Factors of Fluctuation in Glassy Grain Rate and β-Glucan Content and their Control by Fertilizing Technology in Barley Cultivar Shunrai for Barley Rice

In barley for food uses, endosperm glassy grain rate is an important factor that affects pearling quality, while β-glucan has received increasing attention as a functional ingredient. We analyzed the factors affecting endosperm glassy grain rate and kernel β-glucan content from data collected in local growers’ fields and studied nutrient-based techniques to manage these two parameters at the Tochigi Prefectural Agricultural Experiment Station. First, we conducted factorial analysis using the cultivar Shunrai grown in farmers’ fields in Tochigi prefecture. Given that glassy grain rate and β-glucan content are strongly correlated with kernel protein content, we considered that high product quality depended on the management of protein content. Although the glassy grain rate varied with the year, the acceptable glassy grain rate level of not more than 50% was likely to be achieved when protein content was not more than 8%, with the resulting β-glucan content being 4.4%. However, our attempt to reduce protein content by low-nutrient cultivation resulted in substantial yield fluctuations and led us to conclude that this method is not suitable for achieving low glassy grain rate because it is accompanied by yield instability. Trials at the Tochigi Prefectural Agricultural Experiment Station indicated that split application at the beginning of stem elongation and 30 days before had a practical value as a fertilizing schedule because this schedule produced higher yields with lower glassy grain rate than single basal fertilization, albeit with lower β-glucan content. The results also suggested that the advisability of topdressing in light of keeping protein content within the target range could be determined by multiplying the number of stems by SPAD value, both measured 30 days before stem elongation began. The topdressing at 10 days after heading, which is believed to increase β-glucan content, reduced grain quality by increasing glassy grain rate and was therefore was considered unsuitable for Shunrai.