482 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



iiK'tliods of analysis, appear to be similar in every way, but which 

 flill'er niarlvcdly in their normal relations to crops and to crop adapta- 

 tion. When subjected to a careful mineralo^cal examination such 

 soils frequently show marked differences in mineral composition. 

 Important results along this line have been obtained in a work in- 

 volving the complete analyses of widely distributed and important 

 soil t3'pes. These were selected to represent soils of various origins 

 in respect to the materials from which they were formed and with 

 respect to the processes of formation. Special attention has also 

 been given to substances present in small quantity, such as are always 

 ignored in soil analyses, a consideration of Avhich may show differ- 

 ences in composition of soils hitherto assumed to be chemically alike. 

 The vegetable life which a soil supports is known to contain a large 

 number of elements that are ordinarily not considered essential to its 

 growth, and since it has been found that a small amount of arsenic 

 IS necessary for the proper functioning of certain animal tissues, it 

 seems probable that other elements besides the few which have here- 

 tofore been assumed to be the only essential ones, although present 

 in very small quantities in the soil or in the plant, may be equally 

 essential to plants or regulate in some essential way the functioning 

 of the soil. The presence or absence of these rarer elements in the 

 soil and their proper correlation to plant growth are, therefore, of 

 great importance. This work has no parallel in all previous analyses 

 of soils. 



Experiments have been carried on to determine the effect of soluble 

 salts on the physical properties of soils. It has been shown that the 

 effects of such salts in soils on the penetrability, volume change, 

 moisture, and vapor pressure of the soil solution are measurable 

 and larger than generally supposed. A bulletin has been prepared 

 indicating these results. In view of the lack of precise treatment of 

 the surface-action factors in modern literature on soils, agricultural 

 chemistry, bacteriology, biology, and cognate sciences, a thorough 

 study of the fundamental, mathematical treatises extant was under- 

 taken with the object of attempting a condensed correlation of these 

 factors. 



The work on flocculation and sedimentation has been continued. 

 A detailed study of tillage has been made with the object of pre- 

 paring for publication a bulletin on tillage methods. A very large 

 number of mechanical analyses carried out in this laboratory has 

 made it possible to get data for a bulletin discussing the distribution 

 of silt and clay particles between soils and subsoils. It has been 

 shown that in humid regions the subsoils are, in a large majority of 

 cases, heavier than the soils, and the reverse is true in the arid re- 

 gions. This is due to the fact that in the humid regions the run-off 

 carries the finer particles with it and the cut-off also carries them 

 down. 



Previous studies on the absorption of nutrient salts by soils and 

 soil materials have been continued. It has been found that phos- 

 phates which had been absorbed by soils and other finely divided 

 minerals, such as quartz, can be released from the absorbed state and 

 obtained in solution by the addition of various dissolved salts, such 

 as sodium nitrate, potassium nitrate, potassium chloride, potassium 

 carbonate, etc. The fact that phosphate held in a condition not easily 



