92 INVESTIGATIONS ON ROTH AMSTED SOILS. 
ROOT-CROP SOILS. 
The results recorded for the root crops in Barn field are as follows : 
Table 50. — Root crops {Barn field), with mineral manure. 
Pounds 
per acre. 
Nitrogen contained in crops. 36 years (1845-1880) 25.2 
Nitrogen derived from rain, dew, etc. (estimated) 5.0 
Difference 20.2 
The root crops with mineral manure, but without nitrogen, gave, 
on an average of thirty -six years, 25.2 pounds of nitrogen per acre 
in the crops, or, allowing for the 5 pounds contributed by rain, 20.2 
pounds per acre per annum. 
ROTATION LAND. 
The quantities of nitrogen contained in the crops on the two plats 
selected for examination, on an average of the seven courses from 
1848 to 1875, are as follows: 
Table 51. — Rotation land (Agdell field). 
Unma- 
nured. 
Super- 
phosphate. 
Nitrogen contained in crops (7 courses, 1848-1875) 
Nitrogen derived from rain, dew, etc. (estimated) 
Difference 
Pounds 
per acre. 
36.8 
5.0 
31.8 
Pounds 
per acre. 
45.2 
5.0 
40.2 
The average annual yield of nitrogen per acre in the crops was 36.8 
pounds on the unmanured plat, and 45.2 pounds on the plat manured 
with superphosphate. After deducting from each of these quantities 
5 pounds for rainfall nitrogen, we have a soil removal of 31.8 and 
40.2 pounds per acre per annum, respectively. 
Iu no case, however, except in the wheat field, is loss by subsoil 
drainage takes into account; and it is to be noted that, on the rota- 
tion land, a certain proportion of the nitrogen yielded would be due 
bo fixation of atmospheric nitrogen by the leguminous crops of the 
total Ion, which would be more in the case of the superphosphate than 
in thai of the unmanured plat. It is to be admitted, of course, that 
no one of the illustrations given affords exact evidence as to the 
amount of nitrogen actually available from the resources of the soil! 
Ea<Jh illustration that we have given must be judged according to its 
condil ions. 
RAIN AND DRAINAGE (BARN FIELD). 
If \\<- examine the results (shown in the table below) jnelded by the 
60-inch drain gauge, which is kepi fallow, we find that, deducting for 
rainfall, about 29 pounds of nitrogen have been collected annually per 
