50 Report of the Acting Director and Chemist of the 



supplied to plants in the form of water. Growing plants contain a 

 larger amount of water than of any other constituent. More or less 

 of the oxygen and hydrogen of the water is separated in the plant, 

 and in this way plants secure the hydrogen and oxygen which they 

 need to build up their tissues. In this manner water acts as a direct 

 fertilizer. The water is supplied to the soil by rains ; from the soil 

 it is taken into the plant through the roots. In regions adapted to 

 agriculture, plants receiv^e all the hydrogen and oxygen needed, and 

 usually much more, from the rains. Therefore, these elements are 

 not regarded as important parts of fertilizers. 



When water is supplied to plants by irrigation, it can very prop- 

 erly be called a fertilizer, and an extremely important one. 



Nitrogen. — Experiments have shown that nitrogen is essential 

 to the growth of plants ; that the quantities of nitrogen available as 

 plant-food are very small ; that nitrogen is one of the first elements 

 in the soil to be used up; that, of all fertilizing elements, nitrogen 

 is and always has been the most expensive. 



Phosphorus. — The fact that phosphorous compounds are abso- 

 lutely necessary for the maturity of plants indicates that phosphates 

 are essential to complete fertilizers. Soils become deficient in avail- 

 able phosphates quite rapidly, especially in grain-growing regions. 



Sulphur. — Sulphur is kuown to be an essential constituent of 

 plant-food. 



So far as known, plants take it up and use it in the form of 

 sulphates. As a rule, there appear to be in all soils amounts of sul- 

 phates sufficient to supply indefinitely all the demands of crops. 

 As the quantity of sulphur used by plants is very small, soils do not 

 readily become exhausted of this element. Therefore, we do not 

 need, in general, to add sulphur compounds to the soil. Calcium 

 sulphate (sulphate of lime) and potassium sulphate (sulphate of 

 potash) are often present in commercial fertilizers, but they are 

 generally used not on account of the sulphur they contain. Some 

 forms of sulphur compounds render a soil barren, when present in 

 any considerable quantity. 



Chlorine. — While chlorine is kuown to be an essential constituent 

 of plant-food, the circumstances which require its addition to the 

 soil appear extremely rare, except in some cases where it may be 

 used for an indirect benefit. It is added to fertilizers in consider- 

 able quantities in the form of potassium chloride (muriate of potash) 

 but this is largely because this happens to be the cheapest form in 



