Transformations of Inorganic Phosphorus During the Flooding and Draining Cycles of Soil
1986
Sah, R. N. | Mikkelsen, D. S.
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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