However, K is very mobile within the plant. Therefore, symptoms first appear on lower (older) leaves. For both corn and soybean, yellowing will be observed starting at the leaf tip that then extends along the leaf margins down towards the base of the leaf.

Do not confuse K deficiency with N deficiency. Remember, in corn, N deficiency begins at the leaf tip and follows the midrib down to the base of the leaf. In soybean, the entire leaf will begin to turn yellow. For both crops, K deficiency is restricted to the leaf tip and leaf margins.

Since K has limited mobility in the soil, anything that restricts root growth may result in deficiency symptoms. Therefore, as with phosphorus (P), soils with adequate K may still show symptoms due to lack of soil moisture, excessively cold soils, soil compaction, root pruning, sidewall compaction, etc..

K deficiency usually occurs in later vegetative stages as plant demand increases.

Leaves – Symptoms appear first on older (lower) leaves. Yellowing starts from leaf tip and progresses along leaf margins down toward leaf base. Tissue necrosis of leaf margins may occur in severe cases.

Lodging later in the season is possible in sever cases.

Plant and Leaf Tissue Deficiency Levels

Early Growth – recently mature leaf K < 2.0%¹

At Tassel – recently mature leaf ear K < 1.8%¹

Leaves – Symptoms appear first on older (lower) leaves. Yellowing along leaf margins that may turn necrotic (brown). Leaf veins will remain green.

Plant and Leaf Tissue Deficiency Levels

At Flowering – tissue K < 1.5%¹