The monitoring of biological parameters is one of the most essential issues in order to check the soil health and quality when amended with wastewater sludge. The objectives of the model pot experiment were to determine the impacts of wastewater sludge amendment on the plant growth and soil properties. Various soil types [kovárvány brown forest soil (Nyíregyháza), clay loam brown forest soils (Gödöllő) and meadow chernozem soil (Szeged)] were used and amended with various rates of wastewater sludge [Control soil (0), 20, 40, 60, 100 (sludge)%)] of different sources. Rye (Secale cereale L.) plants were grown for 63 days on various sludge/soil ratios in the pots of 3 kg capacity. Different parameters were measured e.g., the relative plant dry matter content, changes in the soil pH and moisture content. Some microbial properties of the rye rhizosphere (e.g., total count of aerobic heterotrophic bacteria, aerobic heterotrophic spore-forming, cellulose-decomposing and phosphate-dissolving microorganisms, fluorescent Pseudomonas, actinomycetes, filamentous fungi and yeasts) and enzymactic activities (FDA, dehydrogenase, catalase, urease, protease, phosphatase, β-glucosidase, invertase and aryl sulphatase) were studied. The soil basal respiration was measured in terms of the quantity of CO2-production. The results indicated that after the application of wastewater sludge, the soil retained its moisture content for a longer period than the free wastewater sludge control soil. Also, soil pH was maintained to be favourable for plant growth more than the control soil. In addition to exhibiting healthy growth and development, the plants also produced the greatest dry matter mass on soils with the largest proportion of sewage sludge (60–100%). The enzymatic activities in the soil samples treated with wastewater sludge were increased in soil with higher sludge doses. There was an increase in the density of the microbial population in the rye rhizosphere as the wastewater sludge dose increased.

Results demonstrated that Gram-negative bacteria were dominant in the rye plant rhizosphere and the ratio between Gram-negative and Gram-positive bacteria in the Kovárvány brown forest soil, clay loam brown forest soil and meadow chernozem soil treated with the Hódmezővásárhely and Nyíregyháza wastewater sludges were 2.106, 2.26, 2.01, 2.367, 2.35 and 3.24, respectively.

Finally, soil treatment with wastewater sludge stimulated rye plant growth, improved the biochemical and microbial properties of the rye plant rhizosphere, promoted the retention of soil moisture and raised the soil pH, which also had a favourable effect on rye plant growth. For maintaining the soil quality, the authors recommend to treat the acidic soil with a ratio of 40–60% wastewater sludge to improve the fertility of the soil.

Keywords: monitoring, rhizosphere properties, rye plant growth, wastewater sludge