REPLACEMENT OF EXHAUSTED ALKALIES. 119 



A harvest of grain is obtained every thirty or forty 

 years from the soil of the Luneburg heath, by strew- 

 ing it with the ashes of the heath-plants (^Erica vul- 

 garis) which grow on it. These plants during the 

 long period just mentioned collect the potash and 

 s-oda, which are conveyed to them by rain-water ; 

 and it is by means of these alkalies that oats, barley, 

 and rye, to which they are indispensable, are ena- 

 bled to grow on this sandy heath. 



The woodcutters in the vicinity of Heidelberg have 

 the privilege of cultivating the soil for their own use, 

 after felling the trees used for making tan. Before 

 sowing the land thus obtained, the branches, roots, 

 and leaves, are in every case burned, and the ashes 

 used as a manure, which is found to be quite indis- 

 pensable for the growth of the grain. The soil itself 

 upon which the oats grow in this district consists of 

 sandstone ; and although the trees find in it a quan- 

 tity of alkaline earths sufficient for their own suste- 

 nance, yet in its ordinary condition it is incapable 

 of producing grain. 



The most decisive proof of the use of strong 

 manure was obtained at Bingen (a town on the 

 Rhine), where the produce and development of vines 

 were highly increased by manuring them with such 

 substances as shavings of horn, &c. ; but after some 

 years the formation of the wood and leaves de- 

 creased to the great loss of the possessor, to such 

 a degree that he has long had cause to regret his 

 departure from the usual methods. By the manure 

 employed by him, the vines had been too much 

 hastened in their growth; in two or three years 

 they had exhausted the potash in the formation of 

 their fruit, leaves, and wood, so that none remained 

 for the future crops, his manure not having con- 

 tained any potash. 



There are vineyards on the Rhine the plants of 

 which are above a hundred years old, and all of 

 these have been cultivated by manuring them with 

 cow-dung, a manure containing a large proportion 



