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It's Role in Plants

Potassium (K) is second to nitrogen as the nutrient most taken in by plants. It plays a very important role in the plant's carbohydrate metabolism, and deficiency of K is very obvious in the many ways plant growth is affected.

Potassium Uptake by Plants:
Of the three major nutrients, only K is taken up as a simple ion instead of synthesized compounds as in the case of nitrogen (N03, NH4) and phosphorus (H2PO4)- Other than NH4, K carries of positive charge, K+.

Potassium's Role in Plants:
K plays a major role in a process known as carbohydrate metabolism. This process converts simple sugar into more complex sugar and starch. A deficiency in K disrupts this metabolism, and the result is an accumulation of simple sugar and a lower concentration of complex sugar and starch. The absence of these will result in symptoms in plants as K deficiency. K is also important for protein formation. Without K, free amino acids and soluble nitrate nitrogen accumulate in the stems and stalks of the plant. Soluble nitrate N must be reduced to amino acid to form protein. K builds up the cellulose within the stems and stalks, which in turn helps maintain water pressure inside the plant. This reduces transpiration and lodging or wilting.

Potassium Deficiency in Plants:
Symptoms of K deficiency show up in the following ways:
1 Leaf scorching (on older leaves): This is caused by K moving from the older leaves to the younger leaves. Usually appears first as interveinal chlorosis on recent, matured leaves. It will start out as a light yellow discoloration, to brown and eventually leaves have a burned appearance.
2 Slender, thin plant stalks that tend to lodge. Irregular growth of corn ears is another example of K deficiency.
3 Soft fruits during warm season, This is especially noticeable in strawberry as summer comes on, and berries tend to be come soft instead of remaining firm.

Availability of Potassium:
Plant nutrients exist in solution as charged particles known as ions. They have either positive (cation) or negative (anion) charge. In order for the nutrients to stay free, there must be an electrical neutrality (equal amounts of positive and negative charges) in the solution.
Since K is a cation (a plus charge) it must be accompanied by an equal negative charge; such as chloride, sulfate, nitrate, etc. in the solution. These are generally present in solution with high pH. (Refer to Fig. 1 above)

K uptake by crops is 4 times that of P, and equal or greater than N. K is attributable to the development of denser root growth, sturdier stems and stalks, and firmer fruits.