PHYTOTOXICITY OF SALTS IN COMPOSTED SEWAGE SLUDGE AND CORRELATION WITH SODIUM CHLORIDE, CALCIUM NITRATE, AND MAGNESIUM NITRATE

Abstract

The phytotoxicity of salts in composted sewage sludge (CSS) was evaluated. Concentrations of sodium (Na⁺), chloride (Cl⁻¹), calcium (Ca²⁺), and magnesium (Mg²⁺) were present at levels that would induce salt stress in plants. Nutrient imbalances were also found that would adversely affect the use of CSS as a growth medium. To further understand the phytotoxic nature of these salts, sodium chloride (NaCl), calcium nitrate [Ca(NO₃)₂] and magnesium nitrate [Mg(NO₃)₂] solutions were used to simulate the composition of salts found in CSS in an investigation of radish (Raphanus sativus L.) seed germination. High concentrations of Ca²⁺ (92.1 mmol.L⁻¹) and Mg²⁺ (27.4 mmol.L⁻¹) inhibited seed germination to an equal extent as did Na⁺ (40.6 mmol.L⁻¹). The lower concentration of Ca²⁺ (10 mmol.L⁻¹), however, significantly relieved the stress caused by NaCl. These results indicated that the composition and total amount of Na⁺, Cl⁻¹, Ca²⁺, and Mg²⁺ in CSS should be carefully monitored before it is used as a soil amendment or growth medium.

Keywords:

• sewage sludge compost
• salt stress
• nutrient balance
• phytotoxicity

ACKNOWLEDGMENTS

This work was financially supported by the National High Technology Research and Development Program of China (2006AA06Z384) and the National Key Technology R&D Program (No.2006BAD10B09 and 2006BAJ10B04).