The determination of phosphate availability for some less conventional phosphate fertilisers

Abstract

More than in the case of the other major fertiliser elements the performance of phosphorus in fertilisers in dependent on the state of chemical combination of the element. As distinct from typical American practice where fully acidulated fertilisers are emphasised, some other countries have moved in part to production of materials of less than full acidulation where some reliance is placed on the reactivity of the original phosphate rock. Solutions of various aliphatic acids and their salts have been used as tests for the availability of phosphorus in fully acidulated fertilisers and, to a degree, for phosphate rocks themselves. Less than fully acidulated products are at present assessed in the same way as fully acidulated materials, but in this and other evaluations problems and anomalies arise which are discussed within the framework of a number of fertiliser systems. Analytical data are adduced which illustrate the effects of some extraneous cations on the results achieved which conflict with some previous opinions. Research towards a fuller understanding of the subject is suggested.