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Nitrogen (N)

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Nitrogen is usually absorbed in greater amounts than any 
other element. Lack of it from the beginning causes diminu- 
tive plants with comparatively larger root systems, smaller and 
lighter colored leaves, and drier leaf tips than the normal plant. 
It does not in general interfere with the processes essential for 
growth in plants like wheat, whose seed contains enough nitro- 
gen to produce another seed in a small plant. When nitrogen 
is deficient, growth proceeds normally but on a diminutive 
scale. But plants with small seed, like lettuce, cannot repro- 
duce unless they are provided with this element. 

Many species can reproduce from the original fund of nitro- 
gen contained in their seed or seedlings without additional sup- 
plies from outside sources. Seed from such plants will germi- 
nate but cannot itself produce viable seed. Many cereal grains 
are in this class. They show increases in growth directly pro- 

Symptoms of Change 

Proportional to additions of nitrogen to the solution until an ex- 
cess of nitrogen becomes available. Then the ratio is no longer 
consistent. The excess produces very lush vegetation with a 
corresponding decrease in the firmness of stems and leaves. 
Foliage is produced rapidly at the expense of root growth, the 
ratio of fruit or seed to vegetation is subnormal, and the con- 
formation of plant parts is off-type. 

In an experiment with wheat reacting to lack and excess of 
nitrogen, the ratio of grain to total weight of plant when ni- 
trogen was deficient was 15 per cent (i, 2, 3) . When the 
element was in excess, the same ratio was 20 per cent (6, 7) . 
In a culture from which nitrogen was removed when the plants 
were three months old, the ratio was 30 per cent (4, 5) . When 
nitrogen was lacking, the plants did not produce enough foliage 
and were unable to manufacture the starch needed for the 
kernels. When an excess of the element was present, too much 
foliage was produced; that is, vegetative growth continued too 

Symptoms of Change 

This also cut down the production of grain. Starch for 
the kernels is not produced from new leaves but only from 
those which have attained some size. If a high production of 
grain is to be obtained, it is necessary for the plants to stop 
forming new leaves after they have attained size. Thus, by 
prolonging vegetative growth the nitrogen excess inhibits the 
formation of the kernels. 

This tendency of nitrogen to cut down the storage of starch 
and sugar is not so important for some flowers and crops grown 
chiefly for their leafy tissue. However, they may also absorb 
an excess. 

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