There are numerous factors that impact protein content in wheat. While environmental factors such as moisture and temperature have large effects on protein content, production practices such as variety selection, seeding date and fertility management can also influence protein content.
Influence of Genetics. Not all wheat varieties have the same potential for grain yield and differ slightly in their ability to convert soil nitrogen to grain protein. We typically see higher yielding varieties with lower protein content, largely due to dilution as protein is diluted by the increased carbohydrate (i.e. kernel number) production seen with higher yields.
Manitoba Data. Jochum Wiersma of the University of Minnesota created the following scatter plot for me that I included in a recent Ag Days 2015 presentation. The figure includes the long term data of varieties belonging to the CWRS & the CWGP classes tested by MCVET. Long term yield data is from 2000 to 2014 expressed as a % of the overall grand mean (66 bu/ac), while protein data is from 2002 to 2014.
As the figure illustrates, there is a grouping of varieties according to class based on the relationship between yield and protein content. However, there is variation with each class and there are a few varieties with higher yield potential that still has protein content appropriate for the CWRS class.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist