A glasshouse comparison of 6 phosphate fertilisers

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Abstract
In a glasshouse experiment the effectiveness of Chatham Rise phosphorite (CRP) as a source of phosphorus (P) for perennial ryegrass and white clover on 6 contrasting soils was compared with single superphosphate, North Carolina phosphate rock (NCPR), Sechura phosphate rock (SPR) from Peru, Tennessee phosphate rock (TPR), and calcined Christmas Island ‘C’ grade phosphate rock (Calciphos). The 6 P sources are ranked in the following order of effectiveness for ryegrass under glasshouse conditions: superphosphate ⩾ NCPR ⩾ SPR > CRP > > Calciphos > > TPR. A marked difference was found in the ability of the 2 plant species to use P from a phosphate rock (PR). SPR was as effective as superphosphate on clover. This was particularly pronounced when the comparison was based upon P uptake data rather than yield data. In fact there was no difference between superphosphate, SPR, and CRP when P uptake by clover was used as the measure of effectiveness. When P uptake by ryegrass was used to assess agronomic performance rather than ryegrass yield data, the reactive PR materials, NCPR, SPR, and CRP were far less effective than superphosphate. The results indicate that both dry matter yield and P uptake data are required to fully evaluate the agronomic effectiveness of PR. Extrapolation of the results of this glasshouse experiment to field situations is discussed.

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