2019 ASHS Annual Conference

Improving soil health is crucial for better nutrient mineralization, especially from organic fertilizers. Three consecutive field trials were conducted at the University of Hawaii, on an infertile Oxisols with low pH and potential micro-nutrient toxicity, between 2018 and 2019 to evaluate the short- and long-term effect of one-time biochar application rates and one application each growing season of fertilizer type and nitrogen (N) application rates on soil health parameters and legume crops growth and yield. The study was conducted as factorial in split plot design with 3 replicates. Biochar application rates were randomly distributed in the main plots (31.8 X 4.5 m each), and combinations of fertilizer type and N application rates were randomly distributed in the sub-plots (4.5 X 4.5 m each). The biochar was obtained from Pacific Biochar Co. and made from macadamia nut shell at 500^OC. At each growing season, 3 crops growth and yield (leaf chlorophyll content, total biomass, and yield) and soil health parameters (root-knot nematode population, Rhizobium nodules development, and CO₂ level) were collected using Solvita kit. The results showed a significant increase in the legume crops growth and yield by 20% under biochar application, compared to control treatment (no biochar application). Rhizobium nodules development was significantly increased by 50% under biochar application compared to control treatment. Root-knot nematode’s root-galling index declines significantly with biochar application. The results showed a steady and significant improvement in soil health and legume crops growth and yield at the 3^rd growing season compared to the 1^st growing season.