Organic phosphorus in Madagascan rice soils

As a first step towards assessing the contribution of organic phosphorus to rice nutrition, the chemical nature of phosphorus in a range of Madagascan rice soils was determined by NaOH–EDTA extraction and solution 31P nuclear magnetic resonance spectroscopy. A considerable proportion of the extractable phosphorus occurred in organic forms (19–44%), mostly as phosphate monoesters, with smaller concentrations of DNA. Inositol phosphates were detected in less than half of the soils, despite their perceived abundance, while phosphate monoesters in the remaining soils consisted of the alkaline hydrolysis products of RNA and phospholipids. Organic phosphorus concentrations were greater in soils rich in organic matter, but there were no apparent differences between soils under conventional flooded rice cultivation and the system of rice intensification. Additional experiments are now required to assess the role of organic phosphorus in the nutrition of rice growing under a range of management and soil conditions.