Impact of a spent mushroom substrate, Agaricus bisporus on chromium and copper speciation in the humus horizon

Spent mushroom substrate used as fertilizing material provides nutrients for plants in forms with a different degree of availability. A two-year experiment was conducted in central eastern Poland (Siedlecka High Plain) to determine the fertilizing effect of substrate previously used to grow mushrooms (Agaricus bisporus) on the total content chromium and copper content and their quantitative content in the fraction in humus horizon pseudogley loessive soil. The experiment included the control (without fertilization), and several fertilized variants: NPK, swine manure, swine manure + NPK, spent mushroom substrate and spent mushroom substrate +NPK. The sequential fractionation of chromium and copper, carried out according to the BCR protocol, in the soil humus horizon under the above treatments demonstrated various concentration of these metals in the extracted fractions and their shares in the total content. Fertilization with spent mushroom substrate alone and with NPK contributed to a decrease in the Cr content in the F2 and F3 fractions, but resulted in an increase in the Cu content in the F1, F2 and F3 fractions after the second year of plant cultivation in comparison with the first year. The highest share of the tested metals in the total content was detected in the residual fraction F4: after the second year for chromium and after the first year of the experiment for copper.