In this study, the effect of sea lettuce (Ulva lactuca) on soil water-holding capacity and the variation by over time were investigated. Sea lettuce (algae) was collected from the Black Sea coast, rinsed with rain water and dried to constant weight. Dried algae were added to soil at rate of 0%, 2.5%, 5%, 10% and 20%. Mixtures were filling the pots and incubated for 0, 20, 40, 60 days at 25 ºC. At the end of the incubation, soil organic matter and water holding capacity were determined. Adding of algae to soil was increased the porosity and water holding capacity. The amount of the organic matter was decreased by the incubation progress. At the 20 and 40 days, micro-porosity was increased, air capacity decreased and water-holding capacity has not changed. At the 60th incubation days, reduction of organic matter content was slowed, air capacity was reached to normal values and water holding capacity was decreased. Total porosity was not changed. At the beginning (0th) and the 60th incubation days, the distinctive dose was obtained at 5% for porosity and water holding capacity increases. Increased doses of the above have been limited. The optimum dose of 5% as determined by the addition of algae was increased soil water holding capacity by 48% on average.

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