80 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
LESSON XL SOIL ADAPTATION TO CROPS. 
Relations between soils and crops (Ref. No. 4, pp. 291-306; or No. 
10, pp. 232-256). — There are a number of important relations between 
the character of the soils and the crops to which they are adapted. 
The climate also has an important effect, not only directly on the 
crop, but indirectly through the soil. Certain crops require long 
growing seasons between frosts, and they are seriously injured by a 
freezing temperature. The amount of rainfall is likewise an impor- 
tant consideration. Some crops growing very early in the spring 
and maturing in the early summer require much less water than do 
those growing during the longer summer season when evaporation, 
not only from the plant itself, but also from the soil, is at the maxi- 
mum. Moreover, there is an intimate relation between the water- 
holding capacity of the soil and the character of the rainfall upon 
crop production. Soils which have a fine texture and deep subsoil 
are able to retain nearly enough moisture from the early spring rains 
to mature crops growing through the summer, provided sufficient 
care is taken to develop a mulch so as to lessen the surface evaporation. 
Again, there is a close relation between the texture of the soil and 
the conditions affecting the quality of the crop, and also the use of 
tools both in planting and harvesting. All of these matters must 
be carefully considered. The following paragraphs are intended 
only as suggestions on some of the more important of these relations 
as they affect some of the more important crops. Crops may, for 
this purpose, be grouped into three classes, (1) tilled crops, (2) 
cereals, and (3) grasses and legumes. 
SOILS ADAPTED TO TILLED CROPS. 
While tilled crops, such as corn, potatoes, sugar beets, cabbage, etc., 
differ among themselves in many important respects, they are alike 
in that they permit tillage of the soil to kill weeds and for the develop- 
ment of a soil mulch to lessen evaporation of water. Most of them 
also grow through the long summer season, making a large growth, 
which requires abundant supplies of all the essential elements of 
plant food. 
Corn (Ref. Nos. 7, p. 576; 10, p. 243). — Corn may be grown in any 
section having a season of 100 days free from frost, but the larger 
yielding varieties require 120 days, and a maximum growth of this 
crop occurs only in sections having relatively warm nights. Higher 
altitudes are therefore not suitable, since they are characterized by 
cool night temperatures. The larger quantity of water used by 
heavy crops of corn can be supplied only by soils having large water- 
holding capacity or in sections where the summer rainfall is relatively 
large. Hence the best results with this crop are secured on com- 
