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Influence of Exchangeable Calcium on Phosphate Retention by Weakly Acid Soils
Author(s) -
Smillie G. W.,
Curtin D.,
Syers J. K.
Publication year - 1987
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1987.03615995005100050014x
Subject(s) - chemistry , soil water , dissolution , phosphate , phosphorite , environmental chemistry , calcium , extraction (chemistry) , soil ph , sink (geography) , metal , incubation , geology , chromatography , soil science , biochemistry , cartography , organic chemistry , geography
The extractability of P from two weakly acid soils that had been amended with three forms of P [KH 2 PO 4 , single superphosphate (SSP), and Chatham Rise phosphorite (CRP)] was investigated in an incubation study under field conditions. In a sequential extraction sequence with water, P release from soils incubated for 9 and 27 weeks with KH 2 PO 4 and SSP declined with increasing extraction number. In contrast, P extracted from CRP‐treated soils increased, indicating a slow dissolution of phosphate rock. Washing with 0.1 M NaCl to remove exchangeable Ca resulted in a large increase in P extracted subsequently with water, regardless of whether sorbed P (as in KH 2 PO 4 ‐ and SSP‐treated soils) or particulate Ca phosphate (as when CRP was added) was the source of the extracted P. A high proportion (up to 80%) of the added P could be recovered by water extraction when exchangeable Ca was replaced by Na. Significantly, P recovery did not decrease with time of contact between soil and P as it did before exchangeable Ca was replaced with Na. The removal of exchangeable Ca accelerates the dissolution of Ca phosphates by creating a sink for Ca. The results obtained suggest that sorbed P may enter into chemical association with Ca, possibly at metal oxide surfaces, and that this interaction with Ca constitutes an important P retention mechanism in acid soils that contain adequate exchangeable Ca.