Assessing biochar as a lime replacement for peat substrates

Peat is used as the base medium in greenhouse production, but its acidic nature requires amendments such as lime to bring the pH up to the recommended ranges of 5.4-6.6 for soilless substrates. Biochar is a sustainable option as a substrate component with varying characteristics of surface area, pH, nutrient supply and water storage. Using less nutrient-rich feedstocks for biochar production has created material with high pH and abilities to neutralize acidic peat. Two different biochars were produced through gasification using pine wood chips (Pinus taeda L.) and rice hulls (Oryza sativa L.). The resulting biochars had pH values above 8.5 and were assessed as potential lime replacements by pulverizing the biochars to KLEINERDAN2 mm to create a powder-form of pine wood biochar and rice hull biochar. These pulverized biochars were amended to a pure peat substrate at rates of 1.78, 3.56, 5.34, or 7.13 kg m^‑3 (3, 6, 9, or 12 lb yd^‑3). In this pulverized form, the two biochars showed little to no effect on neutralizing the peat's acidity; after seven days the maximum substrate pH attained for both pine wood biochar and rice hull biochar was 4.1. The second study increased the amount of pulverized biochar amendments to 10.69, 12.47, or 14.25 kg m^‑3 (18, 21 or 24 lb yd^‑3, respectively). Again, the substrate pH for both biochar types did not reach the recommended minimum for substrates (5.4). While it is clear that biochars made from different feedstocks can produce different benefits and results; additions of these two pulverized biochars did not provide the quick, short-term effects needed for greenhouse production.