ABSTRACT
Urban soils show high variability regarding the content and availability of different nutrients. Nitrogen is usually lower in urban soil than in agricultural soil, because soil sealing in urban areas can have negative consequences for soil fertility and long-term storage of nitrogen. Potassium is rarely deficient, whereas iron and phosphorus can be little available to plants because of insolubilization processes due to higher pH levels resulting from addition of debris (e.g. cement, plaster, etc.) in urban soils. Although organic and inorganic forms of phosphorus (P) are abundant in soils, plant phosphorus availability is restricted as it mostly occurs in insoluble forms. Furthermore, phosphate-solubilizing microorganisms (PSM) (bacterial and fungal strains) are needed for gradual P-release, but PSM are scarcely present in urban soils, so that only 0.1 per cent of the total P may be available to plants.
