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Soil irrigation with wastewater (WW) gives the opportunity to solve the problems of its disposal, final purification or reuse. Many studies have examined mineral soils upon continued WW application. The aim of this paper was to examine the properties of organic soils 3 years after WW application was discontinued. Peat-muck soil planted with Populus spp. or Salix spp., and mineral-muck soil under grasses were irrigated for 4 years with municipal WW at a low (comparable with intensive NPK fertilization) and high WW rate (600 and 1200 mm yearly, respectively). Soils were analysed for organic matter (OM), pH, bulk density (BD), water holding capacity (WHC), P 2 O 5 , Fe 2 O 3 , Al 2 O 3 , MnO, Zn, Pb, Cu, Cr, magnetic susceptibility (MS) and dehydrogenase and catalase activities. The results were compared with control soils which have never received WW. The study showed that only P 2 O 5 , MnO and catalase activity (CA) were significantly affected by former WW application. On average, P 2 O 5 increased by 30 per cent, whereas MnO decreased by 35 per cent with no differences between the two WW rates. CA decreased by 18 per cent at the high WW rate. Most of tested characteristics were determined by soil type. The peat-muck soil showed higher OM, WHC, P 2 O 5 , MnO, Pb and CA than mineral-muck soil and lower BD, MS, Fe 2 O 3 , Al 2 O 3 and Cr. Soil depth influenced Fe 2 O 3 , MnO, Zn, MS and enzyme activities, while basic soil properties (OM, pH, BD, WHC and P 2 O 5 ) were not changed by soil depth. Heavy metals (Zn, Cr, Cu and Pb) were below upper permissible limits.

Purpose Acetylene (C 2 H 2 ) is employed for the quantification of important biological processes such as nitrogen fixation, nitrous oxide reduction, ammonium and methane oxidation, and methanogenesis. Although acetylene is not a natural product, the ability of bacteria to grow on C 2 H 2 is a phenomenon common to soils and sediments. Our experiment was designed to study the modification of CO 2 production, O 2 uptake and microbial biomass (C mic ) in soil in response to the consumption of added acetylene. Materials and methods Two soils (peat-muck and Eutric Cambisol) were incubated under well aerated (60% water holding capacity [WHC]) or flooded conditions, and enriched with C 2 H 2 in the range 0.1-10 kPa (initially, 0.434-63.4 mmol C 2 H 2 kg −1 ) at a constant temperature of 20°C. Gases were measured chromatographically, while C mic was measured by the physiological SIR (substrate-induced respiration) method based on the initial response of microorganisms to glucose amendment. We used a simple calculation of net CO 2 , net O 2 and net C mic (as differences between amended and not amended soils) to estimate the contribution of C 2 H 2 to the total respiration and microbial growth during the incubation. Results and discussion Peat-muck soil consumed more C 2 H 2 than Cambisol (maximum 54.03 vs. 19.25 mmol kg −1 , p<0.001). Acetylene utilization was faster and larger in flooded than in wet soils (16.2 and 7.81 mmol kg −1 , respectively, p<0.05), and followed the tendency observed for C mic . Depending on C 2 H 2 enrichment, air-water conditions, and soil tested, both reduction and stimulation of measured activities were observed in response to acetylene consumption. Low C 2 H 2 uptake, especially in Cambisol incubated at 60% WHC, resulted in the reduction of soil respiration and biomass (by 1-29%). Large C 2 H 2 consumption in flooded soils stimulated CO 2 production, O 2 uptake and C mic , even by 78%, 72% and 43%, respectively. Net CO 2 , net O 2 , and net C mic were linearly positively related to the quantity of consumed C 2 H 2 (p<0.001).Conclusions Acetylene utilization was a combined effect of initial C 2 H 2 , soil properties, and air-water status. The amount of consumed C 2 H 2 was the highest in flooded peat-muck soil enriched with 10 kPa, and lowest in Cambisol at 60% WHC with 0.1 kPa C 2 H 2 . Consumption of 1 mol acetylene induced production of 0.5 mol CO 2 , and uptake of 0.4 mol O 2 . Low acetylene consumption (<6 mmol kg −1 ) resulted in reduction of both soil respiration and microbial biomass.