THE RELATIONSHIP BETWEEN GRAIN-PROTEIN CONTENT OF WHEAT AND BARLEY AND TEMPERATURES DURING GRAIN FILLING

This paper compares the relationship between temperatures at grain fil ling and grain-protein content for wheat and barley. Two similar stati stical models have been developed using historical grain and climate d ata to reliably predict the protein content of wheat and barley at gra in receival sites. Protein levels were predicted using multiple regres sions with the same regression coefficients for all sites. The localit y 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 r ainfall and temperatures at the closest weather station. Rainfall from May to September was associated with a decrease in ASW wheat grain pr otein, and more importantly, the number of days in October above 30 de grees C were positively associated with an increase in wheat grain-pro tein levels. Analysis of protein data from malting varieties of barley (1982-1991) from 160 South Australian hundreds (districts of about 26 0 km(2)) again showed that increased rainfall between July and Septemb er was associated with decreased grain protein. However, the dominatin g influence was the number of days in a row in November above 35 degre es C, which was consistently associated with increased grain protein. This makes an interesting comparison with wheat where October temperat ures were more important despite barley being harvested earlier than w heat.