Review of phosphorus acid and its salts as fertilizer materials

This is a review of the literature, recent unpublished research, and other information pertaining to the use of phosphorus acid (H3PO3) and its salts as fertilizer materials. Early studies on the potential of H3PO3 and its salts as alternative phosphate fertilizers showed that these phosphorus (P)-containing materials were not as effective as phosphoric acids (H3PO4) and its derivatives on growth of the first crop in successive cropping trials. However, a definite growth response to phosphite was seen when compared to the zero-P control, proving that these materials provided nutritional support. Beneficial effects from the phosphite and H3PO3 treatments were observed in the subsequent crops, and were presumed attributable to the probable conversion of phosphite to phosphate in the soil. Studies done more than thirty years later on plant responses to the phosphite anion focused on plant disease control, rather than on the nutrient qualities of such materials. Nevertheless, many plant physiological phenomena caused by the phosphite-active ingredient were discovered as its chemical dynamics were documented. Effects important to plant growth were shown to occur when plants were treated with H3PO3 or its salts even in the absence of plant pathogens. Whereas a certain amount of observed nutritional responses to phosphite is correlated with its conversion to orthophosphate by microbial action and other mechanisms, other nutritional responses were also observed, leading to commercialization of specially formulated H3PO3 derivatives as fertilizers. For example, higher yields in oranges were directly attributed to increased flowering and fruit set after winter pre-bloom foliar applications of commercial phosphite fertilizer formulations. Many horticultural and agronomic crops have exhibited positive growth responses under field conditions to the nutritional support available in fertilizers derived from H3PO3.