40 BULLETIN 140, IX. S. DEPARTMENT OF AGRICULTURE. 



matter would be required in such excessive amounts as to upset 

 the equilibrium of the fruiting and vegetative habits of the tree; 

 that is, the sandy soil would actually become so "mucky" as to 

 give an excessive vegetative growth at the expense of fruit yield, 

 and an important percentage of the fruit obtained would be de- 

 ficient in color. Humus is, nevertheless, the most important factor 

 or agent, as the case may be, in modifying the physical condi- 

 tion of the soil mass so far as the mineral constituents are con- 

 cerned. This it does by partly filling the spaces between the grains 

 of sand, i. e., the coarse particles," and by holding apart the finer 

 particles of clay. In these ways both sand and clay are made more 

 loamy and favorable for plant growth. By increasing the num- 

 ber of particles in a given volume of soil, by helping to group the 

 soil particles into clusters, thus increasing granularity, and also by 

 actual absorption of moisture, humus increases the moisture-holding 

 capacity of the soil and likewise the availability of the mineral 

 fertilizing constituents. 



To change, furthermore, by the addition of humus, the physical 

 condition of a sandy soil to a depth reached by tree roots sufficiently 

 to make its supply of available moisture the same as that of a 

 heavier soil, such as a loam or a clay loam, is unquestionably an 

 expensive process, even were it desirable ; and orchards are grown for 

 profit. Hence this phase of the whole problem is an economic one. 

 It is good business to select soils naturally adapted to the different 

 varieties, rather than to use soils that must be modified to make them 

 suitable. 



Soils so deficient in humus as to be leachy in case of sands, or 

 stiff, intractable, and cloddy in the case of clays, clay loams, and 

 loams should have their humus content increased until these un- 

 favorable conditions for crop growth of any kind be overcome so far 

 as possible. But there are marked limitations even to this funda- 

 mental kind of soil amendment, as it is not possible by the addition 

 of plenty of humus so to change the physical and structural charac- 

 teristics of a given soil that these inherent characters will become 

 negligible so far as its adaptation to crops, or to different varieties 

 of the same crop, is concerned. The agricultural practice of the 

 eastern United States furnishes many examples of the special adap- 

 tation of particular soils to crop varieties. 



In the Connecticut Valley of Massachusetts and Connecticut the 

 physical character of the soil not only determines what specific crops 

 shall be grown on the different types, but the adaptability of those 

 soil types to such special crops has in turn been the principal basis 

 of land valuation there for the last half century. The soils are all' 

 alluvial, and the variation in elevation is in no case more than a 

 few feet. One of the sandy loams is the best type for the wrapper 



