LECTURE IV 



THE FOOD OF CROPS MANURING THE SOIL 



To use manures aright with due attention to 

 economy and efficiency, it is essential that we have 

 a thorough knowledge of soils, suqh as was imparted 

 in the* second lecture. You were there specially 

 invited to regard soil as a medium for conveying 

 sustenance to crops, a storehouse of fertility, a com- 

 pound substance to be kept charged with the essential 

 elements of plant food and never to be suffered to 

 become exhausted of such elements. 



The evils of soil exhaustion are to be met with 

 almost everywhere. We see them in the barren old 

 fruit trees of our orchards, in the stunted growth of 

 our bush fruits, in inferior crops of vegetables, all 

 asking for the sustenance we so foolishly deny them. 



Plant Food. Let us now see what food plants 

 need. It was once thought that the indispensable 

 elements to apply were nitrogen, phosphorus, potash, 

 sulphur, calcium (the metallic base of lime), magne- 

 sia and iron, which are found in plants. But careful 

 experiments extending over several years have proved 

 that, generally speaking, the last four substances may 

 be disregarded, and that for all ordinary purposes 

 nitrogen, phosphorous, and potash in fair proportion 

 form a sufficient manure, as in the example of potatoes 



