THE BROADBALK WHEAT SOILS. 
93 
fere in the drainage. But it is to be remembered thai as there are 
no crops there is qo conservation of nitrogen in root and stubble resi- 
due, nor are any weeds allowed to grow on t lie soil. 
Table 52. — Barn field {rain and drainage). 
Pounds 
per acre. 
Nitrogen contained in drainage from GO-inck gauge (average of 
90 harvest years. 1877-78 to 1896-97). 33.87 
Nitrogen derived from rain, dew, etc 5. 00 
Difference ... 28. 87 
The wheat crops, together with the estimated Loss in drainage down 
[o 27 inches, shov 24 pounds without manure and -27.'.) pounds w ith 
mineral manure; and the question is. whether there is any further 
loss !>y drainage below l'7 inches. Taking into account the nitrogen 
in the crops and thai found in the soil as nitrates down to 27 inches, 
he quantity has been seen to be 35.2 pounds without manure and 
k. 42 pounds with mineral manure; or, taking the total quantity of 
litrogen as nit rates down to 90 inches of depth, the quantity included 
in the w heal crop with mineral manure is tO.47 pounds per acre per 
innum. Obviously, as we have already observed elsewhere, the whole 
If the nitric nitrogen found to any given depth at any one time can 
not be taken as directly representing t he annual aecuniulat ion, and so 
far these results may be l<»o high. 
Then the results for the mixed herbage of the grass land, including 
i small amount <>f fixation by the leguminous crops, show 28 pounds 
bid 34.2 pounds. The. root crops, with mineral manure alone, show 
lily 20.2 pounds. And lastly, the rotation crops— including some 
LeguminossB — have yielded 31.8 and U).2 pounds. It is, however, to 
he again observed that no loss by drainage Is brought into account in 
lie case of either the mixed herbage, the root crops, or the rotation 
land. In the case of the mixed herbage, comprising a great variety 
!>f plants with widely varying rooi habit and root range, and more or 
less vegetation almost all the year round, there would probably be 
comparatively little loss by drainage. With land devoted to root 
crops there would be much more. Land under rotation, on the other 
hand, would certainly lose less than land under a continuous cereal 
crop, like that of the Broadbalk field; though it would lose more than 
permanent, grass land. 
Taking into consideration, therefore, the conditions under which 
the various results have been obtained, we are probably fairly justi- 
fied in drawing the conclusion that, even under the most favorable 
eondit ions of mineral manuring, without man u rial nitrogenous sup- 
ply, the quantity of nitrogen naturally available from the enormous 
(bores found in the Rothamsted soil and subsoil is, on the average, 
only about, or not much more than pounds per acre per annum. 
Forty pounds would probably be an extravagant estimate. 
