Influence of nitrification inhibitors on yields of arable crops: A meta-analysis of recent studies in Germany

Nitrification inhibitors (NIs) delay the oxidation of ammonium by soil microorganisms, maintaining a higher proportion of applied nitrogen (N) in the soil by preventing nitrate-N loss from leaching and gaseous N losses from nitrification and denitrification. Thus, a large number of studies have shown N fertilizers with NIs are more environmentally friendly. In contrast, there are only a limited number of studies about effects of the N fertilizers added with NIs on arable crop yields and the conclusions are also divergent. This study presents a meta-analysis of recent research in Germany investigating the effects of NIs on the yields of different agricultural crops (winter wheat, winter barley, winter rapeseed, potato, grain and silage maize) compared to conventional N fertilization without NIs at a given N rate. Crop yields with and without NIs at a reduced number of N fertilizer applications were also compared. Nitrogen fertilizers with NIs did not significantly influence the yields of all investigated crops. For a given N application rate, the number of fertilizer applications could be reduced by at least one without any significant effect on yield when fertilizers with NIs were used. By contrast, the crude protein content of winter wheat was decreased significantly when the number of applications of NI fertilizers was less than that of non-NI-containing fertilizers. These findings may suggest that the key advantages to using N fertilizers with NIs are helping to protect the environment due to reduced N losses and reducing labor costs due to saving at least one fertilizer application, all while maintaining the yields of the investigated crops.