Abstract
Knowledge of soil nitrogen (N) mineralization in response to different amendments is crucial for improving the efficiency of N use and improving crop productivity. The present study aimed to determine the effects of Azolla pinnata biofertilizer on soil N mineralization under laboratory conditions. The experiment was carried out in the soil laboratory of the College of Agriculture at Hawassa University. Soil samples were collected from the Hawassa Zuria and Wondo Genet districts and then incubated for 56 days at a room temperature of 25°C. Four levels of Azolla pinnata biofertilizer (0, 15, 30, and 45 g kg− 1) and eight incubation periods (0, 7, 14, 21, 28, 42, 49, and 56 days) were arranged in a factorial order and laid out in a completely randomized design (CRD) with three replications. The total available NH4+-N and NO3−-N were determined every seventh day following standard laboratory methods. The results of this study revealed highly significant interactions (P < 0.01) between the effects of the Azolla biofertilizer concentration and the incubation period under laboratory conditions on the total mineralized N, NH4+ and NO3−. The maximum mineralization of N occurred after 42 days of incubation with 45 g kg− 1 Azolla pinnata biofertilizer in soils from both locations (Hawassa Zuria and Wondo Genet). The highest total mineralized N was recorded after 42 days of incubation (39.88 and 48.57 mg kg− 1 soil, respectively). However, the lowest total mineral N content was obtained from the control group. Nitrogen mineralization varied significantly between treatments (P < 0.01 or P < 0.001). Using Azolla pinnata as a biofertilizer significantly increased the mineralization rate of N in the soil, potentially reducing the need for inorganic N fertilizer. By studying Azolla pinnata biofertilizers, researchers can estimate mineralization during incubation, crop nutrient availability, and optimal timing. Field research is necessary to validate these laboratory findings and provide sound recommendations.