284 



ttOAV CROPS FKEO. 



foregoing paragraplis were Avritten. {JaJireshericht il. 

 Ag. Chem., 18G5, 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 Avith various crops during the period of growth. 

 For this purpose he measured olf in the field four plots of 

 ground, each 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 earth was filled in 

 again. This and another — not sifted — plot were planted 

 to sugar beets, 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 difterent 

 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*) : 



AMOUNT OP AMMONIA. 



* It is plain that when the i-esults of analj'«os made on a small amount of soil 

 are calculated upon the 3,500,000 lbs. of soil (more or less) contained in an acre 

 to llie depth of one foot (see p. 158), the errors of the analyses, which cannot be 

 absolutely exact, are enormously multiplied. Wlmt allowance ou;rht to be made 

 in this case we cannot say, but should suppose that 5 per cent would not be too 

 jHHch. On this basis differences of 200-300 lbs. in Table IV should be overlooked 



