KEPOKT OF THE SECRETAEY. Ill 



wells; and they supply the springs and seep-fed streams required for 

 the use of stock. These waters, often neglected, materially increase 

 the productivity and habitability of the Great Plains and of many 

 valleys in the mountain region, and more especially where they are 

 conserved for crop growth through dust mulching. 



LABORATORY INVESTIGATIONS. 



The progress of the laboratory investigations has emphasized that 

 a soil has so many properties, physical, chemical, and biological, each 

 of importance in the production of crops, that it is essentially an 

 individual, and that no two soils are or can be made just exactly 

 alike. EverA'thing in a soil is involved in continual changes, and 

 these changes are of as much importance to plant growth as are the 

 things themselves. Cultural methods never affect one only, but 

 always every factor involved in crop production. For instance, an 

 addition to the store of plant food in the soil sometimes produces 

 undesirable physical or biological conditions, with decrease in crop 

 results. The interrelations between the soil factors influencing crop 

 production and an intelligent control by cultural methods is per- 

 haps the most important problem wdth which scientists are now 

 engaged, and whose solution is a primary object of the Bureau's work. 

 Among the results of the past year's work and of more general inter- 

 est the following msij be cited: 



Relativel}^ small quantities of mineral fertilizers produce pro- 

 found physical changes in the soil water, affecting its movements. 

 The addition of such substances to a soil affects in definite ways that 

 content of water which is the optimum for plant growth, an impor- 

 tant factor, since the soil solution and its accessibility to the growing 

 plant are dominant factors in determining the kind and amount of 

 plant growth. All the physical properties dependent upon the rela- 

 tion of the soil to its water content affect plant growth and are affected 

 by any one of the general methods of soil control, nameh^, tillage, 

 crop rotation, or fertilizers. The relation of ph3'sical properties to 

 the moisture content of a soil is being studied vigorously. 



Soils are far more heterogeneous than the rocks; in fact, all kinds of 

 rock-forming minerals are found in nearly every soil and among the 

 soil particles of all sizes. Certain characteristics of particular min- 

 erals show the nature of the geological processes involved in the for- 

 mation of the soil which affect their adaptation to crops. All the 

 mineral-forming elements may be expected in practically every soil; 

 this has been shown for barium, as well as the usual plant foods. Fur- 

 thermore, even very old soils, long under cultivation, are essentially 

 the same in mineral characteristics as new and virgin soils. Chinese 

 soils, which are authoritatively reported to have been under clean cul- 

 tivation for upward of three thousand years, contain all the common 



