120 



THE SOIL. 



If these quantities of nutritive elements are present in 

 an available condition in these soils, that of Weihen- 

 stephan would contain of phosphoric acid almost 400 

 times, of potash 700 times, and of silicic acid rather 

 more than 190 times, as much as a wheat crop requires : 

 in the soil of Bogenhausen the amount of phosphoric 

 acid, potash, and silicic acid would be twice as large as 

 the hypothesis presupposed. 



The well-known analyses of similar soils by other 

 chemists show that the assumed estimate of the nutritive 

 substances required in a good wheat or rye soil is rather 

 below than above the actual amount ; and, in fact, the 

 future prospects of agriculture would be very gloomy, if 

 the ground was not far richer in nutritive substances than 

 has here been hypothetically assumed. 



This is, perhaps, the place to state the distinction 

 between the fertility of a field and its productive powers. 

 According to the experiments of Nageh and Zoeller, men- 

 tioned above, turf may be so saturated with the necessary 

 nutritive substances as to become an extremely fruitful 

 soil for beans ; and a comparison of the ash constituents, 

 in the stalks and seeds of the crop, with the quantity 

 which had been added to the tmf, shows that the twelve 

 to fourteen-fold quantity of these ash constituents was 

 enough to produce a very abundant seed crop. The 

 porous turf, saturated even in its minutest particles mth 

 nutritive elements, favoured in this case an enormous de- 

 velopement of the roots, to which the largeness of the 

 crops is due. Nothing can be more certam than that its 

 power of production measured by time is very small, and 



