The Effect of Charcoal Amendment on the Lettuce Growth and NO3-N Discharge from the Soil Medium

Three types of charcoal were evaluated as a soil conditioner. The charcoal was made from thinned Japanese cedar (Cryptomeria japonica D. Don), Moso bamboo (Phyllostachys heterocycla Matsum.), and pruned shoots of Japanese pear (Pyrus pyrifolia var. culta Rehd.). The charcoal amendment increased the soil exchangeable cations, but hardly affected the soil CEC. Top fresh weight of the third lettuce crop grown in the soil medium without charcoal amendment substantially decreased in comparison with that of the first crop. Although the first lettuce growth in the medium with charcoal was smaller than without charcoal, the lettuce growth in the second and third crop was more suppressed in the treatment without charcoal than with charcoal. Leaf nitrate content decreased with the charcoal amendment, especially when the pear shoot charcoal was used. NO3-N discharge was smaller from the soil medium with the bamboo or the pear shoot charcoal in the first crop. The bamboo charcoal amendment decreased the discharge in the second crop as well. Although this effect was not observed in the third crop, the total amounts of NO3-N discharge were lower in the treatments with both 0.3-1 cm and <0.3 cm bamboo charcoal, and with 0.3-1 cm pear shoot charcoal. However, none of the soil medium with the cedar charcoal reduced NO3-N discharge in any cropping period. These results suggest that charcoal made from some forestry and agricultural wastes such as bamboo and pear shoots can be applicable for a soil conditioner to increase soil exchangeable cations, to reduce growth suppression in continuous cropping, and to decrease NO3-N discharge from soil.