Owing to the growing volumes of ash and sewage sludge waste, there is a requirement for theoretical and practical research into the use of these wastes as a source of nutrients. However, there are relatively few studies on the transfer of macronutrients in soil-plant systems amended with ash-sewage sludge mixtures under field conditions. The aim of the study was to determine the effect of bituminous coal ash (AC), biomass ash (AB), and municipal sewage sludge (MSS) on the quantity and quality of a grass-legume mixture. During a 6 year field experiment on a sandy loam soil treated with the wastes, applied as mixtures or separately, the plant yield; N, P, K, Na, Mg, and Ca uptake by plants; macronutrient content and ratios in the plant biomass; and the recovery rate of macronutrients by plants were evaluated. The AB-MSS treatment increased the yield in comparison to that where the wastes were applied separately. The N, P, and Ca contents in the plant biomass and N and P uptake under ash-sludge treatments were in the range observed for the ash and sewage sludge. The AB-MSS co-application resulted in the highest K uptake. The AC-MSS treatment increased K and Mg uptake in relation to AC treatment. When AC or AB was added to the MSS, the Ca uptake increased relative to the MSS treatment. The plant biomass under the AB treatment was optimal for biofuel purposes in terms of the chemical composition. The co-application of AC or AB with MSS resulted in the optimum Ca:Mg ratio for fodder purposes. The recovery rate of the macroelements decreased in the following order: K, N, P, Mg, Na, and Ca. The results support the co-application of solid wastes such as ash and municipal sewage sludge to improve productivity, support the recycling of macronutrients, improve sustainability through the reduction of ash and sewage sludge disposal, and reduce reliance on mineral fertilizer.

This study was conducted over the period 2017–2019 in Czesławice (central Lublin region, Poland). The aim of the present study was to compare chemical soil quality parameters (soil pH, available P and K, organic carbon, and total nitrogen content) and soil enzymatic activity (dehydrogenase, acid phosphatase, alkaline phosphatase, urease, protease) in organic and conventional farming systems. The experimental design included two crop rotations (organic and conventional) in which identical plant species were grown: sugar beet-spring barley-red clover-winter wheat-oats. The loess soil on which the experiment was conducted was characterized by the grain size distribution of silt loam, and this soil was categorized as good wheat soil complex (soil class II). The experiment was set up as a split-plot design in triplicate in plots with an area of 40 m². Soil sampling was carried out using a soil auger within an area of 0.20 m² (from the 0 to 20 cm layer) in each plot during the autumn period. Over the 3-year study period, it was found that the organic system contributed to an increased soil content of organic carbon and total nitrogen. Moreover, a significantly higher soil pH value and a favorable narrow C/N ratio were found under the organic system (regardless of the crop species). Under the conventional system, in turn, a higher soil phosphorus and potassium content was observed. Enzymatic tests of the soil in the five-field crop rotation proved significantly higher activity of all the enzymes studied (in particular that of dehydrogenase, protease, and urease) in the organic system relative to the conventional one, regardless of the crop plant. Among the plants grown in crop rotation, sugar beet, and red clover had the most beneficial effect on the activity of the soil enzymes, followed by oats (especially under the organic system). The activity of the studied enzymes in the organic system was positively correlated (statistically significantly) with favorable soil pH, a higher content of organic C, and total N, and C/N ratio.