Leaf Blade Dry Weight and Leaf Area Index × SPAD Value at Anthesis Can Be Used to Estimate Nitrogen Application Rate at Anthesis Required to Obtain Target Protein Content of Grain in Bread Wheat

We analyzed the relationship between growth-related traits at anthesis and protein content of grain at maturity to develop a method of estimating the nitrogen (N) application rates at anthesis required to obtain the target protein content of grain in the bread wheat (Triticum aestivum L.) cultivar Minaminokaori in three crop seasons in southwestern Japan. The protein content of grain had a higher positive correlation with leaf blade dry weight (DW) and the leaf area index (LAI)×SPAD value than with the SPAD value. Moreover, the relationships between leaf blade DW and protein content of grain and between LAI×SPAD value and protein content of grain could be approximated well using quadratic functions for each N application rate at anthesis. Thus, N application rate at anthesis required to obtain the target protein content of grain can be estimated by using these quadratic functions