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Better than expected yields and a very dry fall are causing soils to test very low for available potassium (K). Most of the K in corn is in the foliage an is washed back into the soil by rainfall as the residue decays. Some of the K may also be locked into very dry soil clay particles. If you look at annual graphs of soil available K, September is traditionally the low point in the cycle, but normally the levels rebound quickly after harvest. The lack of fall rains, this year, has delayed that process. If you have already pulled soil tests this fall, you may need to rely on historical soil test levels and crop removal rates to make K fertility decisions.