Biochar is a growth-promoting alternative to peat moss for the inoculation of corn with a pseudomonad

Peat moss has been a standard carrier of inoculum for experimentation and in agriculture. Peat moss is, however, a non-renewable resource. Alternatively, biochar could serve as an inoculum carrier. Here, we tested the effect of biochar-based seed coatings as a carrier for the phosphorous-solubilizing Pseudomonas libanensis inoculum, on corn growth after soluble and insoluble P addition. The survival of P. libanensis was determined based on the measure of colony-forming units from samples of four inoculated guar gum-based biochar coatings and was compared to peat. Storage experiments were performed on inoculated biochars for 22 weeks at 25 °C and on coated corn seeds for 16 weeks at 4 °C. Seed coatings were prepared with inoculated and uninoculated biochars (100 seeds treatment⁻¹), and effects of these treatments are reported on indices of seed germination after 7 days. A greenhouse experiment investigated the effects of the inoculated and uninoculated biochar seed coating on corn plants. The parameters measured from the greenhouse-grown corn plants were germination, fresh weight, dry weight, height, root length, basal stem diameter, leaf area, chlorophyll content, and tissue phosphorous. Our results show that corn plants grown from seeds coated with a biochar from hardwood feedstock are 2 to 10 g heavier than controls and that controls are 4 to 26 % shorter than the plants grown from biochar-coated seeds, where soluble phosphorous is applied. Moreover, corn seeds that were coated with a biochar produced from softwood feedstock germinated more quickly, based on the speed of germination index. Overall, we show that a biochar-based seed coating can benefit sustainable agriculture by carrying P. libanensis and enhancing the growth of corn, but according to parametric statistical tests, it does so without increasing the phosphorous content of the plants.