NATIONAL REACTIVE PHOSPHATE ROCK PROJECT - AIMS, EXPERIMENTAL APPROACH AND SITE CHARACTERISTICS

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 di ffered in reactivity. Sechura (Bayovar) and North Carolina phosphate r ocks were highly reactive (>70% solubility in 2% formic acid), whilst Khouribja (Moroccan) and Hamrawein (Egypt) phosphate rock were moderat ely reactive. Duchess phosphate rock from Queensland was relatively un reactive (<45% solubility in 2% formic acid). Phosphate rock effective ness was assessed by measuring pasture production over a range of phos phorus levels, and by monitoring bicarbonate-soluble phosphorus extrac ted from soil samples collected before the start of each growing seaso n. Other treatments included single large applications of triple super phosphate, partially acidulated phosphate rock and North Carolina phos phate rock applied at 2 rates, and the application of monocalcium phos phate and North Carolina phosphate rock sources without sulfur to eval uate the importance of sulfur in the potential use of phosphate rock f ertilisers at each site. A broad range of environments were represente d over the 30 sites which were based on pastures using annual and/or p erennial 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, an d Colwell-extractable phosphorus ranged from 3 to 47 mu g/g before fer tiliser application. Two core experiments were established at each sit e. The first measured the effects of phosphate rock reactivity on agro nomic effectiveness, while the second measured the effects of the degr ee of water solubility of the phosphorus source on agronomic effective ness. The National Reactive Phosphate Rock Project trials gave the opp ortunity to confirm the suitability of accepted procedures to model fe rtiliser response and to develop new approaches for comparing differen t fertiliser responses. The Project also provided the framework for su bsidiary studies such as the effect of fertiliser source on soil phosp horus extractability, cadmium and fluorine concentrations in herbage, evaluation of soil phosphorus tests, and the influence of particle siz e on phosphate rock effectiveness. The National Reactive Phosphate Roc k Project presents a valuable model for a large, Australia-wide, colla borative team approach to an important agricultural issue. The use of standard and consistent experimental methodologies at every site ensur ed that maximum benefit was obtained from data generated. The aims, ra tionale and methods used for the experiments across the network are pr esented and discussed.