The effect of nitrification inhibitors on the nitrous oxide (N2O) release from agricultural soils—a review

Abstract The use of nitrification inhibitors (NI) is a technique which is able to improve N fertilizer use efficiency, to reduce nitrate leaching and to decrease the emission of the climate‐relevant gas N 2 O simultaneously, particularly in moderately fertilized agricultural systems adapted to plant N demand. The ammonia monooxygenase (AMO) is the first enzyme which is involved in the oxidation of NH $ _4^+ $ to NO $ _3^ - $ in soils. The inhibition of the AMO by NIs directly decreases the nitrification rate and it reduces the NO $ _3^- $ concentration which serves as substrate for denitrification. Hence, the two main pathways of N 2 O production in soils are blocked or their source strength is at least decreased. Although it has been shown that archaea are also able to oxidize NH 3 , results from literature suggest that the enzymatic activity of NH 3 oxidizing bacteria is the most important target for NIs because it was much stronger affected. The application of NIs to reduce N 2 O emissions is most effective under conditions in which the NI remains close to the N ‐ fertilizer. This is the case when the NI was sprayed on mineral ‐ N fertilizer granules or thoroughly mixed with liquid fertilizers. Most serious problems of spatial separation of NI and substrate emerge on pasture soils, where N 2 O hotspots occur under urine and to a lesser extent under manure patches. From the few studies on the effect of different NI quantities it seems that the amount of NI necessary to reduce N 2 O emissions is below the recommendations for NI amounts in practice. NIs can improve the fertilizer value of liquid manure. For instance, the addition of NIs to slurry can increase N uptake and yield of crops when NO $ _3^ - $ ‐ N leaching losses are reduced. It has clearly been demonstrated that NIs added to cattle slurry are very effective in reducing N 2 O as well as NO emissions after surface application and injection of slurry into grassland soils. In flooded rice systems NIs can reduce CH 4 emission significantly, whereas the effect on CO 2 emission is varying. On the other hand, as an effect of the delay of nitrification by NIs, NH 3 emission might increase when N fertilizers are not incorporated into the soil. As compared to other measures NIs have a high potential to reduce N 2 O emissions from agricultural soils. Further, no other measure has so consistently been proofed according its efficiency to reduce N 2 O emissions. From the published data [ Akiyama et al. ( 2010 ) and more recent data from the years 2010–2013; 140 data sets in total] a reduction potential of approx. 35% seems realistic; however, further measurements in different management systems, particularly in regions with intense frost/thaw cycles seem necessary to confirm this reduction potential. These measurements generally should cover a whole annual cycle.