To produce high-quality green tea with reduced amounts of agricultural chemicals and fertilizers, a 10-year field experiment was started in 1998 to determine the feasibility of using bamboo charcoal in the soil. The experiment, conducted in the eastern part of Shizuoka Prefecture, Japan, consisted of 8 plots with an actual cultivating area of 1,600m2.
Today, after three years of this experiment, the bamboo charcoal has tended to retain the supplied fertilizers in the rhizosphere. The bamboo charcoal also tended to keep the soil pH in a range that was suitable for the growth of tea trees. The heights and volumes of the tea trees in the plots in which the charcoal was used were, on average, 20% and 40% greater, respectively, than they were in the negative control. However, no differences were observed in the number of new shoots per tree or in the length of new shoots (stem length of three leaves and the shoot apex). The plot that had the best tea tree growth had been treated with 100g crushed bamboo charcoal (particle size approximately 5 millimeters) per square meter per year.
At this point in the experiment, the use of charcoal in the soil has not yet resulted in any clear differences in key elements in the green tea product made from plucked new shoots.