In order to analyze the importance of soil education, we surveyed a total of 1993 first through sixth grade elementary school students in Tokyo and Tochigi. After the analysis of the data, we obtained the following results: 1) The percentage of students who replied “I would like to know as much as possible about soil” decreased as students increased from first to sixth grade. 2) Students’ surroundings (the number of places with soil) influenced their degree of interest in soil. 3) As their knowledge of soil increased, the percentage of students who replied “I prefer to have as much soil around me as possible” increased. 4) About 68％ of the students who replied “I would like to have as much soil around me as possible” also replied “I would like to know as much about soil as possible.” 5) About 38％ of students who replied “I don’t touch soil at all” replied “I would not like to know about soil.” 6) More than 30％ of the sixth graders, but only about 10％ of the fifth graders in Tokyo replied “I would not like to know about soil.” 7) Of the students in Ichikai-machi, Tochigi, 70％ replied “There are many places with soil close to where I live” and only 10％ of these sixth graders replied “I would not like to know about soil.” Hence, we consider that soil education is important for sixth graders, especially those who live around places with less soil in their surroundings.

This study was conducted to assess the effect of rice variety Koshihikari Kan No.1, which is a mutant with nearly cadmium-free grains produced by irradiation with heavy-ion beams, on the incidence of rice brown spot disease in different paddy fields, including Akiochi. We also investigated the effects of Mn-bearing materials on brown spot disease and rice productivity. A summary follows.

(1) Brown spot disease tended to occur under soil conditions with low P, Si, and exchangeable cation (Ca, Mg, K, and Mn) availability.

(2) Brown spot lesions in flag leaves were induced by low K, Si, Mn, and Fe contents in shoots.

(3) Koshihikari Kan No. 1 rice showed a higher ratio of brown spots than the Koshihikari variety, but it recovered by applying the Mn-bearing material.

(4) Koshihikari Kan No.1 rice contained low levels of Mn and high levels of Fe in its shoots compared to the Koshihikari variety.

(5) The rice grain yield of Koshihikari Kan No.1 rice was lower than that of the Koshihikari variety in paddy fields where brown spot disease has occurred. However, the yield of Koshihikari Kan No.1 was improved by applying Mn-bearing material.

In this study, we examined the relationship between powder properties of ill-crystallized calcium silicate hydrates (C-S-H) synthesized by various methods and the recovery rate of phosphorus (P) from an aqueous solution using C-S-H. The calcium (Ca) ion of C-S-H reacted with P in the aqueous solution and all recovered materials contained hydroxyapatite. P recovery using C-S-H was completed within 30 min and each C-S-H showed a different Ca reaction rate and P-recovery rate. Most of the recovered materials contained no less than 15％ citric-soluble phosphates.

Our research verified that the Ca reaction rate of C-S-H has a strong negative correlation to C-S-H crystallite size estimated by X-ray diffraction. However, the Ca reaction rate did not correlate with other powder properties, such as average particle diameter, specific surface area, and bulk density. Because of a strong correlation between the Ca reaction rate and P-recovery rate, C-S-H crystallite size also has a strong negative correlation to the P-recovery rate. In conclusion, P-recovery rate increased with the decrease in C-S-H crystallite size.