Microbiological activity of soil amended with granulated fertilizer from sewage sludge

Abstract

The study was conducted on a model of a pot experiment in which grey-brown podzolic soil developed from weakly loamy sand was amended with granulated dry organic-mineral fertilizer prepared from municipal sewage sludge. Three levels of pre-sowing fertilization with the granulate were applied: I – a dose which brought nitrogen in the amount of 0.35 g kg-1 d.m. of soil, II – a 50% higher dose, and III – a 100% higher dose. Additionally, a treatment with average mineral fertilization (NPK) was run. The control treatment was non-fertilized soil. Soil prepared as above was placed in pots and sown with white mustard (cv. Borowska) in spring in the 1 st and 2nd year of the experiment. During the experiment, the soil moisture was maintained at the level of ca 60% t.w.c. Microbiological and biochemical soil assays were conducted three times in the first and second years of the experiment, i.e. in May and July and 41 days from harvesting the crop and mixing of its fragmented residues with the soil. The scope of the analyses included numbers of bacteria with low and high nutrition requirements, total numbers of filamentous fungi, cellulolytic, proteolytic and lipolytic bacteria and fungi. Other analyses included determinations of the respiratory activity in soil, the rate of cellulose mineralization and the activity of dehydrogenases, lipase, protease and acid phosphatase. The study showed a stimulating effect of the sludge granulate on the above groups of bacteria and fungi, both in the 1 st and in the 2 nd years of the experiment. The effect generally weakened with time. The fertilization also stimulated the respiratory rate and activity of phosphatase. However, it inhibited the mineralisation of cellulose as well as the activity of dehydrogenases, lipase and protease in soil. The application of mineral fertilization in the form of NPK did not cause any changes in numbers of the analyzed bacterial groups, except a certain decreasing tendency in the second year. In both years, mineral fertilization contributed to the stimulation of the growth of most fungi. It also enhanced the respiratory activity, rate of cellulose mineralisation, and the activity of dehydrogenase and acid phosphatase, albeit only in the first year of the experiment. Finally, in the soil with mineral fertilization the activity of protease and lipase was observed to have declined.