THE PRODUCTIVE POWER OF LAND VARIES. 189 



I 



from unmanured plots were likewise taken into ac- 

 count, we see that this is a general rule admitting of no 

 exception : no two fields have exactly the same produc- 

 tive power ; nay, there are not even two plots in the 

 same field which are identical in this respect. We 

 need only look at a turnip field to see at once that 

 every turnip differs in size and weight from the one 

 growing next to it. This fact is so universally known 

 and admitted, that in all countries where the land is 

 taxed, the amount of the impost is assessed according 

 to the quality of the soil, in some countries in eight 

 classes, in others in twelve or sixteen. 



Since, then, no two fields are alike in productive 

 power, and every field must necessarily contain the con- 

 ditions required for the production of the crops which 

 it yields, it is clear that the conditions for the produc- 

 tion of corn and straw, or of turnips and potatoes, or of 

 clover or any other plant, are in no two fields alike : in 

 one field the conditions for the production of straw pre- 

 ponderate over those for the production of grain, 

 another is better suited for the growth of clover, and 

 so on. 



These conditions, according to their very^ nature, 

 differ in quantity and quality. By conditions which 

 can be weighed and measured, we of course mean no 

 other than nutritive substances. 



The crops reaped from a field afford no indication 

 of the quantity of nutritive substances in the ground. 

 Consequently, the fact that the field at Mausegast gave 

 twice as much corn and one-third more straw than the 

 one at' Cunnersdorf, cannot lead to the inference that 

 the former was upon the whole richer in these propor- 

 tions in the conditions for the production of corn and 

 straw ; for we see that the Cunnersdorf field gave two 

 years after, without manuring, one-half more oat-corn 

 and straw than the field at Mausegast, and in the fourth 

 year above 60 per cent, more clover. Now some of the 

 most important food elements of corn are as essential 

 to clover as to the cereals ; and the food elements of 

 oats are identical with those of rye. 



