42 [February, 1902.] 
IMPERIAL INSTITUTE JOURNAL. 
Vol. VIII. No. 86. 
SCIENTIFIC AND TECHNICAL DEPARTMENT 
OF THE IMPERIAL INSTITUTE. 
4 
THE WHEAT SOILS OF ROTHAMSTED STUDIED AS REGARDS 
THEIR PHOSPHORIC ACID AND POTASH. 
Of all the elements which exist combined in the soil, there are three which are by far the 
most patent in producing heavy crops ; these are phosphorus, potassium and nitrogen. These 
elements exisL in the soil, not free, but combined in the form of various compounds, the 
phosphorus being combined in various phosphates, all of which contain the oxide of phos- 
phorus IT O.i, often called phosphoric acid, and the potassium being combined in silicates and 
other compounds which contain the oxide of potassium, often called potash. Consequently, 
in discussing the richness of a soil, it is usual to reckon how much phosphoric acid, P 3 0 J} 
and potash, K a O, it contains, although these are really present combined with other 
substances. 
By making analyses of the soil, the total quantity of phosphoric acid and the total 
quantity of potash in it are found ; thus the soil in one of the plots contained o‘i20 per cent, 
of phosphoric acid, equivalent .to 3,m lb. in an acre of soil to the depth of 9 inches ; but as 
the agents by which the plant supplies itself with food from the soil are far less drastic in 
their action than those which the analyst employs, the older analyses of soils leave a great 
deal to be desired as guides to the value of a soil as a crop producer and as to its manurial 
requirements. In consequence of this, the attention of chemists for some time past has been 
directed to devising solvent solutions which should give the desired information, namely, how 
much food immediately available for the plant there is in a given soil, and Dr. Bernard Dyer 
has introduced the use of a solution of citric acid containing one part of the acid in 011c 
hundred parts of water, and has found it a satisfactory agent for the purpose. 
The magnificent agricultural experiment station of the late Sir John Lawesat Rothamsted, 
with its record of crops and manures extending over fifty years, afforded unique material and 
data for studying soil in its relation to crops and manures by means of the new solvent. This 
has been done by Dr. Dyer, and the results are published in the Philosophical Transactions 
of the Royal Society of London, 1901, Vol. 194, page 235, under the title — “A Chemical Study 
of the Phosphoric Acid and Potash Contents of the Wheat Soils of Broadbalk Field, 
Rothamsted.” 
The experimental plots had grown wheat year after year, and had received various 
manures, the same plot being treated year by year with the same manure. On examining the 
tables of analyses in conjunction with the history of the plots, it appears that the determinations 
of the total amounts of phosphoric acid and potash throw far less light on what has been 
going on than the determination of the amounts of those substances dissolved out of the soil 
by the use of the one per cent, citric acid solution, although these latter are much smaller 
quantities ; consequently, in what follows, only the citric acid values will be referred to. 
Phosphoric Acid Results. 
Some of the numerous results relating to phosphoric acid are condensed in the followin 
table : — 
SOIL SAMPLES TAKEN IN IS93. 
Plot. 
Annual manuring for 50 
years (with only minor 
variations during earlier 
years). 
Percentage of 
phosphoric acid 
(F.,O.J in fine dry 
soil, 1st 9 inches, 
dissolved by 1 per 
cent, citric acid 
solution. 
The 
phosphoric 
acid (P 9 0 5 ) 
expressed as 
Proportional 
amounts of 
phosphoric acid. 
Average yield per 
acre, 1889-94. 
lb. per acre. 
Wheat. 
Straw. 
3 
Unmanured continu- 
ously . 
’OO7S 
202 
] f 
bushels. 
cwt, 
9 
IOA 
Manured with nitro- 
gen only, in the 
form of ammonium 
salts, since 1844 . 
'OO74 
192 
1 
1 
J l 
i6jr 
T ^-4 
1 
7 
Complete manuring 
with mineral sub- 
stances: phosphorus 
intheform ofsilper- 
phosphate, nitro- 
gen as ammonium 
salts, potassium, 
sodium and mag- 
nesium sulphates . 
*0547 
I41S 
7 ‘ 2 
35 
•2 -» T 
JOC 
11 
Manured with nitro- 
gen and phosphorus 
only, in the form of 
ammonium salts 
and superphos- 
phate . 
d 
O 
c_n 
1050 
5 ‘J 
2 ljr 
2o| 
5 
Manured with phos- 
phorus as super- 
phosphate and po- 
tassium, sodium and 
magnesium sul- 
phates, but no 
nitrogen 
*0642 
1665 
S-4 
15 
10J- 
2 B 
Manured with 14 tons 
per acre of farm- 
yard manure. This 
contains nitrogen, 
phosphorus and 
potassium 
•0560 
I307 
6-6 
41 
. if* 
39 
It should be noticed that in both the plots 3 and ioa, the crops were starving for want of 
available phosphorus. In plot ioa the stimulating action of nitrogen had produced heavier 
crops than plot 3, the unmanured one, yet considerably lower than in plot 1 1 where phos- 
phorus had been supplied in addition to nitrogen. In plot 7 a very complete manuring, 
including phosphorus, nitrogen and potassium, had been supplied and the yield of wheat was 
doubie as great as that of plot ioa, being 35 bushels instead of i6£ bushels ; whilst the yield 
of straw was more than double, being 33-lr cwt. instead of 13^- cwt. Here the available phos- 
phoric acid was '0547 per cent, or 7 ‘2 times as great as in the plots 3 and ioa, which had 
received no phosphorus. Blot 5 had received a manuring complete, except for the absence 
of nitrogen, and the crop, owing to nitrogen starvation, amounted to 15 bushels of wheat and 
ioij cwts. of straw, only a trifle above the crojis on the unmanured land. As the crops from 
this plot had been small, but little phosphorus had been removed in them, and this accounts 
for the accumulation of available phosphorus in the soil, which contained S‘4 times as 
much as in plots 3 and ioa. In plot 21; the land had received heavy dressings of farmyard 
manure and consequently abundance of nitrogen, phosphorus and potassium and, in return, 
yielded heavy crops. Here the available phosphorus was 6 '6 times that in plots 3 and ioa. 
A very interesting question is : — what amount of available phosphoric add is so small as 
to constitute phosphoric starvation. The author concludes that when a soil is found to con- 
tain as little as about *01 per cent, of phosphoric acid, soluble in a I per cent, solution of 
citric acid, it stands in immediate need of phosphatic manure. It is more difficult to decide 
at what point of richness in phosphoric acid the further supply of phosphatic manure is 
unnecessary ; the author thinks that this limit lies somewhere below *04 per cent., probably 
at '03 per cent. 
It must be remembered that these conclusions relate to cereals, and that for root crops, 
more especially turnips, the limits would probably be higher. 
Potash Results, 
In the case of potash, even more than in that of phosphoric acid, a knowledge of the 
total amount present in the soil is no clue as to the need or otherwise for potassic manures. 
The Broadbalk soil contains probably 15 tons of potash in an acre to a depth of 9 inches ; but 
it is in a dormant form, forming a reserve stock for the distant future, and is only very grad- 
ually rendered available for plant use by the natural processes going on within the soil. Even 
with this great reserve of potash the soil is unable to furnish a sufficient annual supply to the 
wheat crop under a system of continuous cropping, unless restitution is made in the form of 
manure. 
The following table gives a selection of some of the numerous results relating to potash: — 
Plot. 
Annual manuring for 
50 years (with only minor 
variations during the 
Percentage of 
potash (K a 0) in 
fine dry soil, xst 
9 inches, dissolved 
The potash 
(K, 0) 
expressed as 
Proportional 
amounts of 
potash. 
Average yield per 
acre. 1889-94. 
earlier years). 
by 1 per cent, 
citric acid solution. 
lb. per acre. 
Wheat. 
Straw. 
ry 
J 
IOA 
11 
Unmanured continu- 
ously . 
Manured with nitro- 
gen only, in the 
form of ammonium 
salts, since 1844 . 
Manured with nitro- 
gen and phosphorus 
only, in the form 
of ammonium salts 
and superphosphate 
■OO32 
•OO32 
•OO32 
S 3 
S 3 
S 3 
1 
I 
f 
bushels. 
13 
1 6h 
21^ 
cwt. 
9 
r 3 i 
13 
Manured with nitro- 
gen, phosphorus 
and potassium, in 
the form of ammo- 
nium salts, super- 
phosphate and po- 
tassium sulphate . 
■0188 
00 
5 ‘9 
3 2 j 
32 
7 
Complete manuring, 
with mineral sub- 
stances : phosphor- 
us in the form of 
superphosphate, ni- 
trogen as ammoni- 
um salts, potassium, 
sodium and mag- 
nesium sulphates . 
•0232 
602 
7' 3 
35 
33j 
5 
Manured with phos- 
phorus as super- 
phosphate and po- 
tassium, sodium and 
magnesium sulph- 
ates, but no nitrogen 
'030S 
799 
9*6 
15 
io| 
2 Ii 
Manured with 141011s 
per acre of farm- 
yard manure. This 
contains nitrogen, 
phosphorus and 
potassium 
•0384 
896 
iro 
41 
39 
From these results it appears that in plot 11, although it had been abundantly supplied 
with nitrogen and phosphorus, the readily available potash had evidently been largely 
exhausted and the yield of wheat, 21-J bushels, and of straw, 20^ cwt., was only about two- 
thirds of that of plot 13, which had received the same manuring except that potassium, in the 
form of potassium sulphate, had been added, and which yielded 32^ bushels of wheat and 
32 cwt. of straw. 
When potassium sulphate was applied, the amount of potash received by the plot was 
about 100 lb. per acre per annum, so the figures show that this manuring caused an accumu- 
lation of available potash in the soil. The potash added in the farmyard manure was about 
double the above amount, and in this plot, too, available potash accumulated. 
As to the critical amount of potash which may be taken as showing that the soil does not 
need any special application of potassium salts, the author considers that when a soil contains 
as much as *oi per cent, of citric-acid-soluble potash, this point is reached, at any rate as 
regards cereals. 
LEATHER FOR BOOKBINDING. 
The interesting report of the Society of Arts’ Committee on Leather lor Bookbinding 
has already been reviewed in this Journal (Vol. vii, p. 20S), where a summary of the 
principal conclusions and recommendations will be found. The experimental work, which 
was necessitated by the enquiry, was entrusted to a small sub-committee of experts, con- 
sisting of Dr. J. Gordon Parker, Professor Procter and Mr. A. Seymour- Jones, who carried 
out a large number of experiments which yielded valuable information upon the subject under 
investigation. The results could, of necessity, only he briefly given in the report itself, but a 
detailed account of the work has now been furnished by Dr. Parker in a lecture at the 
Society of Arts (fount. Soc, Arts, Vol. L. p. 25 J, and, as many of the points investigated are 
of extreme importance to leather manufacturers and bookbinders, they may be dealt with more 
fully than was previously possible. 
It was definitely established to the satisfaction of the Committee that nearly all modern 
bookbinding leathers show a much greater tendency to decay than those used previous to 
1830, and the inference was that this could only be due to modern methods of leather manu- 
facture. A careful examination of a large number of these old bindings, which had proved 
so permanent, revealed the following facts : — (1) the leather was generally thicker than that 
at present used; (2) the fibres of the leather were in the natural condition, i.e., running 
transversely to the surface, whereas in modern leather, owing to the stretching and tight 
setting-out of the skin, the fibres are distorted and run more parallel to the surface ; (3) the 
