ORCHARD SOILS 127 



the various loam soils, depending on the kind and variety 

 of fruit grown. 



When the clay and silt particles predominate, only the 

 fine grades of sand are usually present. If the silt grade is 

 most abundant, the soil is a silt loam. If clay is greatest 

 in amount, the soil is a clay loam. And if the exceedingly 

 fine clay particles constitute more than 30 per cent of the 

 soil mass, the type is a clay, the other 70 per cent being 

 primarily of silt and very fine sand. A soil containing as 

 nuich as 50 per cent clay is very "heavy," while those con- 

 taining 60 to 70 per cent, as at Medford, Oregon, are ex- 

 ceedingly stiff and hard to work.-^ 



114. Soils and subsoils. — Most soils consist of a surface 

 layer which is more fertile and usually darker colored than 

 those l>ing beneath it. It may be veiy shallow or a foot 

 to many feet in thickness. This surface soil determines the 

 richness of the land, since the roots of most crops penetrate 

 but little below it. Its fertility is due to the larger amounts 

 of organic matter and the accumulation of the more readily 

 available plant-foods, together with the activity of the 

 beneficial soil flora. The subsoil, or that which Ues im- 

 mediately beneath the surface, is of great importance to 

 the fruit-grower and its character may vaiy from a sand to 

 an impervious clay known as hardpan. The tree roots 

 should have a wide range and penetrate the subsoil with 

 ease as well as be free from standing water. While the 

 subsoil must not be too well drained and devoid of plant- 

 food, yet an open gravelly loam is usually considered best. 

 If this does not obtain, it may be necessary to tile drain and 

 plow or break up the subsoil for best results. The time to 

 solve this problem or rather to avoid difficulty is when the 

 orchard land is selected. 



The necessity for good depth of subsoil cannot be empha- 

 1 Wilder, H. J. U. S. Dept. Agr. Bull. 140. 1915. 



