EXTENSION COURSE IN SOILS. 87 
On heavier soils, where grain and stock raising is practiced, a 
longer rotation is usually desirable, especially if some of the culti- 
vated land is also to be used for pasture. A 6-year rotation can 
then be worked out, such as the following: Corn, wheat, oats, clover, 
timothy, and pasture, or it can be shortened to five years by omitting 
either one of the grains or the pasture year. 
Rotation for different types of soil on the same farm. — Over a con- 
siderable part of the United States there is such a variation in soils 
within short distances that the relation of one type of soil to the 
other must be fully considered. When a farm includes sand and 
marsh soils which have been drained and brought under cultivation, 
all of the manure should be used on the sandy soil, since the marsh 
soil does not need nitrogen, and can be kept in a high state of fertility 
through the use of moderate quantities of commercial fertilizers con- 
taining potassium and phosphorus, thereby making it possible to 
keep the fertility of the whole farm in a high state. The same 
method may be used when the farm includes clay and marsh soils. 
In such cases'it may be necessary to develop two or more systems of 
rotations on a single farm. All of these matters must of course be 
worked out with reference to each particular case, and the success 
of the farmer depends to a considerable extent on his judgment in 
working out logical systems of cropping adapted to his soil conditions 
as well as to his market and other factors affecting his work. 
Rotation systems for permanent fertility (Ref. No. 5, Chaps. XV and 
XVI, pp. 226-235). — After all, it must be recognized that the most 
important problem in any system of farming is so to conduct the 
cropping and the disposition of the crops that the fertility of the 
soil shall not alone be maintained, but that it shall be constantly 
built up in the best and most profitable manner. Herein lies one of 
the most vital parts of good farm management. The somewhat 
prevalent idea among farmers that simply rotating crops will improve, 
or even maintain, the fertility of soil is without a safe foundation. 
It is true, for reasons stated in the beginning of this lesson, that far 
better results in cropping will be realized from a well-planned rotation 
than from a single-crop system. But actually to build up the 
fertility of a soil one should first understand what elements of plant 
food are low in the soil, then the cropping system, the type of farming, 
the building up of humus and mineral elements through manures 
and fertilizers, and the physical management of the soil should all be 
so studied and planned that gradual soil improvement will result. 
The management necessary to attain this end will vary, of course, 
with the system of farming practiced. 
In vegetable gardening, manure from cities can usually be secured 
in quantity, and the soil can be improved while profits are realized 
from the crops by the purchase of both stable manure and com- 
