74 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



that at no distant time the utilization of low-grade rock may be 

 looked for on a commercial scale. 



The investigations into the possible sources of suppry of nitrogen 

 have been sufficient to indicate that if future developments make it 

 necessary the United States can supply its requirements of this ex- 

 pensive material. 



SOIL- WATER INVESTIGATIONS. 



In my first report to the President, made nearly 16 years ago, I 

 called attention to the fact that rainfall was of little benefit to crops 

 until it had entered the soil, and from there on the benefit was pro- 

 portional to the ability of the soil to retard and regulate its flow 

 toward the sea. The whole question, therefore, of the utilization of 

 the rainfall in agriculture depends first upon the amount of water 

 which enters the soil and next upon its movement within the soil. 



During the last year a very exhaustive study has been made of the 

 depth of free-flowing ground water under the surface of the soil in 

 all parts of the United States, and somewhat as to the movement of 

 this ground water, which has been found in some instances to extend 

 over hundreds of miles between the source of supply and the dis- 

 charge into the sea. 



Having determined the fundamental position of the free water in 

 the soil, it remains to study more intensively than has been possible 

 heretofore the distribution of the water between the ground water 

 and the surface of the land, as well as the effect of cultural methods 

 in properly regulating the supply available for crops. It is believed 

 that methods are now available by which this important but very 

 intricate problem can be worked out. 



SOIL-FERTILITY INVESTIGATIONS. 



Thirty-five to. forty definite organic chemical compounds have been 

 separated from the humus portion of the soil, and a number of these 

 were discovered in the last year. 



Sufficient is known of the subject now to indicate that the soil has 

 certain functional activities and that organic matter is digested in 

 the soil, through the agencies of bacteria, enzyms, fungi, insects, and 

 more purely chemical agencies in a manner similar to the processes of 

 digestion in living organisms. The presence of certain organic bodies 

 in the soil indicates that the functional activities of the soil are pro- 

 ceeding in such a way as to make the conditions beneficial or harm- 

 ful for any particular plant or crop. 



It has been found, furthermore, that through methods of cultiva- 

 tion, of fertilization, and of crop rotation the functional activities 

 of the soil may be controlled within limits so as to put the soil in 



