The determination of the maturity of compost and other organic fertilizers is very important because of possible phytotoxic or phytostimulating effects. The maturity of compost can be assessed on the basis of chemical analyses, and a germination test with different test plants is most often used to determine phytotoxicity. In this research, the maturity of compost produced from the plant residues subsequent to the maintenance of green public areas was assessed using the results of chemical analyses. Simultaneously, a germination test was carried out with the four test plant species (cucumber, garden cress, triticale, and barley) to determine the phytotoxicity of compost extract in a ratio of 1:2.5 v/v (1:3.3 w/v) and 1:10 v/v (1:13.3 w/v) and the three ammonium N solutions (in the concentrations of 200, 400, and 600 mg/L NH₄-N). According to the chemical properties of compost (primarily the C/N, NH₄-N/NO₃-N ratios, and the NH₄-N concentration) and the germination test with cucumber and garden cress, we may conclude that the tested compost was mature and that we did not expect a phytotoxic effect. The choice of a plant is very significant because the germination test with a compost extract demonstrated an undoubted phytostimulating effect on the garden cress and cucumber, with a more pronounced phytostimulating effect of the 1:10 than that of the 1:2.5 v/v compost extract. No such effect was detected on the monocotyledonous test plants triticale and barley since the 1:10 v/v extract had no significant effect, and the 1:2.5 v/v extract had a phytotoxic effect, moderate on the triticale and high on barley. The conclusion is that garden cress and cucumber are suitable test plants for the determination of compost’s phytostimulative effect, but they are not suitable for the determination of phytotoxicity for monocotyledonous plants, especially if the cause of phytotoxicity is a non-ammonium component. Barley is the most suitable species for the determination of compost’s non-ammonium phytotoxicity and nitrogen’s ammonium-form phytostimulative or phytotoxic effect. It would be very useful to conduct a comparative germination test with the compost extracts in the ratios 1:2.5 and 1:10, whereby the 1:2.5 extract would be used as a test of phytotoxicity, and the 1:10 extract for the test of a phytostimulating effect.

Determining the maturity of compost and other organic fertilizers is very important because of possible phytotoxic or phytostimulative effects. The maturity of the compost can be assessed on the basis of chemical analyses, and the germination test with different test plants is most often used to determine phytotoxicity. In this research, using the results of chemical analyses, the maturity of compost produced from plant residues after maintenance of green public areas was assessed. At the same time, a germination test was carried out with 4 test plant species (cucumber, garden cress, triticale, barley) to determine the phytotoxicity of compost (i.e. compost extract in a ratio of 1:2.5 and 1:10) and 3 ammonium N solutions (in concentrations of 200, 400 and 600 mg/L NH4-N). According to the chemical properties of compost, primarily the C/N and NH4-N/NO3-N ratios, as well as the NH4-N concentration, and the germination test with cu-cumber and garden cress, we can conclude that the tested compost was mature and that we do not expect a phytotoxic effect. The choice of the plant is very significant because the germination test with compost extract shows an undoubted phytostimulative effect on garden cress and cu-cumber with more pronounced phytostimulative effect of compost 1:10 than 1:2.5 extract. No such effect was found on the monocotyledonous test plants triticale and barley since the 1:10 ex-tract had no significant effect, and the 1:2.5 extract had a phytotoxic effect, moderate on triticale and high on barley. The conclusion is that garden cress and cucumber are suitable test plants for determining phytostimulative effect of compost, but they are not suitable for determining phytotoxicity for monocotyledonous plants, especially if the cause of phytotoxicity is some non-ammonium component. Barley is the most suitable species for determining non-ammonium phytotoxicity of compost and phytostimulative or phytotoxic effect of ammonium form of nitrogen. It would be very useful to conduct a comparative germination test with compost extracts in the ratio 1:2.5 and 1:10, whereby the 1:2.5 extract is used as a test for phytotoxicity, and the 1:10 extract for testing phytostimulative effect.

The short-term effects of processed waste materials: sewage sludge compost (up to 0.5%), biochar made of paper sludge and grain husk (BC) (up to 2%) combined with plant growth-promoting rhizobacterial (PGPR) inoculum, on the fertility of acidic sandy soil at 65% of field capacity were tested in a pot experiment in separate and combined treatments. The soil pH, organic matter content, total and plant-available nutrients, substrate-induced respiration, arbuscular mycorrhizal fungal (AMF) root colonisation parameters and maize (Zea mays L.) biomass were investigated in experiments lasting two months. The positive priming (21% organic matter loss) induced by BC alone was not observed after combined application. The combination of compost and PGPR with 1.5% BC resulted in 35% higher P and K availability due to greater microbial activity compared to BC alone. Only compost applied alone at 0.5% gave a 2.7 times increase in maize biomass. The highest microbial activity and lowest AMF colonisation were found in combined treatments. In the short term the combined application of BC, compost and PGPR did not result in higher fertility on the investigated soil. Further research is needed with a wider range of combined treatments on acidic sandy soil for better understanding of the process.

Additional Selenium (Se) intake may be recommended in areas of Se deficiency to prevent various human diseases. One possibility for this is biofortification. In this experiment, the effect of irrigation water containing 100 and 500 µg L⁻¹ Se, in the form of Na₂SeO₄, on green bean, cabbage, potato and tomato was investigated in a greenhouse pot experiment with sand, silty sand and silt soils. The chlorophyll content index was usually improved by Se and was significantly higher in potato in sand and silty sand and in tomato in silty sand and silt soils. The Se content of edible plant parts increased 63-fold in the 100 µg L⁻¹ Se treatment and almost 400-fold in the 500 µg L⁻¹ Se treatment, averaged over the four species and the three soils. Irrigation water with a Se content of 100 µg L⁻¹ may be suitable for the production of functional food in the case of green beans, potatoes and tomatoes. However, due to its greater Se accumulation, cabbage should only be irrigated with a lower Se concentration. The use of Se-enriched irrigation water might be a suitable method for Se biofortification without a significant reduction in plant biomass production and without a remarkable modification of other macro- and microelement contents.

Selenium (Se)-deficient diets are a problem in large areas of the world and can have serious health consequences, thus, the biofortification of foods with Se has been an important research field for several decades. The effect of Se-enriched irrigation water was investigated regarding the Se concentration in green peas and carrots. A pot experiment was set up in a greenhouse with irrigation water containing 0, 100, and 500 µg Se L⁻¹ with sand, silty sand and silt soil types. Most of the treatments only slightly reduced the biomass, while the 500 µg Se L⁻¹ treatment caused a significant decrease in the dry weight of carrot root. Treatment with irrigation water containing 100 µg Se L⁻¹ increased the Se content in green peas and carrots 76 and 75 times, respectively, producing foodstuffs where 100 g of a fresh product covered 395% and 92% of the recommended dietary allowance, respectively, averaged over the three soil types. The Se concentration was higher for green peas in sand and carrots in silt. The treatments had little effect on the concentrations of other nutrients. The enrichment of irrigation water with Se may thus be a suitable method for the biofortification and production of functional food under certain conditions.

Organic waste and the compost and vermicompost derived from it may have different agronomic values, but little work is available on this aspect of sewage sludge. A 75-day pot experiment with perennial ryegrass (Lolium perenne) as the test plant aimed to investigate the fertiliser value and organic matter replenishment capacity of digested sewage sludge (DS) and the compost (COM) and vermicompost (VC) made from it, applied in 1% and 3% doses on acidic sand and calcareous loam. The NPK content and availability, changes in organic carbon content and plant biomass, and the efficiency of the amendments as nitrogen fertilisers were investigated. The final average residual carbon content for DS, COM, and VC was 35 ± 34, 85 ± 46, and 55 ± 46%, respectively. The organic carbon mineralisation rate depended on the soil type. The additives induced significant N mineralisation in both soils: the average increment in mineral N content was 1.7 times the total added N on acidic sand and 4.2 times it on calcareous loam for the 1% dose. The agronomic efficiency of COM and VC as fertilisers was lower than that of DS. In the short term, DS proved to be the best fertiliser, while COM was the best for organic matter replenishment.