Crop residue phosphorus: speciation and potential bio-availability
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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.
Mature above-ground biomass of eight different crops sampled from the field was portioned into stem, chaff and seed.
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 (<1 %) in stem residue. The majority (65–95 %) of P in stems was water-extractable, and most of this was detected as orthophosphate. However, this includes organic P that may have been hydrolysed during the water extraction.
This study indicates that the majority of residue P in aboveground plant residues has the potential to be delivered to soil in a form readily available to plants and soil microorganisms.
KeywordsPhosphorus Crop Residues Speciation Organic P Inorganic P
Sodium hydroxide ethylenediaminetetraacetic acid
Nuclear magnetic resonance
The authors thank the Grains Research and Development Centre (GRDC) for providing funding to support this research (DAV00095) and the University of Adelaide for the James Frederick Sandoz Scholarship.
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