BUREAU OF SOILS. 613 



United States Geoloi^ical Survey, and private interests are rapidly 

 exploring the other promising areas. Nuineroiis locations of nitrate 

 have been examined, but none of present commercial importance has 

 been found. A v^ery compreliensive examination of American rock- 

 e.alt deposits and salt wells has been made, showing the universal 

 presence of potash salts, but it has also been determined that there 

 is little prospect of utilizing this source of potash under present 

 commercial conditions. The value of alunite itself and potash salts 

 from it has been shown. An examination of all methods yet sug- 

 gested for extracting potash from silicates has been and is yet in 

 progress, and the conditions under which such a process may have a 

 commercial importance demonstrated. No method has yet been 

 proven commercially practicable, but recent Avo)-k not yet completed 

 makes it seem probable that practically unlimited su})plies of pocash 

 from feldspar and similar minerals may soon be attainable. 



Examination of American phosphate fields has continued, and 

 every known field has now lieen studied on the ground as well as in 

 the laboratory. None of the fields hitherto worked, contrary to pop- 

 ular impression, is exhausted, though some of them are not now being 

 worked profitably. The present fields, together with the unworked 

 areas, are known to contain enough high-grade material to supply 

 three times the present needs of the country for more than a thou- 

 sand 5'ears. The utilization of low'-grade rock with the acid and basic 

 slags of American furnaces has been studied. I^ikewise valuable 

 investigations have been made of the manufacture of phosphate, sul- 

 phuric acid, fish scrap, city wastes, oven by-products, and other 

 methods of utilizing raw products for the production of fertilizers. 



SOIL PHYSICS. 



During the last year a study has been made of the mechanical 

 operations of tillage as they are alTected by the physical characteris- 

 tics of soils and especially by the moisture content and water-holding 

 capacity of soils. Investigations have been initiated on the mechan- 

 ical movement of soils and the interchanges between soil and sub- 

 soil under alternate wetting and drying of the soil. It has lieen 

 shown that the resultant of all the natural forces tends continually 

 to make a soil lighter and lighter in texture, unless corrected by cul- 

 tural methods. Mucli work has been done in improving methods for 

 the mechanical analysis of soils and in designing apparatus for the 

 extraction of potash from silicate rocks, instruments for studying 

 the radioactivity of soils, etc. 



SOIL-raRTILITY INVESTIGATIONS. 



The results obtained in the last year through laboratory investiga- 

 tions in soil fertility have been the most important in recent years. 

 The nature and properties of the c(uistituents of organic matter in the 

 soil as affecting the fertility and infertility of soils has been fully 

 established and .some illuminating facts in regard to soil fertility 

 ascertained. The nature of the organic matter which c()mj)os('s the 

 soil humus has received the same attention which has been accorded 

 it in these laboratories for some years past, and the number of defi- 



