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Water fern Azolla microphylla symbioses with Anabaena azollae which is able to fix N2. Fern growth is strongly influenced by the availability of macro nutrients such as phosphate. The aim of this study was to determine the effect of concentration of phosphate fertilizers and different water levels on the growth and nitrogen uptake of Azolla microphylla. Research was conducted by using randomized block design with three replications. The treatment were  water level which consists of 0 cm, 2 cm, 4 cm, and 6 cm, and the concentration of phosphates (P) which is composed of without and with  15 ppm, 30 ppm and 45 ppm. The results showed that the water level are interdependent with the phosphates concentration to influence  Azolla’s covered area at  7-21 days after planting, wet weight, total dry weight, and total nitrogen uptake of Azolla microphylla. The water level 2 cm at a concentration of 30 ppm of phosphate fertilizers is the best treatment combination to increase Azolla’s covered area at 7-21 HST, wet weight, total dry weight, and total nitrogen uptake of Azolla microphylla.

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Acidic mineral soil generally has mild acidic to high acidic reaction or pH ⩽ 5.5, with very low exchangeable bases that can exchanged and rich in oxide as well as Al and Fe hydroxides. Acidized soil can lead to increased toxicity from aluminum, iron, and manganese element to the plants and deficiency of phosphorous, alkaline cation (calcium, potassium, and magnesium), and molybdenum element as well as soil microbial population. This study aimed to observe the fractionation distribution of metal aluminum (Al), iron (Fe), and manganese (Mn) and soil microbial population in acidic soil horizon. Al fraction parameters included exchangeable Al (Al-exc), non-crystalline Al (Al-o), inorganic non-crystalline Al (Al-po), Organically Bound Al (Al-p), Low- and Medium- Stability Complexes with Organic Matter (Al-Cu) and High-Stability Complexes with Organic Matter (Al-pCu), exchangeable fractionation of Fe and Mn (Fe/Mn-exc), Fe and Mn from Bound to Carbonates/Acid- extractable, Bound to Fe-Mn Oxides/Reducible, Bound to Organic Matter Fe Mn/Oxidizible, Fe- Mn Residual and soil microbial population (total microbes and Acidithiobacillus bacteria). The results, distribution of Al fraction on the upper horizon of Jasinga and Lebak were dominated by stabilized organic amorphous Al fraction with fluctuative decrease of organic matter (Al-pCu), while the lower horizon tended to be inorganic amorphous Al (Al-op). The fractionation distribution of Fe fractionation on Jasinga and Lebak was dominated by Oxidizible Fe fraction. Mn fraction distribution on Jasinga and Lebak were dominated by Mn-residual fraction in each acidic soil horizon. The total population of Microbes and Acidithiobacillus.sp in each soil horizon decreased along with the alteration of soil chemical properties in each soil depth horizon.

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