358 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



SOURCES AND FUNCTIONS OF INGREDIENTS OF PLANT- 

 FOOD. 



The Sources of the Nitrogen of Vegetation. 



An address "On Some Points in Connection with Veireta- 

 tion," delivered at South Kensington by Dr. J. II. Gilbert, 

 has been reprinted in the American Journal of Science (vol. 

 xiii., pp. 20-32, 99-111, 181-195). This treats of the subject 

 of the nitrogen of vegetation in general, and of agricult- 

 ural production in particular, especially as viewed in the 

 light of the results of the well-known experiments at Koth- 

 am stead, England, in which Dr. Gilbert has, in connection 

 with Mr. J. B. Lawes, been engaged for some thirty-three 

 years or more. As a summarizing of those results, by them- 

 selves and in comparison with those of other experimenters, 

 it forms a most valuable contribution to our still extremely 

 incomplete knowledge of the ways of supply of nitrogen to 

 crops, and will form a convenient basis for our resume of 

 this topic. 



Sources of Nitrogen Removed from the Soil by Crops without 



Nitrogenous Manure. 



Crops grown on soils to which no nitrogen is applied in 

 manure remove considerable nitrogen. This nitrogen may 

 be accounted for by (1) the combined nitrogen coming down 

 in rain, snow, etc., which does not exceed eight or ten pounds 

 per acre yearly where observations have been made ; (2) the 

 condensation of ammonia of the air within the pores^of the 

 soil; and (3) previous accumulations within the soil. 



Whether the excess of nitrogen taken by the plant over 

 and above what is brought to the soil by atmospheric pre- 

 cipitation, condensation of ammonia by the soil, etc., comes 

 entirely from the previous stores in the soil; or whether, 

 and in how far, it is otherwise supplied i. e., through as- 

 similation of atmospheric nitrogen by plants and soils is a 

 much-vexed question, on which the summarizing of the re- 

 sults of Messrs. Lawes and Gilbert's experiments throws a 

 good deal of light. Certain it is that as crops are removed 

 year after year their amounts decrease, and that at the same 

 time the store of nitrogen in the soil diminishes wherever 

 accurate tests have been made. In the Rothamstead ex- 



