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This article in SSSAJ

  1. Vol. 47 No. 5, p. 958-962
    Received: Dec 6, 1982
    Accepted: May 16, 1983

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Comparison of Soil Phosphorus Extractants as Predictors of Mycorrhizal Dependency1

  1. J. C. Ojala,
  2. W. M. Jarrell,
  3. J. A. Menge and
  4. E. L. V. Johnson2



To determine which of several soil P extraction techniques best predicted the response of citrus (Poncirus trifoliate X Citrus sinensis) seedlings to mycorrhizal fungi (Glomus fasciculatus), 25 nursery and field citrus soils from southern and central California were collected and analyzed for available P by five methods. Mycorrhizal dependency (MD), defined as the dry weight (mycorrhizal plants)/dry weight (nonmycorrhizal plants) × 100, was significantly correlated with the reciprocal of extractable soil P regardless of the extraction method. Those methods whose results depend most on soil solution P concentrations gave best results. Saturation extract P(PSE, R2 = 0.67***), anion exchange resin P(PAER, R2 = 0.57***), and 1:10 soil to water extract P(P1:10, R2 = 0.51***) were all acceptable for predicting mycorrhizal response. Bicarbonate-extractable P (PB1C, R2 = 0.32**) and ammonium fluoride P (PAF, R2 = 0.19*) were less acceptable. Using regression models, based upon the reciprocal of the extractable-P value, a MD > 200% was predicted where PSE < 0.65 mg L−1, PAER < 62 mg kg−1 soil, P1:10 < 0.66 mg L−1, PBIC < 34 mg kg−1 soil, and PAF < 54 mg kg−1 soil. Where analytical capabilities are adequate, PSE is the preferred method for predicting response, while PAER would suffice where higher analate P concentrations are required. Alternatively, inclusion of both PSE and PAER gave an excellent correlation with response (R2 = 0.82***). Inclusion of DTPA-extractable Mn significantly improved regression equations in all cases except that of PSE, where DTPA-extractable Zn significantly improved the relationship.

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