Abstract

Application of organic nutrient sources ONS for soil amendment may have an enormous advantage that improve nutrient cycling in soil–plant relations. The amount and rate of nutrient release from plant residues depend on their quality characteristics and biochemical composition of the ONS. An Aerobic Mineralization study was conducted in green house experiment to determine the N release dynamics of Erythrina abyssinica (EA), Erythrina brucei (EB) and Ensete ventricosum (EV) (ONS) were randomly collected from Wolaita and Sidama zone of Southern Ethiopia. Surface soil samples (0-20 cm) depths were also collected from Cambisol of Wolaita. Physicochemical properties of the composite soil were analyzed following standard analytical methods. For the greenhouse aerobic mineralization pot experiment, four treatments were designed for EA, EB and EV and control in Cambisols. The incubation was carried out for five consecutive weeks. The treatments were arranged in a completely randomized design (CRD) with three replications. The results of mineralization revealed that the NH4+ concentration was highest in the first week and became almost equal to the concentration of NO3- in the second week, and then it became low and constant at the third to fifth week. While the concentration of NO3- was low in the first week, it became equivalent to the concentration of NH4+ in the second week, and became higher and constant at the third to fourth week after which it started declining. The organic carbon and total nitrogen were also following the same trend.  In general, these ONS had medium to high TN content and they decomposed easily. Thus, they can be used as alternative or supportive organic sources. In their first week of decomposition they furnished NH4+ and from third week on wards they are good for NO3- loving crops, while the second week of mineralization is good for crops loving both inorganic forms of nitrogen. The present study indicates incorporation of EA, EB and EV modifies the fertility of cambisols and shall be taken into account to synchronize between net N mineralization and crop demand. However, more detailed research and field experimentations are needed on decomposition in some other soil types to draw sound conclusions.

Key words: Ammonium, incubation, mineralization, nitrate.