The aims of the PA component of the GRDC Stubble project were to:

• deliver a pilot project to understand how soil parameters, including PAW, vary across a paddock and understand
whether current PA datasets can correlate with PAW

• connect variations in soil moisture with nitrogen supply

• demonstrate the use of NDVI to inform variable rate applications of nitrogen

• determine the economic value of variable rate nitrogen application across paddocks, based on zones

• Electromagnetic (EM) zoning was strongly related to differences in pH at 10–30cm depth in two out of three paddocks.
• All three paddocks showed variability in chemical properties, with the EM zoning showing good separation of chemical properties between zones. This provides confidence that the zoning was suitable.
• Variability in plant growth needs to be examined ‘holistically’ rather than just focussing on one variable. While a paddock may show variation in plant available water (PAW), it may be that sodicity or subsoil acidity is the key limiter in plant performance, not water availability per se.
• Existing precision agriculture (PA) datasets, in conjunction with selected chemistry sampling, can be used to indicate relative change in PAW across paddocks, but not the actual volume of water storage.