Effect of limed and unlimed sewage sludge on the pH of soils of different textures

Abstract

Sewage sludge is a residue that can be used in agriculture due to the presence of organic matter and nutrients. However, it must be stabilized and sanitized, with the application of quicklime being a possible treatment by raising the pH. Thus, the objective of the work is to evaluate the pH in soils of different textures subjected to doses of limed and unlimed sewage sludge. The experiment was composed of a triple factorial 2 x 3 x 6, in which two treatments were used (not limed and limed), three soil textures (sandy, medium and clayey) and six doses of sewage sludge (0, 5, 10, 20, 40 and 80 t ha^-1), with three replications. The dose of quicklime required to raise the pH by 12 was 44 kg m^-3 and 72 kg m^-3, in a period of 2 and 72 hours, respectively. Unlimed sewage sludge caused a marked reduction in soil pH after 21 days, as a result of the decomposition and nitrification process, and application of 80 t ha-1 reduces pH by 4.8%, 9.9% and 9 .6%, for sandy, medium and clayey texture. The limed sludge showed high reactivity in the soil after seven days, with a reduction in the alkanylization reaction over time. In general, for sandy soil, the pH value was around 7.6, while for medium and clayey soils the pH value was 7.4, at a dose of 80 t ha^-1.