Pattern of pore water nutrients in planted and non-planted soilless substrates as affected by the addition of biochars from wood gasification

The primary objective of this study was to evaluate the effects of partial replacement of peat by hardwood (poplar) or softwood (spruce) gasification biochars on nutrient release and retention and the effectiveness of biochars to neutralize peat acidity in non-planted and planted (basil) substrates during 36 days of incubation. Pots (1L) filled with biochars+peat and with limed peat (control) were drenched with fertilizing solutions and watered at pF1. pH and nutrients content in substrate pore water were determined in Rhizon samples taken at 15, 22, 29, and 36 days of incubation. The hardwood biochar was more efficient than the softwood biochar in neutralizing both peat acidity and the acidification induced by root activity. Both biochars improved ammonia removal from pore water; this effect increased with time and was particularly noticeable for the hardwood biochar, which induced an almost complete depletion of the fertilizer-derived NH4 (+)-N. The hardwood biochar also account for high levels of NO3 (-)-N in pore water, even though a decline over time was detected. Both biochars increased pore water potassium with a higher buffering power of the softwood biochar in respect to the hardwood one. Fluctuation of calcium and magnesium concentrations was related with changes in pH due to abiotic and biotic processes. Pore water composition in planted substrates was affected by plant uptake and by root driven changes in substrates' pH.