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Soil Science Society of America Journal Abstract -

Effect of Ammonium and Nitrate Fertilization on Phosphorus Uptake as Related to Root-Induced pH Changes at the Root-Soil Interface1


This article in SSSAJ

  1. Vol. 35 No. 2, p. 301-306

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  1. D. Riley and
  2. S. A. Barber2



Soybeans (Glycine max L.) fertilized with either NH4-N or NO3-N were grown in a growth chamber using soil with four different initial pH levels. Liming the soil used in this research to increase pH decreased the P level in solution. Fertilization of soybeans with NH4-N decreased the pH of the rhizocylinder (root plus strongly adhering soil); fertilization with NO3- increased rhizocylinder pH. The difference between the rhizocylinder pH of the NH4+ and NO3- treatments was as large as 1.9 pH units with an initial soil pH of 5.2 and as small as 0.2 units when soil pH prior to N application was 7.8.

Ammonium-fertilized soybeans absorbed more P and had a higher P concentration than NO3-fertilized soybeans. The results for soybeans grown with NH4+ and NO3- treatments at four initial soil pH levels showed that the P content of the shoots and roots was closely correlated with the pH of the rhizocylinder, but not the pH of the bulk soil. This suggests that the increased availability of P from the soil where NH4+ was used was mainly due to the effect of the nitrogen source on the pH of the rhizosphere soil.

Soybean root length decreased from 180 to 120 m/gram of dry roots as the pH of the rhizocylinder increased from 4.7 to 7.5.

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