A long-term experimental site was built to study effects of the nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) on a bacterial population's diversity and activity in a Cambisol in northern China. Treatments included no fertilization (CK), application of urea alone (U), and application of urea plus DMPP (UD). The annual application rate for the urea was 180 kg N ha -1 , and that of the DMPP was 1.8 kg ha -1. The diversity and composition of the overall soil bacterial community were analyzed using pyrosequencing, and the abundances of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were analyzed using a real-time polymerase chain reaction (RT-PCR) assay. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Gemmatimonadetes, Chloroflexi, Firmicutes, and Planctomycetes in all of the samples. However, compared with treatment U, the relative abundance and identities of the dominant phyla that were increased in treatment UD were more similar to those of the CK treatment. DMPP significantly reduced the targeted ammonia oxidizing bacterial abundance, and the soil potential nitrification rate had a significant positive correlation with the amoA gene copy number of the AOB (r=0.685, n=9, p<0.05) but not of the AOA. The results suggested that long-term application of DMPP to this agricultural soil was relatively beneficial for both urea application and soil bacterial ecosystem reversion.

This study describes the effects of balanced versus nutrient-deficient fertilisation on soil nutrient content and selected oxidoreductase activity and kinetic parameters in a long-term (28 years) field experiment conducted using a phaeozem type soil in the Jilin Province of northeast China. As compared to no or unbalanced fertilisation, balanced fertilisation improved the overall chemical fertility of the soil and significantly increased the activities and Vmax values of soil dehydrogenase and catalase. Compared with control (CK), unbalanced fertilisation (with the exception of P deficiency) significantly increased the total carbon content and soil dehydrogenase activity but had less of an effect on the Vmax of the enzyme, whereas the soil catalase activity and its Vmax were less affected under unbalanced fertilisation conditions. The Km value of soil dehydrogenase increased with the application of chemical NPK combined with farmyard manure but decreased under the application of NPK, NP, and PK. The Km value of soil catalase decreased under the application of NK and showed little difference between CK and the other fertilisation treatments. The variations in the activities and kinetic parameters of the enzymes revealed the benefits of long-term balanced fertilisation, particularly the combined application of chemical and organic fertilisers, by improving the chemical and biological fertility of phaeozem. The results also indicated that unbalanced fertilisation with P deficiency (NK) could enhance phaeozem quality, but this effect was limited.