PRESS BULLETIN No. 111. March 6, 1909.
florida Agrlcullural Experiment l gallon.
THE FORMATION OF NITRATES IN THE SOIL.
BY A. W. BLAIR.
Plants take up the greater portion of their nitrogen in the form of
nitrates, which are fairly simple substances when compared with the humus
from which they are so largely drawn. These nitrates are mostly elaborated
in the soil, though sometimes they are supplied directly in the form of
nitrate of soda or nitrate of potash. It is important that the farmer should
appreciate this, since favorable soil conditions mean the formation of large
quantities of nitrates; while unfavorable soil conditions mean not only a
decreased production, but may even result in a loss of nitrogen.
HOW NITRATES ARE FORME
Nitrogen is found in the humus of the soil, 1 animal and
vegetable materials used as fertilizers, but it exists mplex com-
pounds which are not soluble, and therefore calM I ly used by
plants. These complex substances must be brok mpler ones,
and the nitrogen must become a part of a compoun4.l b le, in order
that it may be taken up by plants. This is effected cf organisms
called bacteria. They seize upon the organic matt -dead roots,
stems, leaves, grass, stubble, manure, cottonseed lood, the re-
mains of animals, etc.-and break it up into siml s, somewhat
as if it had passed through a fire. Carbon oxide
and water are formed. This ammonia is in tu
teria and converted through an intermediate sta
unites with a base (if there are sufficient bases
If lime, potash, soda, or magnesia are present,
nitrate of lime (or calcium nitrate), sodium nitr
magnesium nitrate-all of which are soluble in B be taken up
by plants. Nitrate of soda acts more quickly as n sulphate of
ammonia, because the former is taken up mo Ieidtly by the
plant, while the latter probably nearly always 1i trial action,
indirectly into the nitrate. That sulphate of ammonia is converted int5 a
nitrate is proved by the fact that when it is applied to the soil, there is a
rapid increase of nitrates.
CONDITIONS FAVORING THE FORMATION OF NITRATES.
The following are some of the conditions requisite to the formation of
nitrates in the soil: (1) the nitrifying bacteria must be present in sufficient
quantities; (2) the temperature must not be below about 41 degrees F. nor
above 131 degrees F.- the most favorable warmth being about 98 or 99 F.;
(3) sunlight must be absent; (4) a reasonable supply of moisture is required;
(5) there must be free circulation of air; and .(6) there must be a base
present with which the nitric acid that is formed may unite. In the ab-
sence of a base, this nitric acid reacts injuriously on the bacteria.
Nitrates are formed rapidly in sandy loam soils that are well supplied with
humus, if other conditions are favorable. They are formed more rapidly
and in larger quantities within a few inches of the surface than at a
greater depth. A sample of soil taken in a pineapple field just beneath the
covering of dead leaves and trash, gave 6.26 parts per million of nitro-
gen as nitrates, while another sample taken from the same plot includ-
ing the surface and to the depth of nine inches, gave 2.28 parts per
million. Samples from the same field taken to the depth of 3 to 5 feet gave
only about .34 parts per million of nitrates. This may help to explain the
value of mulching. The mulch protects the surface layer from the intense
light, but still allows a free circulation of air, and thus makes the conditions
for bacterial development more favorable. The mulch also helps to retain
the moisture and prevent sudden changes of temperature, and this favors the
The mild winter climate which Florida has, is favorable to the formation
of nitrates; but the open sandy soil, and heavy summer rains are likely to
bring about their loss through leaching. The loss is not so great, however,
if there is a crop growing on the land during the rainy season.
State papers please copy.