Temporal Changes of Nitrification and Nitrifying Microbes Induced By Dicyandiamide Application to a Soil Applied with Anaerobic Digestion Effluents.

Anaerobic digestion effluents (ADEs) are remaining liquid residuals after organic biomass are anaerobically digested. The ADEs contain abundant plant nutrients such as nitrogen (N) and potassium, and have proven to have similar fertilizer effects as chemical fertilizers. However, it has also been reported that ADEs application to soils can cause more NO₃^--N leaching and N_2­O emission from soils compared to chemical fertilizers. Reducing NO₃^--N leaching and N₂O emission from ADEs-applied soils needs to be improved for alternative use of ADEs to chemical fertilizers. NO₃^--N and N₂O are produced by nitrification in soils, presumably mediated by ammonia-oxidizing bacteria (AOB) and archaea (AOA). Therefore, in this study, an incubation study was conducted to examine the effect of nitrification inhibitor on nitrification and the dynamics of microbes in a soil applied with ADE.

A soil used in this study was Typic Dystrochrept (Tokyo, Japan), oven-dried, and sieved by 2 mm. The ADEs were derived from food waste (FW), cow manure (CM), and sewage water (SW) digestion plant, and applied as 140 kg N ha^-1 based on N recommended rate for Japanese mustard spinach (Brassica rapa). Dicyandiamide (DCD) was used as nitrification inhibitor, applied at 10% of total N applied from chemical fertilizer (CF) or ADE. Nine treatments were included: no amendments, CF only, ADEs only (FW, CM or SW), CF with DCD (CF+DCD), and ADEs with DCD (FW+DCD, CM+DCD or SW+DCD). Soil NH₄⁺-N, NO₃^--N, and pH were analyzed on 0, 3, 7, 14, 21, 28, 42 and 56 day, and AOB and AOA abundance were analyzed on 0, 7, 14, 28 and 56 day of the incubation.

High NH₄⁺-N and low NO₃^--N in the soil are expected accordingly to decreased AOB and AOA abundance in the soil applied with DCD.