Carbon Dioxide and Release of Primary Nutrients in Contrasting Soils Incubated with Feedstocks and Biochar from Cull Potato and Pine Bark

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Disposal of potato waste at landfills results in nutrient losses and pollution of air and groundwater. Biochar from the waste could minimise carbon dioxide (CO2) emission, increase storage of carbon (OC) and recycle nutrients in soil. This study determined effects of biochar from cull potato (CP) and pine bark (PB) on CO2 emission and available nitrogen (N), phosphorus (P), and potassium (K) in contrasting soils. Biochar pyrolysed at 350 °C (CP350; PB350) and 650 °C (CP650; PB650), and feedstocks were applied to Luvisol and Ferralsol soils at rates equivalent to 10 Mg C ha−1 and incubated at 25 °C. The carbon dioxide (CO2-C) was captured in 1 M NaOH and the solution was back-titrated with 0.5 M HCl after 3, 7, 14, 21, 28, 42, 56, and 84 days. A similar experiment was conducted, with destructive sampling, including after 112 and 140 days, for analysis of ammonium-N, nitrate-N, and available P and K. Biochar increased CO2 in the Luvisol but decreased it in the Ferralsol when compared with the feedstocks and the control. Higher CO2 was emitted from PB biochar than from CP in the Luvisol. Ammonium-N increased in the Luvisol, reaching a peak after 14 days, and decreased after 42 days, while, in the Ferralsol, it decreased to below detection after 21 days. Nitrate-N increased with decline in ammonium-N, except in CP, in both soils. Available P increased within 14 days and declined after 28 days, with generally higher levels in the Ferralsol. Available K increased with addition of CP and its biochar, with greater availability at higher pyrolysis temperatures for both soils throughout the incubation. The findings showed that application of CP biochar causes emission of CO2 to increase in Luvisol and decrease in Ferralsol, while available K increase, with no effects on N availability, relative to control soils.