In vegetable fields in Aichi Prefecture, Japan, potassium (K) uptake by crops has been reported to exceed K fertilizer application, suggesting that crops utilize exchangeable K and nonexchangeable K from the mica interlayer. Therefore, we investigated the factors controlling nonexchangeable K and their contribution to crop K uptake in vegetable fields in Aichi Prefecture. Substantial amounts of nonexchangeable K content were detected in the areas where the parent material was mainly granite. Nonexchangeable K was positively correlated not with mica minerals in the clay fraction but with mica minerals of less than 2 mm in size, including sand and silt fractions, indicating that coarse mica minerals in the sand and silt fractions contribute to the amount of nonexchangeable K. In more than 80％ of the soils with high mica mineral and nonexchangeable K content in the coarse fraction, K saturation was below the lower limit of soil diagnostic criteria; nevertheless, crops took up large amounts of K. This suggested that the contribution of nonexchangeable K as a source of K may be sufficient to ensure K uptake even when K saturation is below the soil diagnostic standard.

Soil is an important site for producing food. However, students’ awareness of and interest in soil tend to decline as their education progresses. It has been pointed out that people’s interest in soil and the attention it receives in education have decreased due to the increasing rarity of places with soil within residential areas, along with a decrease in the frequency of appearance of the word “soil” in Science in each revision of the Courses of Study in Japan. Given these circumstances, the phrase “particles of soil” that appeared as part of the fourth-grade science curriculum in Japan’s new Courses of Study is expected to promote education on “soil” in elementary science classes. In addition, in a previous survey on soil, several responses such as “soil protects us from injuries” and “soil heals us” were identified. The “healing effect (amenity) of soil” on the mind can be considered an important issue in soil education and should be confirmed as a new function of soil. However, only a few studies on this issue based on data from a psychological perspective have been performed. This study preliminarily validated the psychological effects of soil by asking university students, who had to take remote classes due to the COVID-19 pandemic, to make shiny mud balls using a commercial product. After making these balls, their feelings and perceptions regarding touching soil became more positive. The evaluation of soil as “clean” increased and as “dirty” or “stinky” decreased. The simulated experience of making shiny mud balls also tended to improve the students’ familiarity with soil.

In a field experiment conducted in Kumamoto prefecture, kyushu, southwestern Japan, we evaluated the accuracy of a model for predicting the amount of nitrogen mineralization from organic amendments, using soil temperature, soil moisture, and acid-detergent-soluble organic N content of organic matter as the main input variables. Models for predicting N mineralization from organic amendments have already been developed; however, there are no examples of time-dependent validation of the predicted values under field conditions; therefore, we examined which factors affected the error of our model under field conditions. Following two tests using five organic amendments, the predicted values underestimated the measured values immediately after the amendments were applied. Consideration of N leaching caused by rainfall from rapeseed oil cake, which is easily mineralizable, improved the accuracy (Willmott’s index of agreement >0.6). However, N mineralization from less mineralizable amendments could not be predicted accurately, potentially owing to the relatively large influence of environmental variance. Analysis of the influence of environmental factors on model error revealed that N leaching had the largest influence, followed by time since the addition of amendments. The underestimation immediately after the addition of amendments was observed. We obtained similar results when any kinetic methods were applied to the data of this experiment. In conclusion, our model for predicting N mineralization from organic amendments inherently underestimated predictions in field conditions soon after application; however, it could be predicted more accurately throughout the experimental period when the influence of N leaching on inorganic N content in soil was considered.