Comparison of biochars derived from wood pellets and pelletized wheat straw as replacements for peat in potting substrates

Authors: Vaughn, Steven; Kenar, James - Jim; Thompson, Arthur - Art; Peterson, Steven - Steve

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2013
Publication Date: 11/1/2013
Citation: Vaughn, S.F., Kenar, J.A., Thompson, A.R., Peterson, S.C. 2013. Comparison of biochars derived from wood pellets and pelletized wheat straw as replacements for peat in potting substrates. Industrial Crops and Products. 51(1):437-443.

Interpretive Summary: Biochar is the solid, carbon-rich product resulting from the pyrolysis (thermal decomposition) of biomass in the absence of oxygen. Biochars are being examined for horticultural uses, including as a replacement for peat moss in soilless substrates used to grow greenhouse and nursery crops. Biochars were prepared from hardwood pellets and from pelletized wheat straw. Both types of biochars had higher pH values and bulk densities than peat moss. When tomato and marigold plants were grown with increasing levels of both biochars, there were no differences in tomato plant weights after 4 weeks of growth, but plant heights increased in all biochar treatments. Marigold plant heights were greater than the control in all but one biochar treatment, but the addition of the biochars had little effect on plant weights. These results indicate that both pelletized biochars would be suitable as replacements for peat in soilless substrates when used at these replacement rates. Reducing peat moss usage is environmentally responsible because replenishing peat moss naturally can take thousands of years and many rare and threatened plants and animals are native to peat moss bogs.

Technical Abstract: Biochar is the solid, carbon-rich product resulting from the pyrolysis of biomass in the absence of oxygen. We are examining biochars for several horticultural applications, including as a replacement for peat moss in soilless substrates used in the production of containerized greenhouse and nursery crops. Biochars were prepared from hardwood pellets and from pelletized wheat straw. Straw biochar had a higher potassium content and pH than the wood biochar. FTIR analyses of the biochars showed much greater volatile content in the straw biochar. Both biochars had significantly higher bulk densities than either peat moss or vermiculite. Substituting biochar pellets (at rates of 5%, 10%, and 15% v/v) for peat moss increased substrate pHs, bulk densities, and electrical conductivities, while having variable effects on physical properties (air porosities, container capacities, and total porosities). Greenhouse experiments were conducted using tomato (Solanum lycopersicum L.) and marigold (Tagetes erecta L.) plants grown in 3.0-L pots. Addition of either biochar had no effect on dry weights of tomato plants after 4 weeks of growth, but significantly increased plant heights in all treatments. Marigold plant heights were greater than the control in all but the 5% wood biochar, but had only a minor effect on plant dry weights. These results indicate that both pelletized biochars would be suitable as replacements for peat in soilless substrates when used at these replacement rates.