Potassium Fixation in San Joaquin Valley Soils Derived from Granitic and Nongranitic Alluvium. Murashkina, M. A., Southard, R. J. and G. S. Pettygrove. 2007. Soil Sci. Soc. Amer. J. 71 (1) p. 125-132. http://soil.scijournals.org/

Abstract: Potassium fixation influences the effectiveness of fertilization in soil-plant systems. A rapid method for measuring K fixation could help clarify relationships with other soil properties, especially mineralogy. Our objectives were to compare some existing measurement techniques for soil K fixation and availability, develop an alternative K fixation test, and evaluate the utility of soil texture and parent material for predicting K fixation in soils derived from granitic Sierra Nevada (SN) and nongranitic Coast Range (CR) alluvium. Potassium pools were estimated by 1 mol L^-1 NH₄OAc and sodium tetraphenylboron (TPB) extractions. Our 1-h fixation method correlated well (R² = 0.95, P = 0.001) with a 7-d procedure, so the 1-h method was used for subsequent work. The SN soils fixed up to 740 mg K kg^-1; CR soils fixed up to 263 mg K kg^-1. There was no significant relationship between K fixation and soil clay or silt content for either parent material. The TPB test had a stronger correlation with NH₄OAc-extractable K in SN soils (R² = 0.77, P = 0.001) than in CR (R² = 0.49, P = 0.001). Plant-available non-exchangeable K (PANK = TPB minus NH₄OAc) did not correlate with K fixation potential for pooled data from all pedons (R² < 0.11), and had negative correlation (R² from 0.97 to 0.99, P = 0.01) for individual pedons. The PANK probably represents K that has already been fixed and satisfies some of the K fixation capacity. The 1-h test is a reliable, rapid method for predicting K fixation potential. Together, the TPB and NH₄OAc tests could be useful for identifying K already fixed by soils, thereby reducing K fixation potential.

Effect of alternative anions (Cl^- vs. SO₄^-2) on concentrations of free amino acids in young tea plants. Ruan, J., Gerend