106 AGRICULTURE 



no profit will remain to the cultivator. 

 But if the yield can be considerably increased 

 at a reasonable expenditure on manure, it 

 will be found that the net profits of the farm 

 are rapidly improved, because the standing 

 expenses of growing large crops are pro- 

 portionately less than those of producing 

 small ones. 



In considering the principles of manuring, 

 one must give particular attention to the 

 Law of Minimum, which may be stated 

 thus : That the yield of a crop depends 

 upon the available supply of that essential 

 element of plant food that is present in least 

 amount. Put into other words,[the law im- 

 plies that no superabundance of plant food 

 generally can compensate for deficiency in 

 an essential element. In popular language, 

 the law may be illustrated by'a chain, whose 

 strength is necessarily determined by the 

 weakest link. All the higher plants, and 

 therefore all farm crops, require to have 

 access to ten elements of food, that is to say, 

 no plant can grow unless everyone of these 

 ten elements is present, and no crop can 

 give a full yield unless they are all present 

 up to the requirements of the crop. These 

 elements are carbon, hydrogen, oxygen, 

 nitrogen, phosphorus, sulphur,^" potassium, 



