Nitrification inhibitor induced microbial NH4+-N immobilization improves maize nitrogen use efficiency in strong ammonia oxidation soil

Abstract

Nitrification inhibitors (NIs) have been acknowledged since 1970s for their potential to mitigate N₂O emissions, enhance fertilizer nitrogen use efficiency (NUE), and improve crop productivity. However, their effectiveness in improving yield and NUE varies significantly across different soil types, with the underlying mechanisms largely unexplored. This study integrates laboratory ¹⁵N labeling incubation experiments with field trials to evaluate the influence of a specific NI, nitraprin, on soil gross N transformation rates, N₂O emissions, maize yield and NUE across three distinct soil types prevalent in China's major crop production zones. These soils include acidic black soil at GZL site, alkaline fluvo-aquic soil at XC site, and acidic red soil at QJ site. The alkaline fluvo-aquic soil (XC) exhibited the highest gross nitrification rates (O_NH4) and cumulative N₂O emissions, while also showing the lowest immobilization rate of NH₄⁺-N (I_NH4). Conversely, the acidic black soil (GZL) had opposite trends. NI application lead to a significant reduction in O_NH4 by 23–53% and in N₂O emissions by 48–85%. Notably an increase in maize yield (by 18.7%) and NUE (by 30.3 %) were observed exclusively at XC. NI addition notably enhanced I_NH4 at XC, due to the suppression of a high nitrification rate, reduced the N losing risk (N/I ratio) and consequently supported higher maize yield. Further analyses highlighted that autotrophic nitrification, predominantly mediated by ammonia-oxidizing bacteria (AOB), particularly the AOB Nitrosospira cluster 3a.2 (D11), is pivotal in regulating soil N₂O emissions and is sensitive to NI addition. This study underscores the significant role that the interplay between O_NH4 and I_NH4 plays in influencing maize yield, NUE, and the effectiveness of NIs across various soil types. These insights are crucial for developing tailored N management strategies that aim to maximize NUE and minimize N₂O emissions.