**4. Additional descriptions of biochar fertilizer by Daikuhara: ca. 1912–1920**

As noted above, Oyaizu proposed a method to produce biochar fertilizer to the government in 1900. The Imperial Agricultural Experiment Station began experiments on biochar fertilizer in 1908. As a response to Oyaizu's popular book, a comment of the station's director (Dr. Yoshinao Kozai) appeared in a newspaper *Jiji Shinpou* on July 25, 1912. In the article, Kozai expressed his personal opinion. He said, "It is great if the proposed biochar fertilizer can increase the crop yield by 20–30%," but also added, "It is premature to make a judgement, because the results from our station are not yet satisfactory and the research is still ongoing."

A year later, a comment of the chief of agriculture department in the Ministry of Agriculture and Commerce (Mr. Hitoshi Douke) also appeared in a newspaper *Tokyo Asahi Shinbun* on November 27, 1913. In the article, Douke said, "We have compared biochar fertilizer with conventional fertilizer for 4 years at several stations, including Nishigahara (**Figure 5**). But we could not find such a big effect as has been reported by some advocators." He continued, "Growing crops with biochar fertilizer requires labor several times more than that with conventional fertilizer. It is premature to say that biochar fertilizer is excellent only from the data of the crop yield."

larger struggle between the two established philosophies, one from the East and the other from

**Figure 6.** A circular crop calendar proposed by Oyaizu and printed in 1917 after his death (left). In the circle, summer and winter are depicted in red and blue colors, respectively, and the seasons rotate clockwise. Field management is described in the inner peripheral part. This calendar is designed to inform farmers on the suitable seasons for each field management practice in the double cropping of rice and *mugi*. It is a part of the schematic diagram called "Har‐ monization of Yin and Yang" with the length and width of 105 cm and 39 cm, respectively (right). The contents of the

**4. Additional descriptions of biochar fertilizer by Daikuhara: ca. 1912–1920**

As noted above, Oyaizu proposed a method to produce biochar fertilizer to the government in 1900. The Imperial Agricultural Experiment Station began experiments on biochar fertilizer in 1908. As a response to Oyaizu's popular book, a comment of the station's director (Dr. Yoshinao Kozai) appeared in a newspaper *Jiji Shinpou* on July 25, 1912. In the article, Kozai expressed his personal opinion. He said, "It is great if the proposed biochar fertilizer can increase the crop yield by 20–30%," but also added, "It is premature to make a judgement, because the results from our station are not yet satisfactory and the research is still ongoing."

A year later, a comment of the chief of agriculture department in the Ministry of Agriculture and Commerce (Mr. Hitoshi Douke) also appeared in a newspaper *Tokyo Asahi Shinbun* on November 27, 1913. In the article, Douke said, "We have compared biochar fertilizer with conventional fertilizer for 4 years at several stations, including Nishigahara (**Figure 5**). But we could not find such a big effect as has been reported by some advocators." He continued, "Growing crops with biochar fertilizer requires labor several times more than that with

the West.

212 Organic Fertilizers - From Basic Concepts to Applied Outcomes

calendar are also explained in Oyaizu [31].

In April 1915, two years after the death of Oyaizu, Daikuhara gave a lecture on soil and fertilizer at Kanagawa Agricultural Experiment Station [33]. In reference to biochar fertilizer, he said, "Biochar fertilizer has been promoted in the past few years. But it should be kept in mind that similar fertilizer had been produced for a long time before it attracted public attention." He introduced several examples of traditional biochar fertilizers in Japan and continued, "Biochar fertilizer is only charred organic matter. It does not have any special function. If I need to say more, biochar fertilizer will improve soil physical properties to some extent. Potassium and phosphorus in the ingredients will be solubilized during the process of production. Some of the nitrogen in biochar fertilizer will be available to crops, but the nitrogen supplied from biochar fertilizer should be ascribed to human waste added to the charred materials."

In the lecture, he noted that the contents of nitrogen, phosphate and potassium in biochar fertilizer were 0.6–0.7%, 0.3% and 0.6%, respectively. He also presented results from a pot experiment in which barley was grown as a test plant. He suggested that decomposable organic matter such as rice straw should be used for the production of compost, whereas slowly decomposable organic matter such as fallen leaves might be more suitable in production of biochar fertilizer. The lecture ended with the following statement, "Furthermore, if we continue to apply a fertilizer with low organic matter content, it is apparent that soil organic matter will decrease gradually and soil fertility will be depleted." He emphasized that about half of the organic matter was lost during the production of biochar fertilizer.

Daikuhara's view of biochar fertilizer had become slightly more positive over time. Inoue stated [30], "In past years, a certain doctor visited Chiba Prefecture. He was surprised very much to see the vigorous growth of crops to which biochar fertilizer had been applied." Again, "a certain doctor" referred to Daikuhara. In February 20, 1908, Daikuhara visited Mr. Yajima Chiba together with Mr. Tadaharu Kato, who was a principal of Mobara Agricultural School. Chiba explained how to grow *mugi* (a general Japanese term including wheat and barley) with biochar fertilizer [34].

Did Daikuhara pay attention to the rate of decomposition of biochar or compost after their application to soil? Now it is well known that biochar is stable in the environment and decomposes very slowly in soil. In the first volume of his textbook entitled, *Dojyogaku Kougi (Lectures on the Science of Soils*) [8], he cited his own results [24]. He wrote, "There is no doubt that the heating treatment not only affects soil microbes but also accelerates the breakdown of soil components". To support this, he referred to partial sterilization, a phenomenon discov‐ ered around 1900. Daikuhara paid attention to works by Sir Edward John Russell and his colleagues in the United Kingdom. Darbishire and Russell [35] demonstrated that partial sterilization of soil by heating to 100°C leads to a marked increase in the amount of oxygen absorbed by microorganisms of the soil. Absorption of oxygen by microbes and the release of carbon dioxide from soil are essentially two sides of the same coin. It follows that Daikuhara knew about the microbial decomposition of organic matter when he made his lecture on biochar fertilizer in 1915. But it is unlikely that he was aware of the very slow decomposition of biochar in soil.

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 soil after application of potassium salt [5].

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 Rothamsted Experimental Station in the United Kingdom [20].

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 the final volume remained unpublished [10].
