MINERAL MATTER. 123 



4. The nitrogen question is of the first 

 importance to the practical cultivator, a large 

 part of his efforts being directed towards 

 securing a sufficient supply of this important 

 plant food. This question also demands 

 especial care and thought owing to the fact that 

 nitrogenous substances are capable of many 

 changes, and that, if carelessly dealt with, 

 there are many ways in which nitrogen may 

 be wasted and lost. 



MINERAL MATTER. 



Of the mineral constituents of plant food, 

 lime has already been mentioned ; others are 

 potash, magnesia, iron, phosphates, chlori- 

 des and sulphates. Of these, potash and phos- 

 phates are often present jn the soil in such 

 small proportions and arc so constantly needed 

 by plants that beneficial results follow their 

 addition to the soil. It is estimated that about 

 the following amounts of potash and phos- 

 phoric acid are removed by the crops men- 

 tioned : 



Potash. Phosphoric Acid. 

 Sugar-cane (30 tons) 70 Ibs. 45 Ibs. 

 Sweet potato (10 tons) 100 25 

 Irish potato ... 75 20 



Corn (grain only,) 



30 bushels) J ... 7 10 



