82 ELEMENTS OF AGRICULTURE 



King took the temperature of a well-drained, sandy loam 

 and of a black marsh soil on five successive days, and 

 found the sandy soil to average 7.5 Fahr. warmer, a 

 difference sufficient to have a very decided effect on crops. 

 It is easy to see why gardeners desire a sandy soil for 

 early truck crops. Few crops begin growth until the soil 

 has a temperature of 45 to 50 Fahr. The best growth 

 does not usually take place until the temperature is about 

 70 Fahr. Different crops differ much in the heat required. 

 Some, like grasses, oats, onions, peas, will grow before 

 the soil is warm enough for corn, beans, cucumbers, etc. 



82. Size of Soil Particles and Crop Adaptation. The 

 size of soil particles affects all the soil activities, and con- 

 sequently must affect the crops that grow on the soils. 

 Timothy will thrive on a heavy, clay soil on which 

 apples, corn, and potatoes will give very poor returns. 

 The sandy soils that are best for market-garden crops 

 will raise very little timothy or wheat. Whitney states 

 that a gram of soil contains two to twenty billion soil 

 particles. He gives the following as the number of soil 

 particles per gram of soils adapted to different crops: 



Early truck 1,955,000,000 



Truck and small fruit 3,955,000,000 



Tobacco 6,786,000,000 



Wheat 10,228,000,000 



Grass and wheat 14,735,000,000 



No person can comprehend such figures as these, but 

 the comparison is the valuable point. The table shows 

 how much coarser the truck soils are than the wheat 

 soils. (See, also, page 78.) 



83. Relation of Labor and Soil. Even if the clay soils 

 would produce good truck crops, they would not be de- 



