Potassium Fixation in San Joaquin Valley Soils Derived from Granitic and Nongranitic Alluvium
- M. A. Murashkina *,
- R. J. Southard and
- G. S. Pettygrove
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 (R 2 = 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 soilsf ixed 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 (R 2 = 0.77, P = 0.001) than in CR (R 2 = 0.49, P = 0.001). Plant-available nonexchangeable K (PANK = TPB minus NH4OAc) did not correlate with K fixation potential for pooled data from all pedons (R 2 < 0.11), and had negative correlation (R 2 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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