70 INVESTIGATIONS ON ROTHAMSTED SOILS. 
Plat 5 has already been discussed partially in the present section, 
and also under the subject of total nitrogen. This plat has had no 
ammonium salts for forty-two years prior to 1893. It has, however, 
yielded persistently higher crops than the unmanured plat, the min- 
erals, no doubt, having enabled it to take greater advantage of the 
moderate quantity of nitrates produced from the soil. In the six 
years 1889-1894, it averaged If bushels of grain and If hundred- 
weight of straw more than plat 3. 
We have seen that, in virtue of this greater annual yield, there has 
been less loss of surface nitrogen than on plat 3, a distinctly larger 
percentage of total nitrogen being now found in the surface soil of 
plat 5 than in that of plat 3. 
We find in 1893, in the surface soil of plat 5, slightly more nitric 
nitrogen than in that of plat 3, though in the first 27 inches the 
quantity is rather less than in plat 3, being intermediate between that 
in plats 3 and 4. 
More interesting is the study of plats 6, 7, and 8 in relation to plat 
5, and for all of these we have fortunately full sets of samples down 
to a depth of 1\ feet. The figures speak so plainly for themselves 
as they stand in Table 35 that it seems scarcely necessary to enlarge 
upon them. The surface soils are all richer than on plat 5. If, 
however, we take the first and second depths together, containing 
respectively in plats 5, 6, 7, and 8, 16.89 pounds, 26.87 pounds, 34.17 
pounds, and 46.57 pounds of nitric nitrogen per acre; or the first 27 
inches, containing respectively 19.12 pounds, 32.68 pounds, 42.71 
pounds, and 55.28 pounds per acre; we at once see that there is a dif- 
ference according remarkabty with the sequence of the increasing 
annual supply of ammonium salts. We see, further, the same con- 
stant differences in nitric nitrogen in the lower depths, down to the 
tenth or lowest depth sampled. And if we take the whole 1\ feet 
comprised in the ten depths, we find per acre in plats 5, 6, 7, and 8, 
25.17 pounds, 52.61 pounds, 74.27 pounds, and 107.32 pounds of nitric 
nitrogen. 
If we deduct from the three latter plats the nitrogen of plat 5, we 
find in round numbers as follows, in the three plats receiving 
respectively 43 pounds, 86 pounds, and 129 pounds of nitrogen per 
acre per annum as ammonium salts. 
Table 86. — Excess of nitric nitrogen in plats 6, 7, and 8, over that in plat 5. 
Plat (i. 
Plat 7. 
Plat 8. 
Nitrotfon in ammonium suits supplied per aero per annum 
N'itrif nitrogen per acre found in soils and subsoils to a depth of 
!M) indies, in excess of plat 5, receiving no ammonium salts 
/ 'omuls. 
43 
96| 
1', >n mis 
86 
49 
Pounds. 
129 
88 
The consistency of these differences is fairly well maintained in 
each of the successive sectional depths. 
