February 28, 1903. 
THE HARDENING WORLD 
181 
Something about Plant Food. 
(Continued from page 114.) 
Chemical investigation has shown that certain mineral sub¬ 
stances, such as lime, potash and phosphates, must be present 
in a soil to assist in the process whereby nitrates are formed. 
It is these compounds or nitrates which plants absorb by their 
roots that supply them with their nitrogenous food. The 
material from which this nitrogenous food is derived is the 
roots and stems of plants that have grown on the soil, vegetable 
refuse which has been dug in, or farmyard manure which has 
been applied. 
In the soil these organic substances have been oxidised or 
decomposed, chiefly by the action of various living organisms, 
such as insects, worms, fungi and bacteria, aided by warmth 
and moisture; and the result is what we call humus. Now, 
the nitrogenous matter contained in the humus of the soil is 
not in a condition to serve as plant food ; to become available, 
it must be converted into ammonia and nitric acid. This is 
accomplished by certain bacteria in the soil, the carbon of the 
humus being at the same time oxidised to carbonic acid. The 
different stages of the work are apparently performed by 
different species of bacteria, and the final products are nitrate 
of lime or nitrate of potash. 
All this teaches us that the amounts of humus matter and of 
nitrogen in a soil are very closely related, and that the former 
is most frequently a measure of the latter. That is to say, a 
warden soil poor in humus is likely to be also deficient in 
nitrogen. It may be mentioned that the fertile soils in tem¬ 
perate zones are always characterised by richness in humus 
matter and nitrogen. 
The following table illustrates the percentage amount of five 
selected constituents—organic matter (humus), nitrogen, 
potash, lime, and phosphoric acid—in five widely different de¬ 
scriptions of soil. The quantities quoted are in water-free soils. 
Selected chemical constituents in different descriptions of 
soil. Quantities in 100 Hr. of each, dry : — 
Oi dinary 
arable 
loam. 
Garden 
bedding 
loam. 
Rich 
garden 
loam. 
Rich 
pasture 
soil. 
Leaf 
mould. 
O ganic matU r 
Nitrogen 
Potash. 
Lime 
Phosphoric acid 
Per cent. 
3-84 
0-13 
0-20 
0*66 
0*12 
Per cent. 
4*05 
0*23 
0*33 
C*67 
0*48 
Ptr rent. 
8*46 
0*45 
0 73 
2*08 
0*10 
per cent. 
14*55 
0*59 
0 75 
1*20 
1*00 
Per cent. 
17*00 
0*47 
0*50 
0*18 
0.13 
The analytical results show that the proportion of plant food 
present in soils is veiy small, even when the land is extremely 
fertile, the bulk of the soil serving chiefly as a support to the 
growing crops and as a sponge to hold water for their use. 
An ordinary arable loam is seen to contain 3 84 per cent, ol 
organic (humus) matter, 0'13 per cent, of nitrogen, 0’20 per 
cent, of potash, 0'66 per cent, of lime, and 0 12 per cent, of 
phosphoric acid. A garden bedding soil of fair texture will 
contain a larger proportion of available' nitrogen, as well as 
other plant food constituents, than the ordinary average loam ; 
the amount of nitrogen being nearly double, the potash con¬ 
siderably larger, and the phosphoric acid four times as much. 
The rich garden loam is about twice as valuable in the a aiious 
chemical ingredients as the garden bedding mould , the ex¬ 
ceedingly large amount of lime—over 20 per cent, would \ ery 
materially assist in the active nitrification of the larger per¬ 
centage of organic humus matter, which is shown to be near \ 
8-)- per cent. In fact, Professor Hilyard has pointed out that 
the presence of lime in a soil, especially when associated with 
humus, much increases the availability both of potas i ant o 
phosphoric acid, so that, smaller quantities of these constituents 
suffice when extra lime is present. , 
We have, further, to remember that a large part of the 
elements of plant food contained in soils is present in such a 
condition that plants are unable to make use of it. _ tor ex¬ 
ample, the rich garden loam, as quoted in the foregoing table. 
would contain per acre, if the soil was cut to 9 in. depth, 
about 127,000 lb. of organic matter, more than 6,000 lb. of 
nitrogen, 11,000 lb. of potash, 31,000 lb. of lime, and 1,500 lb. 
of phosphoric acid, and yet a manurial dressing supplying 
50 lb. of readily available phosphoric acid in the form of super¬ 
phosphate or bone meal, and 50 lb. of soluble nitrogen in the 
form of nitrate of soda, sulphate of ammonia or guano, may 
greatly increase its productiveness. 
It is a pretty well established fact that the only constituents 
of plant food which need be supplied to garden soils are potash, 
phosphoric acid, lime and nitrogen. When it is said that 
these ingredients are lacking, it is not meant that the soil 
does not contain them, butthat it does not supply'the growing 
plants with as much as they need. It is not, therefore, because 
horticultural soils have been worn out of plant food ; it is only 
the more soluble portion that has been used up ; much the 
larger proportion of food is locked up in such combinations 
that the roots cannot get at and use it, that an artificial supply 
of soluble food in manure becomes necessary. 
Practically, therefore, few soils exist which can sustain 
many years’ cropping without diminished yield, unless fer¬ 
tilisers of some kind are applied to add directly to the available 
plant food of the soil, so as to' change that which is already 
present as to prepare it for the use of plants. The whole 
question of fertilisers thus resolves itself into a consideration 
of which of these methods can be pursued to the best advantage. 
Economy in soil management and the maintenance of fer¬ 
tility must consider permanent effects as well as immediate 
results, and hence involves the question of time. The pro¬ 
cesses of Nature act slowly but surely to continuously convert 
the inert elements of plant food in the soil and make them 
available. But this action is so> slow that it is profitable to 
assist Nature in one way or another. 
Gardeners, as a rule, use enormous quantities of farmyard 
or stable manure; in fact, they use nearly 7 lb. of nitrogen 
in the form of dung to get hack 1 lb. of nitrogen in the crop 
grown. And so long as they use nitrogen in this bulky form 
it is undoubtedly necessary to use this large quantity. They 
find it profitable to use it ; but, thanks to the investigations 
of scientific research, we now know how to obtain the same 
result with far greater certainty and at vastly less cost. 
(To be continued.) 
Flowering Grapes. 
Taking a broad view of the matter, we are wont to regard 
the species of Grape (Vitis), including those known as Cissus 
and Ampelopsis, as suitable only for decorative purposes for 
the sake of their foliage, or for the beauty or uses of their fruit. 
A number of American Vines are described by Joseph Meehan 
in “ The Florist’s Exchange ” as worthy of cultivation for their 
sweet-scented flowers, his remarks being as follows : — 
“The sweet-scented Grape of the trade is an infertile Vitis 
riparia, grown and planted by those who want a rapid growing 
Vine to give shade and sweet flowers, but not fruit. The ques¬ 
tion has been asked me whether a seedling of Vitis riparia 
would not be a sweet-scented Grape. Certainly it would, and 
the Concord Grape is sweet-scented; but to be the sweet- 
scented Grape of commerce it must be one which bears no fruit. 
The seedlings of V. riparia may or may not be fruit-bearing. 
When we sow seeds of any of our native species, V. riparia, 
aestivalis, cordifolia, cinerea, or Labrusca, we may get lots of 
plants that will be infertile, and, as these are all sweet-scented, 
I know of no reason why they should not be just as good for all 
purposes as are infertile V. riparia. 
“ This character is peculiar to the American Grape. Seed¬ 
lings of the European, Vitis vinifera, all bear fruit, but when 
we sow seeds of our native ones we take our chances on barren 
sorts. 
“ Bv watching the behaviour of a wild Grape Vine, noting in 
spring if very fragrant and then in. summer if fruit-bearing or 
not, one could soon possess himself of a lot of cuttings of a 
flowering Grape.” 
