Craig Scanlan

Agricultural research in broadacre farming in Western Australiahas a strong history, resulting in a significant public resource of knowledge about biophysical processes affecting crop performance. However, translation of this knowledge into improved on-farm decision making remains a challenge to the industry.Online and mobile decision support tools to assist tactical farm management decisions are not widely adopted, for reasons including: (1) they take too much time and training to learn; and (2) they aren’t integrated with the data they need or with each other, making their use too time-consuming. Meanwhile, as farmers accumulate more data from their machinery, they find themselves unable to use that data to inform decision making.In an ideal future, variable rate technology (VRT) could be programmed to apply optimal rates of fertilisers. However, the existing suite of models and tools are derived from small-scale controlled field experiments and are not suitable forfine-scale paddock management. Using 14 years of data from a farm in the eastern wheatbelt of Western Australia, we investigate the calibration and extension of an agro-economic modelfor spatial prediction of the effects of nitrogen applicationson wheat yield and gross return.We use a simple response curve model, NP-Decide,that was developed in Western Australiaand remains in common use.

In WA, soil testing for mineral N (ammonium plus nitrate) has traditionally been taken from the top 0-0.1 m. Farmers and advisors are now interested in deeper soil testing, in order to know how much mineral N occurs at depth and what this may mean in terms of fertiliser N application decisions. Accounting for topsoil and subsoil test level in N fertiliser use varies markedly among growers and advisors depending on; their own historic applications; use of nitrogen decision support tools (N-DSS’s) such as Yield Prophet simulations or SYN. Other growers use approximate total soil profile N and then add N fertiliser required to reach target yield (i.e. 45 kg N/ha for 1 t/ha of grain). The main question this paper is addressing is “Do I need to soil test to depth for better N decisions?” To answer this we needed to understand: 1. Where in the profile the subsoil N occurs and if it is related to topsoil N, 2. How effective is the subsoil in supplying N for the crop – which depends on root access to subsoil N as affected by subsoil constraints and N leaching, 3. What does this mean for N recommendation systems based on soil testing? and 4. Given the seasonal interaction with yield response, will the subsoil N test results reduce the errors in recommendations enough to justify this extra complexity, cost and effort?

In south-western Western Australia, the incidence of potassium (K) deficiency in wheat has increased steadily, with two-thirds of the arable lands prone to potassium depletion through continued removal in hay or grain and straw. Leaching of potassium especially in sandy soils, where the total potassium pool is small, is also a significant contributor to poor K-use efficiency in farming systems. Adequate K supply is required for obtaining high crop yield and quality and enhancing the efficiency of other nutrients and the ability of plants to tolerate stresses from soil moisture, salinity, temperature, disease and pests. In this study wheat was grown in grey sand in a glasshouse and treated with six levels of soil potassium supply to assess plant responses during the growing season in terms of plant growth, potassium uptake and yield components.