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This article in AJ

  1. Vol. 62 No. 4, p. 524-527
     
    Received: Dec 1, 1969
    Published: July, 1970


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doi:10.2134/agronj1970.00021962006200040029x

Ammonium Effects on Phosphorus Absorption through pH Changes and Phosphorus Precipitation at the Soil-Root Interface1

  1. M. H. Miller,
  2. C. P. Mamaril and
  3. G. J. Blair22

Abstract

Abstract

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.

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