After a field diagnostic call from a grower. I decided to take pictures of the problem for diagnosis. You can see the field wide shot then as one walks the beans the tell tale K deficiency shows up with burn from the outside edge of the petiole. After collecting soil samples from the good and bad areas the resulting 45 ppm difference both low but at the 45 ppm level the deficiency was seen visibly. Finally after a 200lb/acre of muriate that afternoon the recovery of hte plants and quick turn around in the field.