Crop residue phosphorus: speciation and potential bio-availability

Background and Aims Phosphorus (P) mineralisation from crop residues is usually predicted from total P or carbon: phosphorus (C: P) ratios. However, these measures have limited accuracy as they do not take into account the presence of different P species that may be mineralised at different rates. In this study P speciation was determined using solution 31P nuclear magnetic resonance (NMR) spectroscopy to understand the potential fate of residue P in soils. Methods Mature above-ground biomass of eight different crops sampled from the field was portioned into stem, chaff and seed. Results The main forms of P detected in stem and chaff were orthophosphate (25–75 %), phospholipids (10–40 %) and RNA (5–30 %). Phytate was the dominant P species in seeds, and constituted up to 45 % of total P in chaff but was only detected in minor amounts (