EEPORT OF THE SECRETARY. 73 



SOIL PHYSICS. 



The physical properties of soils have long been recognized as ex- 

 ceedingly important in the distribution of crops and in the develop- 

 ment of agriculture. 



The relative amount of sand, silt, and clay and the way these are 

 combined or held together has an important influence on the drain- 

 age and aeration and on the mechanical work of cultivation, and 

 with the organic content of soils has a very important influence 

 on the retentive power of the soil for moisture and the supply of 

 moisture available for crops. The extent to which these physical 

 properties can be influenced by cultivation, fertilization, and by crops 

 themselves is being investigated as a basis for improved and efficient 

 methods of maintaining the soil in suitable physical condition for 

 those proper functions that are adapted to the needs of our staple 

 or special crops. 



FERTILIZER INVESTIGATIONS. 



The investigations along this line have shown that the United 

 States contains ample raw materials for the production of all the 

 standard fertilizing materials that it now demands. 



The groves of giant kelp along the Pacific coast of Mexico, the 

 United States, and xUaska have been found to contain a vast supply 

 of potash salts which can be recovered for agricultural use; and if 

 these kelps are properly protected and the plants are allowed to grow 

 and function normally, the segregation of potash salts from the sea 

 water continues and, by harvesting from time to time, a continual 

 supply of potash can be maintained. 



The mechanical difficulties in the cutting and harvesting of the 

 material are now being taken up by commercial firms in a way that 

 makes it seem probable that adequate methods may be devised to 

 utilize this source for the production of sufficient potash for the coun- 

 try's needs. 



In the meantime, an unremitting search has been maintained for 

 possible surface deposits of potash salts in some of the desert basins. 

 Theoretically, it seems probable that areas may be discovered where 

 segregation of these salts has occurred, and one such deposit, rich in 

 potash, is now actually being exploited commercially. This is espe- 

 cially important since the examinations that have been made of our 

 salt brines seem to show that there is little prospect of success along 

 this line. 



Tlie enormous deposits of phosphate rock in this country have a 

 tendency to induce waste and undue exploitation of high-grade rock 

 only. From investigations now well advanced, however, it appears 



