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This article in SSSAJ

  1. Vol. 50 No. 1, p. 62-67
    Received: Feb 4, 1985
    Accepted: Aug 16, 1985

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Transformations of Inorganic Phosphorus During the Flooding and Draining Cycles of Soil1

  1. R. N. Sah and
  2. D. S. Mikkelsen2



Phosphorus transformations that occur after anoxic soils are drained have been associated with acute P deficiencies in rotation crops following rice. Flooded rice may not respond to P fertilization while rotation crops respond markedly to P fertilization on similar soils. The changes that occur among the inorganic P forms during flooding and after drainage in four soils were investigated. Significant changes in the inorganic P fractions—aluminum-P (Al-P), iron-P (Fe-P), calcium-P (Ca-P), and reductant soluble-P (RS-P) occurred in soils during their flooding and draining cycles. Typically, the Fe-P fractions increased and Al-P fractions decreased when soils were flooded. The Ca-P fraction increased during flooding in two soils that had initially high levels of Ca-P but was almost unchanged in two other soils of lower Ca-P content. The RS-P fraction decreased during flooding in the soils subjected to annual flooding. During the drainage period, Fe-P and Al-P fractions decreased and the RS-P fraction increased in flooded rice-cropped (Oryza sativa L.) soils, probably due to occlusion of Fe-P and Al-P by hydrated Fe and Al oxides. The RS-P fraction in Willows clay, a soil that had not been flooded recently, decreased during the drainage period. Phosphorus added as Ca(H2PO4)2. H2O was recovered mainly in the Fe-P and Al-P fractions. The recovery of Fe-P was greater in flooded-drained soils and Al-P was greater in unflooded soils.

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