CR GSSA - Phosphorus use efficiency

Summary

​A three-year research program was established, with producers in the Central Ranges region of Victoria, to investigate options to improve phosphorus fertiliser use efficiency. Fertiliser is a major enterprise cost for livestock producers. Data from the three regions involved in the Victorian Monitor Farm project indicates the average cost of fertiliser is $3-4/DSE per year. Maintenance phosphorus (P) applications are a requirement for productive sub clover based pastures in the Central Ranges region. It is estimated 40% of farms in the region may also require capital applications of P fertiliser. The Central Ranges producer group are a branch of the Grasslands Society of Southern Australia. They were concerned about the sustainability of P supplies and increasing cost that has been the trend over the past 7-8 years.

One aim of the research was to identify whether serradella, which was thought to be a more phosphorus efficient legumes than sub clover, would grow and persist in the different soil types of the Victorian central ranges. The forage production of serradella was to be compared with sub clover under moderate (≤ Olsen P 10 mg/kg) and high soil phosphorus conditions (Olsen P 15 mg/kg). The use of more P efficient legumes is a possible strategy for reducing the amount of capital P inputs required on low P paddocks and could potentially save producers hundreds of dollars per hectare.

The second aim of the research was to identify whether soil factors (nitrogen, trace elements, acidity, poor nodulation, soil borne diseases) were constraining pasture and sub clover production on paddocks where P, K and S were adequate. Identification of other soil constraints is a strategy to grow more kg dry matter per unit of P applied.

Yellow serradella and French (pink) serradella were found to be more difficult to establish and regenerate than several cultivars of sub clover. Two sites were sown in June 2014 and re-sown 2015, at Glenhope and Pastoria, for the alternative legume trials. Very little serradella regenerated at the two sites in 2016.

During this research project, more results from the CSIRO legume experiments became available which confirmed that the critical P level for serradella was lower than for sub clover.  There was a change in direction suggested to the group for the alternative legume work to sowing larger areas in paddocks to test out the serradellas and trialling some different cultivars that might be better suited to the environment. In May 2016, a group member sowed a large-scale serradella trial at Baynton. This is being monitored as part of a new national project called Phosphorus for Pastures.

The challenge for producers in this region is that sub clover is well adapted and is already present in most paddocks, even those with low-moderate P levels. Establishing and regenerating serradella will be difficult if there is some seed-bank of sub clover to compete with. Selecting paddocks that have been cropped for a few years may improve serradellas ability to establish and regenerate. Also, there has been a lot less work done on breeding and selection of improved cultivars of serradella compared with sub clover. It is still not clear which cultivars of serradella are best suited for this environment.