114 



CASSELL'S POPULAR GARDENING. 



From these results it would appear that in summer 

 the supply of chlorides is very limited ; for a large 

 increase in the rainfall is attended with hut little 

 rise in the quantity of chlorine brought upon the 

 land. In -y^ter, on the other hand, the supply of 

 chlorides in the atmosphere is so constantly renewed 

 from the comhustion of fuel, that an increased rain- 

 fall results in a considerahle addition to the supply 

 of this constituent to the soU. 



The amount of chlorine annually contributed hy 

 the rain of Rothamsted to the land has amounted to 

 14-4 Ihs. per acre on an average of nine years, 1877-86. 



This amount is equal to 24 Ihs. of pure common 

 salt, an amount of chlorides greater than that which 

 is contained in most garden crops. 



Determinations of sulphuric acid in the rain have 

 given a mean of 2-41 per million, or 18'5 Ihs. per 

 acre per annum. 



The following are approximate determinations 

 made, in forty monthly mixtures of rain-water col- 

 lected at Rothamsted, and made by Dr. W. J .Russell, 

 who is investigating the chemistry of rain : — 



Table showino the Amount op Sulphuric Acid in 

 THE Rainfall of the Six Summer and Six 

 WiNTEK Months op Two Years, 1881-3. 



for the fact that, under equal conditions of manuring, 

 the Tm-nip crops are not so large as they are in the 

 North of England and of Scotland, 



Yield of mtrogen by Crops. — If we 



divide the constituents which exist in the various 

 Plants of the garden into two sections, and assume 

 that carbon and water are obtained from the at- 

 mosphere, whUe the nitrogen and mineral sub- 

 stances are derived from the soil, it wUl be necessary 

 in the next plaice to consider what is the amount of 

 nitrogen annually obtained over a given area in 

 different crops when they are gro-vm without any 

 supply of it in manure. 



This point may be illustrated by some results ob- 

 tained in the field experiments, of Sir J. B. Lawes at 

 Rothamsted. The following table shows the yield 

 of nitrogen per acre per annum, in Wheat, in Barley, 

 and in root-crops, each grown for many years in 

 succession on the same land, either without any 

 manure, or with a mineral manure supplying no 

 nitrogen ; — 



Yield of Nitrogen per Acre per Annum in 

 Wheat, Barley, and Root-crops at Rothamsted. 



A part of the sulphuric acid in these rain-waters 

 would be due to coal-smoke, and a still smaller por- 

 -tion is derived from sea-spray. 



The considerable amount of sulphuric acid found 

 in the summer rain points, however, to a further 

 .source most active during high temperatures — 

 namely, the products of the decay of animal and 

 vegetable matter, which naturally takes place much 

 more rapidly in the warmer months. 



The quantity of sulphuric acid would appear to be 

 about sufficient for the demands of ordinary cereal 

 crops of the farm, though unequal to the require- 

 ments of Turnips, Potatoes, and some other garden 

 jjroduots. And it may here be mentioned that the 

 drier atmosphere and smaller rainfall in the 

 Southern and Eastern districts of England accounts 



Crops. 



Wheat.! 



Barleys 



Root- 

 crops 



Oondition 



' of 

 Manuring. 



Unmanured 

 Mineral 

 Manure 



TJnmanured 

 Mineral 

 Manure 



Complex 

 Mineral- 

 Manure 



Duration of Experiment. 



Averag** 



Mtrogtn 



per Acre 



per 



lbs. 



32 years, 1844-75 . 20-7 



24 years, 1852-75 . . 22-1 



24 years, 1852-75 . . 18-3 



24 years, 1852-75 . . 22-4 



Turnips, 8 years, 1845-52 . 42-0 



Barley, 3 years, 1853-55 . 24-3 



Turnips, 15 years, 1856-70 . 18-5 

 Sugar Beet, 5 years, 1871- 



75 13-1 



Mangel Wurzel, 5 years, 



li.76 80 .... 15-5 



L. Total, 36 years, 1845-80 . 25-2 



Bearing in mind what has already been said as to 

 the amount of plant-food annually deposited from 

 the atmosphere to the soil of the garden, the above 

 figures have great interest and significance. 



It may be observed that the annual use of a 

 mineral manure, supplying potash, soda, magnesia, 

 and phosphate of lime, but very slightly increases 

 the yield of nitrogen beyond what may be termed 

 the inherent fertility of the soil, and it would appear 

 that the increase of crop is derived from the accumu- 

 lation within the soil of organic nitrogen, derived 

 from the debris of pre-existing vegetation. 



