Effects of Azolla on Nitrogen Mineralization in Soils of Hawassa Zuria and Wondo Genet Districts, Southern Ethiopia, Incubated Under Laboratory Conditions

Soil nitrogen mineralization plays a critical role in nitrogen availability and balance in soils. The present study aims to determine the effects of Azolla on soil nitrogen mineralization under laboratory conditions. The incubation experiment was conducted in the soil laboratory of the College of Agriculture at Hawassa University. Soil samples were taken from Hawassa Zuria and Wondo Genet districts from a depth of 0–20 cm and processed in laboratory for the experiment. A factorial experiment consisted of four levels dry Azolla biomass (0, 15, 30, and 45 g kg −1 of soil) and eight incubation (0, 7, 14, 21, 28, 42, 49, and 56 days) periods and was laid out in a completely randomized design (CRD) with three replications. 1000 g of sieved processed soils was added to 1500 mL plastic jar to which Azolla dry biomass was added as per the treatment and thoroughly mixed. Then, the moisture content of the mixture was maintained at 60% water holding capacity and incubated at 25°C in the dark for 56 days. The concentrations of available N (NH 4 + ‐N and NO 3 − ‐N) were measured periodically throughout the incubation period. Results revealed that Azolla levels by incubation period interaction effects were significant interactions ( p < 0.001) between the effects of Azolla levels and incubation period under total mineralized N, NH 4 + ‐N, and NO 3 − ‐N. The highest nitrogen mineralization occurred after 42 days of incubation with 45 g kg −1 of Azolla in soils from both locations. The lowest total amount of N mineralized occurred in control soils of both locations. Quantitatively, with 45 g kg −1 Azolla amendment and 42 days of incubation, the total sum of 39.88 and 48.57 mg kg −1 soil N mineralized has been found in Hawassa and Wondo Gent soils, respectively. It is concluded that Azolla biomass has significantly increased the rate of N mineralization in the soil and the total amount of available N, indicating that it has the potential to reduce the demand for inorganic nitrogen fertilizer. However, the total N and C contents of Azolla are important factors in its N‐release capacity. Future research should test these Azolla in a field experiment to confirm the results.