No. 7. DEPARTMENT OF AGRICULTURE. 395 



to blaze the path downward iuto the soil, the big strong root being \ 



a later development. Stiffness, or its opposite mellowness, depends 

 upon the anangeiiient oi" the soil grains and not upon their size; 

 upon the structure, not upon the texture of the soil. 



Contrary to common opinion the most clayey soils are not the 

 stitfest soils. Bricks are not made of clay alone, but of a rather 

 definite mixture of clay and particular grades of sand. Sometimes 

 we find subsoils that approach in varying degree a bricklike com- 

 position. If brought to the surface by the plow, exposed to the 

 air and left undisturbed for a short time the clods bake, and then 

 are reduced with much difficulty. This could be prevented at the 

 surface if the harrow had followed the plow closely, and if stable 

 manure or other organic matter had been mixed with the soil, but 

 a deep subsoil of this sort is not so easily improved nor is it in- 

 viting to a well-branched fibrous root system. The root systems 

 of some varieties of apples, furthermore, overcome a stiff structured 

 subsoil much more successfully than others. In one of the large 

 orchards of the southern Ozark country Ben Davis trees failed in 

 certain spots. They Kvere very unthrifty and not infrequently 

 died. Yet elsewhere in the same row, with identical slope, exposure 

 and treatment the trees wxre in excellent condition, and bore heav- 

 ily. The owner believed, too, that there could have been no varia- 

 tion in the stock. An examination of the subsoil showed it to be 

 exceedingly stiff wherever the trees were effected. Following this 

 cue throughout the orchard it was found that another variety 

 (Mammoth Black Twig) was not effected at all by the stiff sub- 

 soil as the roots forced their way down through it, and the trees 

 showed excellent growth. Not satisfied that the chemical condi- 

 tion of the soil in this case might not have some influence upon 

 the unthrifty trees I had made chemical analyses of these soils, 

 but the results showed that there were no chemical differences worth 

 noting. In this particular case it was apparent that the Ben Davis 

 A\ould not thrive on so stiff a subsoil, whereas the Mammoth Black 

 Twig could successfully overcome it. 



I do not need to call your attention to the self-evident fact that 

 the condition of this subsoil was not amenable to practicable im- 

 provement by the addition of humus, notwithstanding the fact that 

 by this means surface soils may to some extent be changed. In a 

 less pronounced case the growth of deep-rooted crops such as the 

 legumes would have greatly improved the physical condition of the 

 upper subsoil, but once the orchard is planted, or at least after it 

 has reached bearing age, the practical orchardist will hardly try 

 to leave cover crops under his trees so many months of the growing 

 season that their root systems will be sufficiently developed to add 

 humus to the lower subsoil. Yet the roots of a well-developed apple 

 tree reach far into the subsoil. 



The roots of plants and trees do not get their moisture from free 

 ground water, i. e.., water that may flow out in surface streams 

 and underdrains, but from the thin films of moisture that surround 

 every soil particle. This moisture is called capillary water. A 

 tree can get no plant food from the soil except as it is obtained in 

 dissolved form, not in free ground water but in the soil film or 

 capillary moisture. Hence the importance of the texture and struc- 



