44 BULLETIN 140, IT. S. DEPARTMENT OF AGRICULTURE. 
in the world. The rock oak and chestnut growth indicates a soil 
somewhat stronger than that of chestnut alone, as a better supply 
of moisture is maintained ; newly cleared, it is more productive, and 
even on old ground better results are secured from fertilization. The 
subsoil is finer textured, or more clayey, than the chestnut subsoils, 
but still is not so heavy as the white-oak soil. Yet on the latter some 
varieties of apples thrive. 
Carrying the matter of soil adaptation to the different varieties of 
oak a step farther, it is a matter of common observation that poor and 
thin soils often support only the dwarfish blackjack oak and the 
post oak. 
Shreve states in volume 3 of " The Plant Life of Maryland " that — 
While the general distribution of the loblolly pine is determined by historical 
and climatic factors, yet its relative abundance at different localities within 
its area is determined by the character of the soil. * * * It is most 
abundant on light sands and on the Elkton clay. While these soils may seem 
to be very dissimilar in their relation to the movement of soil water, yet the 
texture of the latter causes it to hold to its stores of water so tenaciously that 
plants growing in it often suffer drought when there is an abundance of water 
within very short distance but firmly held by the capillarity of the fine soil. 
This statement indicates that this particular variety of pine 
flourishes on soils that furnish relatively small amounts of moisture 
to vegetation. In comparison, it may be commonly observed that the 
white pine flourishes best on heavy sandy loams and on very light 
mellow loams, soils on which the minimum supply of capillary mois- 
ture available to plants does not descend as low as with the loblolly 
pine soils. 
Since the time when the forests of the eastern States were first 
cleared away for crops, the most common rotation has been corn, 
oats, wheat, and grass. Clover has very often been seeded with the 
grasses. Potatoes, buckwheat, and garden crops have also been of 
importance. All of these crops have shallow root systems except 
clover, and possibly corn which may be classed as medium in root 
penetration. Not enough of the deep-rooted clover has been grown 
on many farms to keep up the supply of subsoil humus, in conjunc- 
tion with the humus supply of the surface soil — plant roots, stubble, 
and stable manure, which do not get below plow depth to any appre- 
ciable extent. This system of cropping with decreasing yields 
makes it apparent that the humus content of the subsoil on most 
farms has been for a long time at a minimum point. Were such a 
supply available to crops the average yield of corn would be much 
increased, and the greater amount of capillary subsoil moisture 
would in marked degree lessen drought injury to shallow rooted 
crops. 
