Chemical Changes in Soil Using Sludge as a Soil Improver at Tree Vegetation

Viktor Kolchakov, Plamen Ivanov, Vera Petrova

Abstract: Present paper presents a study on the chemical changes in soil through the use of sewage sludge at tree vegetation. The study is based on field experiment on Vertisol (Eutric). It is carried out at the experimental field of ISSAPP “N. Poushkarov” in city of Bozhurishte. Two willows clones (Salix alba L. and Salix viminalis rubra) were used for the field experiment. The experiment was implemented in block scheme randomly in threefold repetition. Sewage sludge from the wastewater treatment plant in Sofia was deposited in following variants: control, two, four, and six t/da sludge. Average soil samples from all variants of the experiment are taken in the second year. Samples were analyzed for content of basic nutrients and some heavy metals. It was established a slight increase in pH values by increasing the amount of deposited sludge. There has been a positive effect on mobile potassium, which reaches up to 46.7 and 50.0 mg/100 g soil at the rate of 6 t/da sludge. There has been also a slight increase in mobile phosphorus and mineral fractions of nitrogen with increasing the amounts of sludge. The highest value of mineral nitrogen has been established in the surface soil horizon (0 – 30 cm) in the Salix viminalis rubra variant with 4 t/da deposited sludge (14.4 mg NH4+ + NO3-/kg soil).
The humus content in both types of willows increases in the variants. It reaches 3.68% for Salix alba L. and 4.21% for Salix viminalis rubra in the variant with rate of 6 t/da. The measured amounts of heavy metals are repeatedly below the rate for acceptable content in soils in both types of willows.

Keywords: chemical soil changes; sewage sludge; Vertiso; willows

Date published: 2017-02-21