274 HANDY-BOOK OF HUSBANDRY. 



but feeble power of sending their roots deep into the soil in search 

 of food (as wheat, for instance) should succeed such crops (like 

 clover and buckwheat) as have this power in an extraordinary 

 degree ; that crops which require clean culture, and the expense 

 of whose cultivation is very much increased by the foulness of the 

 land, should follow crops which leave the land free from weeds, 

 (as roots after grain ;) and that crops which require a large amount 

 of decomposing organic matter in the soil should follow the decom- 

 position of the roots and stubble of grass. 



So far as science is able to indicate a guide in this matter, the 

 case is very well laid down in the following quotations from Lie- 

 big:-^= 



" If a given space of a soil (in surface and in depth) contains 

 '' only a sufficient quantity of inorganic ingredients for the perfect 

 '' development of ten plants, twenty specimens of the same plant, 

 ^' cultivated on this surface, could only attain half their proper 

 "maturity; in such a case there must be a difference in the num- 

 "ber of their leaves, in the strength of their stems, and in the 

 " number of their seeds. 



" Two plants of the same kind growing in close vicinity must 

 " prove prejudicial to each other, if they find in the soil, or in the 

 " atmosphere surrounding them, less of the means of nourishment 

 ** thau they require for their perfect development. There is no 

 " plant more injurious to wheat than wheat itself, none more 

 " hurtful to the potato than another potato. Hence vve actually 

 *' find that the cultivated plants on the borders of a field are much 

 ^' more luxuriant, not only in strength, but in the number and 

 *' richness of their seeds or tubers, than plants growing in the 

 *' middle of the same field. 



" The same results must ensue in exactly a similar manner 

 *' when we cultivate on a soil the same plants for successive years, 

 " instead of, as in the former case, growing them too closely to- 

 *■'■ gether. Let us assume that a certain soil contains a quantity of 

 " silicates and of phosphates sufficient for i,ooo crops of wheat, 



* Agricultural Chemistry. J. von Liebig. Giesscn, 1843. 



