Nitrogen Dynamic in a Nitosol in Ethiopia Applied By Corncob Biochars.

Biochar is the carbon-rich product obtained when biomass such as wood, manure, and leaves, is pyrolysed under limited oxygen, and usually used for soil amendment to improve soil environments. Biochars have high cation exchange capacity (CEC), and can improve soil CEC when applied. CEC-enhanced soils can retain nutrient cations such as NH₄⁺, K⁺, and Ca²⁺, which may be plant available. Recently, designed biochars such as CEC enhanced biochars have attracted the interest to change and improve characteristics of biochars. In this study, an incubation study was conducted to evaluate nitrogen dynamics in a Nitosol in Ethiopia applied with biochars with different CEC values.

A soil used in this study was Eutric Nitosol (Jimma, Ethiopia), oven-dried, and sieved by 2 mm. Ammonium sulfate (AS) and anaerobic digestion effluent (ADE) were applied as N source at 46 kg N ha^-1. The ADE was derived from cow manure. Three different corncob biochars (fresh biochar (FB), clay-treated biochar (CB), and H₂O₂-treated biochar (HB)) were pyrolysed at 500°C for 2 hr and sieved by 0.5 mm. Twelve treatments were included: no amendments, biochar only (FB, CB, and HB), N only (AS and ADE), and combination of biochars and N sources. Soil NH₄⁺-N, NO₃^--N, and pH were analyzed on 0, 1, 3, 5, 7, 14, 21, 28, 42 and 56 d of the incubation.

NH₄⁺-N concentration in the soil with FB and CB were increased, but that with HB was decreased, possibly because more NH₄⁺-N was adsorbed strongly by HB, which has highest CEC value, than FB and CB. NH₄⁺-N adsorbed on biochars might be released little by little. Furthermore, because FB, CB, and HB showed higher NH₄⁺-N concentration and lower NO₃^--N concentration than that of no-biochar treatments, biochars might have retained NH₄⁺-N and inhibited nitrification in the soil.