Carp, Kelp and Christmas Island: where to next for fertiliser

Summary

Increased costs of superphosphate prompted producers to consider alternative products to provide similar pasture growth responses. No statistically significant data could be produced in support of superphosphate alternatives regarding increased pasture growth response through soil nutrient content or biological activity.

The initial PDS demonstration site, established in 2009 to evaluate a selection of products against a NIL control and superphosphate, found no products improved pasture growth over three seasons. Additionally, the interpretation of trends in soil properties at the start and end of the demonstration were constrained by reliance on two data points that can fluctuate seasonally.

The extension of the demonstration by two additional growing seasons showed no cumulative effects on pasture growth for any treatment.
Soil sampling from 2013 and 2014 highlighted methodological challenges in the 2013 data due to changes in funding intervals and consequent storage conditions. However, the additional two years of data showed a net importation of nutrients onto the site via the grazing method used, and no further conclusions could be drawn about trends in the soil phosphorus concentrations.

In summary, there were no measured production or economic benefits gained from the application of alternative products to a typical Holbrook pasture and soil type for the six seasons of the demonstration.