Evaluation of a hardwood biochar and two composts mixes as replacements for a peat-based commercial substrate

Biochar (BC) has the potential to be used as alternative container substrate, which adds value to the bioenergy process. But high percentage of BC may suppress plant growth and there is limited research on BC and compost in container. High percentages of mixed hardwood BC (60%, 70%, 80% or 90%, by vol.) mixed with either 5% (by vol.) vermicompost (VC) or chicken manure compost (CM) were evaluated to substitute a peat-based commercial container substrate (Berger BM7), using basil (Ociinzun basilicum) and tomato (Solanum lycopersicum) as test crops. Total porosity, container capacity, air space and bulk density of BC-compost mixes were all in or close to the recommended ranges for container substrates. High percentage of BC incorporation reduced the SPAD readings caused by BC's N-binding effect. BC-compost mixes had no effect on the plants' photosynthetic rates at 5 weeks after transplanting (WAT). At 8 WAT, the growth index (GI), shoot dry weight (DW) and fresh weight (FW), and root and total DW of basil plants in 80BC:5CM, 90BC:5VC and 90BC:5CM were reduced due to high salt and pH while those in other BC-compost mixes were similar to the control. The BC-compost mixes (except 90BC:5CM) did not negatively affect the GI, stem, root and total DW, and red and total fruit FW and DW of tomato plants. Therefore, 5% (by vol.) CM and VC was a good potential amendment candidate for replacing peat-based substrate with 60% and 70% BC to grow container plants. Mixture of 5% CM with 70% BC with the rest the Berger BM7 peat-based substrate is recommended since its wholesale price is estimated at 54% of that of 100% Berger BM7 substrate. These results benefit bioenergy companies by adding value to the byproduct BC and provide economical and sustainable container substrate alternatives for horticultural producers.