Measurement of the effects of pH on phosphate availability

N. J. Barrow, Abhijit Debnath, Arup Sen

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


Aims: Many soil scientists think that soil phosphate availability is highest at near-neutral pH and decreases with decreasing pH. This belief does not appear to have ever been subjected to experimental test. Methods: In a pot trial, we measured response curves to phosphate at seven pH(CaCl2) values ranging from 3.99 to 7.26 using three plant species: mustard (Brassica campestris), lucerne – also known as alfalfa – (Medicago sativa) and rice (Oryza sativa). We used a form of the Mitscherlich equation that allowed us to estimate the phosphate contribution from the soil as well as the slope of the response curve and the maximum yield. Results: Plants grew best near pH 5.5 and worst at near-neutral pH. We think the large decrease in growth with increasing pH was caused by decreasing rate of P uptake by plants. There was a smaller decrease in growth as pH decreased below 5.5. We think this was caused by aluminium toxicity. Conclusions: The conventional belief that phosphate availability is greatest near neutral pH is wrong.

Original languageEnglish
Pages (from-to)217-224
Number of pages8
JournalPlant and Soil
Issue number1-2
Early online date31 Jul 2020
Publication statusPublished - 1 Sep 2020


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