September 21, 1917] 



SCIENCE 



289 



course, iu preparation of soils for irrigation 

 and may result frequently in the removal of 

 several inches to two, three or even more feet 

 of surface soil iu order that a level field may 

 be produced. This is particularly striking in 

 the ease of the well-known and, on genetic 

 grounds, highly interesting " hog wallow " 

 lands which comprise very large areas of the 

 Sacramento and San Joaquin Valleys. On 

 the citrus lands either barley or alfalfa may 

 be grown for a year or more in the preparation 

 of the soil for the citrus trees. Wlierever 

 barley is sown, it is always possible to distin- 

 guish between the spots in the field from 

 which the surface soil has been removed and 

 those which still consist of surface soil. On 

 the latter the barley looks as nearly normal as 

 the given soil type will permit it, whereas on 

 the former the barley growth, if it is at all vis- 

 ible, is stunted and yellow and frequently does 

 not live though the growing season. Only in 

 places where considerable surface soil has in 

 the process of grading become admixed with 

 the subsoil, have I ever noted an approach to 

 good barley growth. 



In the ease of alfalfa, however, I can only 

 recall one or two instances of failure to grow 

 as well on the raw subsoil as on the surface 

 soil. The difference between the behavior of 

 barley and alfalfa on the subsoil in question 

 is probably to be ascribed to the paucity in 

 available nitrogen which is known to char- 

 acterize subsoils. Under such conditions, bar- 

 ley can, at best, only make very poor growth, 

 whereas the alfalfa, if inoculated, is independ- 

 ent of the available nitrogen supply in the 

 soil. It should be added that with the ad- 

 mixture to some extent of surface soil with 

 the subsoil in the process of grading a large 

 enough number of B. radicicola is introduced 

 all through the graded land to insure to alfalfa 

 the necessary nitrogen for its growth, an ad- 

 vantage which that legume in common with 

 others does not share with non-legumes. The 

 case noted in Berkeley by Hilgard regarding 

 which the latter is quoted by Alway, McDole 

 and Eost, is undoubtedly that of an observa- 

 tion on the campus of the University of Cali- 

 fornia, on the surface of which there has been 



so much filling and cutting for a number of 

 years as to render questionable in any instance 

 the real origin of the soil or subsoil observed. 

 In my knowledge of the campus, I have known 

 the excavation of subsoil material which had 

 not long before been surface soil to result in 

 bringing it back to its original condition again. 

 We should not expect such material to be as 

 inert and as unresponsive in growing non- 

 legumes as real subsoil material. Arguing, 

 however, from direct observation, I should like 

 to add that I have frequently observed on the 

 same campus, in places in which deep excava- 

 tions were accomplished, that very little 

 vegetation appeared for a year or more after 

 the true subsoil material had been opened to 

 air, light and the sun's warmth, as well as to 

 the effects of inoculation by dust from surface 

 soils. Such vegetation as did establish itself 

 consisted almost invariably of bur clover. 

 Medicago denticulata. When other plants 

 were present, they were usually found to be 

 alfilaria, Erodium cicutaritim, a plant which is 

 most commonly associated with bur clover on 

 California soils and which probably profits by 

 the nitrogen fixed by the clover. The bur 

 clover plants found on such sterile subsoil ma- 

 terial as is above described have always been 

 found to be abundantly supplied with nodules. 

 The writer's observations lead him to believe, 

 therefore, that subsoils of arid regions are 

 nearly if not quite as raw as those of humid 

 regions and that despite the great differences 

 between the two in many respects, the first 

 will not support plant grovrth to a much 

 greater extent than the latter. The close re- 

 semblance which obtains between our subsoils 

 and our surface soils, and which does not char- 

 acterize the soils and subsoils of humid re- 

 gions, appears, therefore, to be no index to the 

 productivity of our subsoils. I should judge, 

 in fact, from the statements of Alway, McDole 

 and Eost, that the California subsoils are not 

 superior to the N"ebraska subsoils in any re- 

 spect from the point of view here under con- 

 sideration. As above pointed out, it seems 

 fairly certain that the chief cause of the raw- 

 ness of subsoils is the lack of available nitro- 

 gen in them for the support of the non-legume. 



