CONICET | Buscador de Institutos y Recursos Humanos

Intensive agricultural systems have resulted in a depletion of soil organic matter stocks and nutrient content. In the last two decades agronomic systems have shifted towards more sustainable agronomic practices, including those aimed at recovering and maintaining soil health. In this sense, the addition of biochar -a porous, carbonaceous material- to the soil has been shown to be an effective method to enhance carbon sequestration and soil fertility. Pyrolysis is one of the technologies available for biomass conversion which is receiving worldwide attention as a promising pathway to sustainability, as it allows for the complete utilization of the biomass yielding bio-oil, bio-syngas and biochar. In this process, organic material undergoes rapid thermal decomposition in the absence of oxygen, and the yields of products are influenced by feedstock properties and operation parameters.In this study we prepared biochars from different biomass feedstocks: a) leaves and stems of Flourensia oolepis (FO), which is an endemic species of the arid central region of Argentina; b) peanut shells (PS), a waste product of peanut industries produced in large amounts in Córdoba province and c) residues of Phitophora sp. Alga (PhA), a freshwater microalga that grows profusely in local rivers. Biochars were produced from the fast pyrolysis of starting biomasses between 280-350 ºC under vacuum (0.1 -0.05 Torr) in a nitrogen atmosphere.The bioactivity of biochar aqueous extracts was evaluated on seeds of lettuce (Lactuca sativa) at 10 %, 7.5, 5, 2.5 and 1.5 % (w/v). Seed germination was assessed at 24 h interval during three days as described in Silva et al. (2012, Phytochemistry 77: 140-148). FO leaves-derived biochar water extracts exhibited a hormetic type of response, and only a transient inhibition of germination occurred at higher doses (10% w/v). Water extracts between 1.5 and 5 % (w/v) stimulated root and shoot growth up to 225 %. In the case of FO stems, bio-char water extracts did not affect seed germination at any of the concentrations tested; all the seeds germinated producing seedlings with normal morphology. The growth promoting effect of these extracts was even more dramatic than those found in the biochar water extracts derived from leaves. Shoot and root growth was stimulated at all concentrations tested; values ranged from 150 % to as much as 330 % promotion of growth at concentrations between 5 and 7.5 %, relative to the controls. The bio-char water extracts of PS did not affect germination, but seedlings exhibited abnormal morphology (small and dark apexes). Root growth was inhibited at 5 and 7,5 % (w/v) , while shoot growth inhibition occurred only at 5 % (w/v).Bioassays carried out with leachates of PhA biochar showed the presence of fungi and germination was nil. Results show that FO could be considered a promissory species for the production of biochar, and the extremely high promoting effect of water extracts on seedling growth deserves to be investigated in depth. Although results with PS biochar water extracts were not promissory, further testing should be performed to assess if seedlings can attain normal growth.