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 (P 1 ) 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, NaHCO 3 ‐P, NaOH‐P, and HCl‐P). Soil P 1 quantities were HCl‐P > NaOH‐P > NaHCO 3 ‐P (bic‐P) > resin‐P. Higher Olsen‐P soils had higher summation of P 1 fractions than lower Olsen‐P soils. Changes in resin‐P accounted for most of P 1 ‐fraction differences induced by P application and plant uptake. Cropped soils generally contained lower amounts of P 1 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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Yang et al. (1990) studied this question.