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Lack of potassium produces a greater range of symptoms 
among different species than does lack of nitrogen. Plants like 
the cereal grains, which produce central stalks or shoots, die 
prematurely unless provided with this element from the very 
beginning. In crops such as lettuce, beets, and carrots, how- 
ever, the effects of potassium deficiency are less severe, and are  quickly remedied by addition of small amounts of the element 
to the nutrient solution. 

Unlike nitrogen, potassium does not enter into fixed chemical compounds inside the plant. However, crops like potatoes, 
which are predominantly starch, absorb large amounts of it 
and produce better-quality crops if an ample supply is avail- 
able. It is assumed that the element plays an important role 
in photosynthesis of crops rich in starch and sugar. 

The deficiency symptoms of potassium can be described as a 
premature breakdown of the younger foliage. The leaves 
droop and, as deficiency continues, may change in color (be- 
coming either lighter or darker according to species) and die. 
The first symptoms to be noticed are brown spots on the older 
portion of the leaves. 

An excess of potassium makes straw and leaves of plants stiffer 
than normal. Sometimes the tips of the youngest leaves wilt 
and those of the older leaves turn brown. There is no charac- 
teristic off-color of the foliage unless growth is slowed down 

Very few species can reproduce themselves from the small 
amount of potassium contained in their seed. The tuber crops, 
such as potato, are a notable exception. They contain fairly 
large amounts of this element, can make considerable growth 
from that contained in the tuber, and reproduce small tubers 
without additional supplies from outside sources. 

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