The reason i asked the question is one other symptom of K deficiency sometimes  corn plants can be stunted with shorter internodes, thus being shorter while having the same number of leaves as the healthy plants.

 I found this information in the link below.

 "  Potassium deficiency symptoms can occur even though soil potassium levels are sufficient to optimize corn production (>160 parts per million - ppm). This deficiency occurs because corn plants need an actively growing root system and water in the soil to aid in the slow movement of potassium to roots. When soil conditions are dry, root growth slows and the speed that potassium in the soil can reach the plant root and be taken up slows down, potentially resulting in potassium deficiency symptoms. Potassium uptake can also be limited in tilled soils where soils have not settled sufficiently since tillage. The lack of settling results in poor contact between soil particles, slowing down the movement of potassium through soil water to plant roots. Therefore, potassium deficiency is sometimes not seen in the wheel-track areas, where soil is settled and well firmed, but it is seen between wheel-track areas. Further, soils with high amounts of smectite clays collapse in dry conditions, resulting in temporarily making the potassium held by these clays unavailable to plants. Recent research shows that these smectite clays are more common in the eastern part of South Dakota and less common in central and western South Dakota. Other soil factors that limit root growth or water uptake including compacted soil, root pruning by insects, diseases and sidewall compaction of the seed furrow, which can also limit potassium uptake and result in potassium deficiency symptoms even when soil potassium levels are sufficient."


 Corn Potassium and Drought (sdstate.edu)