**Acknowledgements**

nonfiction novel, *Fukugou Osen (The complex contamination)* by Ms. Sawako Ariyoshi, in 1974. Her book [43] became a bestseller. In the book, Ariyoshi wrote that multiple contaminants at even trace levels may have cumulative or even synergetic effects on the environment and human health. She discussed several topics to make her readers aware that environmental pollution can be caused and suffered by everyone. One of the topics she described was the dark side of chemical fertilizer. Local farmers she interviewed said frequently that the "soil is dead," probably due to the application of chemical fertilizer in excess for a long period.

From the late 1970s to the early 1980s, several scientists, especially Drs. Sugiura, Kishimoto and Ogawa, intensively examined the function of biochar as a soil conditioner for afforestation (for example, see [44]). On November 26, 1986, the government designated biochar powder (precisely, wood charcoal powder) and vermiculite as soil amendments, which are effective to improve soil quality, especially water permeability. Nowadays, charred rice husk as a soil amendment mainly for potted flowers and kitchen garden is usually sold at commodity household stores, and it is occasionally produced by rice-growing farmers (**Figure 7**). In addition to this, growing concerns on global warming highlighted the very slow decomposi‐ tion of carbon in biochar, thereby returning carbon from the air to belowground through the

**Figure 7.** Mounds of rice husk being smoldered in a rice field to produce biochar. A dark-colored soil beneath the mounds is a volcanic ash soil distributed widely in Japan. The photo was taken by the authors in Ibaraki Prefecture on August 30, 2014 soon after the harvest of rice. The Waste Management and Public Cleansing Law (revised) was put into operation on April 1, 2001. The revised law prohibited the open burning of wastes except for several cases includ‐

Various possible applications of biochar in relation to agroecosystem management have been evaluated by many scientists worldwide. For example, Fischer and Glaser [45] proposed cocomposting of fresh organic matter and biochar during the composting process. Their idea is

application of biochar to soil, i.e., biochar carbon sequestration [1].

216 Organic Fertilizers - From Basic Concepts to Applied Outcomes

ing the burning or smoldering of agricultural wastes by farmers in a field of their own.

This work was supported by JSPS KAKENHI Grant Number 15K00634.
