4 
THE TROPICAL 
AGRICULTURIST. [Auft. 1, 1903. 
using lime only made it far more necessary 
that he shoulcl put some base upon the soil 
which would neutralise the superphosphate and 
combining with the £cid part of the iulphate of 
ammonia, which provide Liases for nitrication in the 
various manures used. Feeling very strongly how 
much dressings of lime were required throughout the 
land, he wished every strength to Mr. Ilughes's 
elbow in the introduction of a satisfactory snper- 
pho.-phate. 
Mr. Hermann Vose thought that the reader of 
the paper would cigree that well- made super, 
phosphate contained only minute traces of free 
sulphuric acid, the acid in superphosphate beinR 
due to free phosphoric acid. He, therefoie, thougl.t 
the statement should not go forth to the public 
that ordinary tupeiphosphate contained such a 
dangerous substance t-s sulphuric acid in a free state. 
Manufacturers of superphosphate took preat care that 
any excess of sulphuric acid should be absorbed, many 
thousiind tons of phosphate wbicti contained from 
40 to 50 per cent, of carbonate of Jime being imported 
into this country from Belgium for that special 
object. The acid, dsmp, and lumpy condition 
of superphosphates which existed twenty years ago 
did not exist at the present time, so that the advan- 
tages of the new manure were not so great as Mr. 
Hughes had made out. The most interesting part 
of the paper was, that the reader of it had collected 
a number of facts indicating that what was really 
required in the soil was lime. It was necessary that 
a farmer, in order to utilise the manure to the best 
extent, should have plenty of lime on his land, by 
which means .finger and toe disease sometimes 
caused by an excess of superphosphate, could be 
avoided. Five million tons of superphosphates were 
used every year in the whole world ; and although the 
use of basic slag had lai gely developed, it had had 
the effect of increasing the consumption of superphos- 
phate. 
Mr. John Ruffle thought the basic superphos- 
phate to give the best result should be made very 
fine. He suggested as a standard, that 90 per cent, 
of the substance should be sent through 180 holes to 
the linear inch, the remaining 10 per cent, not 
necessaiily coming up to that standard. Such a 
fine substance would be easily dissolved, and could be 
distributed through the soil better than an acid 
phosphate. 
Mr. F. J. Lloyd said he had noticed of late years 
that the result obtained by dressing of a certain 
quantity of superphospate upon a soil had not been 
so great as would have been produced by the same 
amount of dressing if it had been applied to a similar 
soil 20 years ago. In endeavouring to discover the 
reason, he thought, if his ideas were right, he could 
throw some light on the question of phosphatic 
manures. Downing proved that lime in the soil was 
continually sinking, and it was known that the lime 
in the soil which did not sink, was continually 
being taken away in the plant. The consequence was 
there was a tendency in the soil to which lime was 
not applied for the lime to disappear from the top 
surface of 6 or 8 iuches in which a plant mostly lived. 
He believed that the soils of England today in those 
6 or 8 inches were very greatly deprived of lime, and 
that the mere iipplicatiou of lime in any form to the 
surface would not remedy the defect. Why was it 
that superphosphate always gave the best result 
during the first year of its application ; and that 
practically no result could be seen a year after it had 
been applied ? He believed it was due to the 
fact that the phosphate in the superphosphate 
was soluble in water, and, being dissolved in the 
water of the soil, it penelrati d into ihe soil along 
those courses through which the water riowed most 
freely. The root of a plant was always known to take 
the course of least resietance, which would be along 
those same channels. Therefore in the first year after 
the application dt the snperphosphate the plant roots 
travelled along ihose same lines on the borders of 
which the phosphite had been piecipitated, and that 
v/as why the superphosphate gave all its results during 
the fiist year. 1£ the soil to a depth of 6 or 8 inches 
was deprived of lime, the soluble phosphates from the 
superphosphate, instead of being precipitated along 
those courses wh ch the plant root frequently took, 
sank into the subsoil before it met lime to precipitate 
it, and for that reason the same results for a definite 
quantity of superphosphate were not obtained because 
it had been precipitated too low for the roots of the 
plant to utilise it benefically. For that reason he 
believed the introduction of a manure fiee fiom acid 
which would rpply a phosphate of lime in a form 
etsily assimilable by plants would prove of very con- 
siderable benefit to the farmers of E gland. He would 
1 ave liked to deal with the question of how to estimate 
the availiibility of the substances in the soil and the 
subsiances in the manures applied to the soil; but 
it was perfectly evident that not only in England, 
but in every other country where manures" pvere 
applied, the time had come when some authoritative 
booy should lay down a definite standard which could 
be accepted universally as a means of estimating the 
available food in both a soil and a manure. 
Dr. S. Rideal thought it was by no mesins 
proved that biisic slags were at a disadvantage 
compared with the neutralised phosphate suggested 
by Mr. Hughes. The use of slag had increased 
enormously in recent years, due probably to 
the fine grinding, and when one compared the ratio 
of slug used in Geimany, to that of snperphosphate 
in England, one must conclude that basic slags 
had the disadvantages one was led to imagine existed. 
Basic slags certainly had an alkalinity similar to that 
claimed by Jlr. Hughes, and it would be interesting 
to know whether Mr. Hughes had any definite opinion 
as to what the definite phosphate was which existed in 
his neutralised superphosphate. With regard to the 
question of manufacture, was it not feasible that if 
there was a bisic slag which was alkaline and acid 
superphosphates which had injurious effects upon soils 
deficient of lime, then a mixture of the two ground 
together would bear out the theory propounded by 
Mr. Hughes. There was no occasion to convert the 
mineral phosphates into superphosphates. The 
Germans had already realised thai point in the 
tremendous growth of the Thomas slag, and tha 
deficiency of the pig-iron in phosphorous had led the 
German manufacturers to add mineral phosphates 
so as to produce a slag rich in phosphate. That 
seemed to him to be a method by which the 
native mineral phosphates could be converted into 
a basic slag phosphate suitable for use. Tha 
question to be considered was whether it was the 
ratio of lime to phosphate which caused the 
beneficial results. Although lime, phosphate and 
nitrogen were elements of plant life, potash was 
also a very important constituent. Potash was an 
alkaline body which could he used for neutralising the 
superphosphate, and a mixture would then be ob- 
tained containing lime and potash which, he believed 
would be superior to the mixture suggested by the 
reader of the paper. If the potash statistics were 
inquired into abroad as compared with England, it 
would be found that the increase in the Thomas slag 
had been accompanied, in Germany and France by an 
enormous development in the use ( f potash manures. 
The land in this country was starved of potash. He 
thought the problem ought to be studied in relation 
to the alkaline phosphates, and not merely in con- 
nection with lime phosphates of unknown alkali- 
nity. 
Mr. Edward Packard thought there was no 
commercial form of potash which could he applied as 
an alkali to produce the action suggested by Dr. 
Rideal. The Chairman had asked why the reader of 
the paper had not given a large nuijiber ofautbenti- 
