Changes in inorganic and organic phosphorus (P) fractions resulting from 65 years of cropping in a wheat‐wheat‐fallow rotation were studied using a sequential extraction technique. Total P content of the cultivated soil was 29% lower than that of the adjacent permanent pasture; the major loss of P (74% of total P lost) was organic P and residual P. Of the total P lost, 22% was from the extractable organic P forms, whereas 52% originated from stable P.Incubation studies were used to study seasonal P transformations during simulated fallow with and without residue incorporation and P fertilization. Nine monthly additions of cellulose (765 µg C · g−1 soil) with and without P (9 µg · g−1 soil) significantly altered levels of total extractable organic P and inorganic P in incubated soils. Evidence is provided for microbial activity playing a major role in redistributing P into different forms in the soil.

. Can. J. Soil Sci. 61: 373-385. The effect of labile inorganic phosphate (Pi) status of the soil on the decomposition of added cellulose and on the immobilization, mineralization, and redistribution of.native and addcd P in soils was studiecl in a grcenhousc incubation experiment. Cellulose was addcd at 765 pg C.gr soil with and without P (9 pg'g' soil) every 30 days under adequatc N, H2O, and constant tempreature to two soils of different available P status.Lacli of P eventually slowed down decomposition of added C, but this effect was partially compensated for by increased mineralization of organic P (P.) fbrms. Added P was re

Investigations of the rate of P movement between soil inorganic, organic and btomass P compartments were carried out to clarify aspects of P cycling in soil systems.Organic carbon, as dried grass (337o C,0.117a P) and cellulose (43VoC), was added at a rite equivalent to 4000 kg organic material (OM) ha-1 every 30 days for 9 mo to the Ap horizon of a Chernozernic Btack soil kept at field capacity moisture content and 24*2"C.In a third treatment. cellulose was added at the same rate with P (20 kg ' ha-') at KH2POa. Approximately 39Vo and22Va of the P added in grass and with cellulose, respectively, wis found in organic P forms after 9 mo incubation. The remainder was found in NHrCl-, NH4F-and NaOH-NaCl-extractable P forms which constituted part of the labile inorganic P pool and could be extracted by an anion exchange resin. Increases of biomass P during the first 4 or 5 days of each incubation period after residue addition were found io urre.uge 12 p.g P g-1 in the first 3 mo incubation period. After this period, there was a smaller lesponse in microbial P attributable to additions of grass or cellulose.

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