II. Placement effects

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Abstract
The effect of fertiliser placement on the relative efficiencies of superphosphate and fused calcium-magnesium phosphate as phosphorus fertilisers was studied in pot culture and leaching experiments on Te Anau yellow-brown loam. After the fertilisers were incorporated in the soil, powdered fused phosphate and superphosphate were virtually identical as phosphorus sources for white clover at all application rates, and differed little from phosphate added as a solution. Surface application of fertilisers combined with surface watering produced very large differences between fertilisers: powdered fused phosphate provided up to 9.2 times as much phosphorus uptake in plants as superphosphate at equivalent application rates, and granular fused phosphate was markedly inferior to superphosphate. Leaching experiments indicated that fine particles of powdered fused phosphate could move into the soil with percolating water. Differences between the effects of surface-applied fertilisers were explained on the basis of differential movement of phosphate into the rooting zone of plants under the influence of surface-applied water.

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