in the soil which are busy preparing soluble food for the plant. The ventilation 

 of the soil k also required to supply free nitrogen for the use of nitrogen-fixing 

 germs, and to remove the excess of carbon dioxide which is being continually set 

 free in the soil. 



From the soil the plant derives nitrogen, chiefly in the form of nitrates, the 

 ash substances, and water. Fortunately, although ten elements are essential for 

 the growth of the plant, there are only four that particularly interest the farmer, 

 as the other six are usually found in abundance. These four are, nitrogen, 

 potassium, phosphorus, and calcium. A continuous supply of all the essential ele- 

 ments of plant growth is absolutely necessary; for, if one constituent is absent, 

 or present in an insufficient quantity, no matter what amount of the other 

 nutrients may be available, the plant cannot be fully developed. Consequently, 

 just as a chain is only as strong as its weakest link, so the crop-producing power 

 of a soil is limited by the essential nutrient present in relatively the smallest 

 quantity. 



Function of Plant Food Constituents. 



In the .absence of nitrogen the plant makes no appreciable growth. With 

 only a limited supply, the plant commences to grow in a normal way, but as 

 soon as the available nitrogen is used up, the lower and smaller leaves begin 

 gradually to die down from the tips and all the plant's energy is centered in one 

 or two leaves. Nitrogen is one of the main constituents of protein, which is 

 possibly the most valuable part of a plant. . It is also a constituent of chlorophyll, 

 the green coloring matter of plants; hence with a limited supply of nitrogen, the 

 leaves will have a sickly yellow color. Plants with large, well-developed leaves 

 are not suffering for nitrogen. An abundance of this substance will produce a 

 luxuriant growth of leaf and stem, but it will retard maturity, and, with cereals, 

 will frequently cause the crop to "lodge." Therefore, when crops such as cereals, 

 tomatoes, potatoes, etc., are to be matured, an over supply of nitrogen is injurious: 

 but with the crops such as lettuce, cabbage, etc., which are harvested in the green 

 condition, an abundance of nitrogen will, other fertilizing constituents being present, 

 tend to produce a strong vigorous growth, and give crispness or quality to these 

 crops. 



Potassium, or potash, as it is commonly called, is one of the most important 

 and least variable of all the elements of the ash of plants. It is quite evenly 

 distributed throughout the leaves, stem, and seed, and generally occurs in the 

 entire plant in the largest proportion of any of the essential ash constituents. 

 The function of potassium is apparently to aid in the production and transporta 

 tion of the carbohydrates. The flavor and color of fruits is generally credited 

 to potassium. In fact, this element seems to supplement the action of nitrogen 

 by filling out the framework established by the latter. Potash with nitrogen is 

 always an important fertilizer with special crops where the object is to produce 

 sugar, starch — as with sugar beets and potatoes. It is also apparently essential 

 for the formation of protein, and, thus, indirectly aids in fonnation of all 

 organic matter. 



Phosphorus, in the form of phosphates, is found in all parts of the plant, 

 but tends to accumulate in the upper parts of the stem and leaves, and particularly 

 in the seed. Its function is apparently to aid in the production and transportation 

 of the protein. It also seems to aid the assimilation of the other plant food 



