Characterising water limited yield potential in calcareous soils of upper Eyre Peninsula

On the upper Eyre Peninsula (UEP), highly calcareous soils constitute a high proportion (more than 1 million hectares) of soils used for agricultural production (Bertrand et al. 2000, Bertrand et al. 2003). The website ‘Yield Gap Australia’ (http://yieldgapaustralia.com.au/maps/) identifies that the average grain yield on Western Eyre Peninsula (WEP) and UEP is between 41 and 45% of the water limited yield potential (1.5 t/ha for WEP and 1.8 t/ha for UEP). Closing the grain yield gap for wheat on UEP presents a challenge to growers, particularly on highly calcareous soils where nutrient deficiencies are common (Holloway et al. 2001). The production of insoluble minerals through the interaction of soil calcium carbonate with soluble nutrients such as phosphorous and trace elements (Holloway et al. 2001), combined with low soil moisture conditions prevents these nutrients from being readily available to the plant (Lombi et al. 2004). Holloway et al. (1999-2003) demonstrated the possibility of providing phosphorus (P) to the plant in an available form by applying fluid P fertilisers instead of granular fertilisers at seeding.The majority of landholders in Australia, including the western and upper Eyre Peninsula currently use granular fertilisers which require good soil moisture conditions to enable uptake of nutrients by crops. Growers and advisors have noted that highly calcareous top soils dry out quickly after rainfall events, which may contribute to poor water use and nutrient extraction efficiency, and may also be a reason why diseases such as Rhizoctonia solani have greater impact in these soils. In addition, as a risk management strategy, growers often apply lower rates of nutrients than required to achieve the water limiting yield potential (Sadras and Roget 2004, Monjardino et al. 2013). A better understanding of soil moisture, root disease and factors which influence nutrient availability and the efficacy of fertilisers are needed to increase the water limited yield potential of the highly calcareous soils (McLaughlin et al. 2013).Field trials were conducted in 2019 to investigate these factors on the nutrition of wheat on highly calcareous soils.