Suppression of Ammonia Volatilization from an Ethiopian Soil Applied with Corn Cob Biochar.

Anaerobic digestion process is an effective technology to mitigate waste disposal problems in Jimma, Ethiopia. However, this process generates substantial amounts of liquid residues called anaerobic digestion effluents (ADEs). ADEs contain abundant plant nutrients such as nitrogen and phosphorus, which can be utilized as liquid fertilizers for crop production. On the other hand, ADE application to soil can cause ammonia volatilization from soils. To suppress ammonia volatilization, mixing the soil after application or applying biochars to the soil are known to be effective. In this study, an incubation study was conducted to examine the effect of application method of ADEs and application rate of biochar to soil on ammonia volatilization.

A soil used in this study was Eutric Nitosol (Jimma, Ethiopia). The ADE was derived from anaerobic digesters using food waste. The biochar was made from corn cob at 500°C. Twelve treatments were performed mixing three different components; type of fertilizer (ADE or urea), method of fertilizer application (surface application or mixed), and N application rate (0 or 100 kg N ha^-1). Ammonia volatilization from soils was measured on 0, 10, 30 min, 1, 2, 3, 4, 8 h, 1, 2, 3, and 6 d after fertilizers application.

Comparing within the same biochar treatments, ammonia volatilization was significantly decreased from the soil mixed with ADEs than surface application. Under the mixed treatments, 1% biochar rate exhibited significantly lower volatilization than did 2.5% rate. Therefore, it was indicated that both treatments of mixing soil and biochar application with ADEs could suppress ammonia volatilization from soil. In addition, combining biochar amendment and mixing soil after ADE application can suppress ammonia volatilization more, but the rate of biochar has to be carefully chosen.