In the new teaching guidelines announced in 2017, a topic (3) “The earth phase of rainwater and circulation” was added to Unit B “Life / Earth” in the fourth-year elementary science curriculum. Its aim is to adopt a scientific approach when learning about natural disasters in the context of teaching disaster preparedness. Simultaneously, improving teaching styles is imperative toward achieving deep and independent learning supported by discussion. The author delivered on-site lessons about “soil particles and water penetration” at elementary schools on the topic of “The earth phase of rainwater circulation” and has since been working to identify ideal practices in soil education. The context of disaster preparedness has been considered. Four hours were devoted to effort in science and general studies classes. In science classes, observations and experiments were performed to learn “the relations between size of soil, particles and the means and quantity of water penetration.” In general studies, after watching a video about mudslide damage, the students were separated into groups and tasked with thinking about and discussing disaster, preparedness based on their observations and experiments, or the aforementioned video.

Finally, the students made presentations to the whole class. The students seemed to demonstrate adequate understanding and recognition of the importance of disaster preparedness as their opinions and questions were based on the scientific comprehension of soil and relevant disasters. Thus, these on-site lessons could be considered effective practice in soil education, aiding in the development of disaster preparedness education that is in accordance with the new teaching guidelines. This will further motivate scholars to undertake comprehensive studies of soil education in response to the new teaching guidelines, particularly those on cross-curricular teaching and curriculum management.

We improved the rapid method for estimating available nitrogen (AN) to realize optimal fertilizer management by measuring the total nitrogen (TN) extracted over 16 hours from air-dried paddy soils with a solution including ascorbic acid (AA). Using 11 soil samples from Toyama prefecture after the rice harvest, we measured the TN extracted from 3 g of air-dried soil using 50 mL of solution including AA over 16 hours. The extraction temperatures were set at three levels, and AA with four different concentrations was added to the extracting solution. Results showed that the amount of extracted nitrogen was positively correlated with both extraction temperature and concentration of AA up to 0.1％. The correlation coefficient between AN and extracted TN was the highest when the extraction temperature was set to 50°C and the concentration of AA added to the extracting solution was 0.1％ (r=0.98, p<0.01). A negative correlation was also found between the amount of iron extracted from air-dried soil by 0.1％ AA solution and the ratio of extracted TN to AN when TN was extracted with AA-free water. Furthermore, the amount of TN extracted from air-dried soil with 0.1％ AA solution corresponded to AN at a constant ratio regardless of the amount of iron extracted.

It was thus concluded that the addition of AA as a reducing agent to the extracting solution in this method increased the extraction of TN. This was because organic nitrogen was extracted not only by heating but also by the reduction of the extracting solution. We were thus able to evaluate the AN quickly and accurately using the TN extracted from air-dried paddy soils over 16 hours with a solution including 0.1％ AA.