The Australian experience with rock phosphates : limitations and explanations

Gilks R.J., . and Bolland M.D.A., . (1992) The Australian experience with rock phosphates : limitations and explanations. [Proceedings Paper]

The agronomic effectiveness of rock phosphates has been measured for diverse crop and pasture species in many pot and field experiments in Australia. The effectiveness RE of freshly applied rock phosphates relative to freshly applied superphosphate for 164 Australian pot and field experiments ranged from less than 0.1 to 2.5 with the mean value for apatite rock phosphates being 0.26 compared with 0.42 for calcined Fe Al phosphates. Variations in RE values were primarily due to systematic differences in experimental design and fertilizer solubility and not to differences in soil pH plant species the capacity of the soil to adsorb P and mean annual rainfall. All RE values greater than 0.4 were obtained from experiments in which only 1 or 2 levels of fertilizer were applied to soils that were poorly responsive to applied P. It was thus not possible to define the complete response curves required to obtain precise values of RE so that the high values of RE may be inaccurate. In most cases RE values were 0.4 for experiments in which several levels of fertilizer P were applied to highly P-responsive soils so that complete response curves were defined and precise values of RE estimated. The residual effectiveness RV of previously applied rock phosphate relative to freshly applied superphosphate remained low for all experiments and was approximately constant for several years after application being 5-30percent as effective as freshly applied superphosphate. The average value of RV for superphosphate declined by 40percent in the first year after application by a further 15percent in the second year and by a further 30percent over the remaining six years. However the decline in RV differed substantially between sites.

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Abstract

The agronomic effectiveness of rock phosphates has been measured for diverse crop and pasture species in many pot and field experiments in Australia. The effectiveness RE of freshly applied rock phosphates relative to freshly applied superphosphate for 164 Australian pot and field experiments ranged from less than 0.1 to 2.5 with the mean value for apatite rock phosphates being 0.26 compared with 0.42 for calcined Fe Al phosphates. Variations in RE values were primarily due to systematic differences in experimental design and fertilizer solubility and not to differences in soil pH plant species the capacity of the soil to adsorb P and mean annual rainfall. All RE values greater than 0.4 were obtained from experiments in which only 1 or 2 levels of fertilizer were applied to soils that were poorly responsive to applied P. It was thus not possible to define the complete response curves required to obtain precise values of RE so that the high values of RE may be inaccurate. In most cases RE values were 0.4 for experiments in which several levels of fertilizer P were applied to highly P-responsive soils so that complete response curves were defined and precise values of RE estimated. The residual effectiveness RV of previously applied rock phosphate relative to freshly applied superphosphate remained low for all experiments and was approximately constant for several years after application being 5-30percent as effective as freshly applied superphosphate. The average value of RV for superphosphate declined by 40percent in the first year after application by a further 15percent in the second year and by a further 30percent over the remaining six years. However the decline in RV differed substantially between sites.

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Item Type:	Proceedings Paper
Additional Information:	Summary En
AGROVOC Term:	FOSFATO MINERAL
AGROVOC Term:	EXPERIMENTOS
AGROVOC Term:	AUSTRALIA/ EFICACIA
AGROVOC Term:	SOLUBILIDAD
Geographical Term:	MALAYSIA
Depositing User:	Ms. Norfaezah Khomsan
Last Modified:	24 Apr 2025 05:26
URI:	http://webagris.upm.edu.my/id/eprint/15277

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