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This article in SSSAJ

  1. Vol. 38 No. 3, p. 524-529
    Received: Oct 25, 1973
    Accepted: Feb 8, 1974

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Response by Flooded Rice to Phosphate Rocks Varying in Citrate Solubility1

  1. O. P. Engelstad,
  2. Aroon Jugsujinda and
  3. S. K. De Datta2



Studies were conducted in the greenhouse and in the field to evaluate several phosphate rocks for flooded rice (Oryza sativa L.). A close relationship was found to exist between first-crop yield response to applied P and citrate solubility in a series of phosphate rocks representing the theoretical range in this parameter. Greenhouse (TVA) and field data (Thailand) showed quite similar results in this respect.

The same general pattern of effectiveness among sources persisted through the second crop as found for the first crop. The residual effectiveness of triple superphosphate (TSP) remained higher than that of the phosphate rocks; however, the relationship between initial citrate solubility of the phosphate rocks and relative effectiveness in the second crop was rather poor.

A procedure is presented which enables one to make the choice of P source on the basis of both agronomic effectiveness and prices of P in TSP vs. phosphate rock.

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