Dec. i, 1894J THE TROPICAL AGRICULTURIST*. 403 
HOW TO SECURE " NITROGEN " FOR 
TROPICAL CULTIVATION : 
A New Discovery— " Vaccination of Land'' 
—and its Application to Ceylon 
Plantations. 
One of our most experienced planters and carefu 
agriculturists calls our attention to an exceed- 
ingly interesting article reprinted from an Ameri- 
can journal into a home paper and which, he 
thinks, cannot fail to be of value to all planting 
readers of the Tropical Agriculturist. We 
have great pleasure in reproducing it as 
follows, and in adding the practical comments of 
our friend : — 
The Vaccination of Land. 
Some of the most extraordinary agricultural experi- 
ments ever undertaken, considered both practically 
and scientifically, are described in Le Genie Civil. 
Everyone who has ever owned a lawn knows that 
to plough the ground at intervals, and raise a 
crop of certain vegetables, improves the subsequent 
growth of grass ; and a drive through the suburbs 
of any large city will show lawns undergoing this 
treatment, sometimes with a crop of potatoes, 
sometimes with beans, according to the notions of 
the owners or their gardeners. The process by 
which this alternation of crops improves the soil 
has never been very clearly explained. Most peo- 
ple suppose that the repeated digging up of the 
earth, to plant the potatoes and harvest the crop, 
is the secret of the success of the treatment, but 
chemists have fancied for many years that, in such 
rotations of crops, one set of plants might have 
the power of absorbing nitrogen from the atmos- 
phere and conveying it to the soil. With this idea 
a long series of experiments was carried out fifty 
years ago by the greatest chemists in Europe, 
who analysed various plants, the air in which they 
grew and the soil, before they were planted, during 
their growth, and afterward, and came to the una- 
nimous conclusion that the absorption and storage 
of nitrogen by growing plants was an impossibility. 
For all this, farmers continued to observe that certain 
plants, particularly of the leguminous tribe, such as 
clover, lucerne, sainfoin, and some others, instead of 
exhausting the soil, seemed to enrich it, so that, even 
after the leaves and stems had been cut and carried 
away, the roots alone, left in the ground, sensibly 
increased its fertility. Analysis showed that these 
roots contained a considerable quantity of nitrogen. 
If, according to Bossingault, Lawes, Gilbert, and 
others, it was impossible that this nitrogen should be 
derived from the atmosphere, it must be drawn from 
nitrogenous matters in the soil. The inferenoe would 
be, in this case, that nitrogenous manures would 
be beneficial to crops requiring so much nitrogen 
for their growth ; yet it is well known to farmers 
that these plants not only derive no benefit from 
nitrogenous fertilisers, but are injured by them, 
while, although through the nitrogen contained in 
their roots they improve the soil greatly for succeed- 
ing crops of other plants, they injure it for them- 
selves ; and leguminous crops, cultivated too long 
in the same ground, become sickly. It was not until 
a few years ago that science and observation were 
reconciled, by the persistent investigations of M.M. 
Hellriegel and Willfarth, who demonstrated beyond 
question the fact that the leguminosse do, in growing, 
absorb large quantities of nitrogen from the air, 
but with the singular condition that the absorption 
of nitrogen begins only with the appearance of a 
diseased state, which is marked by the development 
of tubercles, about the size of a millet seed, on the 
roots, and is apparently, caused by minute animals, 
which are always found in the tubercles, 
and seem to give tho plant the nitrogen- 
absorbing power. Further investigations showed that 
the young, healthy plants lived on the nitrogen already 
contained in the soil, and that it was not until this 
was exhausted, and the plants began to suffer, that 
the nitvogou-absorbing excrescences made their ap- 
pearance ; aud proved, also, that the (iny inhabitant? 
of the tubercles were, as a rule, confined to one 
species of plant, the acacia microbe, for example, 
refusing to live on the bean, or the clover microbe 
on the lentil. 
It is evident that a plant capable of absorbing 
nitrogen, which is a costly as well as indispensable 
adjunct to farming, and of storing it up in the soil 
for its master's profit, is a valuable possession ; and, 
as only diseased plants have that property, it is 
obvious that it is desirable to spread the nitrogen- 
storing disease. With this view, several skilful farm- 
ers in France and Germany have, within the past 
two or three years, been trying experiments, by 
"vaccinating," as they say, fields of leguminous 
plants, by sprinkling them with earth in which tuber- 
I culous plants have been growing, or water in which 
they have been soaked ; and the results have been 
extraordinary. Analysis has shown that a single 
crop of tuberculous leguminosse, if the tops are 
ploughed in, adds to the soil from five to twelve 
thousand pounds of nitrogen, worth from eighteen 
to forty-five dollars, to the acre ; and even when the 
tops are cut and carried away there is, enough 
nitrogen left in the roots to insure a good crop of 
cereals on the same ground the next season, without 
other fertilisers. In 1890, a tract of old, peaty soil 
was " vaccinated " with a ton and a half to the 
acre of earth from a diseased field. Besides this, five 
hundred and twenty pounds to the acre of scoria from a 
dephosphorating furnace were spread over the 
ground, and about a thousand pounds to the acre of 
kainite, but very little nitrogenous manure. The 
tract was then sown with clover, which produced 
nearly three tons of hay to the acre. The next 
year, a virgin peaty soil was treated with half a ton 
to the acre of sand, from a field which had borne 
a crop of " serradelle," a small leguminous plant, 
unknown to us. The sand was harrowed in. No 
other manure of any kind was put on. The ground 
was sown with winter rye. In May, thirty-five 
pounds to the acre of serradelle seed was sown among 
the rye. The rye produced a good crop, and, after the 
harvest, the serradelle, which had absorbed and fixed 
about sixty pounds to the acre of atmospheric nitrogen, 
was ploughed in, as green manure. The next year, the 
land was planted with potatoes, and similar potatoes 
were planted in neighbouring fields, which had not 
had the new treatment, but were simply enriched with 
barn-yard manure. At the harvest, the yield from 
the vaccinated fields, which had received no other 
manure, was from twenty-eight to sixty-two per cent, 
greater than from the manured fields, according to the 
variety planted. The most surprising result from the 
treatment appears, however, to have been obtained in 
Prussia, where a tract newly brought under cultiva- 
tion was divided, and part vaccinated with earth from 
a lupin field. The whole was then sown with lupins ; 
and the yield from the vaccinated portion was five 
and one-half times as great as that from the other 
portion, for equal areas. 
On this our correspondent makes the following 
extremely useful remarks for the consideration of 
his brother planters : — 
The difficulty for us will be in finding the right 
legume that will grow the tubercle, producing the 
microbo that will absorb free nitrogen for us. It 
strikes me that the article suggests a reason for tea 
improving and yielding well under, and grown in con- 
juction with, grevilleas, toons and Albizzias. They 
all seem to have the tubercle referred to and it is 
probably the seat of the useful microbe. Though the 
article seems in some parts exaggerated a bit, it is 
full of suggestiveness and indicates that the microbe 
theory in the point referred to, will lead to an ex- 
planation of many conflicting and difficult points in 
agriculture. If the grcvillea is found to be the col- 
lector of nitrogen indicated, sowing it broadcast, and 
digging in the seedlings, may be a simple method of 
increasing the supply of nitrogen, though on the 
other hand its dominant element, lime, may act 
detrimentally and might counteract the beneficial effects 
if ropeated too often. I have seen no indication of 
harm, however, from several applications of tho fallen 
leaves to the same spot. The analysis of toona and 
Albizzia. leaves which fall annually* I have uo{ geon 
