Abstract
Grain quality (volume weight, α-amylase activity, protein content and ash content) was investigated on 128 winter wheat samples, Hokushin variety, collected in central Tokachi region from 2002 to 2004. There was no significant relationship between the grain quality and grain yield, or among the grain quality components. Volume weight showed a relatively high correlation with grain weight (r=0.67**—0.91**) and the percentage of whole grain (r=0.65**—0.90**) in each year. The mean grain weight was higher the lower the temperature in the ripening period; 2003 > 2002 > 2004. The mean volume weight in 2003 was also higher than that in 2002 and 2004. The activity of α-amylase was low in all three years examined because of the limited precipitation just before the maturing stage. The mean protein content in 2002 and 2004 was 10.2 and 10.3%, respectively, which were appropriate values, but was 9.4% in 2003, which was unfavorably low. The protein content of the grain showed a relatively high correlation with nitrogen and potassium contents of wheat straw (r=0.55**—0.80**). The mean ash content in 2003 and 2004 was 1.44 and 1.53%, respectively. Phosphorus and potassium accounted for about 40% of the ash content. The ash content of grain was highly correlated with the phosphorus content (r=0.92**—0.96**).
