emissions ( Li et al., ). Urease is the enzyme responsible for the conversion of urea into carbon dioxide (CO 2 ) and NH 3 .…”

Can stabilized nitrogen fertilizer sources reduce losses through multiple loss pathways?

“…Across many studies, nitrification inhibitors alone or combined with urease inhibitors have resulted in a consistent decrease in N 2 O emissions on average (Table 2), with effect sizes ranging from 8 to 100% (Snyder et al, 2009; Qiao et al, 2015; Thapa et al, 2016; Lam et al, 2017; Li et al, 2018). In one meta‐analysis, nitrification inhibitors reduced N 2 O emissions across different land uses, climatic conditions, and for a range of soil texture and pH (Li et al, 2018).…”

“…Pan et al (2016) reported that urease inhibitors decreased NH 3 emissions by 54%, whereas Saggar et al (2013) reported a 45% reduction. Urease inhibitors mitigated NH 3 volatilization across a range of soil types and pH, land use, and annual precipitation gradient (Li et al, 2018). However, high soil carbon content and temperatures may potentially reduce the efficacy of urease inhibitors (Saggar et al, 2013).…”

“…Meta‐analyses also indicate a possible trade‐off between N 2 O emissions and NH 3 volatilization when applying nitrification inhibitors. Specifically, research has demonstrated that NH 3 volatilization increased with the application of nitrification inhibitors (Lam et al, 2017; Li et al, 2018), coinciding with a decrease in N 2 O emissions (Qiao et al, 2015; Pan et al, 2016; Li et al, 2017). However, urease and nitrification inhibitors can be combined to reduce both NH 3 and N 2 O losses (Li et al, 2017).…”