COMPOSITION OP SOILS AND THEIR ACTION. 57 



setts, a few years since imported some barley from 

 Holland, and some of it was used for seed by farm- 

 ers in the vicinity. It was infested by an insect 

 which spread rapidly, and compelled the farmers to 

 abandon barley as a crop for two or three years. 

 The insect is now extinct, and barley is again culti- 

 vated with success. 



• A fifth inference is, that crops liable to be infest- 

 ed with peculiar weeds should not be cultivated in 

 succession, but by a rotation should be exposed to a 

 culture that will eradicate them. The culture of 

 corn and roots that require repeated hoeings is found 

 effectual in destroying many weeds that get a foot- 

 hold in grass-lands, and by seeding lands in rotation 

 exhaustion is prevented, and the soil kept clean, in 

 good tilth, and prepared for any valuable crop re- 

 quired to be grown upon it. Pernicious weeds of- 

 tener obtain a foothold with the grains than with 

 any other crop, as these shade the ground but little, 

 and afford a chance for vegetation about their stems 

 which thick-growing or large-leaved plants do not. 

 Farmers find that charlock and redroot are thus dis- 

 seminated in their wheat-fields, and that a rotation 

 of crops is necessary to clear them of these pestif- 

 erous intruders. 



Another important inducement to a rotation of 

 crops, but one which is often overlooked in consid- 

 ering the matter, is the greater advantages that can 

 be derived from manure where this system is pur- 

 sued than where it is not. Every farmer is aware 

 of the fact that there is a wide difference among 

 cultivated plants as to the effect produced by the ap- 

 plication of manures. Some can scarcely receive 

 too much, or have it furnished too directly. They 

 are gross feeders, and appear to de^'our the elements 

 of nutrition without stint or injury. Corn, and the 

 roots generally, are of this class. Others seem to 

 be more delicate, and are either destroyed outright 

 by too large quantities of unfermeated manures, or 



