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Published online 1 July 1970
Published in Agron J 62:524-527 (1970)
© 1970 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
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Ammonium Effects on Phosphorus Absorption through pH Changes and Phosphorus Precipitation at the Soil-Root Interface1

M. H. Miller, C. P. Mamaril and G. J. Blair2

The addition of NH4+ ions to a fertilizer P band is known to increase the absorption of P. This study was conducted to further clarify the mechanisms responsible for this phenomenon.

Pellets of 33P labelled monocalcium phosphate (MCP), MCP + K2SO4 or MCP + (NH4)2SO4 were placed 1.25 rm to the side of a corn root tip growing in the soil at the surface of a box with a sloping removable front. Roots in the vicinity of the pellet, and the shoots, were harvested 15 days later.

Fertilizer P concentration in the shoots was doubled by the addition of K2SO4 and tripled by (NH4)2SO4. Autoradiographs of the area surrounding the pellets indicated an accumulation of P on the surface of roots in the MCP treatment but not in the MCP + (NH4)2SO4. Autoradiographs of root cross-sections confirmed this observation. Electron microprobe scans of root cross-sections indicated a precipitation of Ca and P at the soilroot interface in the MCP and MCP + K2SO4 treatments. The pH of the soil-root interface was 0.6 units lower in the MCP + (NH4)2SO4 than in the MCP treatment. The higher ratio of H2PO4-/HPO4= ions at the lower pH is thought to be responsible for the prevention of the precipitation and the increased absorption of P in the presence of (NH4)2SO4.

Key Words: Electron microprobe • 33P autoradiographs

1 Contribution from Dept. of Soil Science, University of Guelph, Guelph, Ontario, Canada. The financial assistance of the National Research Council of Canada is gratefully acknowledged.

2 Professor of Soil Science and Postdoctoral Fellows, respectively

Received for publication December 1, 1969.




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The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome
Copyright © 1970 by the American Society of Agronomy.