INTEGRATED USE OF DRY AZOLLA BIOMASS AND INORGANICNITROGEN FERTILIZER FOR SOIL AND TOMATO (Solanum Lycopersicon L.) PRODUCTIVITY IN SELECTED DISTRICTS OF SIDAMA REGION, ETHIOPIA

Abstract

Declining soil fertility and insufficient fertilizer application can limit crop yield. Integrating Azolla used as a source of organic nitrogen, with inorganic nitrogen fertilizers presents a promising strategy to improve soil health and crop productivity in tropical agroecosystems. This study was initiated to characterize soil, evaluate the effects of integrated application of Azolla dry biomass and inorganic nitrogen fertilizer on soil nitrogen mineralization, yield and nitrogen use efficiency of tomato in Hawassa Zuria and Wondo Genet, Sidama Region. The research conducted included soil characterization, through greenhouse, field and laboratory experiments with four specific objectives: (i) to characterize and classify soils at experimental sites,(ii) to determine the influence of Azolla dry biomass and inorganic N-fertilizer applications on selected soil chemical properties and as well as yield and yield components of tomatoes under greenhouse conditions,(iii) to evaluate the integrated effects of Azolla dry biomass and inorganic nitrogen fertilizer on soil chemical properties, nitrogen use efficiency, growth and yield of tomatoes, and (iv)determine the effects of Azolla dry biomass on soil nitrogen mineralization under controlled conditions. The first experiment, aimed to characterize and classify soils at experimental sites. A representative pedon was opened at each site to a depth of 2 x 2 x 2 m, and the profiles were described using the Guidelines for Field Soil Descriptions (FAO, 2006). A total of 12 disturbed and 12 undisturbed soil samples were collected from each diagnostic horizon at Jara Gelalicha, Hawassa Zuria and at Aruma, Wondo Genet locations. The soil analysis results showed that the surface horizon textural class of the pedon of Jara Gelalicha is sandy loam, whereas the textural class of the pedon at Aruma is sandy clay loam. Based on the World Reference Base for Soil Resources (WRB), the soils of the study areas were classified as Eutric Cambisols (Loamic) in the Jara Gelalicha area and Eutric Andosols (Loamic) in the Aruma area. Generally, the sitespecific soil characterization and classifications could offer crucial information for designing soil management options to increase soil productivity. The second experiment, aimed to determine the influence of Azolla dry biomass and inorganic nitrogen fertilizer on soil chemical properties, yield and yield components of tomato under greenhouse. The treatments included four levels of Azolla dry biomass (control (0), 25, 50, and 75 g pot⁻¹) and four levels of inorganic N 2 fertilizers (0 (non-fertilized), 0.23, 0.46, and 0.69 g pot⁻¹). The pot experiments were set up using factorial combinations within a completely randomized design (CRD) with three replications. In a greenhouse pot experiment, the interaction between Azolla dry biomass and inorganic nitrogen had a significant impact on various plant characteristics. The best results were achieved with the combined application of 75 g Azolla pot-1 and 0.69 g pot-1 of N, resulting in the highest marketable fruit yields at the Hawassa Zuria and Wondo Genet locations, which were 1088.43 g/plant and 833.73 g/plant, respectively. Field research is required to confirm the greenhouse findings and provide appropriate recommendations. Therefore, a third experiment, aiming to evaluate the integrated use of Azolla dry biomass and inorganic N fertilizers on soil chemical properties, growth and yield components, and nitrogen uptake and nitrogen use efficiency of tomato production was conducted under field conditions. Two-year field experiments were conducted in the Hawassa Zuria and Wondo Genet districts of the Sidama region. The experiment took place over two years in (2022/23 and 2023/24), a factorial combination of four rates of dry Azolla biomass (0, 5, 10, and 15 t ha⁻¹) as an organic nitrogen source and four rates of inorganic N fertilizer (0, 46, 92, and 138 kg N ha⁻¹) was evaluated. The treatments were arranged in a randomized complete block design (RCBD) with three replications. The combined two-year data showed that the highest marketable fruit yields in the Hawassa and Wondo Genet locations were 23.76 t ha⁻¹ and 26.35 t ha⁻¹, respectively. This was achieved by adding 15 t ha⁻¹ of Azolla biomass and 138 kg ha⁻¹ of nitrogen. It is integrated application of 15 t ha-1 of Azolla and 138 kg N ha-1 is recommended for tomato production in both districts. The combined application of 15 t ha⁻¹ and 138 kg ha⁻¹ led to the highest fruit N uptake (1093.48 kg ha⁻¹ in Hawassa Zuria and 1486.94 kg ha⁻¹ in Wondo Genet, while the control treatment had the lowest. The final experiment was aimed to determine the effects of Azolla dry biomass rates on soil nitrogen mineralization under controlled conditions. In addition, an incubation experiment using a completely randomized design (CRD) with three replications was conducted to determine the combined application of four rates of Azolla dry biomass (0, 15, 30, and 45 g pot⁻¹) and eight incubation periods (0, 7, 14, 21, 28, 42, 49, and 56 days of incubation). The results showed that the highest nitrogen mineralization occurred after 42 days of incubation with 45 g kg⁻¹ of Azolla in soils from both locations. The highest total mineralized N was found after 42 days of incubation in Hawassa Zuria and Wondo Genet (39.88 and 48.57 mg kg⁻¹ soil, respectively). Field research is essential to confirm the laboratory findings and provide appropriate recommendations.