2. UNSUITABLE SOIL STRUCTURE. 



a. Light Soils. 

 Disadvantages of Sandy Soils. 



The way in which the individual soil particles are related to one another, 

 is termed the structural condition. If the constituents of the soil are simply 

 laid one above the other in separate grains Ave speak of a separate granular 

 structure. In soils under cultivation, however, the individual soil particles 

 are found united into different kinds of aggregates, called a friable structure. 

 While, in the first case, each soil grain has a homogenous constitution, the 

 soil grains in the second case are porous and not homogenous, therefore 

 can be more easily transformed. The content in soluble salts, the activity 

 of the animal world in the soil and the action of plant roots and their se- 

 cretions, as well as the physical processes of working the soil, determine the 

 formation of a friable structure. The amount of space between the indi- 

 vidual grains will vary according to their size and arrangement. Ramann 

 calculates the porosity volume of equally large soil particles, according to 

 whether the particles are arranged regularly in rows on top of one another 

 or between one another, as fluctuating between 47.64 per cent, (greatest 

 porosity) and 25.95 P^r cent, of the whole volume (closest stratification) ^ 



While in the friable structure, because of the different individual par- 

 ticles, a continuous change in size and arrangement takes place, due to me- 

 chanical and chemical influences, in the separate granules, most distinct in 

 stony and gravelly soils, the physical relation is more regular and therefore 

 more significant. 



We have already spoken of the influence of actual sandy soils and the 

 changes which roots can experience when growing in cracks in rocks. The 

 injuries to vegetation, which are caused by too loose a structure of stony 

 soil at the disposal of the root, seem lessened when the blocks of stone are 

 weathered to rubble. Fine, earthy particles are produced, especially when 

 the stones are easily decomposed (many granites, Gneiss, Syenite, etc.) af- 

 fording the roots more abundant food and firmer support. Next to the great 

 possibility of being rapidly heated through, the factor acting most injuriously 

 is great dryness, which prevents a decomposition of organic substances lead- 

 ing to the formation of humus ; this, under certain circumstances, forms 

 moors. Forestry in mountains must take such conditions into account. Sandy 

 soils come under consideration for field cultures on the level. As soon as 

 these possess greater admixtures of clayey substances (loamy sand) or of 

 humus, they form most productive soils and therefore find in this discussion 

 no further consideration. Sandy soil is unfavorable for cultivation only 

 when the sand is truly quartz sand and is either pure or is present in a very 

 high per cent. (70 to 90 per cent.) 



Ramann, Boclenkuntlo, 2ncl. Ed., p. 222. Berlin, J. Springer, 1905. 



