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. 
