1918] SOILS FERTILIZERS. 213 



" The ratio between the nitrogen content and the dry matter of the crops 

 varied little in the three soils — Cookeville, Crossville, and Gallatin — which aver- 

 aged 93.11 gm. of dry substance per gram of nitrogen. The crops from the 

 Jackson soil, however, gave a ratio of 120.01 gm. of dry substance per gram 

 of nitrogen. A low nitrogen content was found to characterize alike the grain 

 and the straw of the wheat, also the millet hay from the Jackson soil. 



" In every instance the cropped soils maintained a decidedly higher nitrogen 

 content than the uncropped. This difference was noticeable both in the surface 

 soil and in the first 6 in. of the subsoil, but the results from the 12- to 24-iu. 

 depth were inconclusive. The losses of nitrogen from the surface soils under 

 comparable conditions were as follows : Cropped, Cookeville 2.1, Crossville 1.2, 

 Gallatin 12.4, and Jackson 0.4 per cent; and uncropped, Cookeville 6.8, Cross- 

 ville 6.2, Gallatin 18.2, and Jackson 4.2 per cent. The average combined saving 

 in surface soil and subsoil nitrogen for the three most representative types — 

 Cookeville, Crossville, and Gallatin — was 8.4 mg. per gram of air-dry crop, or 

 9.3 mg. per gram of dry substance harvested. 



" In uncropped experiments surface soil treated with ground limestone showed 

 appreciable loss of nitrogen as compared with untreated. Under cropping, how- 

 ever, three of the four soils showed more nitrogen at the end of the 5-year 

 period in the limed cylinders than in the unlimed. This result is attributed to 

 the offsetting of the direct loss through liming by the conservation of nitrogen 

 brought about through increased crop production. The effect of applications of 

 acid phosphate and muriate of potash on the content of soil nitrogen was not 

 appreciable under cropping. No experiments were made under imcropped 

 conditions. 



'• Where no crops were grown, top-dressings of nitrate of soda resulted in a 

 small but evident loss of soil nitrogen. Under cropping the nitrated cylinders 

 showed a greater supply of both soil and subsoil nitrogen than the unnitrated, 

 the difference being slight for the soil but more pronounced for the subsoil. 

 This result, as in the case of the ground limestone, is attributed to the more 

 than balancing of the direct loss through nitrating by the conservation of nitro- 

 gen brought about through increased crop production. 



" Manure applied to the surface soil of uncropped cylinders did not increase 

 the nitrogen content of the subsoil. Under cropping the nitrogen content of the 

 subsoils from the manured cylinders averaged somewhat higher than that from 

 the nnmanured ; that is, manure applied to the surface soil conserved the supply 

 of nitrogen in the subsoil. 



" If the loss of nitrogen fi-om both the soil and subsoil be coi sidered, the loss 

 from the Cookeville, Crossville, and Gallatin soils was in each case greater than 

 can be accounted for in the crops removed. In the case of the Jackson soil, 

 however, this was not so, the subsoil showing a moderate loss but the surface 

 soil of the cropped cylinders a slight gain. 



" The Jackson soil, which gave in many respects decidedly different results 

 from any other, is noted as the only one to give evidence of the fixation of at- 

 mospheric nitrogen to a marked extent. To attribute this nitrogen accumula- 

 tion to other exterior sources was considered untenable. 



" The general conclusion is drawn that not only the cropping but also the 

 manurial treatments conserved both the soil and the subsoil nitrogen to a total 

 depth of about 1 ft., directly in proiX)rtion to the crop increase. This conserva- 

 tion does not, of course, prevent a loss of soil nitrogen through either chemical 

 or biological processes induced per se by an applied substance such as ground 

 limestone. In such a case the two opposing factors may or may not balance 

 each other. Since cover crops are often advocated because they catch soluble 

 nitrogen that would otherwise be lost by leaching, attention may be called to 



