PHYSICAL PROPERTIES OF SOILS IO5 



tion and exposure to the atmosphere that the soil received in fill- 

 ing the boxes, and also because the boxes were probably under- 

 drained. 



Other experiments made at the Kansas, New York, North 

 Dakota, Iowa, and Minnesota Stations, show that the greatest 

 proportion of the roots of plants develop in the surface foot of 

 the soil, but appreciable quantities of roots may penetrate much 

 deeper. These experiments were qualitative. Further quantita- 

 tive experiments are needed, as it is very important for scientific 

 soil studies, to know the quantitative distribution of the roots of 

 various plants in various soil types and in various sections of the 

 country. 



The depth to which roots of some plants may penetrate is 

 shown in the following table, taken from experiments made in 

 Kansas and North Dakota. The subsoil was in some cases a 

 stiff, clay soil. 



DEPTH OF PENETRATION OF ROOTS OF PLANTS. 

 Alfalfa 6 to 10 feet. Clover 2^ feet. 



Corn 2>^ to 6 



Grasses 2^ to 3 



Millet 2 to 3 



Oats 4 



Rye 3 



Sugar beet 3^ to 4 



Cowpeas 3 



Kaffir corn... 3^ to 5 



Milo maize 3^ to 4 



Potatoes 3 



Sorghum 3 % to 4 



Wheat 4 



Effect of Depth of Soil on Plants. The depth to which the 

 roots of plants penetrate depends both upon the character of the 

 soil and the habit of the plant. The roots of plants can penetrate 

 easily in a sandy subsoil, but may have difficulty in entering heavy 

 clay. 



In general, the deeper the roots can penetrate the soil, the 

 better the growth of the crop. Roots which occupy 12 inches of 

 soil will have twice as much soil to draw upon for moisture and 

 for plant food, as those which occupy only 6 inches. They will 

 also have twice as much space in which to expand their roots. 



The experiments of Lemmerman 1 may be cited as showing the 

 effect of root space upon plant growth. He grew mustard in pots 

 of the same surface area, but of different depths. One vessel of 

 1 Jahresber. f. Agr. Chem., 1903, p. 42. 

 8 



