424 EXPEEIMENT STATION BECOKD. 



weeks as compared with the blank soils. In the following 2 weeks the accu- 

 mulation of nitrate nitrogen was depressed, showing a deficit of nearly 7 mg. as 

 compared with the corresponding blank soils. After that there was an 

 enhanced accumulation until at the end of 8 weeks the addition of the 0.2 gm. 

 of NaNOa had resulted in a greater accumulation of nitrate nitrogen equivalent, 

 on the average, to 12.915 gm." 



The author concludes that "periodicity in the accumulation of nitrates in the 

 soil may be due to both the temporary prominence of species especially capable 

 of transforming large amounts of nitrate into protein nitrogen as well as to 

 the mere rapid increase of various decay organisms and their intense utilization 

 of nitrates for the building of their bodies." 



Investigations on methods of determining the lime requirements of soils, 

 H. R. Christensen and O. H. Larsen {Ccnthl. Bakt. [etc.], 2. Aht., 2.9 (1911), 

 A'O. 12-l.'t, pp. 3.'t7-380). — These investigations have already been noted from 

 another source (E. S. R., 24, p. 527). 



The color of soils, W. O. Robinson and W, J. McCaughey ( U. 8. Dept. Agr., 

 Bur. Soils Bui. 79, pp. 29, figs. 2). — This bulletin reports the results of studies 

 on causes of colors and their relation to productiveness in soils, with particular 

 reference to red and yellow soils, and on physical and chemical properties of 

 Iron compounds and their solutions. 



" Generally speaking, the color of a soil is dependent upon the content of 

 organic matter and ferric oxid, the latter being more or less hydrated. The 

 thicker the film of organic matter and ferric oxid coating the soil grains, the 

 darker the soil. ... It is probable that the thickness of film surrounding the 

 soil particles is the predominant factor determining color." 



Decaying organic matter was found effective in causing a solution of iron in 

 the soil water. The dissolved iron is transported only to a limited extent, owing 

 to the readiness with which it is oxidized to the slightly soluble ferric oxid. 

 It is usually reprecipilated within a short distance, frequently filling crevices 

 from which its parent mineral has been removed. 



The authors are of the opinion that suiEcient difference does not exist between 

 soil temperature of the northern and southern States to cause a change from a 

 hydrated to a dehydrated iron oxid. Mineralogical examinations showed a 

 larger proportion of secondary quartz grains in red than in yellow soils, the 

 secondary grains being characterized by included iron stains and by not possess- 

 ing the clear gaseous or liquid inclusions which characterize the primary quartz 

 particles. Basic rocks, or rocks rich in ferrous minerals, yield a red soil, and 

 acid rocks, which are relatively low in iron-bearing minerals, yield a yellow soil. 

 Red soils may also result from yellow soils by continued weathering agencies 

 with little erosion, and yellow soils from red soils where erosion agencies and 

 water transport have been active. 



The movement of soil material by the wind, with a bibliography of eolian 

 geology, E. E. Free and S. C. Stuntz (U. 8. Dept. Agr., Bur. Soils Bui. 68, pp. 

 272, pis. 5, figs. 2). — This bulletin brings together, correlates, and summarizes 

 the known data of eolian geology as bearing upon soil formation, translocation, 

 and control. It includes not only a comprehensive review of the literature of 

 the subject but also many of Mr. Free's own observations, made in many cases 

 to clear up obscure points or apparent discrepancies in the work of other inves- 

 tigators. An extended bibliography is given. 



The discussion emphasizes the fact that the wind plays an important part in 

 soil genesis, " and is not the least of the great dynamic agents which we now 

 know affect the soil. . . . Wind action, both in removal and transfer, must be 

 regarded as an important item in the newly emphasized dynamic explanations 

 of the soil and its fertility." 



