Sewage Sludge Biochar Effects on Phosphorus Mobility in Soil and Accumulation in Plant

In the course of analysing sewage sludge biochar (BC) as a material containing phosphorus loads, we determined the following: effect of thermal conversion of three different sewage sludge biochars on the content and availability of P in biochars (BC-1, BC-2 BC-3), effect of their application on selected forms of P in soil and on the accumulation of this component in Poa pratensis L. biomass. Regardless of the type of BC, the contents of P-H₂O and P-CaCl₂ were lower than the contents determined in unconverted sewage sludge. A significant increase in the content of P-CaCl₂ compared to the control was noted in the soil of treatments where 1 and 2 % additions of BC-2 and BC-3 were applied. Soil pH (r = 0.826; p ≤ 0.05) and the content of Ca-exchangeable (r = 0.712; p ≤ 0.05) had the strongest effect on the content of P-CaCl₂ in soil; however, no significant relationship was found between the amount of P-introduced with BC, the contents of Al-ox., Fe-ox. and the content of P-CaCl₂. Significant (p ≤ 0.05) increase in the phosphorus content in plant biomass was noted in all treatments compared to the control. Regardless of the type of biochar applied, the highest amount of P-uptake was determined in treatments where the greatest addition of BC (2 %) was introduced into the soil. A significant relationship between P-uptake and the amount of P-introduced with BC into the soil (r = 0.726; p ≤ 0.05) was demonstrated.