112 



CASSELL'S POPULAR GARDENING. 



the aqueous deposits of rain, hail, snow, mist, fog, 

 and dew, part of which is the return from previously- 

 existing generations of plants or animals elsewhere, 

 and pai-t the product of new formation, does un- 

 doubtedly contribute materially to the annual yield 

 of plant-food; and, being a source comparatively 

 easily estimated, it has been the subject of a good 

 deal of experimental investigation. 



From the Rothamsted researches, which have been 

 published in the Journal of the Royal Agricultural 

 Society* we find that the annual rainfall at this 

 station varied during thirty-four years (1853 to 1886) 

 from 18-56 inches in 1864 to 36-13 inches in 1879, 

 the average being 28-64 inches. 



From 152 analyses of rain, snow, dew, and hoar- 

 frost, representing the daily collections from June 22, 

 1881, to January 5, 1882, we find an average of 

 0-248 of nitrogen as ammonia per million of water, 

 the extremes observed being 5-491 and 0-043. The 

 variations in analysis of the rain-water are dependent 

 on the richness of the atmosphere in ammonia and 

 on the quantity of tLe rainfall, the smaller deposits 

 always containing the larger proportion of plant- 

 food. A heavy rainfall descending in a short time 

 is found to be poorer in ammonia than the rains of 

 light showers distributed over a considerable period, 

 the former rains having come in contact -with a 

 relatively smaller volume of air than the latter. 



The influence of the quality of the rain on the 

 proportion of ammonia it contains will be plainly 

 seen from the author's arrangement of thirty-nine 

 monthly analyses of rain-water according to the 

 amount of rainfall in each month, as illustrated by 

 the folio-wing table : — 



Averagre 

 Baiufall 

 in Inches. 



Rainfalls helow 1 inch 



„ between 1 and 2 inches 

 „ between 2 and 3 inches 

 ,, above 3 inches . 



Nitrogen 

 as Ammo- 

 nia per 

 Million. 



0-621 

 1-530 

 2-473 

 4-727 



1-06 

 1-17 

 0-91 

 82 



The amount of nitrogen, or plant-food, annually 

 carried to the soil by rain varies considerably in 

 different years and in different localities. Mr. 

 "Warington says, in his " Chemistry of the Farm," 

 that the average of many experiments on the Conti- 

 nent gives 19-23 lbs. of nitrogen per acre; while the 

 following table by Lawes and Gilbert shows that at 

 Rothamsted, in Hertfordshire, on an average of 

 three years, with a, mean rainfall of 28J inches, 

 there was scarcely 7 lbs. per acre carried to the soil 

 by rain and the minor deposits. 



• Vol. ivii. (1881), and Vol. xix., ss. Part II. 



Table showing the AMorNT or Niteooen, as 

 Ammonia and Nitric Acid, in the Rainfall 

 OP Three Yeabs at Rothamsted, in Pounds 

 PER Acre. 



It is seen that the available combined nitrogen so 

 estimated is computed to supply but a small propor- 

 tion of that annually removed fsom the soil by the 

 different crops grown. 



Thus on an average of three years 6-1 lbs. of 

 nitrogen as ammonia only are supplied to the soil 

 per acre each year, and, in addition, on an average of 

 two years 0-74 lbs. of nitrogen in the form of nitric 

 acid, giving a total of 6-84 lbs. of nitrogen. If, 

 however, we only regard the two years in which the 

 nitric acid was actually determined, the total nitrogen 

 becomes 7 '29 lbs. per acre, equivalent to 46 j lbs. of 

 ordinary nitrate of sodium. 



The amoimt of ammonia supplied to the soil by 

 rain does not, of course, represent the whole quan- 

 tity furnished by the atmosphere ; we have also to 

 take into account the direct absorption by the soil 

 itself, which, in a moist soil, would doubtless be con- 

 siderable. 



Boussingault, to whose patient investigations the 

 horticulturist owes much, has given the following 

 analyses of rain, dew, and fog, from samples collected 

 at Paris and Liebfrauenberg, in Alsace, during the 

 year 1853 :— 



Table showing the Combixed Nitrogen in Rain, 

 Dew, and Fog, in Grains per Imperial 

 Gallon. 



^ d bo 



H.-S 



Bain -f ^^^^ 



\ Liebfrauenberg 



Dew Liebfrauenberg {«^-X ; 



FO(P i^^B 



* ( Liebfrauenberg- 



0-2808 

 0-04f0 

 0-5125 

 0-0744 , 

 10.3092 

 0-2503 



