The majority of phosphorus (P) within the European Union is wasted through sewage sludge (SS) disposal (Van Dijk et al. 2016). Recycling of SS on agricultural soil is, therefore, one of the approaches for closing the P loop. Direct soil application of stabilised SS is currently common practice bringing several other benefits for soil quality. The dry SS usually contains 50–70 mass % of organic matter (Kacprzak et al. 2017), which is considered to be relatively bioavailable and is easily mineralised after application to soil (Hattori and Mukai 1986, Kacprzak et al. 2017). Even so, soil application of SS results in an increment of cation exchange capacity (CEC) of soil (Singh and Agrawal 2008), higher soil content of humic and fulvic acids (Urbaniak et al. 2017) and total content of organic carbon (C org ) (Albiach et al. 2001). Consequently, soil water holding capacity and soil aggregate stability increase while the bulk density of soil decreases after the application of SS. However, soil application of SS also represents a significant risk of soil contamination by a wide range of organic and inorganic pollutants and/or pathogens commonly contained in SS (Clarke et al. 2017, Kacprzak et al. 2017, Száková et al. 2019). Pyrolysis of SS may overcome these problems, and therefore it represents a promising technology for SS pre-treatment before soil application. During pyrolysis, SS and resulting BC become disinfected due to high processing temperatures, and, at the same time, SS organic matter undergoes a variety of chemical transformations resulting in its higher stability and resistance against microbial degrada- tion (Mašek et al. 2013, De Rosa et al. 2018). It has been well demonstrated that BC application to soil may result in a significant increment of soil pH, CEC Changes in availability of Ca, K, Mg, P and S in sewage sludge as affected by pyrolysis temperature Filip Mercl*, Zdeněk Košnář, Lorenzo Pierdonà, Leidy Marcela Ulloa-Murillo, Jiřina Száková, Pavel Tlustoš Department of Agro-environmental Chemistry and Plant Nutrition, Czech University of Life Sciences Prague, Prague, Czech Republic *Corresponding author: mercl@af.czu.cz Citation: Mercl F., Košnář Z., Pierdonà L., Ulloa-Murillo L.M., Száková J., Tlustoš P. (2020): Changes in availability of Ca, K, Mg, P and S in sewage sludge as afected by pyrolysis temperature. Plant Soil Environ., 66: 143–148. Abstract: Pyrolysis is a promising technology for sewage sludge (SS) treatment providing several improvements of SS properties for soil application. However, information on the infuence of pyrolytic temperature on the avai- lability of nutrients in resulting biochar (BC) is limited. In this study, anaerobically stabilised SS was pyrolysed in a laboratory fxed-bed reactor at 220, 320, 420, 520, and 620 °C for 30 min in the N 2 atmosphere. Pyrolysis resulted in a higher total content of all studied nutrients in BCs. Aromaticity and hydrophobicity of BCs increased with increasing temperatures while solubility decreased. Relative availability (% from total content) of nutrients in BCs was in order: Ca > Mg ~ K > S > P. Pyrolysis at 220 °C produced acidic BC with a higher content of acetic acid-extractable nutrients compared to non-pyrolysed control. An increment in pH and a signifcant drop in the content of available Ca, Mg, K and S were found at temperature 320 °C. Pyrolysis at 320 °C increased the content of available P by 28 % compared to non-pyrolysed SS. At the temperature of 420 °C and higher, available contents of all studied nutrients were lower than in non-pyrolysed SS. Keywords: torrefaction; biosolids; disinfection; plant nutrition; phosphorus; recycling Supported by the Ministry of Agriculture of the Czech Republic, Project No. QK1710379, and by the European Regional Development Fund, Project NUTRISK No. CZ.02.1.01/0.0/0.0/16_019/0000845. 143 Plant, Soil and Environment, 66, 2020 (4): 143–148 Original Paper https://doi.org/10.17221/605/2019-PSE