448 
THE TROPICAL AGklCULTURIST, [Jan. i, 1894. 
cannot give even an ajjiiroxiination to the average 
ainonnt of nitrogen in the rainfall of a (•ouiitry. 
At the close of a jierioil of heavy rainfall in 
Colombo, in Octoher 1891, after nearly ^8 inches 
of rain liad fallen, tiie aiith(jr estiniate'l the 
aniount of nitrogen i)resent in a sanjjile of rain 
water as aiiiiiioniacai and organic, nitrogen, and 
found the same to be '0903 |iarts per jiiillioti. 
The nitrogen Jiresent as nitric aci<l was -0340. 
The author also determined the ainount of nitrogen 
present as ammonia in the i ain of the 14th of JSlarch 
3892 (a moderate rainfall) and found it to he 
•Jl parts per million. Two determinations are 
of course far too few upon whicii to base anytliing 
like an accurate estimate, but taking the am- 
nioniacal nitrogen at "1 jiarts jier millitni, and the 
Colombo rainfall at 88 inches per annum, «e get 
about 2 lbs. per acre jier annum of nitrogen in 
the form of ammonia ; or with a rainfall ')f 
119 inches as in the yeai' 1891, 2-7 lbs. of 
ammoniacal nitrogen. 'J'lic amount of nitric 
nitrogen would be from ^^ to '9 Dks. per acre 
per annum. The total nitrogen would thus be 
from 2"7 to 3'6 lbs. per acre per annum. It is prob- 
able, however, that an extended series of rain- 
water analyses might show this estimate to be 
much too low. The ])roportion of nitioge)i in 
rain water is greatest in the lirst ixirtion of a 
shower, and especially in that wliicl) falls after 
drought, so that reliable <lata cannot be olitained 
unless analyses are made representilig the entire 
year's rainfall. 
The power of soil and of vegetation to detain 
the ammonia which falls as rain may be gathere<l 
from the fact that at the time wlien the 
nitrogen, in the form of ammonia in Colombo 
tain Water near to the sea was at least '1 parts 
Ser million, that in the town ^^■ater from Labugama 
reservoir was under -01 parts per million. 
We have .seen that a crop of tea, on a 
moderate estimate removes from the soil 19i lbs. 
of nitrogen per acre per annum ; tiiat a rather 
heavy crop of coffee, including seed, ])ul|>, 
and leaves, according to iMr. Hughes' 
estimate removes about 21 lbs. But the supply 
of available nitrogen in rain water, taking even 
tlie highest estimate before ns, viz., that at the 
Mont Souris Observatory at Paris, is only 12 .36 lbs. 
of nitrogen per acre per annum. It is eviilent 
then that the atniosjjheric supjily of nitrogen 
is insufficient to meet the demands of growing 
crops, which have therefore U> draw upon the 
store of nitrogen existing in the soil, in com- 
Mnation with organic matters. This store must 
get gradually reduced beyond the point necessary 
to .sustain an abundant crop. It therefore be- 
come.s necessary to replenish the suj)i)ly of 
nitrogen by the application to the soil of 
nitrogenous manures. 
Pliosjjhoiic Arid. 
The next most important constituent of plant 
food is phosphoric acid. The original source of 
this substance is the igneous rocks in which it is 
found, in small proportion, usually less than a 
half per cent, and often much less, in combination 
with lime. As the proportion in soils is usually 
small, it is readily reduced beyond the point 
necessary for fertility, and it has therefore to 
1)6 supplied to the soil in the form of phosj)hatic 
manures. Seed crops, as a rule, make a great 
demand on the phosphoric acid of the soil, as 
this substance is specially assimilated by the 
eeeds of plants; but a leaf crop, as in the 
pase of tea, may also make a heavy demand on 
the fliQsphoric' acid of the soil, 
rotiiih. 
Most soili- contain sufficient pota*")! for tlie Uhm\ 
of ]dant«, but if the demaml made by a ciop 
on this constituent is large, the |Mjta»!li in tlie 
natural felspathic iiigiediciitH of the Moil may 
become too slowly available, lieuce jMjtaeh has 
either to be supjilied in niaiiure for cci tKiii cropi-, 
oj- it must I'c liberated from its combinations 
in the .soil by the application of liiiio. 
Li inc. 
Soils generally contain suHicicnt lime to meet 
the demand of jilants for this ingredient. I'lios- 
jihoric aci<l in manure is geneially combined with, 
or accompanied by lime, so that, when iihosphoric 
acid is added, lime is also abided. \Vhen lime 
by itself is directly a'bled to the soil, it ii- not 
added with the \iew of su]iplyiiig this eleiiieut of 
jilaiit food, but of decomjiosing the mineral anil 
organic ingredients of the soil, and thus indirectly 
supplying the other forms of plant f«MKl. Lime is 
also added to improve the mechanical condition 
and to correct the acidity of the soil. 
To restore fertility to soil, some laud re«iuiref> 
the a<ldition of nitrogenous manure only; other 
only jihospliatic manures : and. in some canes, only 
potash manure is sutticient. In many instances, 
however, crops are benefited by all three con- 
stituents. 
Kigures are not available for illustrating tlie 
degrees of advantage <ditaineil by the more 
common Ceylon products from the three im- 
portant elements of jilant food in manure ; 
although, no doubt, Ceylon planters could supply 
information on the subject in general terms. The 
following table <if agricultural experiments in 
the manuring of the cotton plant, at the Soiith 
Carolina Experiment Station, carried on at tlie 
Darlington ami Spartanburg Farms, the lau<l« of 
which are of different character, answers the 
question— does the cotton jilant lienefit by the 
presence in the manure of the three constituents : 
nitrogen, ))otasli- and i)hosphoric acid?* "The 
figures given in the table rejiresent the yieUl 
per acre of lint cotton in lbs., and are the 
averages of three years' dujtlicate tests on ea<di 
farm. The third column gives the average of 
the two farms." The figure " 1 " in the table 
inilicates a full dose of each ingre<lient as cal- 
culated from the analysis of the cotton plant 
f<n- a crop of 300 lbs. of lint per acre. 
Docs Cotton require Nitrogen. Pottrsk, and 
Phosphorir Acid ? 
Average (_'rops for 
1888, 1889, & 1890. 
Fertilizer — Dose.s 
Unfertilized 
1 Nitrogen 
1 Potash 
1 Phosphoric Acid 
1 Nitrogen, 1 Potash 
1 Potash, 1 Phosphoric Acid 
1 Nitrogen, 1 Phosphoric Acid 
1 Phosphoric Acid, 1 Nitrogen, 
] Potash 
o 
B r 
<£. 
o = 
06 
a; c 
x" 
-<t 
74 
96 
85 
117 
80 
98 
71 
125 
98 
148 
171 
159 
143 
197 
170 
162 
208 
185 
203 
230 
216 
298 
338 
318 
* From the Bulletin of the Agricultural Ex 
periment Station of the University of Tennessfe State 
Agricultural and MechaftjcaJ College, 
