THE TROPICAL AGRICULTURIST. [September 2, 1889. 
of only 2 tons 12J cwt. per acre. The better result 
by the nitrate is doubtless due to the nitrogenous 
supply being more immediately available, and more 
rapidly distributed within the soil, and so inducing 
a more extended development of feeding roots. 
These negative results by the nitrogenous manures 
alone confirm the conclusion that by the continuous 
growth of the crop on' this land it was the available 
supply of mineral constituents within the root-range 
of the plant, more than that of nitrogen that be- 
came deficient. 
The last two lines of the table show, that with a 
combination of minerals and nitrogenous manures there 
was an average of nearly 61 tons per acre, which 
is higher than the estimated average produce of either 
division of the United Kingdom ; and more than one 
and a half times as high as in Ireland in recent years. 
These results may be taken as fairly indicating the 
characteristic manurial requirements of the crop, and 
that both mineral and nitrogenous manures are required 
to give full crops. 
The last column shows the average precentage of 
diseased tubers under each of the several c editions 
of manuring. It may be seen that, without manure 
and with purely mineral manures, the proportion of 
diseased tubers is much less than where nitrogenous 
manures were applied. Consequently, with luxuriance 
of growth and high produce, the disease is most 
prevalent. 
A point of considerable interest was brought to 
view in the fact that there was, under every condition 
of manuring, a very much larger proportion of diseased 
tubers over the first four years, when the Rook was 
grown, than afterwards with the Champion. The 
very bad result over the first period was, however, 
doubtless in great measure due to the character of 
the climate also, which included some exceedingly 
wet and unfavourable seasons. 
"Produce without Manure, and with 
Farmyaed Manure." 
The following table shows the average results (per 
acre per annum; for each of the farmyard manure 
plot6, compared with that of the unmanured plot, 
over the whole period of twelve years, 1876-1887. 
Unmanured — 
Farmyard man 
ure, six years ; 
unmanured, six 
years — — 
Farmyard manure 
and superphos- 
phate, seven 
years; farmyard 
manure alone, 
five years — 
Farmyard manure, 
superphosphate, 
and nitrate of 
soda, six years ; 
farmyard man- 
ure alone, six 
years* — — 
1 13* 
3 12, 
4 7j 
4 15| 
Small. 
Diseased 
Total 
CD -li 
a & 
0 5 
a & 
0 1| 
CO -U 
S B 
EH © 
1 19J 
0 6J 
0 3| 
4 2f 
0 6§ 
0 
4 18| 
\ 0 61 
0 9| 
5 11J 
Per cent 
Per cent, 
3'15 
4.56 
4-93 
1-82 
Comparing these results with those obtained by 
artificial manures alone, we find that farmyard man- 
ure, which, besides an abundanoe of mineral matters, 
and a large amount of organio substance rioh in car- 
bon, supplied annually about 2001b. of nitrogen — gave 
considerably less produce than an artificial mixture 
of minerals and ammonium salts of nitrate of soda, 
supplying only 80 lb. of nitrogen per acre perannum. 
The f';i<;t being, that it is only the comparatively small 
* The superphosphate, but not the uitrate, was 
Applied in the seventh year, 1882. 
proportion of the nitrogen of farmyard manure which is 
due to the liquid dejections of the animals that is 
in a readily and rapidly available condition, whil i that 
due to more or less digested matter passing in the 
solid matter, is more slowly available, and that in 
the litter remains a very long time inactive. Hence, 
the addition of nitrogen, as nitrate of s di, to the 
farmyard manure had a very marked etfect. 
It may be mentioned that, over the last six years, 
farmyard manure, together wi n the residue of pre- 
viously spplied farmyard mauu: e, superphosphate, and 
nitrate of soda, only yielded o.n average of about 
4 tons of tubers ; and that farmyard manure and 
the residue of farmyard manure and superphosphate, 
only gave about 4j tons, whilst farmyard manure 
alone gave, over the first six years, 5J tons, is a 
clear indication that the later seasons were some- 
what less favourable for luxuriance with such ma- 
nures. 
The last column of the table shows, as before, 
that the proportion of diseased tubers was the greater, 
the greater the amount of nitrogen supplied, and 
the greater the luxuriance. 
The next point of interest is the amount of some 
of the more important chemical constituents of the 
tubers stored up in the crop, under the influence of 
the different manures, and especially the increased 
amount for a given quantity of nitrogen supplied 
in manure. 
The average amount of nitrogen annually stored up 
in the tubers grown without manure was, notwith- 
standing the amount supplied in the seed, only 
14 9 lb., or less than would be yielded in Wheat or 
Barley under the same conditions. 
On the other hand, the direct application of 86 lb. 
of nitrogen per acre per annum, in the form of am- 
monium salts alone, only raised the amount taken up to 
19'7 lb., and when supplied as nitrate of soda alone, 
to only 23 lb. The incapacity of the plant to avail 
itself of the supplied nitrogen in the absence of a 
sufficient available supply of mineral constituents, is 
thus strikingly illustrated. 
With the same applications of nitrogen, but in con- 
junction with the mixed mineral manure, the amount 
of nitrogen stored up in the tubers is raised from 20 
tt>. to about 50 lb. 
It is remarkable that, by the use of superphos- 
phate alone, 30 tt>. more potash are taken up per acre 
than without manure, and that only 3 lb. more are 
taken up under the influence of minerals alone, which, 
besides superphosphate, supplied annually nearly 150 
lb. of potash. It is well known that one special effect 
of superphosphate applied to spring sown crops, is 
greatly to increase the development of feeding-root 
within the surface soil ; and thus it would seem that 
under its influence, probably on both soil and plant, 
the Potato has been enabled to obtain a large amount 
of potash from the stores of the surface soil. 
It is, however, when the mineral and nitrogenous 
manures were supplied together, that the greatest 
amount of potash is taken up. Indeed under the in- 
fluence of this combination, nearly one half of the 
150 lb. of potash annually supplied is recovered in the 
increased produce. 
But little is definitely known of the special func'i ->n 
of individual mineral constituents in vegetation. It is, 
however, pretty clearly established that the presence 
of potash is essential for the formation of the chief 
non-nitrogenous matters— starch and sugar ; and here 
in the Potato we find a greatly increased amount of 
potash in the heaviest crops, that is to say iu tho.-e 
in which the largest amounts of starch have been 
formed. 
In regard to the application of farmyard manure 
for the Potato crop, the results seem to indicate that 
this plant is able to avail itself of a less proportion 
of the nitrogen of manure than any other larm ciop. 
Yet, in ordinary practice, farmyard manure is not only 
largely relied upon for Potatoes, but is often applied 
in larger quantity for them than for any other crop 
It is probable that, independently of its liberal 
supply of all necessary constituents, its beuefioial effects 
are in a considerable degree due to its influence on 
