Effects of Dicyandiamide in a Soil Applied with Anaerobic Digestion Effluent.

Anaerobic digestion effluents (ADEs) are remaining liquid residuals after organic biomass are anaerobically digested. 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 ADE application can increase N_2­O emission from soils. Reducing N₂O emission from ADE-applied soils could be beneficial for alternative use of ADE to chemical fertilizers. Therefore, in this study, an incubation study was conducted to examine the effect of nitrification inhibitor on nitrification in a soil applied with ADE.

A soil used in this study was Typic Dystrochrept (Tokyo, Japan), oven-dried, and sieved by 2 mm. An ADE was derived from cow manure 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, and was applied at 10% of total N applied from chemical fertilizer (CF) or ADE. Five treatments were included: no amendments, CF only, ADE only (ADE), CF with DCD (CF+DCD), and ADE with DCD (ADE+DCD). Soil NH₄⁺-N, NO₃^–-N, and pH were analyzed on 3, 7, 14, 21, 28, 35, 42, 49, and 56 d of the incubation.

In all treatments, NH₄⁺-N decreased and NO₃^–-N increased during the incubation. Both NH₄⁺-N decreasing rates and NO₃^–-N increasing rates were smaller in soil with ADE+DCD than in soil with ADE. In addition, cumulative amounts of NO₃^–-N with ADE+DCD were lower than ADE treatment. Nitrification inhibition effect by DCD was observed in soil applied with ADE. On comparing NH₄⁺-N decreasing rates and NO₃^–-N increasing rates, ADE+DCD showed more gradual changes than CF+DCD did. It was found that DCD may affect differently in soils applied with ADE or CF.