1917] SOILS FERTILIZERS. 425 



time. This irregularity in the escape of the soil gases from cropped paddy 

 soils is a purely physical phenomenon, and is caused by the roots of the crop 

 forming, in conjunction with fine soil, a surface layer which resists the pas- 

 sage of the gases. The gas is thus trapped and retained in the soil until the 

 accumulation is sufficient to cause a passage to be forced, or until the decay 

 of some of the roots opens out such a passage." 



With reference to the change in the composition of the soil gases under the 

 action of a paddy crop, it is shown that "the physical retention of the soil 

 gases through the action of the roots of the crop, taken in conjunction with 

 the oxidizing action of the film, offers a simple and complete explanation of 

 the change in composition of the soil gases under the action of the crop." 



With reference to the relations of green manures to the soil and crop, the 

 conclusion is drawn " that the nitrogen of these manures has little actual 

 manurial value, that the crop is mainly dependent upon soil nitrogen for its 

 support, and that green manures owe their efficiency mainly to their indirect 

 action on the soil and by increasing root aeration." It is tentatively concluded 

 that the practice of bringing green manure into paddy soils from external 

 sources is preferable to growing a green crop on the soil to be puddled in, 

 owing to the loss of nitrogen incident to the latter method. 



Maintaining the nitrogen supply of the soil, A. W. Blaib {Neto Jersey 

 Stas. Bui. 305 {1911), pp. 5-16, figs. 8). — A general discussion of the soil nitro- 

 gen supply and its maintenance is followed by the results of an eight-year ex- 

 periment in which wheat and rye were grown continuously on one-twentieth- 

 acre plats of sandy loam soil with and without a leguminous green manure 

 crop of cowpeas and soy beans grown between the time of harvesting the 

 grain crop and the fall seeding of the following crop. While the yields of wheat 

 and rye were small on all plats, those on plats receiving green manure treat- 

 ment were from 50 to 100 per cent greater than those without green manure 

 treatment. 



The average yields for the legume plats and also those without legumes for 

 the last four years were smaller than the corresponding averages for the 

 entire eight years. This is taken as an indication that the nitrogen supply of 

 the soil is not being maintained even where the leguminous crop is grown. 

 The average gain in nitrogen for the legume plats for the last four years, as 

 indicated by the amount recovered in the crop, amounted to about 15 lbs. 

 annually. 



It is suggested that farmers endeavor to maintain the nitrogen supply of 

 their soils by growing leguminous crops either as a part of the regular rotation 

 or as green manure crops between the main crops of the rotation as often as 

 possible, and that for the most crops they further supplement the nitrogen 

 thus secured by the use of a few hundred pounds of a material supplying 

 nitrogen in a readily available form. 



Fertilizers and increased production, F. T. Shutt (Amer. Fert., 46 (1917), 

 No. 10, pp. 44, 46. 48, 52). — The author reviews Canadian experience with 

 fertilizers, and concludes "that the exclusive use of fertilizers will neither 

 keep up the fertility of the soil nor yield profitable returns; that it is on soils 

 of medium rather than poor quality that a lucrative response from their em- 

 ployment is to be expected ; that they can profitably be used to supplement the 

 home source of fertility, farm manures ; that the largest returns are not neces- 

 sarily from the largest applications; and that it is on the money crop of the 

 rotation, such as potatoes, that their application is most profitable." 



Is the recovery of the nitrogen in sewage sludge practicable? W. R. 

 CoPELAND (Jour. Indus, and Engin. Chem., 9 (1917), No. 4> PP- S74-376). — Ex- 

 periments conducted at the sewage testing station at Milwaukee, Wis., are 



