In a two-year field experiment (2008-09), the effect of increasing doses of compost produced from municipal sewage sludge with or without the addition of active substance PRP®SOL (PRP Technologies, France) on urease and dehydrogenase activities during cultivation of winter wheat and spring rapeseed was studied. The experimental design included a control treatment with standard mineral fertilization and three levels of organic fertilization. The used compost doses were equivalent to 100, 200, and 300 kg N·ha^-1. Organic fertilization was carried out on 28 September 2007. In 2008 and 2009 the whole experimental area was fertilized with active substance PRP SOL at a 150 kg·ha^-1 dose and multicomponent fertilize Polifoska 6 at a 200 kg·ha^-1 dose. Due to the low nitrogen content in Polifoska 6 (6% N), urea top-dressing for winter wheat and spring rapeseed was applied at a dose of 100 kg N·ha^-1 in two times periods. Soil samples for chemical analyses were collected from the arable layer (0-25 cm) under winter wheat four times: April, May, and July (soil sampling times I to III), and after its harvest at the end of August 2008 (sampling time IV). In spring 2009, spring rapeseed was sown in the same field, and soil samples for analyses were collected in the same times I to III (April, May, and July), while soil sampling time IV following the rapeseed harvest fell at the beginning of August 2009. It was found that fertilization with a triple dose of compost with a PRP SOL addition increased the soil pHKCl value as compared to control soils. Higher organic carbon (OC), nitrogen (N), and phosphorus (P) contents were found in the soils collected from experimental plots being fertilized with a double and a triple dose of municipal sewage sludge compost with a PRP SOL addition. Significant increase in urease activity was found between soil sampling times I and IV (specify the treatment here). The applied fertilization with single and a triple doses on compost with or without PRP SOL increased the urease activity on average by 30.4 between soil sampling times I and IV. The largest increase in dehydrogenase activity was observed between soil sampling times I and III and in control objects. The applied fertilization with a triple dose of compost with or without PRP SOL increased the dehydrogenase activity on average by 18.65% between soil sampling times I and III.
The applied organic fertilization together with active substance PRP SOL stimulated the enzymatic activity of urease and dehydrogenase in all cases.