EXTENSION COURSE IN SOILS. 85 



it permits the growth of crops on different kinds of soils occurring 

 on the farm; and, most important, it permits a cropping system 

 whereby soil fertility may be improved. 



Advantages of rotation to the soil. — The advantages of a rotation of 

 crops or cropping systems in its relation to fertility are (1) it per- 

 mits the use of manure on those crops to which it is best adapted; 

 (2) it aids in preventing diseases or other unfavorable conditions 

 which may develop on soil kept continuously in one crop; (3) it per- 

 mits tillage calculated to improve the tilth; (4) it aids in the eradi- 

 cation of weeds; and (5) it permits the growth of crops which will 

 result in an addition of humus and nitrogen to the soil. 



We have already seen that raw manure can be used to much 

 better advantage on certain crops, especially such rank-growing 

 crops as corn, sugar beets, cabbage, and cotton, which permit inter- 

 tillage, than on small grains or many of the vegetables. 



The advantages of a rotation of crops in lessening diseases are 

 becoming more and more apparent as our agriculture becomes more 

 fixed. The growth of any cultivated plant on a given area or even 

 in a given neighborhood continuously for a number of years is almost 

 invariably followed by the appearance of some specific diseases 

 or insect enemies, which are attached in one way or another to the 

 soil on which the crop is grown. The development of the corn-root 

 fungus, the cabbage diseases, the flax-wilt diseases, and many 

 others which might be mentioned are evidences of this fact. While 

 many of these diseases can be treated with specific remedies, applied 

 to the seed before sowing or to the plant in the proper stage of devel- 

 opment, it is nevertheless a very great aid in reducing difficulties 

 of this kind to have the crop grown but one or two years on a given 

 piece of land and then have it followed by other crops not subject 

 to the same diseases. 



Good tilth may be much more readily maintained on soils diffi- 

 cult to work by a rotation of crops than when the same crop is 

 grown continuously. For example, the use of heavy clay land for 

 meadow and pasture, in which the development of sod occurs makes 

 it much easier to keep such soil in good tilth than when it is kept 

 continuously in tilled crops. 



A large part of the labor of land tillage is concerned in the eradi- 

 cation of weeds. A rotation of crops greatly aids in this matter. 

 Some weeds are entirely unable to withstand the crowding of grasses, 

 and the use of land as meadow and pasture will naturally kill them. 

 Others, on the contrary, develop under these conditions and can be 

 removed only when the land is in tilled crops which permit culti- 

 vation. The planning of any rotation must take into account the 

 eradication of noxious weeds when these constitute a serious diffi- 

 culty on the farm. 



