**5. The use of biochar fertilizer during and after the Pacific War in Japan: ca. 1940–present**

From the present perspective, we feel that both Oyaizu and Daikuhara devoted themselves to improving Japanese agriculture from a holistic viewpoint. In the last section, we briefly examine the influence of their achievements on later generations.

In December 1941, Japan triggered the Pacific War. During the war, the production of ammo‐ nium sulfate decreased sharply from 1.24 to 0.24 million tonnes per year (**Figure 2**). The production of superphosphate also decreased to as little as 0.01 million tonnes per year. These sharp decreases were because imports of the key ingredients were stopped by the war and also because the ammonia produced by the fertilizer industry was converted to nitric acid due to the critical demand for the production of explosives [21]. In addition, the production of commercial organic fertilizers such as rapeseed oil cake and fish meal also decreased during the war.

Because of the shortage of all commercial fertilizers, the government encouraged farmers to produce traditional homemade fertilizers, including heated soil fertilizer [37] and biochar fertilizer. Dr. Shingo Mitsui, an outstanding soil scientist, began to reevaluate and extend the findings of Daikuhara [38]. When he began these experiments in 1939, the use of heated soil fertilizer was almost extinct in Japan [26].

In the second volume of his textbook [9], Daikuhara stressed the importance of the maintenance and improvement of soil fertility. At that time, the three fertilizer elements (nitrogen, phos‐ phorus and potassium) were known to the public, and the effects of chemical fertilizer were exaggerated. Daikuhara criticized the crowd of "three-element admirers," possibly in a similar frame of mind that Oyaizu had toward Daikuhara. He wrote that soil fertility is controlled by various factors, including chemical factors such as the contents of nutrients and organic matter, and also physical factors such as aggregate structure, soil depth and moisture content. He emphasized that application of three elements in the form of chemical fertilizer was not the only solution and that application of organic matter and lime to soil is indispensable, consid‐ ering the climate, soil type and farm management in Japan. His thoughts had become more holistic. This may have been related to his extensive research activities, especially on the denitrification after application of sodium nitrate to paddy soil [36] and on the acidification of

Part of his wishes was realized by younger soil scientists, including Dr. Matsusaburo Shioiri. In Konosu experimental field of the Imperial Agricultural Experiment Station, the longest field experiment in Japan was started from 1925 with the aim to evaluate the effect of application of organic and chemical fertilizers on the yield of rice and wheat and the fertility of soil [17]. It was about 80 years after the world's longest field experiment had been launched by the

In 1921, Daikuhara was appointed as a professor at Kyushu Imperial University. Two years later, he was appointed as the Director of the Agricultural Experiment Station in the Province of Korea. After this, he became the President of Kyushu Imperial University and Doshisha University. While working actively as the President of Doshisha University, he passed away in 1934 [4]. His series of textbooks on soil science was to be composed of three volumes, but

**5. The use of biochar fertilizer during and after the Pacific War in Japan:**

From the present perspective, we feel that both Oyaizu and Daikuhara devoted themselves to improving Japanese agriculture from a holistic viewpoint. In the last section, we briefly

In December 1941, Japan triggered the Pacific War. During the war, the production of ammo‐ nium sulfate decreased sharply from 1.24 to 0.24 million tonnes per year (**Figure 2**). The production of superphosphate also decreased to as little as 0.01 million tonnes per year. These sharp decreases were because imports of the key ingredients were stopped by the war and also because the ammonia produced by the fertilizer industry was converted to nitric acid due to the critical demand for the production of explosives [21]. In addition, the production of commercial organic fertilizers such as rapeseed oil cake and fish meal also decreased during

soil after application of potassium salt [5].

214 Organic Fertilizers - From Basic Concepts to Applied Outcomes

the final volume remained unpublished [10].

**ca. 1940–present**

the war.

Rothamsted Experimental Station in the United Kingdom [20].

examine the influence of their achievements on later generations.

In a textbook of fertilizers published in 1942 by Dr. Hideo Misu [39], the biochar fertilizer proposed by Oyaizu was described as one of 178 types of fertilizer. The composition of the product (38–51% moisture, 0.74–1.06% nitrogen, 0.28–0.70% phosphate and 0.63–0.85% potassium) was reported to vary depending on the type of ingredients used for smoldering and the amount of human waste mixed in. This fertilizer was thought to have small direct effects from the fertilizer elements and some indirect effects from the charred carbon. In contrast to the previous negative descriptions of biochar fertilizer by scientists, a short biography of Oyaizu was published as an independent book chapter (at least twice in 1938 by Sakurai and 1941 by Iyoda), in which he was described as one of the great agricultural experts.

In August 1945, the war came to an end. A year after, Oyaizu's book [2] was republished again with some revisions [40]. It was more than a generation after the original was published. The title of the book was shortened by removing the word *Tenri* (almighty), and the first chapter was simplified by omitting the theory of Yin and Yang. These revisions suggest strongly that the Japanese people at that time accepted Western knowledge and that the theory of Yin and Yang proposed in the original was regarded as out of place or out of date.

In 1945, the capacity of factories in Japan to produce ammonium sulfate was only about 10% of the capacity in 1941 because of the insufficient maintenance of the equipment and also because of the air raids during the war [41]. After the war, the government put an emphasis on the production of ammonium sulfate [41]. Its production level had recovered by 1949 and peaked in 1959 and 1966 (**Figure 2**). During the period of rapid industrial growth, Japan's farming systems were modernized with the use of agricultural machines, pesticides and fertilizers. Traditional fertilizers, which required time and labor to produce, became to be regarded as old-fashioned. The textbook written by Misu was revised and republished in 1949 [42]. In the revised book, biochar was described more specifically as *mokutan matsu* (wood charcoal powder) having several indirect effects on crop growth. At the same time, the term *kuntan* (biochar) disappeared together with Oyaizu's name.

In the 1970s, the domestic production of rice became sufficient to meet demand. The govern‐ ment started to pay farmers to reduce rice production by introducing the *gentan* policy in 1970. Things began to change. The public attention to food shifted from the quantity to the quality. The environmental pollution caused by industrial activities had come to be widely recognized. By that time, Itai-Itai disease and two outbreaks of Minamata disease had been identified and were known to be caused by the improper management of wastes containing toxic metals by large incorporations in Japan.

*Silent Spring*, written by Ms. Rachel Carson in the United States, focused on the detrimental effects of pesticides on the environment and became popular around the world after its publication in 1962. In Japan as well, the newspaper *Asahi Shinbun* published the serialized 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 application of biochar to soil, i.e., biochar carbon sequestration [1].

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

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 similar to Oyaizu's idea to harmonize the composition of biochar fertilizer by addition of human waste. Although we cannot go into detail here, we have also examined the effect of heating of sewage sludge on the mineralization of nitrogen [46] and the uptake of nutrients by a leafy vegetable [47]. These experiences led us to focus on the earlier works by Oyaizu, Daikuhara and Mitsui.

In addition to the agricultural studies, research has been carried out from the viewpoint of soil formation over the centuries. For example, *Terra Preta de Indio*, which is widespread in the Amazon basin, is a well-known anthropogenic soil whose high organic matter content is probably the result of the long-term input of biochar produced by pre-Columbian Indians [48] in combination with the stabilization of humic substances by aluminum and iron in the strongly weathered soils [49]. Likewise, the input of charred grassland plants that are highly stable in soil is hypothesized to be responsible for the formation of black, humus-rich volcanic ash soils distributed widely in Japan [50] (**Figure 7**).
