96 HOW CROPS FEED. 
composition of standard crops, and with the quantity con- 
tained in appropriate applications of nitrogenous fertil- 
izers, 
The average atmospheric supply of nutritive nitrogen 
in rain, etc., for 12 months, as above given, is much less 
than is necessary for ordinary crops. According to Dr. 
Anderson, the nitrogen in a crop of 28 bushels of wheat 
and 1 (long) ton 3 cwt. of straw, is 454 Ibs; that in 24 
tons of mendow hay is 56 lbs. The nitrogen in a crop of 
clover hay of 2} (long) tons is no less than 108 lbs. Ob- 
viously, therefore, the atmospheric waters alone are in- 
capable of furnishing crops with the quantity of nitrogen 
they require. : 
On the other hand, the atmospheric supply of nitrogen 
by rain, etc., is not inconsiderable, compared with the 
amount of nitrogen, which often forms an effective manur- 
ing. Peruvian guano and nitrate of soda (Chili saltpeter) 
each contain about 15 per cent of nitrogen. The nitrogen 
of rain, estimated by the average above given, viz., 8} lbs., 
corresponds to 58 lbs. of these fertilizers. 200 Ibs. of gua- 
no is for most field purposes a sufficient application, and 
400 Ibs. is a large manuring. In Great Britain, where ni- 
trate of soda is largely employed as a fertilizer, 112 Ibs. 
of this substance is an ordinary dressing, which has been 
known to double the grass crop. 
We notice, however, that the amount of nitrogen sup- 
plied in the atmospheric waters is quite variable, as well 
for different localities as for different years, and for differ- 
ent periods of the year. At Kuschen, but 2-24 lbs. were 
brought down against 21 Ibs. at Proskau. At Regenwalde 
the quantity was 15 lbs. in 1864-5, but the next year it 
was nearly 30 per cent less. In 1855, at Rothamstead, 
the greatest rain supply of nitrogen was in July, amount- 
ing to 1} lbs., and in October nearly as much more was 
brought down; the least fell in January. In 1856 the 
largest amount, 2} Ibs., fell in May; the next, 1 lb., in 
