The influence of long-term sewage sludge application on the activity of phosphatases in the rhizosphere of plants

Model experiments using rhizoboxes were carried out in order to evaluate the influence of different plants (wheat, rape) on the changes in water extractable contents of P, the pH/H2O value and the activity of acidic and alkaline phosphatase in soil of plant rhizosphere. For this experiment, a Cambisol with different long-term fertilizing systems was used: (i) control (with no fertilizer application), (ii) sewage sludge, and (iii) manure. A low content of water-soluble P was observed in close vicinities of root surfaces (up to 2 mm) at all the studied variants. The control variant reflected a significantly lower content of water-soluble P in the rhizosphere than the fertilized ones. The activities of the acidic and alkaline phosphatases were significantly higher in the rhizosphere than outside it. The long-term application of organic fertilizers significantly increased phosphatase activity; the activity of the acidic phosphatase was significantly higher in the rhizosphere of rape plants than in that of wheat. The variant treated with manure exhibited an increased activity of both the studied enzymes in comparison with the variant treated with sewage sludge. In the latter case, the portion of inorganic P to total soil P content increased. In all the variants, soil of the rape rhizosphere showed a trend to lower pH/H2O value, whereas the wheat rhizosphere showed an opposite pH tendency.