622 ClKC TLAK No. 7. 



especially sensitive to an acid condition, and a aTTuoTi solution has been 

 foimd very injurious to clover roots. When the importance of the 

 legume as a means of soil rejuvenation as well as a source of proteid 

 animal food is remembered, this factor becomes exceedingly critical, for 

 both legumes and live-stock are necessary to a permanent, self-contained 

 system of soil productiveness. The distribution of certain species of 

 plants is governed largely by the content of lime in the soil. The chest- 

 nut, for example, avoids a soil rich in lime ; so does the arbutus and the 

 rhododendron ; on the other hand, the natural success of alfalfa is closely 

 associated with an abundance of lime in the soil. 



(c.) The micro-organisms, particularly certain bacteria, are now 

 recognized as an important constituent of the normal soil. Especially 

 important are those forms concerned with the element nitrogen. The 

 ultimate source of nitrogen is the atmosphere, but in its free form it is 

 not available to the higher plants. In commercial fertilizers it costs 

 1 5. to 25 cents per pound. Its transformation from the free atmospheric 

 condition to forms available to crops is chiefly a function of certain 

 species of soil bacteria which thrive in a neutral or slightly alkaline 

 solution and are especially promoted by lime carbonate. They are of 

 three classes : one lives free in the soil and can depend on atmospheric 

 nitrogen; the second lives in nodules on the roots of clover, alfalfa, 

 beans, etc., and gives these crops their special manurial value; the third 

 group effects the formation of nitrates from the various forms of organic 

 matter which come ijito the soil. In other words, however rich the soil 

 may be in humus, which is the storehouse of soil nitrogen, the nitrogen 

 becomes available only through the processes of ammonification and 

 nitrification which take place best in a soil rich in soluble lime carbonate. 

 We thus see the direct relation between lime and the nitrogen question. 

 This is made more clear by the table of results obtained by Dr. Lyon on 

 the Cornell University farm with limed and unlimed Dunkirk clay loam 

 soil. The plots were planted to alfalfa. The difference between the 

 plots was first recognized by the much darker green color of the limed 

 section. Analyses were made of the alfalfa plants, the weed plants, and 

 the soil extract, from each plot, with these results : 



