Updated nutrient response curves in the northern and southern regions of Australia

Soil testing is a key strategy in the efficient use of expensive fertilizer and other nutrient inputs, ensuring that the mix of nutrients applied match the fertility status and crop demand for the likely seasonal conditions. However, for soil testing to be effective in both these roles there needs to be a well-documented relationship between the soil test result and the likely response to applied nutrients. An analysis of the available soil test-crop response information in the BFDC database conducted at the initiation of the MPCN2 program identified gaps that existed for key crops, soils and regions. The majority of these gaps related to (i) crops that are either new to cropping regions and/or occupy a relatively low proportion of the cropped area (e.g. grain legumes broadly and oilseeds in the northern region); (ii) emerging nutrient constraints (like potassium [K] and sulfur [S]) that have previously been adequately supplied in soils with moderate clay contents; or (iii) to issues associated with changing profile nutrient distributions resulting from a combination of reduced tillage and fertilizer management strategy (e.g. especially elements with limited mobility like phosphorus [P] and K).
While some of the initial projects funded under MPCN2 have been targeted at these gaps in knowledge, the on-farm trials run with grower groups/consultants have not been as effective as hoped due to a number of factors. These include (i) the relatively low frequency in the crop rotation and the narrow planting windows of the target crops, reducing the number of site-years of data from the trials established; (ii) the need to revisit response relationships in the ‘well researched’ species like wheat to account for issues of changing profile distribution and fertilizer application strategies (e.g. deep placement to address subsoil depletion, or accounting for subsoil enrichment due to long histories of fertilizer application); (iii) poor choice of experimental sites, due to a combination of inadequate pre-sowing soil testing and choice of sites based on the quality of the research collaborator rather than the likelihood of the site being fertilizer responsive; and (iv) an inability to adequately cover the range in seasonal conditions and crop yield potentials that reflect crop nutrient demand and fertilizer recovery in relatively short 3 year projects.
This project will ensure that by 2020, growers and their advisers in the northern and southern regions will have access to updated nutrient response data in the Better Fertiliser Decisions database for a wide range of crop species and nutrient responses. This will be achieved by running a smaller number of intensely managed sites across the Northern and Southern regions, with sites chosen on the basis of very specific characteristics (including in-field variability and a vertically stratified assessment of nutrient availability. Tighter control of agronomic practices and crop sequences and a more detailed approach to soil and plant sampling will ensure each experimental data set can be interpreted in terms of fertilizer recovery, crop response and the economics of fertilizer use. While this approach will necessitate a less geographically dispersed series of experiments, it will allow a tighter focus on the gaps in soil test-crop response relationships the project is trying to address.
Each site will have an establishment year, where a range of fertilizer rates and tillage practices are used to establish a range in soil test values for the nutrient in question, with crop response related to the performance of an unfertilized control. In subsequent seasons, soil sampling will redefine the soil test range for the next crop season, and a soil test-crop response relationship can be derived for that site-season combination. Extrapolation beyond these sites will be achieved by growing a benchmark species (e.g. wheat or sorghum) in each season, along with the target species. The relative responsiveness of the lesser known species can then be extrapolated to other soils and seasons where trials for the benchmark species have been conducted.
The project will generate the following outputs
(i) By December 2016, a review and synthesis of the available macro-nutrient response curve data will identify and prioritise the gaps in the current data for important crops.
(ii) By March 2018 and each subsequent year, data and analysis of the results from field experiments generating locally validated nutrient response curve data will be collated and entered into the BFDC database.
(iii) By June 2020, a Final Technical Report amalgamating the key findings, new knowledge and conclusions of the project will be written to provide an overall interpretation of the work.