Potassium Availability in Nason Soil as Influenced by Ammonium and Lime1
- L. W. Murdock and
- C. I. Rich2
A greenhouse experiment was established to find if NH4+ increases K+ availability when Nason silt loam is limed to pH 7.0 as suggested by previous laboratory studies.
Two oat crops were grown in soil at 3 lime levels (1, 5, and 15 g/1,000 g), 2 K levels (0 and 0.5 meq/100 g) and 2 N sources [Mg(NO3)2 and NH4NO3]. At high soil pH, potassium uptake was significantly greater where the N source was NH4NO3 as compared to Mg(NO3)2. The results support soil extraction data which show that at about pH 7.0, NH4+ ions are considerably more efficient in displacing K+ from this soil than are Mg2+ ions. It is concluded that the smaller NH4+ ions are able to penetrate to exchange positions not accessible to large hydrated Mg2+ ions.
The results do not support an explanation of the differential K uptake based on the antagonistic effect of Mg2+ ions on K+ nor due to an effect caused by lower soil pH with NH4NO3 fertilization.
Although K fixation occurs at high pH in this soil, this fixation does not appear to be associated with greater collapse of expansible vermiculite. In fact, it is shown that liming caused the vermiculite to be less subject to collapse on K saturation. The reason for the greater fixation at high pH may be that there is less competition for the specific sites by H3O+ ions and thus greater opportunity for selection of K+ ions which are of similar size.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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