The Hawaiian gazette. [volume] (Honolulu [Oahu, Hawaii]) 1865-1918, 1915-11-05
USING LESS WATER
MAKES BETTER GROWTH
Too Much Water In Soil As Bad
As Too Little
Best Amount For Growth Can Be
Determined BY Laboratory Tests

Much attention has been given in re-
cent years to making better use Of the
water where irrigation Is practised AMI
to making the soils more rctentive o.
moisture in districts where the rainfall
is insufficient
What is the best percentage Of
water, is question that might well
be asked. The physicists have deter.
mined, by theory and laboratory tests,
that the best moisture content Of a soil
to promote most rapid growth of crops,
and also the point at which the labor
Of cultivation is the least, is at just
that degree of water retaining capacity
where each soil particle Is wet, but
where there is no surplus free water in
the minute spaces between them. That
lis to say soil moist enough TO supply
growing crops with the large guanti1
ties of water which they require must
have air as well as water in its pores.
Critical Moisture Content
1t has been proved that when a soil
I 20 ~ thio SohuitioH C"tiNatAOh 10
easiest.
This exact point Of optimum water
supply can be determined by very
simple laboratory experiment, and is
termed the "critical moisture con
tent. If more than the critical mois-
ture content is retained in a soil IL
becomes hard to plow and is also not
in good condition for crops to grow to
best advantage because the soil con.
taius too much water and not enough
air.
A soil may be moist to the touch
and in appearance and yet not have
enough free water in II to grow crops.
Taking the "critical moisture con
tent" as the optimum moisture con.
dition, the point at which plants no
longer can take water from the soil Is
known arbitrarily as the "wilting
point yet at this point the soil Is
! by no means dry. At the other ex-
treme would be the point of satdra-
ton when alt the air is driven out of
the soil and Its place taken by water.
Water Holding Capacity "E@.
Some experiments recently made at
the College of Hawaii with red"
cane soils from Maui are interesting
as showing what the satutation, crit.
cal and whiting points are. The air
dried soil weighs approximately eighty
pounds per cubic foot, so that an acre
of soil to the depth OF one foot would
weigh, in an absolutely dry condition,
about 3,5O0,000 pounds. In reality an
acrefoot of soil never gets absolutely
dry, but this weight may be taken as
representing the mineral "skeleton"
Of the soil absolutely devoid Of free
water ...'H.
1t was found that this red cane soil
contained $50 per cent of air spaces,
so that II all the air was displaced with
water a cubic foot OF the red dirt
would weigh 1878 pounds, while an
acre to the depth Of one foot, saturated,
would weigh over 5,545,O00 pounds.
At the whiting point, or when the
roots of plants were no longer able to
take enough water out Of the soil to
sustain growth, IL was found that near.
~ One-ffth of the weight of the soil
was water. There was still 1873 per
cent of water in the soil Stated an.
other way, although an acre foot of
this red soil still held $4,000 gallons of
water, it was too dry TO grow a crop or
sustain the life of plants. NJ.
At the "critical" moisture point,
where growth would he best If Just that
degree of moisture could be maintained,
the water per aere.foot was $4,000
gallons. Hence there would be n mar
gin of only about 1900 gallons Of
water held in the first acre-foot of red
cane soil between the condition Of
moisture where growth Is best aud tho
point where growth ceases, or say
an inch and twO.thirls of water. a." r..
Saturated Soil is Poisonous O.. -.
Passing above this point in the d.
rcctiOn of saturation, growth is again
retarded, because plants find rs much
difficulty in drawing moisture from the
coil when there is too much water as
when there is too little. II the, soil
were to be kept saturated few crops
"Ould live many days,
1t naturally follows that irrigation,
to produce ideal soil conditions must
take into account something more than
the available water supply or an eight
lays labor schedule. On many planta.
tions irrigation practise is governed
very largely by rule of thumb and con.
vCnicnce.
To Use Water Best Dc.
There have been abundant expert,
ments which prove that for all soils
there is an ideal moisture condition at
which r"int all crons grows most rapid.
ly.-fcrtiIity, temperature and other
Conditions being equal In other words
there are good reasons for irrigation
ps for all other agricultural opera
tions, if they can only be discovered
Too much water is Just as bad as tor
little. besides being wasteful, There l.
need of soil tests on every irrigat I'd
plantation to find out just where the
"rritiral moi 'ture content" lies. II
lay modification OF field practise IL,
wotcr content of the soil can be main
tanned at that nptiuum level, an al
a.. g nj hl la male towards maia