104 Capacity of a Soil — Practice and Theory. [August, 



CAPACITY OF A SOIL TO ENDURE CONSTANT CUL- 

 TIVATION. 



The capacity of a soil to support for a series of years, the culti- 

 vated crops, depends mainly upon the following conditions: 



1. Upon the quantity of water it can imbibe or retain, during 

 the seasons which would be considered dry. 



2. On the amount of nutritious matter which maybe introduced 

 without waste. 



A supply of water must ever be regarded as one of the most 

 essential things in the cultivation of all crops. This water must 

 be retained long enough to act upon the nutriment in the soil; 

 it must not escape immediately from the superior part of the soil, 

 or that part through which it usually ramifies. The quantity of 

 nutriment which may be condensed in a soil, depends too upon its 

 retentiveness for water; if it is too porous, it is speedily washed 

 out and lost, if too close, it is not received into it but is lost by 

 exhalation from the surface. In cultivation then, we seek to 

 modify both extremes; the object in all cases being to secure that 

 texture, which shall give it certain relations to water, which 

 experience and reason have determined to be the best. 



PRACTICE AND THEORY. 



The practice of agriculture has advanced with far greater ra- 

 pidity than its theory. Indeed, so far in the back ground is the 

 theory, and so imperfect in its development, that it may be re- 

 garded as existing in expectation rather than in fact. The ad- 

 vancement of agriculture then, cannot be ascribed to theory, 

 neither can it be said to be under its guidance or direction. 

 There have been, no doubt, many suggestions which have spiung 

 up from doctrines to a certain extent, which are theoretical, still 

 the practice of agriculture is rarely governed by them. 



The fact, however, must still be maintained, that its perfection 

 can be attained only by the aid of a sound theory. This will do 

 for agriculture, what it has already done for astronomy, geolo- 

 gy and chemistry. That the practice of agriculture has advanced 

 far towards perfection without the aid of theory is not very sur- 

 prising, when it is considered that its operations are very simple 

 and that the results flow from them with great certainty. This 

 fact has prevented that special consideration of phenomena, 

 which would have come to pass in more complicated arrange- 

 ments. Besides the phenomena with which agriculturists are 



