896 



or farm pasture the difference between the proportion of nitroj^en in 

 the surface soil and in the subsoil is far greater than in the case of ara- 

 ble land, and the line dividing the surface soil and subsoil is generally 

 sharply drawn." In the case of the growth of legumes this increase is 

 very striking. "The facts i)oint to a considerable and long-continued 

 gain of nitrogen in the surface soil when arable land is laid down under 

 favorable conditions in permanent pasture, and to a gain of nitrogen 

 in the soil, or to its utilization by crops from sources beyond the surface 

 soil when leguminous i^lants are cultivated either alone or as members 

 of a rotation." Whether this increase comes to an appreciable extent 

 from the subsoil, numerous determinations of nitrogen in the subsoil 

 have not definitely decided. From observations at Kothamsted. Lin<'oln 

 (Xew Zealand), and in Barbadoes it was found that 3.37, 1.74, and 3.77 

 pounds of nitrogen peracre, respectively, was brought down in rain, snow, 

 etc., annually. "It is evident that if the ammonia and nitric acid of the 

 air are to be of any considerable agricultural importance they must be 

 taken up directly by crop or soil t-o an extent far beyond that which 

 takes place through the medium of rain. The amount of anunonia and 

 nitric acid in the air is certainly extremely small, but th«' air that is in 

 contact with crop and soil is being constantly renewed. It is thereft)re 

 by no means im])ossible that the quantities absorbed may become con- 

 siderable." The direct absori)tion of ammonia, nitrites, an«l nitrates 

 from the air by the soil and crop, and the fixation of free nitrogen are 

 discussed at some length. " For the present we can not, I think, aflirm 

 that soils are enriched by the free nitrogen of the air except through 

 the meilium of a leguminous crop." 



There is a limit, however, to this accunuUation ol' nitrogen both with 

 permanent pastures, with leguminous crops, and with arable land receiv- 

 ing every year a liberal dressing of hjnnyard manure. Tabulat<Hl data 

 showing the decrease of nitrogen in Kotluuiisted soils under diller- 

 ent conditions of culture are given, and the causes of their losses are 

 discussed. 



'riio addition of organic matter t<» a soil cither as crop or weed residue or as farm- 

 yard niannre at onee makes that soil a snitalde home for the animal life, the fungi 

 and the bacteria, whose funetion it is to reduce organic matter to the condition of 

 inorganic matter. An increase of organic plant residue or manure thus creates some 

 of the conditions favorable to its own di'struction. The rate of oxidation in the soil 

 is now no longer what it wa.s; the oxidizing agents have increased with the material 

 to be oxidizcil. If, therefore, a soil is laid down in pasture or receives an annual 

 dressing of farmyard maiinre, the nitrogen in that soil will only incre.ase so long as 

 the annual increment of organic matter exceeds the annual decrement of oxidation. 

 If this increment is a limited quantity it will be mat before long with an army of 

 destroyers competent to effect its destruction. The richest soils are thus mr>st liable 

 to waste and demand the greatest exercise of the farmer's skill to preserve their <on- 

 dition. 



Wiion the conditions of tlie soil are changed, as when the pasture is plowed ni> or 

 the arable land is left without manure, there is at tirst a rajjid loss of soil nitrogen, 

 but the rate of loss soon diminishes. Tiie army of oxiilizing (»rganisms has been 

 reduced bv starvation. The organir matter niost easily attacked has disappeared. A 



