INORGANIC ELEMENTS OF MANURES AND CROPS. 367 



On looking at this table we perceive that a medium crop of wheat 

 takes from one acre of ground about 12 lbs., and a crop of beans 

 about 20 lbs. of phosphoric acid ; a crop of beet lakes 11 lbs. of the 

 same acid, and further, a very large quantity of potash and soda. It 

 is obvious that such a process tends continually to exhaust arable 

 land of the mineral substances useful to vegetation which it con- 

 tains , and that a term must come when, without supplies of such 

 mineral matters, the land would become unproductive from their ab 

 straction. In bottoms of great fertility, such as those that are brought 

 under tillage amidst the virgin forests of the New World at the pres- 

 ent day, it may be imagined that any exhaustion of saline matters 

 will remain unperceived for a long succession of years ; for a suc- 

 cession of ages almost. And in South America, where the usual 

 preliminary to cultivation is to burn the forest that stands on the 

 ground, by which the saline and earthy constituents of millions of 

 cubic feet of timber are added to the quantities that were already 

 contained in the soil, I have already had occasion to speak of the 

 ample returns which the husbandman receives for very small pains.* 

 Under circumstances, in the neighborhood of large and populous 

 towns, for instance, where the interest of the farmer and market- 

 gardener is to send the largest possible quantity of produce to mar- 

 ket, consuming the least possible quantity on the spot, the want of 

 saline principles in the soil would very soon be felt, were it not that 

 for every wagon-load of greens and carrots, fruit and potatoes, corn 

 and straw, that finds its way into the city, a wagon-load of dung, 

 containing each and every one of the principles locked up in the 

 several crops, is returned to the land, and proves enough, and often 

 more than enough, to replace all that has been carried away from it. 

 The same principle holds good in regard to inorganic matters, which 

 we have already established with reference to organic substances. 



The most interesting case for consideration is that of an isolated 

 farming establishment — a rural domain, so situated that it can obtain 

 nothing from without, but exporting a certain proportion of its pro- 

 duce every year, has still to depend on itself for all it requires in the 

 shape of manure. I have already shown, with sufficient clearness, 

 I apprehend, how it is that lands in cultivation derive from the at- 

 mosphere the azotized principles necessary to replace the azotized 

 products ff the farm, Avhich are continually carried away in the 

 shape of grain, cattle, &c. I have now to show how the various 

 saline substances, the alkalies, the phosphates, &c., which are also 

 exported incessantly, are replaced. I believe that I shall be able, 

 with the assistance of chemical analysis, to throw light on one of 

 the most interesting points in the nature and history of cropping, and 

 succeed in practically illustrating the theory of rotations. In what 

 is to follow immediately, I shall always reason on the practical data 

 collected at Bechelbronn, and which have already served for the 



* The first breaks of the early English settlers in North America are now either very 

 indifferent soils, or they have only been restored to some portion of their original fer- 

 tility by manuring ; so that the supply of fertilizing elements is not ineirfiaustible — 

 Eno Ed 



