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This article in SSSAJ

  1. Vol. 38 No. 5, p. 795-799
    Received: Dec 5, 1973
    Published: Sept, 1974



Rhizosphere pH as Influenced by Plants, Soils, and Nitrogen Fertilizers1

  1. R. W. Smiley2



The rhizosphere pH (pHr) of field and container-grown wheat plants was measured and compared to the nonrhizosphere soil pH (pHb). The predominant form of N supplied to the roots was a major factor influencing the pHr. The pHr was generally lower than pHb where NH4 was supplied, higher where NO3 was used, and relatively unchanged where both forms were added. Differences in pHr of up to 2.2 units were recorded for NH4- vs NO3-fed wheat plants (Triticum aestivum L.) in pots. Differences of up to 1.2 units occurred in the field. The pHb and pHr also differed by as much as 1.2 units. Changes in pHr were correlated with the concentrations of NH4 in potted soils, although the acidifying influence of NH4 decreased with time, as nitrification proceeded. Reductions in pHr values persisted longer in NH4 treated, fumigated soils, and in non-fumigated soils where NH4 fertilizers had been treated with a nitrification suppressant. The pHr differences in NH4- vs NO3-N treated soils were reduced by organic amendments. Difference with respect to pHr were found among wheat varieties and plant genera. The ability of plants to alter the pHr was related to assimilation of NO3 primarily in the roots (monocots) or shoots (dicots).

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