Potassium Fixation in San Joaquin Valley Soils Derived from Granitic and Nongranitic Alluvium
2007
Murashkina, M.A. | Southard, R.J. | Pettygrove, G.S.
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 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 (R² = 0.77, P = 0.001) than in CR (R² = 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 (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.
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