16 
Colorado Experiment Station 
potassium in the soil causes a dwarfing of plants and interferes with 
the manufacture of starch by the leaves. A deficiency of magnesium, 
iron, or nitrogen also reduces the amount of starch production in 
leaves. Too much nitrogen in the soil is said to make a plant more 
susceptible to frost injury. 
Excessive quantities of nitrates in the soil are extremely injurious 
to plants. Certain Colorado soils have the power of fixing atmo- 
spheric nitrogen and this fixation often proceeds to the point where 
cultivated plants are completely killed over a localized area. Truck 
gardens, alfalfa, oat, barley and sugar beet fields often develop 
barren patches on which nothing will grow. Equally serious is the 
damage done to apple and cherry orchards in which many trees are 
completely killed. Often an entire orchard will be lost from this 
cause. 
This excessive fixation of nitrogen is due to the activity of certain 
bacteria which live in the soil. These organisms take free nitrogen 
from the air and change it into the form of nitrates. The nitrates 
are dissolved in the soil water and as a result of evaporation be- 
come concentrated near the surface of the soil. This trouble is 
spoken of as ‘‘Nitre Injury.” 
The physical condition of the soil also has much influence on the 
health of plants. A heavy clay soil that packs easily is often in- 
jurious to plants. A course sandy soil often will not hold sufficient 
water for the plant growth. A lack of water will cause a plant to 
wilt or die. Too much water prevents air from reaching the roots 
of plants and brings about an unthrifty condition. 
A nitre spot. (Original in Colorado Experiment Station Bulletin 155, by Headden.) 
