Effects of Growth Diagnosis Using Visible Canopy Images and Variable Rate Nitrogen Application at the Flag Leaf Appearing Stage on the Grain Protein Content of the Wheat Cultivar ‘Sanukinoyume 2009’

Abstract

Variable rate nitrogen application is considered to achieve a high yield and/or grain quality in wheat. In this study, we examined whether variable rate nitrogen application at the flag leaf appearing stage (GS37) increases grain protein content, which is important for the quality evaluation of wheat. In addition, we tested the availability of growth diagnostic index calculated from canopy images at GS37 as an inexpensive growth diagnostic method. Grain protein content was significantly increased 0.15 to 2.3% by application of 5 g m^-2 nitrogen at GS37. The increase in grain protein content was due to the increase in grain nitrogen accumulation by about 2 g m^-2 by supplemental application of 5 g m^-2 nitrogen. The growth diagnostic index calculated from canopy images was significantly correlated with nitrogen accumulation above ground at GS37, and six indexes showed the same slope and intercept in two cropping seasons. In the third season, we conducted a verification test to evaluate the effect of variable rate nitrogen application at GS37 in achieving high stabilization of grain protein content, based on the growth diagnostic index. Yields varied in the range of 180 to 509 g m^-2, but grain protein content was similar, ranging from 11.6 to 11.8%. Variable rate nitrogen application at GS37 based on the growth diagnostic index calculated from canopy images was considered to be an effective cultivation method for achieving high stabilization of grain quality in wheat cultivar ‘Sanukinoyume2009’.