Condon globe. (Condon, Gilliam Co., Or.) 189?-1919, 1913-07-25

ceases by reason OF exhaustion Of the
soil fuid IL probably less than 10 per
cent. and the difference measures the
store OF water additional 10 the eur
rent rainfall on which the plants may
draw. This difference Us per cent Of
-four feet. or ~ acre incbes--si6 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 exbalation
from growing plants. A grass plant
will in the course OF hot day exhale
its own weight OF water. and a 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 wnter 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 n the
entire quantity were utilized In ordi-
nary farming the water IN not fully
conserved and applied 20 plant growth.
80 that practically the ~ acre inches
OF effective soil fluid growth would not
suffice TO produce crop or even per-
init 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. lf properly cultivated and wa
tered the average acre foot Of soil.
weighing some 2000 tons dncluding
the contained water. retains efficiency
for centuries. but 10 be even moderate
~ 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 sea
| son.
TO become effective in plant growth
water must enter the soil body. take
ND 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
circulation. and the relative quantities
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 aud fiuid parts requir-
ed 10 maintain efficiency are about
equal and something like to 1000.
In nature the Hora 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'
i ally throughout the United States the
actual yield per unit OF water Is con
sIderably less than the ratio OF dry
1 matter to water determined by plant
/ exhalation. A fair to good crop from
| an acre q. e., an acre FOOT of fertile
soil supplied with four acre feet OF
water during the year may be put al
a ton Of grain and three tons OF stover
| and stubble. or four tons In all-equiv-
alent to 1880 of the weight of the
/ water. With lessening of the aggre
gate water supply (whl. n of course
includes rainfall, accumulated ground
water. subsurface flow and irrigation
the yield dlminlshes more rapidly thar
the quantity of water. virtually ceas
Ing when the supply falls below al
acre foot. while with augmented sup
ply the yield increases more rafldlJ
than the water so long as the tillagt
aud character of crop are adapted t
full use OF the entire supply.
With present knowledge the ratio is
0f 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 succulen
vegetables or Of juicy fruits or fresl
forage may be several times that o
grain. nuts or dry forage, so that |
will probably be found needful In tim,
to work out ratios for particular crops
Just as 1t is now convenient to reckol
yields per acre in different averages 70
the several crops,
IN the course Of his work on irriga
tion Powell recognized the necessit
for determining "the amount of waite
which is needed to serve an acre o
tand" and spoke of this service as tn
duty" of water measurable In acr
leet, and irrlgators have frequently ap
piled the phrase to the measure of tn
water rather than of the service pei
formed by the water-a service sus
ceptible of useful measurement only 1
terms of what the water does In tina
production which furnishes food fo
man and forms the foundation for hr
man industries and institutions, 81
J pending more precise determination
} the agricultural duty of water may b
: defined as the production OF one cn'
!; uhousandth part of its weight in ave-
age plant crop or one four-thousandt
OF Its weight In grain.