A dual radiotracer study of transformations of organic, inorganic and plant residue phosphorus in soil in the presence and absence of plants

Abstract

The rates of transfer of P from plant residues added to an acid soil into various soil P pools and the rates of transfer of inorganic P from soil solution into other soil P pools were studied by simultaneous use of 32P-labelled plant matter and 33P-labelled soil in the presence and absence of growing plants. Equilibration of 33P-labelled phosphate solution added to soil reached a steady state with soil ALP and Fe-P pools within 1 day after addition. The Fe-P pool was much more stable than the A1-P pool since it was not depleted by cropping. This non-labile pool 'fixed' over 30% of the 33P added and similar amounts of the 32P released from plant residues. About 50% of the 32P from plant residues was found in inorganic P pools 11 days after addition. This rapid release was attributed to the presence of soluble inorganic P in the residues. A further 10% was released slowly over the remainder of the experiment. Cropping only marginally slowed rates of transfer of inorganic and released residue P into non-labile pools. Cropping had no effect on the rates of release of P from crop residues.