64 FUNDAMENTALS OF FRUIT PRODUCTION 



The Influence of Soil "Alkali.'' — It should not be inferred from the 

 emphasis that has been placed upon moisture and aeration in determining 

 root distribution that other factors are of little significance. Other 

 factors are often controlling. 



For instance in reporting upon an investigation of the effects of alkali on 

 citrus trees Kelley and Thomas^" state: "It is especially interesting that the 

 roots of the lemon trees have not penetrated deeply in this soil, more than 95 

 per cent, of them being within 18 inches of the surface. There is probably 

 some connection between this fact and the higher concentration of alkali salts 

 found in the third and fourth feet." 



Applications to Orchard Practice. — The whole subject of the distribu- 

 tion of the root system of orchard plants may be summarized in this way : 

 though different species of plants and different varieties of the same 

 species have characteristic habits of root growth, the extent and the 

 distribution of their root systems are profoundly influenced by environ- 

 ment. Root development, both as to amount and direction, may be 

 regarded as a response of the plant to this environment. The functioning 

 of that part of the plant above ground is conditioned to a very important 

 degree by the functioning of the part of the plant below ground, and 

 therefore by the distribution of the roots in the soil. Root distribution 

 is under control to the extent that soil conditions — texture, moisture, 

 aeration and nutrient supply — are under control and to a certain extent 

 by the pruning that is afforded the top, a matter discussed in detail later. 

 If the soil is one in which these conditions are not favorable for a suitable 

 root distribution or in which they cannot be made favorable, it should 

 not be devoted to fruit culture, because fruit culture cannot be successful 

 on it. As soon as the orchard is planted, or before if possible, and as 

 long as the orchard remains, it is well to study from year to year the way 

 in which various soil treatments influence those factors determining root 

 distribution and then employ those practices that lead indirectly toward 

 ideal root systems. Orchards do not die out or become unprofitable only 

 because of fungi, bacteria, summer drought or winter cold. These are 

 always possible contributing factors and often determining factors, but 

 in many cases the fundamental cause of distress is a root system inade- 

 quate for requirements of the tree in an emergency — inadequate perhaps 

 because too shallow, or in too severe competition with the roots of other 

 plants or because it is not exploiting enough soil. Sometimes, though 

 the contributing causes to the death or failure of the trees may be un- 

 avoidable, the fundamental factor may be completely under control. 



Summary. — In terms of response to gravity and the evaporating 

 power of the air, soil moisture may be classified as gravitational or free, 

 capillary and hygroscopic. Only the capillary moisture is available to the 

 plant in any considerable amount. The capillary supply is derived from 



