¹⁵N-labeled ammonium sulfate was used as fertilizer to construct a labor-saving fertilization system for two-rowed barley for food, and the soil fertility in barley plants and the content, contribution ratio, and utilization rate of nitrogen for each fertilization were clarified. The nitrogen content of the basal dressing, topdressing at tillering stage, and topdressing at panicle formation stage was 1.52-1.80 g m^-2, 2.58-2.60 g m^-2, and 2.62-3.25 g m^-2, respectively. The nitrogen content from soil fertility was 4.90-5.82 g m^-2, and was higher than that from each fertilizer application. The nitrogen contribution rate of grain containing nitrogen from the basal dressing, topdressing at tillering stage, and topdressing at panicle formation stage was 12-14%, 20-21%, and 21-27%, respectively. The nitrogen contribution rate of soil fertility was 40-45%, and was the highest, suggesting the importance of soil fertility. The fertilizer nitrogen utilization rate for basal dressing, topdressing at tillering stage, and topdressing at panicle formation stage was 30-36%, 65%, and 66-81%, respectively. The nitrogen composition of barley grain during the maturity period was 86-87%, within which 54-60% was derived from the fertilizers applied. Fertilization of barley plant is a system applied during the first half of growth, and the nitrogen composition ratio of two-rowed barley at 54-60% fertilizer application was high. Therefore, in constructing a labor-saving fertilization system, a controlled availability fertilizer, from which nitrogen is eluted in the first half of growth, should be selected to ensure stable yield.

Yield of eddoe (Colocasia esculenta (L.) Schott var antiquorum Hubbard & Rehder) is greatly reduced if sufficient irrigation is not provided during the summer due to its high water requirement. However, conventional manual irrigation systems require labor and a large amount of groundwater. Here we adapted an automated system of drip irrigation to eddoe cultivation in an attempt to reduce labor and irrigation water consumption and to examine the growth properties and ecophysiological responses. Common to all three years from 2018 to 2020, our drip irrigation managements maintained higher soil moisture content during the period after the end of the rainy season, resulting in the increased above-ground growth and dry matter production, tuber growth rate, and final tuber yield in the late growth stage relative to the no irrigation management. The eddoe plants grown under drip irrigation had higher root length, water uptake rate, leaf water potential due to higher pressure potential, which may contribute to the higher stomatal conductance, and photosynthetic rate during the drought after the rainy season. Our results suggest that soil water regulation by drip irrigation is effective for avoiding drought and yield loss of eddoe.

To clarify the adaptability of cultivation of paddy rice by direct sowing in early winter, we compared the seedling establishment at 11 locations in Japan in two seasons (2018/19 and 2019/20) using different coating types and sowing dates. Although winter–sown seeds (October, November, January) had poorer seedling establishment than spring-sown seed (April), seed coating decreased the gap between winter-sowing and spring-sowing. Seedling establishment was not affected by the sowing date between October and November in Aomori, Iwate, Akita, Yamagata (2 locations) and Fukushima prefectures over the two seasons. On the other hand, in Niigata prefecture, the seedling establishment was poorer in October than in November due to untimely germination after sowing, and in Mie, Hiroshima and Fukuoka prefectures, it was better in January than in November. In contrast, in Hokkaido, seedling establishment was better when sown in October than in November.　The ratio of seedling establishment per unit seed survival rate was 55% (2018/19) and 69% (2019/20) for seeds sown in spring. The seedling establishment in 2019/20 was higher than in 2018/19 at many locations. The maximum seedling establishment at 11 locations ranged from 39% to 86%, which satisfied the target seedling establishment of 35%. These results showed that seed coating is effective over a wide area for improving seedling establishment of seeds direct sown in early winter.

To attain both high yield and superior grain quality in rice cultivation, I compared the yielding abilities of ‘Niji-no-kirameki’, a new high yielding rice variety with superior appearance quality and those of an elite rice variety ‘Koshihikari’ under the conditions of early, standard, and no topdressing in normal and late transplanting for two years in the North Kanto area of Japan. ‘Niji-no-kirameki’ had a slightly larger sink size due to the much heavier thousand grain weight compared to ‘Koshihikari’ although top dry weight at the full heading stage was similar in the two varieties. The total spikelet number per unit area (TSN) was smaller in ‘Niji-no-kirameki’. ‘Niji-no-kirameki’ had a higher percentage of ripened grain (PRG) in spite of the slightly larger sink size, resulting in a much higher yield. This might be related to the longer filling duration in ‘Niji-no-kirameki’. Topdressing considerably increased the yield. The yield was slightly higher with standard topdressing than with early topdressing. The high yield obtained by both early and standard topdressing could be attributed to the large sink size and to the high leaf color value during the grain filling period particularly with standard topdressing. Late transplanting resulted in a much larger TSN, much lower PRG and similar yield in 2020 and smaller TSN, lower PRC and much lower yield in 2021 compared to normal transplanting.

Field experiments using a high-yielding rice cultivar ‘Hokuriku 193’ and two progeny lines were conducted across three years in Nagano Prefecture, the highest-yielding area for rice in Japan. The characteristics of growth, dry matter production, yield and yield components were compared at the high yielding level of over 1200 g m^–2 for rough brown rice. The two progeny lines of ‘Hokuriku 193’ showed lower shoot dry weight than ‘Hokuriku 193’ owing to growth duration shortened by early heading. The abundance of available carbohydrate for grain filling represented by the sum of stem non-structural carbohydrate at full heading and dry matter increase during grain filling tended to be lower in the two progeny lines. The total grain number was higher in line A than in ‘Hokuriku 193’ while the thousand grain weight was lighter. The sink capacity represented by the product of grain number and weight were similar or slightly smaller. The ratio of filled grain was similar to that of ‘Hokuriku 193’ or slightly lower. The brown rice yield of line A was lower than ‘Hokuriku 193’. On the other hand, the sink capacity of line B was improved by a heavier thousand grain weight with similar grain number. The ratio of filled grain was lower. As a result, brown rice yield of line B was similar to that of ‘Hokuriku 193’ despite shorter growth duration. Given that earlier heading can avoid low temperature during grain filling, line B is a promising line for Nagano prefecture.

The high-yielding winter wheat variety ‘Kitahonami’ is the most widely cultivated variety in Hokkaido, Japan, accounting for more than 50% of the country’s domestic wheat production. In this study, we studied the factors underlying the high-yielding ability of ‘Kitahonami’ based on ripening physiology. ‘Kitahonami’ and an older variety ‘Hokushin’, were cultivated in 2014/2015 and 2015/2016; and, the dry matter weight and nitrogen accumulation in each organ and site were examined throughout the ripening period. In 2014/2015, the grain yield was significantly higher in ‘Kitahonami’ than in ‘Hokushin’, owing to the higher number of grains per unit area in the former. Although the number of grains on each ear in ‘Kitahonami’ was lower, the higher grain weight resulted in a higher yield in 2015/2016. The total dry weight increased linearly from heading to maturity in ‘Kitahonami’ while it increased significantly around the milk-ripe stage in ‘Hokushin’, tapering off thereafter. Therefore, in ‘Kitahonami’, the crop growth rate (CGR) was lower in the first half of the ripening period and higher in the second half than in ‘Hokushin’. ‘Kitahonami’, had a low grain nitrogen concentration in the second half of the ripening period, which led to a low grain nitrogen content in 2014/2015. The varietal characteristics leading to low grain protein content were clarified based on nitrogen metabolism during the ripening period.

Three kinds of green manure crops (Crotalaria juncea, C. spectabilis, Sesbania rostrata) were cultivated from May to September were cultivated to evaluate biomass production and subsequent buckwheat growth in Okinawa. Biomass and uptake of several minerals were smallest in S. spectabilis and highest in C. juncea and S. rostrata, but Mg uptake was significantly higher in C. juncea than in S. rostrata. The growth and grain yield of the autumn buckwheat depended on the green manure biomass. In particular, they were similar following S. rostrata as application of inorganic fertilizer alone (control plot). The growth and grain yield of February sown buckwheat sown in February and grown with inorganic fertilizer in all plots after buckwheat sown in October was marginally better in the green manure plots than in the control plot. SPAD values in the leaf at the first flowering node at 54 days after sowing were significantly higher in the green manure plots than in the control plot. The SPAD value had a significant high positive correlation with the grain N content. I consider that N mineralization was slower in the green manure plots than in the control plot. I infer that the development of branches and grains was promoted in the green manure plots as a result of continued N supply until the late growth stage.

For the early maturity and high palatable rice cultivar, ‘Tsukiakari’, to attain the maximum grain yield of 750 g m^–2, it is important to achieve 35700 spikelets per square meter. We examined the relationship between growth parameters and amount of nitrogen application at the panicle neck node differentiation stage, to attain a high yield and high palatability. Based on a significant linear regression between growth traits, shoot nitrogen content and leaf color based on the single photon avalanche diode (SPAD) value at full heading stage were estimated to be 13.4 g m^–2 and 41.9, respectively, when 35700 spikelets per square meter was achieved. Growth parameters showed a close correlation at the panicle neck node differentiation stage, represented by a significant linear regression. The normalized difference vegetation index (NDVI) value was in the range of 0.26–0.75 and showed a positive and close correlation with growth index value (plant height cm × number of tillers per square meter × SPAD value), indicating that NDVI can be used to estimate the growth index value in ‘Tsukiakari’ at the panicle neck node differentiation stage. We also elucidated that the NDVI value was greatly affected by water depth in the paddy field, and developed a calculation model to estimate the growth parameters of ‘Tsukiakari’ at the panicle neck node differentiation stage by adjusting the NDVI value to the water depth.

In this study, we examined the effects of topdressing before overwintering using the wheat cultivars ‘Ginganochikara’ and ‘Siranekomugi’ in farm fields in Higashimatsushima City and Natori City after tsunami inundation. Number of stems, number of spikes, culm length, and above-ground dry weight increased with topdressing treatment. However, the extent of these effects varied depending on the year or the field, with factors including soil properties exerting a great influence. In addition, it was found to be unlikely that topdressing before overwintering would reduce flower quality. Therefore, topdressing before overwintering is important as a means to promote growth after wintering, and to increase grain yields in farm fields in cold regions.

Relationships of six vegetation indexes to the aboveground biomass and nitrogen content at tillering and stem elongation stages were compared in a wheat cultivar ‘Satonosora’; normalized difference vegetation index (NDVI) measured with the portable crop growth sensor GreenSeeker, NDVI, green NDVI (GNDVI), simple ratio (SR) and chlorophyll index green(CI_green) measured with a spectroscope, and plant canopy coverage ratio (PCC) calculated from digital images. The aboveground biomass was highly related to PCC, followed by GNDVI and CI_green. These relationships were stronger than that to NDVI. The values of PCC, GNDVI and CI_green fitted with nitrogen content better than NDVI especially at the stem elongation stage. Unlike the other indexes, CI_green was not saturated even during the stem elongation stage, suggesting that it is suitable for estimating the nitrogen content at this stage. While PCC increased consistently throughout the survey period, the other vegetation indexes decreased temporarily under a dry soil condition at an early developmental stage. Therefore, for the indexes obtained with a spectroscope, an improved measurement method that is resistant to environmental fluctuation including soil moisture would better explain biomass and nitrogen content in wheat.