We evaluated effects of high nitrogen (N) input on grain yield, grain quality and taste of rice grown at a low planting density under a cool climate in Aomori prefecture, Japan. We grew a rice cultivar “Mashhigura” under four combinations of two basal nitrogen and two planting densities for three consecutive years. Climate conditions differed among years especially at the early tillering stage; air temperature and solar radiation in 2016 were lower than in 2014 and 2015, resulting in lower tiller production in 2016. Although in 2014 and 2015, no yield reduction was observed by the low planting density, the yield was significantly reduced by the low planting density under a normal N condition. This yield reduction caused by the low planting density was compensated by a high N input. Grain appearance, eating quality and protein content were not significantly affected by planting density and N input. The income was stable at a high level under the conditions of low planting density with a high N input.

“Setokirara”, a wheat cultivar for bread in western Japan, has high yield potential, although its grain protein content (GPC) could be lowered when the yield level was high. The objective of this study was to examine the effects of intensive nitrogen fertilization during stem elongation (INFSE) for achieving both high yield and high GPC in “Setokirara”. The effects of increased nitrogen at an early stage and/or increased total nitrogen in wheat obtained by INFSE were also examined. In 2015/16 and 2016/17, grain yield in the INFSE group was 11-40% higher than that of the conventional fertilized wheat (control) with a 16-23% increase in spike number per unit area. GPC in the INFSE group did not decrease despite the increase in yield. Thousand grain weight in the INFSE group was 2.3 g heavier than that in the control group in 2016/17 when precipitation was moderate and hours of sunlight was sufficient during grain filling. The increase of nitrogen applied at an early stage and increase of total nitrogen had a small effect on the yield of wheat given INFSE. Nitrogen accumulated in the aboveground organs at maturity was around 12-16 g m^–2 across treatments even though total nitrogen applied ranged from 16 to 30 g m^–2. INFSE increased the yield without decreasing GPC in “Setokirara”. Therefore, INFSE would be useful for cultivating high-yield wheat cultivar for bread.

In order to clarify the possibility as an inter crop for backwheat in Okinawa low phosphorus tolerance of groundnut (Arachis hypogaea) was investigated by comparison with soybean (Glycine max) and sesbania (Sesbania cannabina) in volcanic ash soil (akadama soil) and acrisols (red soil) in which phosphorus is fixed by aluminum and iron, respectively. The effects of arbuscular mycorrhizal fungi on the growth, nodulation, and phosphorus uptake of the three legumes were also examined. I found that growth of the three species declined due to the decreased amount of phosphorus fertilizer applied under akadama soil cultivation; however, groundnut showed less decline than soybean, and groundnut showed more vigorous growth than sesbania when cultivated with a small amount of phosphorus fertilizer (0% and 0.1% of phosphate absorption coefficient). The nodule weight of groundnut was similar to that of soybean and lower than that of sesbania under all phosphorus conditions. At the early growth stage, root length of soybean and sesbania was markedly decreased under phosphorus-deficient conditions, whereas that of groundnut was not. Root development during the early growth stage in groundnut appears to be secured under phosphorus-deficient conditions by the large amount of phosphorus contained in its seed. The aboveground biomass and phosphorus uptake of groundnut cultivated in red soil without arbuscular mycorrhizae were similar to those of soybean and lower than those of sesbania in superphosphate and slightly soluble phosphorus (Al-P and Fe-P) fertirizer conditions. However, the aboveground biomass and phosphorus uptake of groundnut cultivated in red soil with arbuscular mycorrhizae were similar to those of sesbania under all superphosphate conditions and higher than those of sesbania under slightly soluble phosphorus conditions. Although groundnut can develop roots in soil with low phosphorus fertility because of the large amount of phosphorous in its seed, infection with mycorrhizal fungi may be necessary to ensure sufficient continued growth.

Damping-off is one of the most threatening factor for quinoa growth and yield. In this study, to clarify the cause of the occurrence and to find a method to suppress of damping-off in quinoa (Chenopodium quinoa Willd.), we carried out field experiments in the experimental field at Nihon University from 2014 to 2017. The damping-off ratio remarkably varied with the sowing time. Damping-off occurred from the emergence stage to fourth leaf stage at all sowing times, but, not after the fourth leaf stage. The reason for the difference in damping-off ratio with the sowing time was not the difference in temperature or sunshine hours but the difference in precipitation. The damping-off ratio was also decreased under a lower soil moisture condition. Thus, one method to suppress damping-off was to decrease the soil moisture at an early growth stage. There were no significant differences in the damping-off ratio among 12 cultivars. Rhizoctonia spp. and Fusarium spp. were observed from the seedlings with damping-off symptoms. We considered that those fungi caused damping-off in quinoa seedlings. Damping-off was suppressed by the broadcasting of more than 2g per m2 of Dakoreto wettable powder to the soil surface. From this study, we identified a cause of damping-off in quinoa and suggested a method to suppress damping-off in quinoa.

As part of a study to clarify the mechanism of the allelopathic activities in barley straw on the early development of paddy weeds in northern Kyushu, we examined the effect of water immersion taken from fresh straw and incinerated straw (ash) on seed germination of mustard spinach (Brassica rapa var.perviridis) seeds. Water immersion from fresh straw inhibited the germination of mustard spinach, while that from the ash did not. Since a similar trend was observed with or without addition of soil to the water immersion, the inhibitory effect of mustard spinach on seed germination was considered to have derived directly from the fresh straw or its ash rather than from a degradation metabolite of the straw by soil microorganisms. The water immersions from fresh straw and their ash were examined for phenolic substances using liquid chromatography/TOF-mass spectroscopy. As a result, five active substances were identified, and (±)-2-phenylpropionic acid at a concentration of 2 ppm was found to markedly inhibit the seed germination of mustard spinach.

This study aimed to develop a simple model to predict the culm length of rice cultivar “Koshihikari” supplied the standard level of nitrogen top-dressing in Chiba prefecture, Japan. The prediction would be useful to decrease the risk of promoting the culm extension and lodging by modifying the amount and timing of nitrogen topdressing. We analyzed the data set of “Koshihikari”, which were obtained from field experiments with three or four cropping seasons in a year for 12 years in Chiba prefecture, Japan. By the multiple regression analysis based on the results obtained by the forward stepwise method, a simple model to predict the culm length was developed (RMSE = 3.01 cm). In this model, plant length, tiller number, and leaf color (SPAD value) at the panicle formation stage, the daily minimum temperature and global solar radiation were selected as the explanatory variables. The model estimated accurately the culm length of independent experimental data sets at Chiba-city, Sanmu-city, Katori-city in Chiba prefecture (RMSE = 2.68～2.76 cm). The risk of lodging increased above the threshold of 90 cm in culm length. The accuracy rates regarding the diagnostic estimation of culm length, that is, whether culm length exceeds the threshold value or not, were 77～91%. These accuracy rates were higher than those by the conventional estimation method, which have been used in Chiba prefecture. This model would be more useful for deciding the optimum amount and timing of nitrogen fertilizer for topdressing than the conventional method.

Effects of sowing date on yield and yield components of linseed (Linum usitatissimum L.) were studied. Seeds of variety Lirina were sown at one-week intervals from February to December in 2015 and 2016. At least 40 days and 600 growing degree days (based on 5°C) from sowing were needed for flowering. It was possible to produce seeds by spring, summer, and autumn sowing. In spring sowing and in summer sowing, later sowing reduced yield and three yield components, namely, the number of capsules per unit area, the number of seeds per capsule, and single seed weight. In autumn sowing (harvest in the next spring), on the contrary, later sowing increased the yield and the three yield components. The decrease in yield in late spring sowing was considered to have been caused by the high temperature after flowering and that in late summer sowing by the low temperature during maturity. Plants sown early in autumn were vulnerable to lodging and resulted in low yield. It is concluded that the optimal sowing dates for linseed production lie between mid-February and mid-April (spring sowing), between late July and early August (summer sowing), and between middle October and late November (autumn sowing).