2018 ASHS Annual Conference

Biochar, a product of biomass that is heated in an oxygen limited environment (pyrolysis), has been reported to improve soil quality and increase plant growth. To quantify and further characterize such effects of biochar, three experiments were conducted: (1) a greenhouse trial on an acidic tropical Ultisol, which evaluated the aluminum (Al) detoxifying potential of biochar, using Desmodium intortum, an Al sensitive forage legume as the test plant; (2) a greenhouse trial using nitrogen (N) fertilizer sources, both organic and synthetic, with and without biochar, which measured the capacity of biochar to regulate/release N to Chinese cabbage (Brassica rapa Chinenesis group) growth; and (3) a field trial on a highly weathered Oxisol, which documented the long-term, field-condition effects of biochar on a variety of crops [sweet corn (Zea mays), okra (Abelmoschus esculentus), and soybean (Glycine max)]. Our results show: (1) At an application rate of 2.5% (approximately 25 tons/ha), a kiawe-wood biochar could reduce Al toxicity and increase D. intortum growth as much as lime (CaCO₃) applied at 3 cmolc/kg (1.5 tons/ha). CaCO₃ equivalent (represented by ash content) and COOH, OH functional groups on the biochar surface were likely responsible for these effects. (2) At a same total N rate of 200 mg/kg, cabbage yield was much higher in the presence of a wood-based biochar (at 2%) than when urea or organic N fertilizer was applied alone, and yield increased became even more pronounced in the 2nd harvest than in the 1^st. This increased N use efficiency could be attributed to biochar properties, such as large surface area and numerous tiny pores. (3) Under field conditions, corn yield ( first season) was nearly doubled in the presence of 2% biochar (derived from macadamia shells) when N was applied as urea or blood meal (10% total N) at 150 or 300 kg N/ha rate. Interestingly, the effect of biochar on plant growth seemed to extend beyond N nutrition because the treatments receiving biochar but no N input also out-yielded those having N input but no biochar. The prolonged/aging effect of biochar will be further studied in future time.