Biochar is a recently coined term for charred organic matter used as a soil amendment. Although the term is relatively new, the substance has been used for a long time throughout the world, including Japan. After we read a Japanese book entitled Nibai Shukaku Tenri Nouhou (How to Double Crop Yield by Almighty Farming System) originally published in 1912, we found that there were conflicting opinions between the author (Mr. Katsugoro Oyaizu) and soil scientists of the time (Dr. Gintaro Daikuhara and others) on the benefits of the use of biochar fertilizer. Previous publications on this topic have been written in Japanese from a sociological viewpoint. By referring to the literature published at the beginning of the twentieth century in Japan, we attempt to shed light on the conflict between traditional knowledge of biochar fertilizer and new concepts of soil science imported from the Western countries. We also describe briefly the socioeconomic impacts on the use of biochar fertilizer in the later generations.
Part of the book: Organic Fertilizers
Sewage sludge is often heat-dried to eliminate water and pathogens. However, heat-drying can also change the form of nitrogen (N). To improve our understanding of this phenomenon, we examined the heat-induced changes in the rate of N mineralization from soils and organic wastes. Published results revealed that the response to the heating temperature differed between soils and organic wastes. As the heating temperature increased to 200°C, the rate of N mineralization increased in soils but decreased in organic wastes. In organic wastes such as sewage sludge, the content of mineralized N tended to decrease sharply when heating temperatures increased to 150–200°C. Furthermore, our results obtained from heat-drying of sewage sludge at 180°C indicated that the rate of carbon (C) mineralization decreased with increasing heating period after the sludge temperature reached 180°C. The C in sewage sludge heated at 180°C for 120 hours after complete drying contained more humin and aromatic C than that in sludge that was heat-dried at 180°C without the additional heating period. These results suggest that the heat-drying treatment can be divided into the drying and denaturing periods and that the temperature of the sludge, not that of the reactor, affects the quality of the end-product.
Part of the book: Nitrogen in Agriculture