Effect of Sewage Sludge Applied to Sandy Soils on the Sorption Complex Properties

Properties of soil sorption complex are thought to be one of the most important elements which affect its fertility and properties of plants. Extended sorption complex is the element which immobilizes and absorbs a variety of soil contaminants. Characteristics of sorption complex are affected by e.g. organic matter, humic relationships which occur during decomposition of organic matter, clay materials, pH, hydrolytic acidity. Soil reaction is regarded to be one of the most important indicators of soil fertility. Soil reaction largely determines its physical, chemical and biological properties. Foundation acidity affects the structure firmness and the related water and air conditions. One of the methods of disposal of sewage sludge, which is based on its fertilizing properties, is its use in nature, e.g. in farming (if all the permissible standards are met). However, the sludge used for soil fertilization might also contain heavy metals which cause soil contamination and are accumulated in plants. The effect of application of organic fertilizers on soil reaction and other properties of sorption complex are also essential. The authors of the present study aimed at analysis of the effect of use of sewage sludge and selected organic fertilizers on changes in sorption properties in the fertilized soils. Sewage sludge was (for comparison purposes) was introduced to sandy soil. One of organic additions was also composted pine bark. The experiment was carried out under conditions of pot experiment. The following doses of organic fertilizers were used: 0, 10, 50, 100 and 200 Mg/ha (maximal reclamation dose according to current recommendations at the time of experiment) which were calculated per pot with 10 kg of sandy soil. After 1, 2 and 3 years from fertilization, changes in active and hydrolytic acidity were analysed in the fertilized foundations. The contents of organic matter, total of alkali in sorption complex S, soil sorption capacity T in fertilized soils was also determined. In summary of the obtained results, one can conclude that the use of organic fertilizers, either manure or sewage sludge, considerably affects properties of sorption complex in fertilized soil. Organic fertilization improved soil properties. The total of exchangeable alkali and sorption complex capacity also increased. However, it was only manure used during the experiment that contributed to a reduction in the acidity of the fertilized soils in each case. It was found that the use of sewage sludge has significant effect on long-term phenomena of soil acidification. These mechanisms are confirmed by the obtained values of hydrolytic acidity