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The objective of the study was to assess the effects of long-term application of liquid manure from pig production and digestate from manure fermentation installation for biogas production on chemical changes in the soil, i.e.: soil reaction, accumulation of available forms of phosphorus, potassium, and magnesium in the soil arable layer, as well as the phosphorus balance. The assessment was carried out in two highly productive farms specialising in pig production, located in the Zachodniopomorskie Province. The soils under the study were treated with slurry and digestate annually for subsequent 12 years. The assessment of changes in nutrient content and accumulation was performed twice: after 10 and 12 years of fertiliser treatments. The rate of changes in soil reaction due to slurry and digestate application varied depending on the analysed field. Irrespective of the analysed field, 12-year application of slurry caused a drop in soil pH by an average of half a unit. The direction of changes in the content of available nutrient forms in the soil varied depending on the element evaluated. Notwithstanding the analysed field and the type of slurry used, a decrease in the content of available forms of potassium in the soil was observed. Slurry fertilisation did not affect magnesium contents in the soil. In the study period, the content of magnesium remained unchanged. Among the evaluated nutrients, an increased nutrient content in the soil was only found in the case of phosphorus – as a result of application of liquid manure in combination with mineral fertilisation. In the analysed farms, in the case of fields fertilised with slurry and digestate, the phosphorus balance was positive, and ranged from 15 to 40 kg P·ha−1. The obtained values of the phosphorous balance strongly suggest that regardless of the type of liquid manure used on the farm, measures should be taken to introduce changes in the scope of fertilisation plans, with particular emphasis on the principles of balanced fertilisation.

Due to the fact that soils in Poland are mostly light soils, there is a need to improve their physical, chemical and biological properties. In addition, as a result of the decrease in the number of farm animals, a decrease in production of natural fertilizers can be observed. Low production of natural fertilizers speaks in favor of agricultural use of municipal sewage sludge in Poland. Municipal sewage sludge is composed of large quantities of macronutrients necessary for plants. This waste also contains significant amounts of organic substance. Chemical properties, including a high content of nitrogen, phosphorus, and often calcium, speak in favor of environmental use of municipal sewage sludge. Increasing requirements with respect to environmental protection cause the necessity to assess the effects of using organic waste for fertilization. In a farm located in the commune of Iwanowice (Małopolska province), municipal sewage sludge was applied under spring barley cultivation. The soil on which municipal sewage sludge was applied was classified into the category of heavy soils with neutral reaction. When assessing the content of available nutrients (P, K, Mg) in the soil, their low content was determined. After application of municipal sewage sludge in a dose of 24 Mg fresh matter per hectare, which corresponded to 5.34 Mg DM·ha−1, under spring barley, beneficial changes in chemical properties of the soil were observed. An increase in soil abundance in organic carbon and total nitrogen was observed, as well as an increase in the content of available forms of phosphorus, potassium and magnesium. Based on the results of the conducted chemical analyses, it was established that biomass of spring barley fertilized with sewage sludge contained more macronutrients (N, P, K, Na, Ca and Mg), which improved its feed value. The field experiment showed that application of municipal sewage sludge increased uptake of macronutrients by spring barley.

The effect of addition of different materials, i.e. sludge, ash and peat, as well as different doses of mixtures of ash and sludge and ash peat, on the total content of heavy metals (Cr, Zn, Pb, Cu, Cd, Ni) and their fractions was studied. Application of municipal sewage sludge, ash-sludge and ash-peat mixtures in the experiment caused a gradual increase in the content of studied heavy metals in soil. The ash was characterized by a low content of heavy metals as compared to municipal sewage sludge. After application of peat and its mixtures with ash a decrease of content of heavy metals was observed, and when the peat was used alone the greatest increase in the organic C content in the substrate could be seen. Distribution of heavy metals in the fractions separated in different combinations shows large variations, depending on the tested metal and the studied variant. Chromium, zinc, lead, and cadmium have been accumulated mainly in the residual fraction (FV), and most of the copper and nickel have been specifically bound with organic matter (FIV). It has been found that the alkaline materials application to the soil decreased the solubility of most heavy metals, which results in a limitation of their uptake by plants. Chromium and copper were an exception, since their solubility increased with the alkalinity of the substrate. An exception was chromium and copper, which solubility increased with the alkalinity of the substrate.