Wheat protein trends in northern and central NSW, 1958 to 1993

According to the Australian Wheat Board, the average level of protein in the Australian wheat crop is declining with a marked decline in the Australian Standard White (ASW) grade. Data on wheat protein concentration were collected for 125 wheat receival sites along with wheat production, area sown to wheat, and monthly rainfall in northern NSW from 1958 to 1993. Protein trends of the major wheat segregations were examined along with the effect of year-to-year variation in winter rainfall and the impact of the segregation and storage system on trends in protein. The variation in protein content was inversely associated with variation in yield (-1.55%/t . ha) and was attributed to year-to-year variation in winter rainfall (May to October). For the period for which the wheat segregation system has operated, 1970 to 1993, ASW in the study region has apparently declined at the rate of -0.11%/year. Expansion of the storage and segregation system and access to load-by-load protein testing in the early 1980s led to a large proportion of wheat that had been delivered into ASW, in the 1970s, being redirected into higher protein segregations. Redistribution of wheat receivals in the 1970s around the 11.5% protein level removed this distortion and indicated a rate of decline for wheat <11.5% of -0.06%/year. In the absence of segregations, the weighted average protein was declining at a rate of -0.08%/year and accounting for year-to-year variation in rainfall the underlying trend in protein was -0.04%/year. Allowing for the year-to-year variation in rainfall and the limitations of the segregation system the decline in protein in wheat redistributed below 11.5% was -0.05%/year and may reflect a run-down in soil fertility. Wheat in this category was increasing significantly, over time, as a proportion of total receivals.