Summary. Field-based cutting trials, which formed part
of the National Reactive Phosphate Rock Project, were established across
Australia in a range of environments to evaluate the agronomic effectiveness
of 5 phosphate rocks, and 1 partially acidulated phosphate rock, relative to
either single superphosphate or triple superphosphate. The phosphate rocks
differed in reactivity. Sechura (Bayovar) and North Carolina phosphate rocks
were highly reactive (>70% solubility in 2% formic acid),
whilst Khouribja (Moroccan) and Hamrawein (Egypt) phosphate rock were
moderately reactive. Duchess phosphate rock from Queensland was relatively
unreactive (<45% solubility in 2% formic acid). Phosphate
rock effectiveness was assessed by measuring pasture production over a range
of phosphorus levels, and by monitoring bicarbonate-soluble phosphorus
extracted from soil samples collected before the start of each growing season.
Other treatments included single large applications of triple superphosphate,
partially acidulated phosphate rock and North Carolina phosphate rock applied
at 2 rates, and the application of monocalcium phosphate and North Carolina
phosphate rock sources without sulfur to evaluate the importance of sulfur in
the potential use of phosphate rock fertilisers at each site.
A broad range of environments were represented over the 30 sites which were
based on pastures using annual and/or perennial legumes and perennial
grasses. Rainfall across the network of sites ranged from 560 to 4320 mm, soil
pH (CaCl2) from 4.0 to 5.1, and Colwell-extractable
phosphorus ranged from 3 to 47 µg/g before fertiliser application.
Two core experiments were established at each site. The first measured the
effects of phosphate rock reactivity on agronomic effectiveness, while the
second measured the effects of the degree of water solubility of the
phosphorus source on agronomic effectiveness.
The National Reactive Phosphate Rock Project trials gave the opportunity to
confirm the suitability of accepted procedures to model fertiliser response
and to develop new approaches for comparing different fertiliser responses.
The Project also provided the framework for subsidiary studies such as the
effect of fertiliser source on soil phosphorus extractability, cadmium and
fluorine concentrations in herbage, evaluation of soil phosphorus tests, and
the influence of particle size on phosphate rock effectiveness. The National
Reactive Phosphate Rock Project presents a valuable model for a large,
Australia-wide, collaborative team approach to an important agricultural
issue. The use of standard and consistent experimental methodologies at every
site ensured that maximum benefit was obtained from data generated. The aims,
rationale and methods used for the experiments across the network are
presented and discussed.
Pasture production and soil phosphorus fractions resulting from six previous annual applications of triple superphosphate or Sechura phosphate rock