Methodologies for assembling and interrogating N, P, K, and S soil test calibrations for Australian cereal, oilseed and pulse crops

During the past 50 years, 3800 field experiments yielding over 5200 treatment series were conducted in Australia examining yield responses to applied N, P, K, or S fertiliser applications to cereal, oilseed and pulse crops. The experiments all had accompanying soil test data. These data were entered into multiple Microsoft Access® database templates and then consolidated into a single national online MYSQL® database. A web application (named the BFDC Interrogator) was also developed to rapidly access the national database (BFDC National Database) and construct soil test calibrations between percentage of the maximum grain yield achieved (hereafter called percentage relative yield) and soil test values recorded for specified ranges of regional or national experiments. Search parameters were applied to define soil test calibrations. These included farming system (dryland or irrigated), year of experiment, soil type, crop type, soil test, depth of soil sampling and soil test units. Other data filters based on site metadata, such as method of nutrient placement, can be applied to enable more definitive calibrations. The calibrations are used to derive critical soil test values at 80, 90 and 95% relative crop yield with 95% confidence limits. However, the soil test criteria at 90% relative crop yield with 70% confidence limits have been chosen as the single calibration and reliability standard for all crops and soil tests. Corresponding yield increase (t/ha)–soil test relationships for an applied nutrient can also be accessed. The BFDC National Database and BFDC Interrogator can now be accessed online by trained, registered users. This paper describes the methodologies that underpinned the progressive development of this tool. Through the commitment of the grains and fertiliser industries, it is anticipated that the calibrations will be used to improve decision support systems used to generate fertiliser recommendations for Australian cropping industries.