146-5 Crop Residue Phosphorus: Speciation and Availability.



Monday, October 17, 2011: 9:20 AM
Henry Gonzalez Convention Center, Room 213A, Concourse Level

Sarah R. Noack, School of Agriculture, Food & Wine - Soils Department, The University of Adelaide, Glen Osmond, Australia, Ronald Smernik, Soil Science, The University of Adelaide, Glen Osmond, Australia, Therese McBeath, Ecosystem Sciences, CSIRO, Glen Osmond, Australia, Roger Armstrong, Department of Primary Industries Victoria, Horsham, Australia and Michael McLaughlin, CSIRO, Glen Osmond, SA, AUSTRALIA
Phosphorus (P) mineralisation from crop residues is usually predicted from total P or C:P ratio. However, these measures have limited accuracy as they fail to account for the presence of various P species which control the rate of P mineralisation from residues. Detailed P speciation on NaOH-EDTA extracts of crop residues was determined using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Mature above-ground biomass of eight different crops from the field was separated into stem/leaf, chaff and seed. The main forms of P detected in stem and chaff were orthophosphate (35-75%), 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 material. The most important differences between cereal and legume residues were the absence of phytate in legume chaff and the presence of RNA (10-15%) in legume seeds. The majority (65-90%) of residue P in stems was water-extractable, and most of this was detected as orthophosphate. However, this includes organic P that was hydrolysed during the water extraction. This indicates that the majority of residue P in aboveground plant residues has the potential to be delivered to soil in a readily available form.
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