SOILS — FERTILIZERS. 217 



termine the action of the soil surface film on the soil gases and the nature of 

 the agents to which the changes produced could be ascribed are reported. 



It was shown in the previous report that the gases formed in swamp rice 

 soil apparently have an important connection with the aeration of the roots of 

 the crop. It was found in the later experiments that " the organized film in 

 contact with the surface of swamp rice soils utilizes the soil gases in such a 

 manner as to bring about an increased oxygen output from the film leading to 

 a correspondingly increased root aeration. The film contains bacteria which 

 possess (1) the power to oxidize methane and hydrogen, and (2) to assimilate 

 directly methane and carbon dioxid. These changes either directly or indii-ectly 

 result in the production of CO2 which is in turn assimilated by the green algse 

 with the evolution of oxygen. ... 



" The practice of green manuring, by increasing the output of the soil gases, 

 brings about an increased activity on the part of the film resulting in an in- 

 creased oxygen production and root aeration. An important indirect function, 

 then, of green manuring is to bring about a greater root aeration and so induce 

 greater root development and cropping power. 



" The oxygen concentration of the water entering the soil appears to be one 

 of the main factors which regulates the growth of the crop." 



Effect on soil moisture of chang'ss in the surface tension of the soil solu- 

 tion brought about by the addition of soluble salts, P. E. Karraker 

 {U. 8. Dept. Agr., Jour. Agr. Research, 4 {1915)^ No. 2, pp. 187-192, figs. 2). — 

 Experiments are described in this paper, the results of which indicate that 

 changes in the surface tension of the soil solution arising from the application 

 of fertilizer salts are of no importance in affecting the moisture condition of 

 the soil. 



The effect of different methods of preparing a seed bed for winter wheat 

 upon jrield, soil moisture, and nitrates, L. E. Call (Jour. Amer. Soc. Agron., 

 6 (1914), No. 6, pp. 2^^9-259, figs. 2). — Investigations, extending over five seasons, 

 on the influence of different methods of preparing the seed bed for winter wheat 

 upon conservation of moisture, liberation of plant food as Indicated by avail- 

 able nitrogen, and the growth of the crop as determined by the production of 

 grain and straw are reported. The soil used is a dark brown silt loam about 10 

 in. deep, the subsoil to a depth of at least 6 ft. being a i*eddish -brown silty clay 

 loam. 



The results obtained demonstrate the value of working ground plowed early, 

 and also show the importance of early plowing even though it is impossible to 

 work the ground as quickly as it should be worked after the plowing is done. 

 " Ground worked early, regardless of the method of working, has usually pro- 

 duced a comparatively high yield, while ground worked late, regardless of the 

 method, has usually resulted in a low yield. . . . 



" There is very little, if any, correlation between the amount of moisture 

 in the soil at seeding and the yield of wheat secured. . . . Tho>;e plats 

 which produced high yields used nearly if not quite aU of the available moisture 

 in the soil, while the low-yielding plats left in the soil from 1.5 to 5 per cent of 

 available moisture. Apparently, the low yield was not the result of a deficient 

 supply of moisture." 



The yield of wheat bore a close relation to the nitrates in the soil at seeding. 

 Fertilization with sodium nitrate did not increase the yield of wheat on the 

 field plowed in July, but on corn ground, where a seed bed was prepared for 

 wheat by double disking the ground after the corn crop was harvested, fertili- 

 zation with the same quantity of sodium nitrate increased the yield nearly 100 

 per cent. " It appears, therefore, that on late-plowed ground or on ground 



