Biochar media addition impacts apple rootstock growth and nutrition

The effects of biochar soil amendment on perennial plant nutrition and growth are poorly understood. We investigated the effects of a green waste biochar on apple rootstock (Malus domestica var. M26) nutrition and growth in a series of pot trials. Apple rootstocks were grown for 5 months in both soil and sand media, with and without biochar, under a range of fertilization, pH, and soil biological regimes. Plant biomass and leaf nutrient concentration of apple rootstocks and substrate-induced respiration (SIR) of the soil were measured. Addition of biochar was associated with significant increases in leaf concentrations of calcium (Ca), boron (B), and sulfur (S) for apple rootstocks grown in sand. Increased uptake of S has not previously been reported and may be the result of the relatively high S content of the biochar used in this trial that resulted from the low temperature used to pyrolize the biomass. Plant dry mass significantly increased by between 75% and 220% where sand was amended with biochar for every fertilization treatment. Small, but statistically significant, increases in soil pH, from pHc (CaCl₂ extraction) 4.7 to 4.9, were found after the addition of biochar but no significant effect on soil SIR was detected. Our results indicate that biochar has positive effects on apple rootstock nutrition and growth in a sand but not in a sandy loam soil.