Within-field variation in wheat quality: implications for precision agricultural management

In this study, 9 Western Australian fields sown to dryland wheat were monitored using precision agricultural techniques, in order to understand implications for processing quality of the grain. Four fields received variable inputs of N fertiliser, and 6 received variable seed rates. In most cases, there was a very large variation within-field in grain yield, protein content, and protein quality, and such variation was related to variation in soil acidity, soil nitrate, and soil organic carbon, and specific weed and pest problems in some fields, as well as variation in the inputs. Grain protein content was positively correlated with soil nitrate levels in 6 of the 7 fields for which soil analyses were carried out. For several of the larger fields, separate harvesting of zones within the fields having differences in grain protein content would have enabled a greater proportion of the grain to be in a higher return quality grade. In 7 of the 9 fields, variation in protein quality (sodium dodecyl sulfate-sedimentation volume, SDS-SV) was greater than variation in protein content. The different measures of protein quality (SDS-SV, polymeric protein (glutenin) content, and glutenin molecular weight distribution) sometimes followed similar spatial trends, but in many cases did not. Therefore, total protein estimates are probably suitable measures for predicting within-field variation in protein quality. In none of the 9 fields was there overall a negative relationship between grain yield and protein content, although limited moisture availability can affect such relationships. The results suggest that the use of precision agricultural methods to manipulate inputs such as fertiliser, lime, or seed rates to increase yield does not have a negative effect on protein content. Farmers, therefore, can use precision agricultural methods along with other approaches to maximise wheat yield and grain protein content/quality at the same time.