20 SOILS AND FERTILIZERS 



about 5 per cent, of clay. Soils of this nature when 

 supplied with about 3 per cent, of organic matter will 

 contain from 5 to 12 per cent, of water. The best 

 conditions for crop growth exist when the soil con- 

 tains from 5 to 7 per cent, of water. In a sandy soil 

 vegetation may reduce the water to a much lower 

 point than in a clay soil. On account of sandy soil 

 giving up its water so readily to growing crops nearly 

 all is available, while on heavy clay, crops show the 

 want of water when the soil contains from 7 to 8 per 

 cent., because the clay holds the water so tenaciously. 

 When potatoes are grown on soils where there is an 

 abnormal amount of water the crop is slow in matur- 

 ing. For early truck purposes in northern latitudes, 

 sandy soils are the most suitable because they warm 

 up more readily, and the absence of an abnormal 

 amount of water results in early maturity. Excellent 

 crops of potatoes are grown on many of the silt soils 

 of the west which have a materially different com- 

 position from the type given. A soil may have all 

 of the requisites physically for the production of good 

 potato and truck crops, and still be unproductive on 

 account of some peculiarity in chemical composition. 



13. General Truck and Fruit Soils. — For fruit grow- 

 ing and general truck purposes the soil should contain 

 more clay and less sand than for early truck farming. 

 Soils containing from 10 to 15 per cent, of clay and not 

 more than 40 per cent, of sand are best suited for 



