Washington standard. [volume] (Olympia, Wash. Territory) 1860-1921, 1913-09-12


soil fluid is probably less than 10 per
cent. and the difference measures the
store of water additional to the cur
rent rainfall on which the plants may
draw. This difference % per cent OF
four feet. or 10 acre incheS-S16 tons
per acre, may be denoted the effective
soil fluid of average soil.
The rate of soil plant circulation and
the quantity of water passing through
soil and plants during the growing
season are indicated by the exhalation
from growing plants. A grass plant
will in the course of Il hot day exhale
its own weight of water. and young
leaf of wheat or rye exposed to the sun
may even eXhale its own weight in an
hour
The maintenance Of the soil plant cir
culation required for crop production
generally involves repeated additions
of water during the growing season.
for the effective soil fluid within four
feet of the surface would at the OBJ
served rate of plant Transportation suf-
fee for but meager yield even If the
entire quantity were utilized. In ordi-
nary farming the water Is not fully
conserved aud applied to plant growth.
so that practically the - acre inches
of effective soil fluid growth would not
suffice to produce Il crop or even per
NIT any yield whatever from most
types Of soil. though under certain
conditions water may be drawn from
greater depths in the subsoil than four
feet If properly cultivated and wa
tered the average acre foot OF soil.
weighing some 1000 tons including
the contained water,. retains efficiency
for centuries. but to be even moderate
ly productive this soil must convey to
the crop plants fully Is acre feet Of
water, or an amount equivalent to its
own weight. during each growing sen-
son.
To become effective In plant growth
water must enter the soil body. take
up both mineral salts and organic sub
stances in solution and pass thence
into the plants and on Into the air.
This Is the normal course of soil plant
anu tIC
Of the solid and fluid parts of the soil
involved in plant growth probably cor
respond fairly with the strength OF
the solution. or one to several hundred.
Pending precise determinations. 1t may
be assumed that the strength OF the
solution forming the soil fluid and the
ratio OF the solid and fluid parts requir-
81 En- tod, off, tNns NJ
equal and something like to 1000.
In nature the fora varies with the
rainfall from sparsely distributed cacti
and other desert plants to luxuriant
forests, and as lands are brought un-
der cultivation the crop yields vary
from place to place and from season to
season with the rainfall or with the
water supplied by irrigation. Gener-
ally throughout the United States the
actual yield per unit Of water Is con-
siderably less than the ratio Of dry
matter to water determined by plant
| exhalatiOn. A fair to good crop from
an acre a. e.. an acre foot, Of fertile
soil supplied with four acre feet Of
water during the year may be put at
a ton OF grain and three tons Of slower
and stubble, or four tons in all-equiv-
alent to 1-1360 of the weight Of the
water. With lessening of the aggre-
gate water supply (whl~n Of course
includes rainfall, accumulated ground
water. subsurfnce flow and Irrigation
the quantity Of water. virtually ceas-
ing when the supply falls below an
acre foot, while with augmented sup
ply the yield increases more rapidly
than the water SO long as the tillage
and character Of crop are adapted to
full use Of the entire supply.
| With present knowledge the ratio Is.
Of course, but rough approximation.
Measurements are vague and expert
ences variable, soils differ both in COM
| position and In the texture controlling
circulation. and the yield Of succulent
vegetables or Of juicy fruits or fresh
forage may be several times that Of
grain. nuts or dry forage. so that it
will probably be found needful in time
to work out ratios for particular crops.
just as 1t is now convenient TO reckon
yields per acre in different averages for
the several crops.
In the course Of his work on irriga-
ton Powell recognized the necessity
for determining 1.-The amount Of water
which is needed to serve an acre Of
land" and spoke of this service as the
duty" Of water measurable in acre
feet, and irrigators have frequently ap-
piled the phrase to the measure Of the
water rather than Of the service per-
formed by the water-a service sus-
ceptible Of useful measurement only in
terms Of what the water does in that
production which furnishes food for
man and forms the foundation for hui
man industries and institutions. So,
pending more precise determinations.
the agricultural duty of water may be
defined as the production Of one one
thousandth part of its weight in aver
age plant crop or one four-thousandth
of its weight in grain.
Naturally the cOefiicient for plant
toll