UP-TO-DATE FINDINGS ABOUT ACID SOIL 
FERTILITY 
H. K. BUTTON 
Feeding Your Crops Correctly—How Sulphur Paves 
the Way for Good Potatoes—What Manure Really Does 
P I ME was, and not so long ago, when sulphur was re¬ 
garded by the layman as a cure for the itch and by 
some theologians as “atmosphere” for the sub-base¬ 
ment of eternity. Now the up-to-date plant grower 
finds in sulphur the means of a controlled soil acidity as well 
as a probable escape, wholly or in part, from the purchase of 
expensive acid phosphate. 
Every year the problem of intensive cultivation gets more 
difficult and the rewards to the skilful become greater. Stable 
manure is now almost out of reach, and the grower of field crops 
must turn to green manures and fertilizers. Now this combi¬ 
nation sounds good, but in practice we find that continuous 
Potato culture demands a soil too acid for the growth of any 
green manure but Rye, and even that fails to decay as rapidly 
as it should. In short, if the land is sour enough to insure good 
smooth potatoes, it is too sour for the best use of green manure. 
There has been only one practical suggestion as to how to 
meet this problem. When the farmer has raised Potatoes as 
long as he thinks wise, he must lime his land for a rotation. In 
former days lime was spread with a free hand and in large 
excess, but our up-to-date farmer sends a sample of soil to the 
soil laboratory to find the lime requirement or amount of lime 
that will be absorbed by the acids of the soil and leave no sur¬ 
plus. This done, he adds the proper amount of lime and sows 
his soil improvement crops which niay occupy the land for one, 
two, or three years. When the time for Potatoes again comes 
around, the land is plowed and flowers of sulphur sown broad¬ 
cast, 200 to 300 pounds to the acre. The reactions of the soil 
(bacteria) reducing this to sulphuric acid give just the neces¬ 
sary acidity to insure beautiful smooth potatoes. 
A FINE adjustment in regulating the reaction of the soil is 
possible through the choice of fertilizer materials. Ni¬ 
trate of soda sweetens the soil, while sulphate of ammonia leaves 
an acid residue. Contrary to general belief, acid phosphate 
has no effect on soil acidity, but potash in the form of sulphate 
or muriate displaces large amounts of lime and contributes to 
the acidity. Much of the benefit of ground bone is due to the 
residue of lime. 
Feeding a plant correctly is just as complex a matter as 
feeding an animal and as yet we have touched only the begin¬ 
nings of the problem. Indeed, the majority of the farmers 
who are actually raising crops for a living have not begun to 
feed their plants at all or else give them “brand” fertilizers of 
an unknown origin, just because they are called “Trucker’s 
Delight” or “ Potato Special ” or “ Harvest King.” It is not to 
be wondered at, therefore, that ordinary people don’t know 
much about feeding plants. 
A second new wrinkle in soil fertility is the use of sulphur to 
make available the phosphorus in rock phosphate. Now the 
idea of using raw or rock phosphate has appealed to many 
people since Dr. Hopkins so clearly demonstrated its use on 
prairie soils. “Twice as much phosphorus for half as much a 
ton” sounds good to most of us. In actual practice rock 
phosphate has proved better for the Middle West than for the 
Atlantic Coast. Now it is shown that we can make the phos¬ 
phorus available by converting the sulphur to sulphuric acid 
which is absorbed by the finely ground phosphate rock. In 
this way there is a steady supply of available phosphorus as 
the plant grows. Thus far, this method has been mostly used 
in intensive gardening, greenhouse and coldframe work, but 
with added experience it may spread to general field culture 
and reduce the costs of raising our staple crops. The present 
plan seems to be to use 100 pounds of commercial flowers of 
sulphur mixed with 500 pounds of finely ground rock phos¬ 
phate. If this is mixed with manure or in a compost heap the 
action is more rapid as the humus furnishes food for the bac¬ 
teria which oxidize the sulphur. 
The phosphate rock will absorb all the sulphur and prevent 
any increased acidity of the soil. With rising freight rates 
which must increase the already high cost of fertilizers, it is 
believed that this method will prove of great economy. 
W E MUST revise the statement, undisputed in most text¬ 
books of agriculture, that acid soils are largely due to the 
decay of green manure. When a large amount of organic 
matter is mixed with the soil, its rate of decay depends upon 
the dryness of the organic matter, the intimacy of its admixture 
in the soil and, most of all, on the temperature and moisture of 
the soil. When decay is complete, nothing is left but nitrate, 
water, and gases. There is no permanent increase of acidity 
in ordinary well-cultivated soils as a result of the decay of green 
manure. When the soil is already acid, the decay may be 
checked just as vinegar preserves cucumbers, and it is probable 
that at such times plant poisons or toxins, which do great harm, 
are formed. 
Green manures aid in getting hold of the lazy nitrogen of the 
air. Everybody knows about the nitrogen gatherers on the 
roots of Clover, but not so many people know of the free-living 
bacteria, called azotobacteria, which are able to get their 
energy from the decaying matter of the soil and gather their 
nitrogen from the soil air. These azotobacteria are closely de¬ 
pendent upon a sweet, aerated soil, and plenty of decaying vege¬ 
table matter; but, as these are needed in any case, we may just 
add a little more and set it to work to fix nitrogen. 
This settles many an old dispute as to the ability of non¬ 
legumes (as Oats or Rye) to add nitrogen to the soil, and we may 
safely say that this class of manure at least causes nitrogen to 
be added to the soil. It also explains the effectiveness of stable 
manure which has long been known to be out of all relation to 
the amount of plant food contained. When we apply stable 
manure we not only apply the 10 pounds of nitrogen that the 
chemists can find but we apply also several hundred pounds of 
fuel for the bacteria which feed on the dissolved and decaying 
fibers and rustle their own nitrogen, which, like all thrifty be¬ 
ings, they leave behind them as a legacy to all the earth. 
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