Long term effect of sewage sludge additions on populations of Nocardia asteroides,micromonospora and Thermoactinomyces in soil

Actinomycetes are considered to be members of the autochthonous component of the soil microflora. However, nocardiae and, to a lesser extent micromonosporae, can exhibit a sustained zymogenous-like response when complex recalcitrant organic substrates are added to soil in the form of dried sewage sludge. Numbers of Nocardia and Micromonospora do not increase when wet sludge, which contains less organic matter, is added to soil. In contrast, Thermoactinomyces did not follow this trend and greater numbers were isolated from the wet, rather than the dried, sludge plots. Results of herbage produced by the dried sludge plots indicate that plant nutrients were continually mineralized during the 3 yr following sludge addition.