A critical assessment of the suitability of phosphite as a source of phosphorus

This is the authors' abstract. We don't add key points for this paper.

Marketing of phosphite‐containing preparations for foliar application, together with recent reports of positive yield responses, has revived the question as to whether phosphite (HPO₃⁻ ) is a suitable P source for plants. Two experiments using zucchini (Cucurbita pepo L. convar. giromontina) have been conducted to evaluate the P‐nutritional effect of phosphite either provided via the substrate or as a foliar spray. Plants grown in a P‐deficient substrate were severely damaged when phosphite was applied as foliar fertiliser and more drastically when provided via the substrate. Growth of P‐deficient plants receiving phosphite as a foliar spray was impaired in a dose‐dependent manner after foliar P application (concentrations 0.0, 0.9, 2.7, and 4.5 g P L–1), while foliar provision of phosphate improved plant growth and yield. In the youngest leaves of phosphite‐treated plants, which had developed after foliar spray, phosphite accumulated to considerable extent, reaching a similar concentration as phosphate at tissue level. These results confirm that P‐deficient plants are very sensitive to phosphite, which represents a nutritionally ineffective form of P. It should thus not be considered as a form of P suitable for fertiliser manufacture.