Biochar from pyrolysis of differente biomasses as a potential soil amendment: Evaluation of phytotoxic effects in Lactuca Sativa

SILVA, MARIANA; PILONI, ROXANA; NIEVA LOBOS, MARÍA LUZ; SCOPEL, ANA; MOYANO, E. LAURA

Termas de Chillán

Congreso; TLMC 2016. Segundo Taller Latinoamericano de Materiales de Carbono para Medio Ambiente y Energía.; 2016

Intensive agricultural systems have resulted in a depletion of soil organic matterstocks and nutrient content. In the last two decades agronomic systems haveshifted towards more sustainable agronomic practices, including those aimed atrecovering and maintaining soil health. In this sense, the addition of biochar -aporous, carbonaceous material- to the soil has been shown to be an effectivemethod to enhance carbon sequestration and soil fertility.Pyrolysis is one of the technologies available for biomass conversion which isreceiving worldwide attention as a promising pathway to sustainability, as it allowsfor the complete utilization of the biomass yielding bio-oil, bio-syngas and biochar.In this process, organic material undergoes rapid thermal decomposition in theabsence of oxygen, and the yields of products are influenced by feedstockproperties and operation parameters.In this study we prepared biochars from different biomass feedstocks: a) leavesand stems of Flourensia oolepis (FO), which is an endemic species of the aridcentral region of Argentina; b) peanut shells (PS), a waste product of peanutindustries produced in large amounts in Córdoba province and c) residues ofPhitophora sp. Alga (PhA), a freshwater microalga that grows profusely in localrivers. Biochars were produced from the fast pyrolysis of starting biomassesbetween 280-350 ºC under vacuum (0.1 -0.05 Torr) in a nitrogen atmosphere.Thebioactivity of biochar aqueous extracts was evaluated on seeds of lettuce (Lactucasativa) at 10 %, 7.5, 5, 2.5 and 1.5 % (w/v). Seed germination was assessed at 24h 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 to225 %. In the case of FO stems, bio-char water extracts did not affect seed germination at any of the concentrations tested; all the seeds germinatedproducing seedlings with normal morphology. The growth promoting effect of theseextracts was even more dramatic than those found in the biochar water extractsderived from leaves. Shoot and root growth was stimulated at all concentrationstested; values ranged from 150 % to as much as 330 % promotion of growth atconcentrations between 5 and 7.5 %, relative to the controls. The bio-char waterextracts of PS did not affect germination, but seedlings exhibited abnormalmorphology (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 carriedout with leachates of PhA biochar showed the presence of fungi and germinationwas nil. Results show that FO could be considered a promissory species for theproduction of biochar, and the extremely high promoting effect of water extracts onseedling growth deserves to be investigated in depth. Although results with PSbiochar water extracts were not promissory, further testing should be performed toassess if seedlings can attain normal growth.