Some characteristics of organic soils irrigated with municipal wastewater

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), P₂O₅, Fe₂O₃, Al₂O₃, 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 P₂O₅, MnO and catalase activity (CA) were significantly affected by former WW application. On average, P₂O₅ 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, P₂O₅, MnO, Pb and CA than mineral‐muck soil and lower BD, MS, Fe₂O₃, Al₂O₃ and Cr. Soil depth influenced Fe₂O₃, MnO, Zn, MS and enzyme activities, while basic soil properties (OM, pH, BD, WHC and P₂O₅) were not changed by soil depth. Heavy metals (Zn, Cr, Cu and Pb) were below upper permissible limits. Copyright © 2010 John Wiley & Sons, Ltd.