02475naa a2200205 a 450000100080000000500110000800800410001902400390006010000160009924500910011526000090020650000750021552017620029065300110205265300300206365300230209365300280211670000140214477301110215810593162018-11-28       2017    bl uuuu     u00u1 u    #d7 a10.1080/00103624.2017.14161342DOI1 aNÚÑEZ, A.  aPotassium dynamics in western uruguayan agricultural mollisols.h[electronic resource]  c2017  aArticle history: Received 4 January 2017 // Accepted 13 November 2017.  aABSTRACT. Knowledge of soil potassium (K) dynamics and quantification of plant-available K reserves are essential for the correct management of this nutrient. The objectives of this study, conducted in six Uruguayan mollisols, were to (i) determine the contribution of plant-available nonexchangeable K to plant nutrition, (ii) compare the ability of the ammonium acetate (NH4OAc) method and the sodium tetraphenylboron (NaBPh4) method to determine plant-available K, and (iii) quantify the effect of K fixation and release processes on the ability of both methods to estimate changes in K availability due to different K balances. In a greenhouse experiment, perennial ryegrass (Lolium perenne, cv. Horizon) was grown over a period of 320 days in six soils fertilized with 0, 100, 200, and 400 mg K kg?1. We measured plant K uptake and the changes in soil K status related to different K balances using NH4OAc and NaBPh4. Use of NaBPh4 resulted in a more accurate determination of plant-available K (R2 = 0.97 vs. 0.78) and soil K balance (R2 = 0.73 vs. 0.63), but neither of the methods was suitable for identifying positive K balances. However, when positive balances were established by K addition and incubation without plant growth, both methods related well with K balances. Again, NaBPh4 was better than NH4OAc (R2 = 0.98 and 0.88, respectively). The more accurate determination of plant K uptake and the strongest relationship with K balance of NaBPh4 was due to the extraction of exchangeable K plus a proportion of plant-available nonexchangeable K. Soil?plant interactions enhance soil K fixation in forms that are available to plant absorption but are not extractable by the chemical methods considered in this study.  © 2017 Taylor & Francis.  aILLITE  aNONEXCHANGEABLE POTASSIUM  aPOTASSIUM RESERVES  aSODIUM TETRAPHENYLBORON1 aMORON, A.  tCommunications in Soil Science and Plant Analysis, 30 November 2017, Volume 48, Issue 21, Pages 2558-2572.