Moisture and nutrient limitations, particularly nitrogen, commonly affect crop production in the grain-growing region of northern Australia. In this region, grain protein contents of cereal crops (wheat, barley, sorghum) are used retrospectively to distinguish, with reasonable certainty, crops to which nitrogen supply had limited grain production in that year. Using precision agriculture technologies, we collected site-specific yield and protein data of sorghum and barley paddocks during 1999. These coincidental maps were kriged onto a common grid, then interrogated, using regional trial data, to locate sites where nitrogen was yield limiting. The procedure, although at this stage still restricted to nitrogen, offers insight into the variation within a paddock on nitrogen supply, the likelihood of nitrogen limitations, and forms a management strategy for ongoing nitrogen application
