284 HOW CROPS FEED. 
foregoing paragraphs were written. (Juhresbericht 4. 
Ag. Chem., 1865, 29.) 
Bretschneider’s experiments were made for the purpose 
of estimating how much ammonia, nitric acid, and nitro- 
gen, exist or are formed in the soil, either fallow or occu- 
pied with various crops during the period of growth. 
For this purpose he measured off in the field four plots of 
ground, cach one square rod (Prussian) in area, and sepa- 
rated from the others by paths a yard wide. The soil of 
one plot was dug out to the depth of 12 inches, sifted, 
and after a board frame 12 inches deep had been fitted to 
the sides of the excavation, the sifted carth was filled in 
again. This and another—not sifted—plot were planted 
to sugar bects, another was sown to vetches, and the 
fourth to oats. 
At the end of April, six accurate and concordant anal- 
yses were made of the soil. Afterwards, at five different 
periods, a cubic foot of soil was taken from each plot, and 
from the spaces between that bore no vegetation, for de- 
termining the amounts of nitric acid, ammonia, and total 
nitrogen. The results of this analytical work are given 
in the following Tables, being calculated in pounds for the 
area of an acre, and to the depth of 12 inches (English 
measures*) ; 
TABLE I, 
AMOUNT OF AMMONIA. 
aad nod Beet plot. Vetch plot. Oat plot. Vacant plot. 
End of April, 59 59 59 59 59 
12th June, 15 48 41 32 28 
30th June, 12 41 24 40 32 
22d July, 9 29 39 22 29 
13th August, 8 15 16 11 43 
0 16 16 7 23 
9th September, 
*It is plain that when the results of analyses made on a small amount of soil 
are calculated upon the 3,500,000 lbs. of svil (more or less) contaitned in an acre 
to the depth of one foot (see p. 158), the errors of the analyses, which cannot be 
absolutely exact, are enormously multiplied, What allowance ought to be made 
in this case we cannot say, but should suppose that 5 per cent wonld not be too 
much, On this basis differences of 200-300 lbs. in Table IV should be overlooked, 
