ORCHARD SOILS 125 



most fruit-trees will flourish over a rather wide range of 

 soil types but some are better than others and some types 

 are to be avoided entirely. The classification of soils accord- 

 ing to the usual standard should, therefore, be considered 

 first. 



112. Soil defined. — Soil has been described as "the 

 broken and weathered fragments of rock that cover in a 

 thin layer the solid part of the earth and that furnish the 

 foothold and, in part, the sustenance for plant life." ^ An 

 understanding of the soil has involved a many-sided and 

 complex investigation, for soils vaiy in an almost infinite 

 number of ways and the adaptation of various kinds of 

 plants to a given soil is far from constant. These conditions 

 involve on the student of pomology a necessity for study 

 of soil conditions as a basis for orchard production. 



113. Soil classification. — As regards origin, soils are 

 classed as either "sedentary " or "transported," depending 

 on their geological histoiy. Soils are composed of minute 

 particles of the various minerals of which the rocks of the 

 earth are made up and the fineness with which they are 

 ground, together with the proportionate mixture of these 

 particles, gives a basis for classification. The method of 

 arriving at this information is called a mechanical analysis. 



Four general groups of soil particles are recognized in 

 agriculture as a basis of classification: sand, silt, clay, and 

 humus. The size of the particles composing each of these 

 series has been standardized by the United States Bureau 

 of Soils as follows: 



Coarse sand 1/25 to 1/50 of an inch in diameter. 



Medium sand 1/50 to l/lOO " " " " 



Fine sand l/lOO to 1/250 " " " " 



Very fine sand 1/250 to 1/500 " " " " 



1 Lyon, Fippin, Buckman. Soils, Their Properties and Manage- 

 ment. New York, 1915. Rural Text-Book Series. 



