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Potassium (K) fertilizer plays an important role in increasing crop yield, quality, and nitrogen use efficiency. However, little is known about its environmental impacts, such as its effects on emissions of the greenhouse gas nitrous oxide (N 2 O). A nitrogen-15 (15N) tracer laboratory experiment was therefore performed in an acidic agricultural soil in the suburbs of Wuhan, central China, to determine the effects of K fertilizer on N 2 O emissions and nitrification/denitrification product ratios under N fertilization. During 15-d incubation periods with a fixed initial N concentration (80 mg kg−1), K application increased average N 2 O emission rates significantly (1.6–10.8-fold) compared to the control treatment. N 2 O emissions derived from nitrification and denitrification both increased in K-treated soil, and denitrification contributed more to the increase; its contribution ratio rose from 32% without K fertilizer to 53% with 300 mg kg−1 of K applied. The increase in N 2 O emissions under K fertilization is probably due to an increase in the activity of denitrifying microorganisms and acid-resistant nitrifying microorganisms caused by higher K+ concentrations and lower soil pH. Combined treatment with potassium chloride (KCl) and N fertilizer produced lower N 2 O emissions than combined treatment with potassium sulfate (K 2 SO 4) and N fertilizer during 15-d incubation periods. Our results imply that there are significant interaction effects between N fertilizers and K fertilizers on N 2 O emissions. In particular, combining N fertilizers with fertilizers that reduce soil acidity or contain Cl or K ions may significantly affect agricultural N 2 O emissions. Image 1 • K fertilizer application significantly increased N 2 O emissions in agricultural acid soil. • Denitrification was an important pathway of N 2 O production in agricultural acid soil. • Potassium fertilizer increased the contribution of denitrification to N 2 O emission. [ABSTRACT FROM AUTHOR]

Potassium (K) fertilizer additions can result in high crop yields of good quality and low nitrogen (N) loss; however, the interaction between K and N fertilizer and its effect on N 2 O emissions and associated microbes remain unclear. We investigated this in a pot experiment with six fertilizer treatments involving K and two sources of N, using agricultural soil from the suburbs of Wuhan, central China. The aim was to determine the effects of the interaction between K and different forms of N on the N 2 O flux and the abundance of nitrifying and denitrifying microbial communities, using static chamber-gas chromatography and high-throughput sequencing methods. Compared with no fertilizer control (CK), the addition of nitrate fertilizer (NN) or ammonia fertilizer (AN) or K fertilizer significantly increased N 2 O emissions. However, the combined application (NNK) of K and NN significantly reduced the average N 2 O emissions by 28.3%, while the combined application (ANK) of K and AN increased N 2 O emissions by 22.7%. The abundance of nitrifying genes amoA in ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) changed in response to N and/or K fertilization, but the denitrifying genes nar G, nir K and nor l were strongly correlated with N 2 O emissions. This suggests that N or K fertilizer and their interaction affect N 2 O emissions mainly by altering the abundance of functional genes of denitrifying microbes in the soil-plant system. The genera Paracoccus, Rubrivivax and Geobacter as well as Streptomyces and Hyphomicrobium play an important role in N 2 O emissions during denitrification with the combined application of N and K. • Potassium addition reduces nitrate-stimulations on soil N 2 O emissions. • NNK treatment lowers the abundance of nirK and norB and most denitrifiers than NN treatment. • Soils with lower N 2 O emissions have a lower norB/nosZ ratio. [ABSTRACT FROM AUTHOR]