Soil Inorganic Phosphorus Fractions and Their Uptake Relationships in Calcareous Soils
- Jae E. Yang and
- Jeffrey S. Jacobsen
Crop responses to recommended P-fertilizer applications are erratic in high pH, calcareous soils of Montana. The objective of this research was to evaluate relationships between soil inorganic P (P1) fractions, Olsen-P, and plant uptake. Soil-incubation and plant-growth experiments were conducted on samples of six calcareous soils from P-responsive locations in Montana. Rates of P were 0, 11, 22, and 33 mg P kg−1 applied to soils in a randomized complete-block design with four replications. Spring wheat (Triticum aestivum L. cv. Newana) was grown successively during three, 4-wk growing periods. Fertilized soils were incubated without plants during the same period. Soils were subjected to a sequential-fractionation procedure (resin-P, NaHCO3-P, NaOH-P, and HCl-P). Soil P1 quantities were HCl-P > NaOH-P > NaHCO3-P (bic-P) > resin-P. Higher Olsen-P soils had higher summation of P1 fractions than lower Olsen-P soils. Changes in resin-P accounted for most of P1-fraction differences induced by P application and plant uptake. Cropped soils generally contained lower amounts of P1 in each fraction than noncropped soils. Highly significant (P > 0.01) correlations were found for Olsen-P vs. resin-P, P uptake vs. resin-P, and P uptake vs. Olsen-P, but not for Olsen-P vs. bic-P, resin-P vs. bic-P, and P uptake vs. bic-P. Resin-P was the best indicator of P-uptake responses on these soils to P applications and should be considered in the prediction of crop responses.
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