Effect of Ammonium and Nitrate Fertilization on Phosphorus Uptake as Related to Root-Induced pH Changes at the Root-Soil Interface1
- D. Riley and
- 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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