120 
INVESTIGATIONS ON ROTHAMSTED SOILS. 
inches of soil, as against a calculated deficiency, owing to cropping, 
of 92 pounds. From these facts, as well as from the higher output of 
potash from this plat, there seems to be little doubt that the magne- 
sium sulphate, like the sodium sulphate, has acted as a potash solvent, 
but to an appreciably greater extent, especially in the subsoil. 
We now pass on to plat 13, which has received, in addition to ammo- 
mum salts and superphosphate, a liberal annual dressing of potash 
far in excess of the demands of the crops. The excess of supply of 
potash per acre over the output of potash in the crops should leave 
the plat richer than plat 11 to the extent of 4,052 pounds per acre. 
We find soluble in dilute citric-acid solution in the 27 inches of soil 
an excess, as compared with plat 11, of 827 pounds. Of this quantity 
404 pounds per acre is in the surface soil, 288 pounds in the second 
depth, and 134 pounds in the third depth, indicating a descent of the 
potassium salts. The citric-acid-soluble accumulation, even in the 
whole 27 inches, however, although so great, is not much more than 
20 per cent of the expected accumulation. Either, therefore, much 
of the potash has been washed down to lower depths still, or it has 
" reverted" into some form of combination with the bases of the soil 
in which it fails to be dissolved by weak citric-acid solution. 
Plat 7 is manured like plat 14, but has, in addition to potassium 
salts, received also an annual dressing of sodium and magnesium 
salts. This plat has on the average yielded 1-J bushels more grain and 
If hundredweight more straw per acre than plat 13, while in the last 
six years (1889-1894) it gave 2f bushels more grain and 1£ hundred- 
weight more straw per acre. Its larger yield of crops has entailed a 
distinctly larger output of potash, so that the estimated excess in the 
soil (3,662 pounds per acre more than plat 11) is 390 pounds less than 
on plat 13. Citric acid dissolves, however, from this plat 115 pounds 
more potash per acre than in the case of plat 13 in the surface soil and 
11 pounds more in the second 9 inches, but 56 pounds less in the third 
9 inches, leaving a balance of 70 pounds per acre in favor of plat 7 in 
the whole 27 inches. On the whole, and mainly in the surface soil, it 
would seem that the magnesium and sodium salts have effected the 
retention of considerably more of the potash in an easily soluble 
condition. 
Plat 5 is a duplicate of plat 7, with, however, the important excep- 
tion that it has received no nitrogenous manure whatever. It yields 
but meager crops — better, it is true, than those of the wholly iimii;i- 
QUred plat — even now after fifty years. It has given less than half the 
quantity of grain yielded by plat 7 and about three-eighths of the 
straw, its estimated excess of potash as compared with plat 11 is 
5,242 pounds per acre, or 1,580 pounds more than plat 7. The sur* 
face soil is richer in ci 1 ric-acid-sol u ble potash than that of plat 7 by 
20:5 pounds per acre, t he second It inches by 225 pounds, and the third 
