S80 
THE TROPICAL 
AaRICULTURIST. [Deo. 2, 1901. 
in some oae food, will the grain have a nortiial 
compoHitiot, or will it prove to contain less of the 
element in which the soil is dtii-ieot, than is com- 
mon to it ? Whilst the stems and leaver of a pl;<nt 
vary very much in composition, that of the seed 
remains usually very constant, and the question was, 
"would grain produced from a soil deficient, say in 
phosphoric acid, be itself deficient in tbis substance ? 
He has therefore tested tbis quesiion by growing 
plants in pots of the particular soil under exami- 
nation, to which manures of diliereut composition 
were added. Aftar the grain wns perfected, he has 
anilyaed it to see if, fronn its comp:)9ition, the de- 
ficiencies of the soil mie^ht be dettcted. The work 
is comparatively new and is probably s'ill incomplete, 
but the last pa,per published indicated that whilst 
the method might be used for one particular crop, 
any one soil would have to be tested in ceUtion to 
its value for e«.ch crop separately. This naturally 
entails a very great deal of labour. 
The foregoing relates to methods in which it has 
been sought to utilise the services of the plant itself 
to answer the qaostion — •" In what respect is this 
or that soil deficient " ? 
I turn now to the question of applying testa ia 
the chemical laboratory. 
Some investigators, more particularly in Germany, 
attempted to apply certain dilute solvents to tKe 
soil, which might provide a measure of the available 
plant food. 
Such a method has a great advantage over any 
cultivation experiment, becuuse it can be accomplished 
in a bhort time On the other hand, many considered 
that such tests were unsuitable. If the chemisl 
takes a portion of soil and submits it to any treat- 
ment, he ia submitting the whole of that portion to 
a like treatment. The roots of the plant, on the 
other hand, do not come in contact with more than 
a certain limited number of soil particles. 
About ten years ago Dr. Dyer of London took up 
the matter in a somewhat different manner. 
The agricultural value of some of the experiment' 1 
fields at Rothamstfcd was known with great accuracy. 
Here a plot of land was known to be ceficient iu 
phosphoric acid, there anolher which was with equal 
certainty deficient iu potash, and Dr. Dyer raised 
the question whether it might not be possible to 
find a chemical standard which, though more or less 
arbitrary in itself, would have a definite relation to 
the known qualifications of some of the flothamsted 
soils. 
Dr. Dyer's method of procedure may be stated 
very biiefly. It may be assumed that much of the 
food of plants exists in the soil in a more or less 
insolubie state, and that it is rendered soluble by 
the action of the juices of the roots, which are acid. 
The amount of such acidity was therefore determined 
in the roots of a great number of plants, and from 
the result of this investigation an artificial acid 
solution was prepared. This resembled more or less 
the root sap. Dr. Dyer then allowed this to act on 
certain of the Kothamsted soils for a given time, 
and determined the amount of potash and phosphoric 
acid ^hich has been dissolved. In order to illua- 
tr»te the result obtained, the following may be 
quoted ; — 
Propoi tions of ^'■readily available phosphoric" acid 
in Eothamsted soils. 
Thirty-nine crops of Barley had hem taken 
off the land. 
Yield 1890 
Manures used per acre. Bushels ' °^ readily 
grain. 
Plot 1—0. Unmarinred 
continuously 13 
2—0. 3J cwt. super- 
phcsphate 1675 -0463 
1 — A. 200 lb. ammonia 
ealts 24'5 .oqgo 
M«nuresnrpd npracre "^ield, 1890. % of readily 
Manures used per acre. Bushels soluble PjO. 
soiuble O j 
■0055 
2— A. 
1— AA. 
2— AA. 
200 lb. ammonia 
salts and 3^ cwt. 
euper-phosphate 
275 lb. titrate of 
soda 
275 lb. Nitrate of 
BOda and 3i cwt. 
superphosphate. 
grain. 
335 
29-5 
47-5 
•0425 
•0967 
■0350 
In this statement is- set out in the first column 
the manures employed on the different plots, and 
in Lbe second column the yield of barley per acre 
in 1890, that being the thirt>-niuth crop. The 
effect or phutphates will be readily perceived. Piot 
1 — O, whicQ has always remained unmanured, yielded 
13 bushels, the next plot manured with phoaphatea 
yielded 16J bushtls. Similarly, from plot 1 — A 
manured with ammonia salts, 24i bushels were reaped, 
whilst an addition of phosphates raised the 
yield to 33} bushels. Tne third pair of plots yield 
similar evidence. 1 — AA, manured with nitrates 
yielded 2t*J bushels, whilnt an addition of phoaphatea 
effected a yield of 47 i bushels. 
It is cleat, then, that ploli 1—0, 1 — A, and 1 — AA 
were all in need of phospnoiic acid. 
When these several soils and others also, for I 
only give here a small extract of Dr. Dyer's work 
in order to illustrate his method, were treated with 
a dilute solution of citric acid, it was found that 
these soils yielded the proportions of phosphoric 
acid which are found in the third column of the 
statement. From these figures you will see how very 
great is the difference between the amounts of 
readily available phosphoric acid in the aoila of the 
several plots. Where barely had been grown for a 
long aeries of years without phosphatic manure, the 
propottiou of readily a\ailablo phosphoric acid had 
fallen to a very low figure, •OUS or "006. Where 
phosphates had been annually applied to the laud 
the proportion wcs Uiany times greater. 
Tile deduction which Dr. Dyer made, was tha', 
if a soil cont in less than •Ol f;er cent, of readily 
available Pj O^ or less than •005 per cent, of readily 
available K, 0, such a soil ia probably in need of 
an artificial supply of this plant food. 
It is very desirable to bear in mind that this 
standard is not one made arbitrarily by Dr. Dyer, 
but one which was indicated by the Rothamsted soils. 
It did not however follow that a standard which 
was applicable to llothemsted soils would be equally 
applicable to soil;* generally. The methoa has been 
since applied to soils iu other parts of the world, 
and apparently it has a remarkably Uniterm value. 
Iu India I have had a like experience. Applying 
It to the soils of the different experimental tarixit, 
it has chown that at Poona, iNngpore, Cawnpore 
and Dumradn these is rather more than the "01 per 
cent, of available Pj O in the soil, and at none of 
these farms have bones proved of material value 
as manure. On the other hand, the soil at Bnrdwan 
contains a low proportion of phosphate, and it is only 
at this farm that bones have proved of any value. 
The evidence which has been gained in England 
with Dyer's method has gone to show its general 
applicability for the determination of tha soil's re- 
quirements for potash as well as for phosphoric acid. 
In India no manurial experiments has been mado 
at the Farms to test the question whether the soil 
ia in urgent need of an artificial supply of potash, 
but I may mention that most, if not all, these soils 
contain more available potash than what, according 
toj Dr. Dyer's test, is a minimum quantity. Thus, 
so far as these two elements are concerned, one 
may say that the chemist has supplied a meuns of 
detecting whether any particular land is urgently ij^ 
need of an artificial supply of tbem or uot, 
