A lightweight and inexpensive GreenSeeker handheld crop sensor was used to investigate the growth diagnosis of stable, high-yielding rice. We formulated seasonal upper and lower limits for NDVI and a target growth volume for rice yields of 700 g/m². A high positive exponential correlation was observed between NDVI and growth volume (plant length×number of tillers×leaf color value). The correlation can be expressed by a single exponential formula, regardless of growth stage year. Topdressing based on growth diagnosis by NDVI ensured a target panicle number and leaf colors for two years. Growth diagnosis by NDVI demonstrated high yield levels of 700 g/m² over two years in various weather conditions. Therefore, it can be concluded that the GreenSeeker handheld crop sensor is useful in diagnosing the growth of stable, high-yielding rice.

Based on the Aizu-nosho and Tochi-cho documents established in the 17^th century, we analyzed the soil classification method used by farmers in the Aizu District in the early modern period. In the agricultural textbook “Aizu-nosho,” written by a farmer, soils (tsuchi) were classified into nine taxa in descending order of farmland grade: yellow ma-tsuchi (Yamadori-ma-tsuchi), black ma-tsuchi, white ma-tsuchi, suna (sandy)-ma-tsuchi, no-ma-tsuchi, su (sour)-ma-tsuchi, suna-tsuchi, no-tsuchi, and su-tsuchi. These taxa were characterized by bulk density, color, taste, texture, and structure and were related to crop suitability. Tochi-cho was a public land survey record of villages in the Aizu District. Soil descriptions in 209 villages were provided. In Tochi-cho, soils were classified by combining three items, soil type, color, and mixture, and a total of 62 taxa were recognized. The major soil types were no-tsuchi, ma-tsuchi, suna-tsuchi, and “typeless,” and the minor types included neba (sticky)-tsuchi, su-tsuchi, sibu (acerbic)-tsuchi, reki (wet)-tsuchi, kawagomi (river dust)-tsuchi, ara (loose)-tsuchi, and shi (death)-tsuchi. The colors were basically black, white, and red. Soils rich in sand and stone were described as mixtures. The grade of farmland was significantly different for each soil taxon in Tochi-cho. However, the median grades of taxa were in the same order as described in Aizu-nosho. Comparing the location of villages with the topographic map, it was found that the ma-tsuchi taxon is predominantly distributed in the lowlands rather than the mountains and terraces, but vice versa for the no-tsuchi taxon. The location of the soil types does not match the taxa used in current soil maps. This study revealed that farmers in the Aizu District used their senses to classify soils finely and regarded taxa as an indicator of land productivity in the early modern period.

Recently, it has been realized that the soil pH of some farmlands in Japan has decreased. Therefore, in this study, we clarified this phenomenon using two soil conditioners, calcium carbonate (CC) and sulfur trioxide (ST). The purpose was to investigate the effects of soil pH changes induced by these conditioners on rice straw decomposition and methane emission from paddy fields in Japan’s cold regions. We applied CC to 10 t ha⁻¹ and ST to 12 t ha⁻¹, and measured methane flux by the closed chamber method in 2015 and 2016. As a result, soil pH reached 7.0 and 5.2 in CC and ST plots, respectively, but remained at 5.5 in the control plot. From October 2014 to April 2015, rice straw decomposition rates in CC, ST, and control plots were 34.5, 27.8, and 31.8％, respectively. The CC plot had the highest methane emission rate. On the other hand, the methane emission rate was the lowest in the ST plot due to sulfate reduction. In 2015, methane emission rates were 37.8, 11.7, and 31.4 g CH₄ m⁻² in CC, ST, and control plots, respectively. Based on this study, it is important to determine the components of soil conditioners and adjust soil pH so that the decomposition of rice straw and methane emission from paddy fields are balanced.