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Highlights of the Frontiers of Potassium Science Conference T. Scott Murrell Potassium Program Director, IPNI 2018 Great Plains Soil Fertility Conference, Denver, CO. 6-7 Mar. 2018. https:// conference.ipni.net. Historical Concept.

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  1. Highlights of the Frontiers of Potassium Science ConferenceT. Scott MurrellPotassium Program Director, IPNI2018 Great Plains Soil Fertility Conference, Denver, CO. 6-7 Mar. 2018.

  2. https://conference.ipni.net

  3. Historical Concept “Soil K exists in three forms: unavailable, slowly available, and available.Unavailable K – unavailable K is found in minerals (rocks). The K is released as soil minerals are weathered, but so slowly as to be unavailable to growing plants in a particular crop year.”

  4. Mica Weathering Fanning, D.S. V.Z. Keramidas, and M.A. El-Desoky. 1989. Micas. p. 551-634. In J.B. Dixon and S.B. Weed (eds.)Minerals in Soil Environments. 2nd ed. SSSA, Madison, WI. Figure 12-11.

  5. New Concept:Mineral ”weathering” can occur rapidly in the rhizosphere General mechanism:Mica – K + movement of hydrated cations in the interlayer = vermiculite Mortland, M.M. et al. 1956. Soil Science 82:477-481; Hinsinger, P. et al. 1992. Soil Science Society of America Journal 56:977-982;Hinsinger, P. and B. Jaillard. 1993. Journal of Soil Science 44:525-534;Hinsinger, P. et al. 1993. Journal of Soil Science 44:535-545.

  6. Historical Concepts Available K – Readily available K is made up of the K found in the soil solution plus the K held in exchangeable form by soil organic matter and clays.Slowly available K – slowly available K is ‘fixed’ or trapped between layers of certain soil clays…becoming unavailable or only slowly released.

  7. Extractant Exchangeable K on Micas and Illites:Ammonium Acetate and Mehlich III Extractants Hydrated ions mineral layer Na+ K+ NH4+ Mg2+ Ca2+ Mehlich, 1985; Warnke and Brown, 1998

  8. Potassium Contribution from Interlayers:Contribution of Illite Interlayer K to Sorghum K Uptake Rao, C.S. and M.S. Khera. 1994. Journal of Plant Nutrition and Soil Science 157:467-470.

  9. Ways Plants Access K from the Rhizosphere RHIZOSPHERE BULK SOIL fungi bacteria n o i t a r t n e c n o c K ROOT acids andcarboncompounds distance from root mucigel

  10. Rate of Release of Non-Exchangeable K(Soil with mostly mica and some vermiculite) S.A. Barber (1995): 7-16 lb K2O per acre foot of water was the most observed soil solution K concentration range for 142 U.S. Midwestern soils Threshold? Barber, S.A. 1995. Soil nutrient bioavailability: A mechanistic approach. 2nd ed. John Wiley and Sons, New York, NY; Springob, G. and J. Richter. 1998. Z. Pflanzenernähr. Bodenk. 161:323-329.

  11. Different Varieties May Differ in Their Abilities to Access Non-Exchangeable K Trehan, S.P. et al. 2007. Communications in Soil Science and Plant Analysis 36:1809-1822.

  12. Illite and Smectite Differ in the Exchangeability of Interlayer Cations Illite Smectite Dzene, L. et al. 2017. Journal of Physical Chemistry C 121:23422-23435Lammers, L.N. et al. 2017. Journal of Colloid and Interface Science 490:608-620

  13. Transforming Smectite to Illite Decreases Cation Exchange Capacity Lee, J.O. et al. 2010. Applied Clay Science 47:99-104.

  14. Exchangeable K vs. Bioavailable K:A Possible Picture Exchangeable Bioavailable K Exchangeable Non-expansiblephyllosilicate minerals(mica, illite) Expansiblephyllosilicate minerals(smectite, vermiculite)

  15. Variability in Soil Test Correlations Decreases the Accuracy and Precision of K Rate Recommendations A B Barbagelata, P.A. and A.P. Mallarino. 2013. Soil Science Society of America Journal 77:318-327.

  16. The Importance of Collecting Supporting Data in Soil Test Correlation Studies • Plant FactorsAt a given soil test level, different varieties of a given species may differ in their abilities to • acquire K from the soil(different K uptake efficiencies) • utilize K physiologically for vegetative and reproductive growth(different K utilization efficiencies) • Soil FactorsAt a given soil test level, different soils can differ in their K supplying power • Collecting supporting data may allow us to parse larger, more variable data sets into smaller, more site-specific data sets that more accurately predict crop response White, P.J. 2013. Journal of Plant Nutrition and Soil Science 176:305-316.

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