Yoichi Torigoe’s research while affiliated with Nihon University and other places

High altitude leafy vegetable cultivation in profit-oriented fields in Japan are abundantly fertilized and characterized by plastic mulching. Our goal was to evaluate the close link between soil nutrient amendment, yield and nutrient uptake of three leafy vegetable production systems of small and middle scale producers characterized by an array of farm management practices. A participatory methodology using questionnaires together with on-farm and homestead discussions and observations were employed to obtained information about the farm management practices. Plant sampling was carried out at harvest and analyzed using standard methods. Results showed that yields for the same crop from high-nutrient input cropping system (B) was not significantly different (p > 0.05) to that of low-nutrient input systems (A, C and AFC). However, there was a significant difference (p < 0.05) in terms of nutrient content of the harvested parts indicating excess nutrient applied in high-nutrient input cropping systems. In addition, more of N, K, Ca and Mg taken up were left in the system as residues after harvest than was taken out in the form of harvested farm produce. P content of the harvested part was greater than that in the crop residue. Harvesting methods were not uniform (time, crop residue) resulting in some significant differences between nutrient content of the harvested parts and crop residues indicating that farm management practices may not necessarily result to any significant gain in yields but may lead to significant differences in the nutrient content.

Rice blast disease occurs in rice production areas all over the world and is the most important disease in Japan. Remote sensing techniques may provide a mean for detecting disease intensity for large area without being subjected to raters. This study evaluated the use of airborne hyperspectral imagery to measure the severity of panicle blast in field crops. Hyperspectral remote sensing imagery was acquired at the dough stage of rice grain development in northern Japan. The most consistent relationship, with high R² and low P, was the simple band ratio R498 to 515/R700 to 717 (i.e., the reflectance at 498 to 515-nm divided by the reflectance at 700- to 717-nm). The band ratio of R498 to 515/R700 to 717 increased significantly (P < 0.001) with increasing visual estimates of disease incidence, defined as the percentage of diseased spikelets (R² = 0.83). Assessment of disease distribution and severity could provide useful information for making decisions regarding the necessity of fungicide application and estimate potential yield loss due to the disease.

The objective of this study was to evaluate the optimum sowing time and planting density of soybean cultivar, Tsukuizairai. Field experiments were carried out in the experimental field at Nihon University from 2012 to 2014. When Tsukuizairai were sown in May, the rate of damaged seed by stink bugs and delayed stem senescence increased. In the case of 30 cm row width and 7.5 cm intrarow spacing, marked lodging occurred in the July sowing plots due to the longer stem length and thinner stem diameter. Thus, the optimum sowing time is from June to July, and the optimum planting density is from 11.1 to 22.2 plants per m-2 for soybean cultivar, Tsukuizairai. The protein content of seeds was not affected by sowing time and planting density. However, that of Tsukuizairai was lower than that of Enrei and Tachinagaha. Thus, the subject of the Tsukuizairai cultivation is the production of high protein content seeds in the future.

A clear understanding of how crop root proliferation affects the distribution of the spore abundance of arbuscular mycorrhizal fungi (AMF) and the composition of AMF communities in agricultural fields is imperative to identify the potential roles of AMF in winter cover crop rotational systems. Toward this goal, we conducted a field trial using wheat (Triticum aestivum L.) or red clover (Trifolium pratense L.) grown during the winter season. We conducted a molecular analysis to compare the diversity and distribution of AMF communities in roots and spore abundance in soil cropped with wheat and red clover. The AMF spore abundance, AMF root colonization, and abundance of root length were investigated at three different distances from winter crops (0 cm, 7.5 cm, and 15 cm), and differences in these variables were found between the two crops. The distribution of specific AMF communities and variables responded to the two winter cover crops. The majority of Glomerales phylotypes were common to the roots of both winter cover crops, but Gigaspora phylotypes in Gigasporales were found only in red clover roots. These results also demonstrated that the diversity of the AMF colonizing the roots did not significantly change with the three distances from the crop within each rotation but was strongly influenced by the host crop identity. The distribution of specific AMF phylotypes responded to the presence of wheat and red clover roots, indicating that the host crop identity was much more important than the proliferation of crop roots in determining the diversity of the AMF communities. © 2016, The Microbiological Society of Korea and Springer-Verlag Berlin Heidelberg.

The objective of the present study was to determine the optimum sowing time of three quinoa ecotypes (Altipllano, sea level, and valley) for high seed yields in south Kanto, Japan. Pot experiments were conducted in the experimental field at Nihon University during 2011, 2012, 2013, and 2014. In this experiment, the following quinoa varieties were used NL-6, Baer Cajon and Cauquenes (sea-level type), Amarilla de Marangani, Blanca de Junin, CICA-127, ECU-420, ECU-525, Ingapirica, and Narino (valley type), 94R and Isluga (Altiplano type). The quinoa seeds were sown on March 29, June 17 and September 22, 2011; March 27, June 17 and August 28, 2012; March 26, June 15 and 5 September 5, 2013; and March 27, June 17 and August 28, 2014. When the sea-level type and Altiplano type seeds were sowed from March to September, the seeds could be gained in all sowing plots. However, the seed weights of all varieties were the highest in the sowing plots of March. And the seed weights in the sowing plot of March were significantly higher than that in the other sowing plots. The sea-level type and Altiplano type quinoa had almost the same seed growth reaction for day length and day temperature. Thus, to gain a high seed yield of the sea-level and Altiplano type quinoa, March was the optimum sowing time in south Kanto, Japan. When the valley-type seeds were sowed from March to June, the seeds could not be gained, except in 2012. In 2012, the seed weights and seed numbers in sowing plots of March and June were significantly lower than those in the sowing plot of September. Thus, to obtain a high seed yield of the valley type quinoa, the optimum sowing time in south Kanto, Japan was from August to September.

The objectives of this study were to evaluate the optimum planting density of quinoa (Chenopodium quinoa Willd.) variety NL−6 from the standpoint of efficiency for light utilization, dry matter production and seed yield. Field experiments were carried out in the experiment field at Nihon University in 2012, 2013 and 2014. In 2012, the row width was 50 cm, and the planting density was from 50 to 300 plants m−2. In 2013, the row width was 30 cm, and the planting density was from 100 to 400 plants m−2. In 2014, the planting density was 100 plants m−2, and the row width was from 15 to 60 cm. In the case of 50 cm row width, there were no significant differences in the extinction coefficient and relative illuminance on the soil surface at flowering and seed filling stage, in crop growth rate (CGR) from flowering to seed filling stage, and in seed yield among plots. In the case of 30 cm row width, the extinction coefficient and the relative illuminance on the soil surface in 300 and 400 plants m−2 were higher than those in 100 and 200 plants m−2, and the relative illuminance on the soil surface was lower at flowering and seed filling stage. However, there were no significant differences in the CGR from flowering to seed filling stage and seed yield among plots. The extinction coefficient in the 15 and 30 cm row width plots was higher than that in the 60 cm row width plot, and the relative illuminance on the soil surface was lower at flowering and seed filling stage. At a lower planting density and wider row width plots, the seed yields in the branch were higher than that in higher planting density and narrower row width plots. Therefore, we concluded that quinoa variety NL−6 needs from 50 to 100 plants per m−2 to get high seed yield regardless of planting density and row width. Seed yield was significantly correlated with the top dry weight at the seed filling stage (r=0.701*). Thus, the heavy dry weight at the seed filling stage is very important to increase the seed yield of quinoa variety NL−6.

The objectives of this study were to evaluate the varietal difference in the occurrence of delayed stem senescence (DSS) and cytokinin level in the xylem exudate in soybeans and the relationship between the occurrence of DSS and cytokinin level in the xylem exudate. Pot experiments were carried out in the experiment field at Nihon University in 2010, 2012 and 2013. In this experiment, we used 11 soybean varieties, which were cultivated in the Kanto region, Japan. The degree of DSS (DSS score) was positively correlated with the days from sowing to flowering stage (S-R2), and was higher in the varieties with a longer length of S-R2, though the correlation was not significant. Under some conditions, the DSS score was negatively correlated with S-R2. Moreover, the DSS score was positively or negatively correlated with the main stem diameter, total node number, stem dry weight and seed weight depending on the growth parameter or sowing date. Thus, we concluded that the DSS score was not correlated with the growth parameters. On the other hand, the level of cytokinins such as t-ZR and iPA shown by their amount in xylem exudate from a plant at the seed filling stage was negatively correlated with the DSS score. Thus, we consider that one of the reasons for varietal difference in DSS occurrence may be the difference in cytokinin content of stem and leaves after the seed filling stage.

Nitrate-N (NO3-N) leaching in intensive crop production systems is an important issue due to its potential as a pollutant and a valuable resource. This study aimed at evaluating NO3-N leaching using on-farm measurements and modeling of 12 commercial fields of leafy vegetables characterized by an array of farm management. Real-time monitoring of the soil moisture, temperature and bulk electrical conductivity (ECb) using a capacitance/resistance sensor (5TE) was carried out to verify the temperature index and the leaching constant integrated in the soil nitrogen (N) balance estimation system. Results showed that measured soil temperature strongly correlated to model estimates. Values of the leaching constant were 0.0006 kg kg-1 and 0.00075 kg kg-1 (in 2013) both of which were close to the model value of 0.0007 kg kg-1. Values in 2012 were either too high (0.00127 kg kg-1) or too low (-0.0010 kg kg-1). NO3-N leaching ranged from 13.50 kg ha-1 to 72.71 kg ha-1 in 2012 and 8.66 kg ha-1 to 41.10 kg ha-1 or 0.00 kg ha-1 to 41.10 with or without rye, respectively. NO3-N leaching in single cropping systems of 2012 was higher than in double cropping systems of 2013. Key words: Capacitance/resistance sensor, FAO reference evapotranspiration, Leaching, NO3-N, Soil N balance estimation system.

Introduction of cover crops may improve the diversity of arbuscular mycorrhizal fungi (AMF) in roots and soil under crop rotational systems; therefore, it is necessary to determine the potential for AMF communities to improve sustainable food production. We investigated the impact of cover crops, including wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), pea (Pisum sativum L.), and hairy vetch (Vicia villosa Roth.), on the AMF communities in their roots in autumn and spring sowing seasons with PCR-DGGE analysis. Although all four cover crops impacted the AMF community structure in roots, the diversity of AMF communities was unchanged among crop type or sowing season. Redundancy analysis (RDA) demonstrated that AMF communities within crop type were significantly different. However, the AMF community structures were not influenced by growing season, suggesting that growth stage in crops may be more responsive to shaping AMF community structure in crop roots than host crop identity.

In this study, to clarify the effects of sowing time on the emergence of quinoa (Chenopodium quinoa Willd.), we evaluated the effects of water potential in soil, temperature and sowing depth on the emergence of quinoa. In field experiments, the emergence ratio of August sowing plots was lower than that of the June and October sowing plots. The water potential and temperature of soil after sowing in August sowing plot moved higher than those of the other plots. Emergence ratio of quinoa was not affected by the temperature from 20℃ to 34℃. And emergence ratio of quinoa was not affected by the water potential in soil from -5kPa to -20kPa at sowing. However, the quinoa did not emerged at -40kPa of water potential. From above that, we considered that the changes of emergence ratio with sowing time were affected by the dry condition of soil after sowing. And from -5kPa to -20kPa of water potential in soil at sowing time, the emergence ratio of 1.0cm sowing depth was higher than that of the other sowing depth. In this study, the optimum sowing depth of quinoa was 1.0cm.