VALUTAZIONE DELLE POTENZIALITÀ DEL BIOCHAR COME COMPONENTE DEI SUBSTRATI DI COLTIVAZIONE

The possibility of using biochar as a soil amendment for agricultural land has been intensively investigated, but it is only recently that biochar is proposed for greenhouse applications. Biochar can be used as a partial substitute of commercial peat for the cultivation of potting plants, so reducing the use of a non-renewable material like peat. In fact peat has a slow regrowth rate of 0.5-2 mm per year, and costs of extraction and transportation of peat are increasing. In this dissertation, the effects of four biochars added to a peat-based growing media are explored. Biochars are produced via pyro-gasification of plant derived feedstocks, (chipped and pelletized poplar and spruce wood), and analized for their properties useful to predict their behaviour in a potting mix. All the studied biochars are alkaline, show good physical stability (lack of shrinking), are richness in basic cations, particularly potassium, and show different particle size distributions. The first experiments carried on on mixtures of biochar and peat focuse on: 1) the liming power of biochars; 2) the influence of biochars on the pore water composition; 3) the effects of biochar application on the plant growth and nutrient uptake. When added to an acidic peat in a dose of 30% v/v , biochars neutralize both peat acidity and the acidification induced by root activity, that is inversely related to the size of particles and not influenced by biochars pH. Incubations of mixtures with and without plants highlight a dramatic influence of biochars on pore water composition.The poplar wood biochar induces an almost complete depletion of the fertilizer-derived NH4 +-N and high levels of NO3 --N in pore water, even though a decline over time is detected. On the contrary, in the sprucewood biochar added mixture NH4 +-N is immobilized in a lesser extent and only trace amounts of NO3 --N are detected. Further, the abilities of biochars to adsorb ammonia and nitrate are explored and a greater capacity for ammonia adsorption is detected. Then biochars are loaded with ammonium and an incubation test and a plant growth trial are performed on the ammonium-enriched materials added to a peat based growing media, compared with (NH4)2SO4 and with a loaded zeolite. Ammonia from the loaded biochars are more bioavailable than that carried by zeolite and both the studied biochars promote plant nitrogen uptake. Lastly, a trial is conducted in a commercial greenhouse using two biochars for total replacements of lime and partial substitution of the inorganic component (perlite). The growth of Ciclamen persicum plants results only slightly influenced by the biochars while pore water solution composition is deeply modified by the biochars. It can be concluded that biochar efficiently substitutes lime in buffering peat acidity and may be used as a partial replacement for peat and a source of potassium. Its highly reactive surfaces account its potential to significantly alter soil solution chemistry.