Effects of combination of organic and inorganic fertilizers on abundances of nitrifiers and denitrifiers and their function in yellow-cinnamon soil

Objectives Soil nitrification and denitrification are two key pathways in nitrogen cycling. The paper studied the effects of combined application of organic and inorganic fertilizers on nitrification or denitrification, aiming to provide theoretical base for the scientific nutrient managements in maize and wheat rotation system.

Methods A field experiment was conducted in the yellow-cinnamon soil, located in the Cuiyuan Experimental Base of Anhui Agricultural University. Using no nitrogen fertilizer as control and at the same total N input levels in winter wheat and maize system, five combination ratios of inorganic and organic fertilizers were setup: only inorganic fertilizer (T1), ratios of inorganic fertilizer to organic fertilizer with 2∶1 (T2), 1∶1 (T3) and 1∶2 (T4) and only organic fertilizer (T5). The abundances and functions of nitrifiers and denitrifiers were quantified, and the abundances of denitrifiers and ammonia oxidizing microorganisms by quantitative PCR techniques, and denitrification capacity, N₂O/(N₂O+N₂) ratio, soil respiration, nitrification potential, relative contributions of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) to nitrification potential were measured.

Results The nitrification potential of the T1 and T5 was higher than those of the other treatments. Increased inorganic fertilizer ratio could significantly increase the abundance of AOA and its contribution to nitrification, compared to the increased organic fertilizer ratio. The denitrification capacity and soil respiration were increased with the organic fertilizer increasing, and the denitrification capacity and soil respiration of T5 were significantly higher than those of the other treatments. The abundances of nirS and nosZ-type denitrifiers were increased with the organic manure increasing, while the abundance of nirK-type denitrifiers was decreased. The denitrification capacity was positively correlated with the abundances of nirS or nosZ-type denitrifiers, organic matter and dissolved organic carbon, respectively. However, there was no significant correlation between the denitrification capacity and nirK-type denitrifier abundance.

Conclusions Our findings suggested that proper combined application of organic and inorganic fertilizers could decrease the nitrification potential, and regulate the role of AOA and AOB in nitrification process and effectively reduce soil denitrification loss, compared to the application of only inorganic or organic fertilizer.