The Relationship Between Grain-Protein Content of Wheat and Barley and Temperatures During Grain Filling

Abstract

This paper compares the relationship between temperatures at grain filling and grain-protein content for wheat and barley. Two similar statistical models have been developed using historical grain and climate data to reliably predict the protein content of wheat and barley at grain receival sites. Protein levels were predicted using multiple regressions with the same regression coefficients for all sites. The locality effect is absorbed in the regression intercept derived for each site. Australian Standard White (ASW) wheat data for 109 silos throughout South Australia for the years 1971-1991 were analysed in relation to rainfall and temperatures at the closest weather station. Rainfall from May to September was associated with a decrease in ASW wheat grain protein, and more importantly, the number of days in October above 30ºC were positively associated with an increase in wheat grain-protein levels. Analysis of protein data from malting varieties of barley (1982-1991) from 160 South Australian hundreds (districts of about 260 km²) again showed that increased rainfall between July and September was associated with decreased grain protein. However, the dominating influence was the number of days in a row in November above 35ºC, which was consistently associated with increased grain protein. This makes an interesting comparison with wheat where October temperatures were more important despite barley being harvested earlier than wheat.