Phosphorus is the primary nutrient input that drives legume growth and nitrogen fixation in the pastures of southern Australia.  It underpins high productivity and profitability.  However, P-fertiliser costs have doubled since 2000 and a tightening in future supply seems inevitable.  Both factors are expected to lead to a steady increase in the fertiliser-costs of production.

It is estimated from previous research (Simpson et al. 2014) that it will be feasible to develop pasture systems that require ~30% less P fertiliser annually by promoting and developing the use of pasture legumes that yield better in low P soils and have lower ‘critical’ soil-test P requirements for maximum yield than the mainstream species and cultivars used presently across southern Australia. 

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The project builds on research that has shown that P accumulation in a grazing system soil is significantly reduced when it is managed at a lower soil test P concentration (Simpson et al. 2015), and on work that has identified high-yielding pasture legumes with lowered P requirements (Sandral et al. 2015). Together, these innovations mean that low-P grazing systems are now within reach.  The novel pasture systems will also reduce the risks of P loss from agriculture to the natural environment and will reduce input costs.

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Outcomes

Specific outcomes that were to be delivered by the project include:

(i)  Development of low-P pasture systems based on highly P-efficient serradellas (Ornithopus spp.), using a combination of farmer-participatory and traditional research. 

(ii) Identification and then promotion of the most P-efficient cultivars of subterranean clover (Trifolium subterranean

(iii) Development of the knowledge and genetic/agronomic protocols necessary for development of subterranean clover cultivars with P-efficient root traits analogous to those of serradella species. 

(iv) Updates to the industry decision support tool (“Five Easy Steps” soil-P management tool, http://www.mla.com.au/extension-training-and-tools/producer-case-studies/five-steps-to-better-phosphorus-use/ ) to include the principles and management that underpin the achievement of highly-productive, P-efficient pasture systems.  This tool applies to pastures grown on acid soils across southern Australia (~35M ha) and is already in use in many farming districts.

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ASHEEP Involvement

ASHEEP had two trial sites located in Grass Patch & Neridup. The sites were chosen for their sandy, low nutrient soil profiles. The sites were sown to Serrdella in 2017 and were treated with low, medium and high rates of P fertilizer to determine the effect of these treatments on Serradella production. 

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The original objectives of the project (outlined above under 'Outcomes') were modified during the course of the project once it was realised that in the soil types at the ASHEEP sites, the P had been leached to depth and that there was residual P in the deeper soil profile. The activity at the experiment sites was then shifted to focus on improving knowledge of the P-fertiliser and general management of serradella-based pasture systems.

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References:

• Simpson RJ, Richardson AE, Nichols SN and Crush JR (2014) Pasture plants and soil fertility management to improve the efficiency of phosphorus fertiliser use in temperate grassland systems. Crop & Pasture Science 65, 556-575.

• Simpson R, Stefanski A, Marshall D, Moore A, Richardson A (2015) Management of soil phosphorus fertility determines the phosphorus budget of a temperate grazing system and is the key to improving phosphorus-balance efficiency. Agriculture Ecosystems & Environment 212, 263–277.

• Sandral G, Simpson R, Price A, Hildebrand, et al.. 2015 Phosphorus efficient pastures: response of alternative legumes to fertiliser application. 4pp. http://www.agronomy2015.com.au/papers/agronomy2015final00248.pdf