112 



CA8SELL'S POPULAR GAEDEXIXG. 



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 part 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 Eothamsted 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 j^ears (1853 to 1886) 

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

 the average being 28-64 inches. 



From 152 anal5'ses 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 the 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 thii-tj'-nine 

 monthly analyses of rain-water according to the 

 amount of rainfall in each month, as illustrated by 

 the following table : — 





Average 

 Eainfall 

 in Inches. 



Nitrogen 

 as Ammo- 

 nia per 

 Milhon. 



Rainfalls below 1 incb. 



0-624 



1-03 



„ between 1 and 2 inches 



1-530 



1-17 



between 2 and 3 inches 



2-473 



0-91 



above 3 inches . 



4-727 



82 



The amount of nitrogen, or plant-food, annually 

 carried to the soil by rain varies considerabh' 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 10-23 lbs. of nitrogen per acre; while the 

 following table by Lawes and Gilbert shows that at 

 Eothamsted, in Hertfordshire, on an average of 

 three years, with a mean rainfall of 28|- inches, 

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

 by rain and the minor deposits. 



* Vol. xvii. (1881), and Vol. xix., ss. Part II. 



Table showixg the Amount of Nitrogen, as 

 Ammonia and Xitric Acid, in the Eainfall 

 of Three Years at Eothamsted, in PorxDs 

 PER Acre. 







Jsitrogen i>er Acre, as 



Years. 



EainfalL 



Ammonia. 



Nitric 

 Acid. 



Total 

 Nitrogen. 



ill 



Inches. 

 29 01 

 29-17 

 27-22 



lbs. 

 5-20 

 5-82 

 7-28 



lbs. 

 [0-74] 

 0-72 

 0-76 



lbs. 



5- 94 



6- 58 

 8-00 



Mean . . 



28-47 



6-10 



0-74 



6-&4 



It is seen that the available combined nitrogen so 

 estimated is computed to supply but a small propor- 

 tion of that annvially removed from 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, gi^ing 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| 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 fm-nished 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 

 horticultiuist owes much, has given the following 

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

 at Paris and Lieb£rauenberg, in Alsace, dming the 

 year 1853 :— 



Table showing the Combined Nitrogen in Eain, 

 Dew, and Fog, in Grains per Imperial 

 Gallon. 



Eain 



( Paris. 



."titJ eS bo 



Dew 

 Fog 



( Liebfrauenbere 



.jLieWrauenberg.;"— 



( Paris .... 

 "(^ Liebfrauenberg 



0-21C0 0-0708 0-2808 

 0-0350 0-0140 0-04PO 

 0-4340 07S5 0-5125 

 0-0714 0-0030 0-0744 

 9-6000 0-7092 10.3092 

 0-1790 0-0718 0-250S 



