The ranch. [volume] (Seattle, Wash.) 1902-1914, 1908-09-01
RECLAMATIO
SOME INFLUENCES OF IRRIGATION
UPON SOIL FERTILITY


the soluble salts D6Sln their upward
march toward the surface, where the
plant roots may draw them in for the
plants use. Thus, when a surplus
of water is found within the soil, the
plant food is by the action of gravity
carried down into the soil and it is
only when the soil becomes drier and
the soil moisture is being evaporated
from the surface that the plant food
is being brought within reach of the
plants. This is well illustrated by
the appearance of alkali land at diff
ferent seasons of the year. During
the wet season and early spring, the
alkali lands do not have upon their
surface that white cru5r of alkali found
during the hot summer and fall
| months. During a heavy rain, the
white crust upon the alkali lands will
| disappear, but in a very short time
after the sun appears and evaporation
begins the white crust will gradually
appear The explanation is simple.
| The rain water dissolves the alkali
and takes it into the soil, but this
same water being evaporated at the
surface deposits there again the alkali
which a short time before was dissolv-
ed and taken into the SOIL
Our results show conclusively that
certain of the plant foods including
the nitrates move up and down in the
| soil with the movement of the soil
moisture and by keeping a bounteous
supply OF water in the SOIL large
part of certain plant foods may be
| kept beyond the reach of plants and
thus the plant will be deficient in
certain of it's elements. This fact be-
comes of prime importance in plant
production for quality may in many in
stances be more important than guam
| tity. This is we'll illustrated by the
results obtained in the growing of po-
| tatOeS for starch manufacture. Our
experiments demonstrate that the per
cent OF starch in potatoes increases as
the amount and frequency of irriga-
ton increases. Here is an illustration
of where it is desirable to keep GER
tain Of the plant foods beyond the
reach of the roots rather than a con-
centratiOn near the surface.
The results show, beyond the ques-
ton of doubt, that certain of the
plant foods may be carried to a con-
siderable depth below the surface.
This being true, it is possible then
|
of most of it's fertility by the applica-
ton of too much irrigation water
| Take for instance, a shallow soil with
a gravel subsoil the water reaching
this soil soon seeps beyond the reach
of the surface. Take again a soil
which has been drained by tile laid
at depth of three to five feet,
heavy irrigation results in part of
the water so applied, reaching the
drains and carrying with it some plant
food. 1t is a common practice in
draining soil for the removal of alkali
by teaching to keep continuous
stream of water running out the tile
by applying irrigation water to the
surface. 1t is possible in this way to
remove so much plant food that, al
though the alkali is leached out, the
land is not fertile and some artificial
fertilizer must be employed.
A too bounteous application of ir-
rigation may result in serious de-
pletiOn of the soil, and, even in cases
where there is plenty of plant food,
| injudicious irrigation will result in a
smaller crop, a poorer quality of prod
uct, or both, and it is only by thorough
understanding of the influence of soil
moisture upon plant production that
we hope to make the best use of irri-
cation water.
In conclusion, we will say that dur
ing the coming summer we propose
to extend our Investigations on irri-
cation VS.. soil fertility to include
study of the effect of irrigation upon
the potash, phosphoric acid and hui
mus contents of the soil. We hope
that by such study we will be able
to offer scientific explanations of many
of the obscure plant phenomena which
puzzle agricultural Investigations to-