Effect of Biochar on Growth of Chrysanthemum and Tomato Plants in Containers

Biochar (BC), the byproduct of fast pyrolysis of pine wood, was investigated as potting substrate on greenhouse-grown chrysanthemum (Chrysanthemum nankingense) and tomato (Lycopersicum ‘Heritage’) in containers.  Biochar was mixed with pine bark (PB) or a commercial substrate (SB) at 0, 20%, 40%, 60%, 80% or 100% (vol.) ratio. Tomato seedlings  and chrysanthemum rooted cuttings were transplanted in containers with the BC-based substrates. Compared to 100% PB, growth index (GI) of chrysanthemum was not significantly higher or lower when BC was blended in the potting mix at 20%, 40%, 60%, 80%, or 100% ratio.  The number of flowers was similar for all mixes except 80% BC/20% PB.  None of the fresh weight and dry weight of chrysanthemum plants grown in potting mixes with BC was lower than that of plants grown in 100% PB.  Growth index of chrysanthemum plants was higher for all mixes with BC than 100% SB.  Plants grown in mixes with BC had more flowers than 100% SB and their fresh weight and dry weight were higher than those grown in 100% SB. For tomato plants, in BC/PB mixes, plants grown 20%, 80%, and 100% BC had only slightly lower GI than plants in 100% PB, and plants in 40% and 60% BC had slightly higher GI than those in 100% PB.  In BC/SB mixes, GI of tomato plants grown in mixes with BC was similar to that of plants in 100% SB.  Plants grown in mixes with up to 60% BC had similar or higher fresh weight and dry weight than 100% SB. The pH of mixes with BC may be higher than 100% PB on 16 days after planting (DAP), but was lower than 100% PB on 44 DAP.  EC of BC/PB mixes was similar at 16 DAP and 30 DAP, but EC of potting mixes was generally higher with higher percentage of BC in the potting mixes on 44 DAP.  The pH of mixes with BC was higher than that of 100% SB on 16 DAP and 30 DAP, but was similar to 100% SB on 44 DAP.  EC of mixes with BC was lower than 100% SB at 16 DAP and 30 DAP, but was similar to 100% SB on 44 DAP.