119. Soil moisture lecture prepared for field men, Great Western Sugar Company, presented at Greeley January 14 and at Loveland January 15, 1926

By

~. J~.

Parsi

a .1

Irrig~til):

:'".nginccr

,

U.

u.

De"i)t.

o:!"'

£?;riC<..1~t'ure

,

or

1

,

1:

L:

s ~

~;

c

l

o •

It

is

to

lY:

recn·rize

:1t i;" E'

out3et

t~ at

it

"i.

1.

ot

be T)Ossitlf.

for

·s

to

iisc1·~s 3-t

thi. ...

t

L e ·

l_

PDc.sn

of this

ir

port;J.nt

:ub~

.,t

.

iS C OTIS)

rb.bly

i:~"'VO lv

kiter

is

;:;~,

colorless liqui

"'

fOr'ivec by

two

gases

,

hvdro

o·t-'n

and

ox;,rc:

P-n

.

It

5

s

s

eldor.

,

if

ev

..,r,

fOll!ri

to

be purr., a.ltcr

c:01

inr in contact

wit:·

t1•r; ec.:1. t

•

Rain

\i'a

ter

is consi J.ered. to be 1 e st co: t-

r-i

n ted

~n(,

trr

r

~ore,

ne_:.J•ly

n

r(- a::.,

it

fa

1ls

fron

tb

e

sky

.

Pure ;'later to dri

n-c

is

r1ot ·

)petizin( ,

it is flb.t;

t"·

is is

l

ec~use ~·e

have G1J.

.

ltiv:....tec1..

a t<.1.ste fo., it in its ir·:pur

stute

,

but t",is i._pu.,..c

wate..--

,

of

eourse

,

beca se of' it ...

br..L. ~

n

t....l,.,.,o

t

~lni

vers'-1.1

SQ

VG""'t

in ....

ont...Lc

t

1;i t1

the s oi

1

is

,

ca-pa.

~le

for a

sor~"ltion il

to

t.

0

nlant

of

t

"r

1Jlcmt

i

s

accor

lis1'::e

b~r

7hJ.t

is

kno·m -

s os

·oses

.

~e:.t£-r

··

)c,

is

of

c..dvar..tago

to plant

a.n

=mirr.:-tl

i.s

th~t

rnon

ro

linj

."ic·.~.ti011,

dl.J..t: to

loweriY.lD'

ten

..

psr-turss,

it

is

to-.m~

t'b_t

t:bis

for:rrcJ.t;_on

of

sol·

r·;;

ss

,

or

i c ,

occurs

:;.t

~l

c

surf

...

ce rc:...th

r

t.

"'C!.·~

th bot to!"' or

ir~tc~i

or of'

tl,e l"qt1ir

.

?

t ral

SL'i"''

noint,

sho

1 t~~is b-

otherr,·jse, Ol.U'

l~;;,

e

...

it'O '"i

freezP.

.o· "~"St

o_t

t

G

bot

-

l

~~,

effec)t, tnl. m

:f~noation

of

fist"'

:._nn

nt1er

aquatic

ni

~

, """n·,

too, tr'e

i

e

'7

1lc

10t

beth

·191

,util ,,

t~

su"'- er b8

-cw

.

.ls8

o"'

t

1£ i. :suJ ... ti

n of tJ

<

ton

la~1er1.

vrould be

tr·::.e

in

t:v~

nature 0

soils

t'

at

'.:h

8

sn i

1

rra

1

-i11

the snrinf

lT'

plantino-

tilre

.

U V_.L"""''~'L. ...

i

t-r

::·o)~

1

e

....

t

than

')t ,,

rA

li

quietS

,

•vh

ic

1:

ugair

i

a

!f2T""' r

a

tc; i

· ,_ a·~v 1_tt~r;c

_frorr

_t:hc:

~

-is

the :ro

i

:r

or

tr2.,..,sm~tati01 ~~

··

i"'h

l l

~a.tcria

s a.r.·

rove'

f

o

root t

lc'lf

-plac

•

It

is not

rry

i-1~ention

s.t tris

ti:rrt:

to isa1.1ss

trr

s1Jbj

ct of soilf:

that is,

their fo1ration a..l!d cte:mical constitu nts

.

s tris bas bEen

t'J;oroly

iscusse"'

b

f

r,

you last

VJee'r,.

w.· tcr in t e soil

!m.Ss

as : 11 as the

'i

sc ,ssion

of

closely relate -,-1e1,on

.luter,

o-r u:oist1re witf-1in the soi

,

is sai'

to hs.ve

three distinct

·0rrrs or co,_ ..

_

1-

Hyg.

·o

s .o··,ic

.o

i

sture

2

-

"a,ill:.;.rJ

J:~Oi..,ture

·=> fo

11

,.,..

oJ•

3

-

.ree

,

grEl.vit-: ..

tiODb-1,

gro-u.nd

,

h~llrostatic

water, o., bottoF

;v

tor

.

::J:y.n-rosccP_Iic \

at.~r

is

thu

t

Tl

oi.;:, tu ·e

Jonta

i·

ed h:

the

ro i

1

v!lic

1

is

1

ot

L">..va

·

la.bl e

fo1.. ,!l:J.nt

11.

sc

.

:ro

rive ;IOU

a clear

C01'

1

_CG1ltion

as to

_{this C')J "ition,}

let

_"OS

_{t;_;l:-}

a

It

is

nb,.j_

..._,s

thc:.t if

t ...

i~-5

soil be

left

at

t:hi

ter) -rat·!T.e for

r .

_... 1

_tjr.e

_,

_all

_t:b

_{.oi..,tnro th}

_.1

_{ein c nt L}

_,-~

_{·ill be}

_e:melle

_•

prees 'J

.,

it

\""ill b

-"m;md

absor tjon

of

moistTn·c fro

tl'E

air-

.

1

_his

_{increased as a}

_.rce

_1tage

_{i ... -;} 1

_{movn as}

_tl'P

_{JoEff5 ci~}

_nt

soil.

ce_

t

.

It

is ...

lso obvious

that

tt.is coef ....

'ici

t

noul

e

reduced

d.S t!ts

tcr

l)A::.-a

-tur- is incr

ase~

..

,

::11~ i

order thf..t

e_i·-it

coir:a·isons be

ossible

it

is

nccess

-ar..,.r to

eteJ: i:"e

t"i

is constr.:1nt J:nder

c

defirite soon5 fie tern rature

.

of obta."i."ing -:ater for its 1)hysica.l needs, but it is four d that it -plc.ys an hpor

-tart Ja:rt to tlw adv.

nta~e

of the

lant in

prGventi~'1.3"

the heating of the soil to

the

daneEr

noi

t,

tbis boing ue

to excessive sunshine

n't'!

t:e soil surface

•

.Also

,

t"J~is :::·il:r

of

moisture

assists in

brealci"r:p·

-~0'11

the

chernimJ

constituents of the soil

:p::.rt:i les iJJ.to avc.ilable

~~ant

f0od

.

It

as been

f

m.lno_

that crons would suffer

rratf.!ially or

nossiol~r

be lost on soils·

oi'

l

o

w hygrosconic pow:;r

•

.... 1

he

r-o::;t

in;portc.rt phase of th:: water

cor~tent

in

ttc

soil is

1-c-:.ov.n

as canillary

rrois

tut·

e

.

In

order

t:i1<-..t ~TG :, ""~all

get a c

l

ear ern cent :ion of

tr•i

s

cnn+i

t1on,

j

t \Vill

be

necessar-7 for us to

~

i

verge

c--0r''G""Tra

t

'-"'nr.

t:cy

to

unders

tn.n

t

e :pheno

10_1on

of ca

-r

o

m

our

common exp3ri ence,

it is easily

d

erconstra

ted

that i

J.~

we v:ere

to plJ:-;n·e

a

1ru:r

l- into

~tEn·

rJ.nc1

wi

thdrav7

it,

we

v;ould

observe a certt..il1

w

..

ount

of

water

dJ

-herin3"

to

tb

··

surface of

tris

sphe

r

e

.

Th

i

s

f

i

lrr of vra

t

e r s

ti

c ': s

o

t '

i :.;

r ar ... 1 e b c

-ca~

se of v.nat is knm•m as surfa

c

e tension, nolecular

<:1ttraction, or adresion

.

I

t

is important that

we:,

s:'ooul

get a very c

l

ear idea of

surface tension in order

that

v·e

r.-.ay

:pr

o

nc:rl;:,." un

.erst:rnc1

tho

phenowenon

of caui llary rise of

\Vater

i:'l

soils

.

N

o

d

o

ubt, all of us ha.vo had

ex-r:criencG ·pith a clay 1}i:pe an

soap

suds in

bloving

b1Jb

-bles

v~Joich

float off into the air displaying a

~vonderful aiTt:l.y

of color

.

Bov.;ever,

the color c

have

nothing to

o

\Ji

th surf_ ... ce

tension

.

'.lith a clay

pine and

soa-p bub

-ble

e are e;.ble

,

by

increasi-:: the -pressure

,

to increase the size of this

t

1bble

,

aTLd

,

i f

tb

stoF

of thr; --Ji-pc be ex:posed

to

norrral

atmospher

·

c pressure, ·:·

ob e-rve

that

tl-'e

b·~l

ole

:ill

irrrrer,iately

reduce in

size

.

the:; stretcbed r en:brane of t:be bublJle is rE._e;_.sed i'r

!"'

-pTess·

re,

it c

,i'tr'~~ts,

the

san:e

as an

infl

te

1.

ru.bber balloon.

It

is

not

i n ssjbl

for

u::::

to

irr:a~h~"

tlat if

inside this

S1

Jap

b"J.bhle

vvc vrere

to h._v

our

!arble

fixed in

_s0rP

rr · ner

~ _s11 ~11

t

d.t

i;ihe:n

tl1c bubble

wus

rerluced in

size and becaus · of botlJ bci

~~cs

sphcri.ca.l

i1

fO_'r', +;"bE

1'.

-obvious

t:b..at this str

t

~heel

!"er.b:rane o

"3.ter

rc~resents

a

1

ERSurv..b ..

:;:orce

t

at

is btsi:n_g

exerted at ver7 point on

t~

e su:rfa c

of

t(r.

rnarl'f

.

'.2hen,

t

00,

-re rray

loo'c at tl'

i ...

frorr

anot -r noint

o,. ·

~-c~·;.

If

G

·e

L

e

to

t

1

e a

oo

p

of

fire

t'hrcad ;:.nd

·

-..=...ve

tl~i::;

sut.11)orting

a film o ... · sO:J.:!!suds

t

·hen,

vircn

SU1'J')Orte

by

&n outsi e o ·

secon ar-7 loop of

ire,

if the

fi

l

..

is brokP11

insid

L e thr€u.d loop

tt

i

s

iou

r

thrt

tnis

threa

.• j

11

')e

it

'1~e. i~tely

dravm

int0 L

ei.rcula:r

fo::.~

, due

to

the a.ctj on o;·

surfsce

te:!lsj on

.

It if.

..-:·o11n, t'h<..~.t

it is nossible to

floc;~.t

a

lliPl-,ly

po~i~hr1

nee

1

or the

S1Jr

-fac

oft.,..

v~~utcr,

vsn

t1o t}'e

de:r,sit

or

·e

"

f"1t

o; steel

i .. ,

sev .... 11 ti·rrcs

tl'lu.t

of

wa tE ••

ter

uU

rfa.C

•

·:rr-

f:ct th1t s-pjders and

·

.;ater

-

s1d')

t~:rs ca11

ws.-....

k

0"7' "'"1',

if

~rm

c· oo se, on

th

v~.:...,

t ,

311rface is

b

eca·Ase of

tl

is

sa e for .c

o. s

t

;·et

crr<d

S'1rface

o

f

th c

v.·a

t r

.

In surrri:ng

u>~

this

idea

,

,e find

trat

tle

at .r surfacFJ

r:y be

loo -ed

1..P')OD ..:.~.S

b&LJ..cr

under

u

stress

t

o"·

,

in

other

vorrls~

'taving an

G

st- · c s,_,.

-face whie:i is in a st:resse

co:1~ition.

:ai

dro

s

are

sp_erical for this

same

reason

.

:..:olten

loa

"

\Vt.Gn

poured

fr~r ....

a hi£,'h elevation assurres S1")'er.:.r;al drops

or

s11ot Jhic

is .. n

R:X o;.

le of

this

phenr1roeDo

•

Ul')Ol1

clos, ex ...

r

·n'""'t ion it

ill

br: foun' that vnen

~

.. ter is

i·~

contact

i

th unother surf1ce

,

at

tbis poil

t

of

co

tact~

it

is seen

thu..t

trr

;ate:r

s

u

r

f

ace

is~;

.htlJ

e=.cv'""ted; '"

so,

thc1t

vess(,l ray

cnntain .1or

v~ater

in

voltt! e

th9..n the actual or

tr11s

voluTe of

the c:;I

-tainer.

s

'"~FJa."l.r,

bov e

tbe

r

i •

'i

1

_{he reason for this}

_is

_t~

_{. surf ce tensj.on \ l"ich}

_SU""

_norts

t~is e-tr~ l~Gr

or slic of

~ter

at th to

•

In

or er that

VJG r:a"'tT

g-et

clc·

rcr

'1ictu.rG. it w111 be necessary

£'01

-:J.s to fir

ou ·

~bout

the

::tc·~u~l c0r.

i

-tions

ht

~hr::

SllrfaCA of

t!

c ...;··

te~.

.:e

<1.ro

'""11

a•ra:t·e ot

the fact that - uro v,ater

is

c~.~""90sed

of rrolec,J_:es ',.:1vi1g

t

o p3.rts of' hydroeAn and one of o-;rgen

.

..t

5'"'1

e

point

\.i

t'tin

t~1A

rrass of tl"' v::..ter, th se rrolec·A. es are eq·x::, l:.u attr cted

a 1

short

distance

.

Let

ll..S

first

i

arin- tJ-at

tY.is noi 1t is

w 11

wit: ir the

r.-ass

o:

wat

- Y '

ett

snt·~

ist

me..

r:

ow

ti"'e

su."f co.

S

1l811

t is point

is

jn

equilj

brim.

,

o:r

attr~.ct

d

0

·1a

ly

iu

all directi::ms

.

Hext, 1 ct ·1s

i1

a.["ine

t!

at

t"

is

poil1t

or

r.ol

cule

be raise

,

an

as wo annroaci1 tbc sur.f:1.ce sor.r.e p0int vrill

1)6

reached

\'ihel

t

C

ttracti -

dO\i'll ar

is great

r

than

tl"'e attractiOL

ur

<;.;.rd beca.USO Of the

crrea.tor nurr1>er of

Y>"olecu

es

l1elow;

o

:r,

conve:· s;ly

,

because of

trP

fe'\?el

P"Olec

los

s tbi s point

r}

:

pproacheS

o.n·

J'€C.~Ches the ~'Utrir

SUrface,

i t

is founr

thc...t th8 cttraction

dOV•111_~lrd

is

so

e.

r:·

suTablc

11-:1_1-.,:tit

,

vinere-....s

the

c.~ttraction

u•-r:ard

i

s

zero

bec~'"'S

of there

.

beinO" no

~"'Olenules be:,ro1

t1"e

S'

r:facc

,

t ....

t is

,

v.utor

Y"'Olecv

es

.

It is

t

0

be

o·Jscr-ve

,

'tnr:n, thnt

bcct.use

o:f this

unbaJ,.._nce ·

cnn

i tj

on

t!lo

su1f ce

r-u·t

.;~.ssure c.~

strEtc"'red

eorcHtion

in omer that e

ui1ib~·iw~

be

cst~1.bli.srcr".

'Ji

tr

tni

s

i

le.: .. in

r

ii1~

v·c

~i

11

nov, try to

·ex~1l

... in v:hy

th~

'

tor v:

11 rise in

ele

-1_.11

_{his is}

_brcc.:

_se

_t

_"

r. ~ttracti:~n

o-'-"'

t.

e

mo1_ecmles of the ... aterial of tho

copt··cti~~

sD.rfac, xerts ,...,

gro~te:r

force

t~.an

the

~ol~culcs

of the

1ate

r

it!:elf

.

di'"f')Y)ai.

in the wat r t1-e

molecules

of

thE. ~oorcc:..u._o:

.. ., had

~greater

=ttraction

:fnr

the

rr~oleC'

le

Of the water

ti"~a11 t:h.H.t

wi

thin

t1c

r..ass

Of '\'

1

_{ter its}

1

_f

_,

_{thus n..a,sir:" tbe}

v~1t

r to stic' or

'here

.

I

t is believe

Dow

t11:...tt -\-c

have

10r

inc:.

i

le

...

of

thr;

·o:

enorl'!en :1n o

surface

tens

·

on

,

an~

the

di._,cuss

ion

l

ea'

in~.;

u

~

to this

p:1

int is very

nec-ssar~v-

fo·

..

t~

c

·e~sJ

t

~t

'Jtlnillary

action is cxnl=ir·e

~~ro:r: t-·H:> J~, .... 1r1~Joint

s

il

·ass?

cor::'""~act

soli

but

i

Tlste'd

ioJ

so~

c:t;

ing

~o!Y"'osed

of

'":Orl"Se

:.nd

e: ~rer

...

1;1

fj11e

pa_

-ti· ....

lE u,

rrixed,

c..t11'

1

_{tho..,...c. a}

₀

_1crein

_{co 1tuino· 111Lmerous}

_SL~~ll.

_irrc::--1

_{t ..}

_r

_po.Sst.~.g

v ys · i'J 1

• C...7

be loo :ed

u-no"t')_

a

t

1bes of i.Jrrall

iel,r::.eter

.

6-s-i tior.,

it

L:;

o' erv

d t~-~t L

wat r ""

i

se

3

to a me&.surab le

he~

.0·l1t

ins::

de

t:b

t

J

e

a

ove

t'

E.

o~1t0~ f' ·rate.~.

surfaee,

t:his

rise

eing

inv~'"rsel'

rono.

tion:;A.l

t0

t!".r·

size

of

t,,

tube.

.::J_t

i3,

t:r(

s! .

.t,_ler

t}~e tu'~o

the

greate_

tho rise.

..:'h,

fact

-h

t

the a.ter rises

i n

t'lis tube is

lJGCc.J.USe

o::

surface

t

ns·on, or Ue

grevte."

attr·~tion Of

tr

£

SS

for

th

water

.

Incj_dentally,

.ereur~, ~.-

i

1 l1a.

:..J.

greatsr

c...ttracti01

for

it

s ov-'11

o

l

e

c-_11

,

s, \ ;

11

not

here

to

flass

,

~m

in

t~is

case a

dA~_essio~

is

o

serve~.

In the

soil

these;

J:'lu..re:rous

irrigu ....

r

ranjfi~

....

tions

of

t!::

e.3C

l·Lsnage

"'1_~7S

_·rrs:7

_{bt ...}

s-su!!.e

to be

cu

)

.

_l ... ry tubes ::.ten inn'

·

n

all

·rections,

ar:c'

t~is,

then,

i.s

'\Jhy

the

soil

moisturE

of

water

is

.

ovod

out

thru th

soil

~.ss.

give

~rou vorq

i·:oea

~.iS

to t1 e

rani

ity

find

extent of this

1

over

ent

,

I hare

·irC'[kt.re

for

~,~,_, t'

is airvr.&.t, showi:n

thR

rise

-oy ca illnry acti o:n, __ oisttu·e in

v

r-ious

tvpes of

Jo

lor·ro

soils~

..

hese

ra:.r

br-; icJentif:lod

01

the

chc...rt as

follows:

1-

rer.trJ.ten

fal1"

soil,

4

miles

ec...st of

.'ort

ollins

2-

~~o

llegG

£

rrr

3 i

1

a.t ~ort

Collins

3

-

...

oc'ry

}or

s il

4-

Gr:.n

.June

t

1 on s 'Ji 1

5-

Eads

--

plains area

o.

eastern

Colora

o

6-

"'anon

Citr.

'(1:

is iaerd.r

s·

ows tr._ t for the lie-hter or s

1nd,,

soils t!.e rate of action is

r·~'ch

.reat-er than

for

tl:e he:rry or clcPf-Y soils.

Frorr thP

standnoint o:f

o1.rr

cap1llary tubt il-·

lustr-tion jus'; ··-c:rti.or:o_"', it

n

i["ht

be

3.ssur1ed tha.t

boca·use

of tl•e s!all

S.ja.C

or

nas-sage

va-·rs

in

t

R

finer _ctEri;ls,

the water

rri£"ht

rine

ore ra:;i

ly

b cause

of

the

a:p-parent greater effect

of

thr.

3,

rface te

sjon.

However,

thi.

s

is

not

true

brcause

the i11teri or- resi

sto.n

ce is

greater

than is

fo md in

the

passage

v1a:rs

of tr

e

coarser

or sandy materia 1.

It

has

been

observed that

~ten

the

l~Ner

end of

vertical gJass

soil

tubes

are

i~ersed

in a pan

of

water,

the

rise at

~irst

has

been

as much as one

inch

per

:rrinute.

Tl"is

rats,

however,

Yery ranidly

drcreases,

a:nd after

a :pe:rjoc

of

in

soru~

types

of

soils has been

observed to

reach

a

height

of

n:orc

than 10 feot.

Gne

might

be inclt

1ed

to tr

_

inl{

that

t

_ e a? ount

of

n:oisture

in the capillary tube,

that is,

a

tube

cv,-tai1:1j·,g soil --;here tl:e rate

of ascent is observed

as

to tir-

,e

,

t

1a

t

trc:;

Hstribution of t1is r'Jist1re

is

uniformly less as we

o u-p the soil

col-unn

frcrr

th

e

\'tater surfa.ce.

b·

tioT' of

Ji'1

ist

re as

found

n·

MnLa·~-!1"lin

for

c.m.

Id

aho

sandy

soil.

He

~i

.ds

t:T1a

t

the

r·aYir'tm

,...oncentTatian

i<'

at ...

oint

fror.

1/t.

to

1/7

of t1,c

r.~oist

colurrn

.

It

is

fiJr

t

h

r bcl_ieve

t t.:1t

t

he

w

ter o·

rr--oi~h.rre

asce,

t

d ,e to capil

ar;-

action

is

not

at a uni "'Or!1

rate,

bl

t

seerrs

tl"'

!lOV6 U}_Wa r s

in

t11f

forr

of

a

w

ve.

"'

o

far,

v1e

h

ve rrentione

h~rg-rosco,ic

rroisturE=

an

..

canil

g,r-;r

r-oisture.

r~he

ti~ird ~Oi"lition

of

wate1~

in the soil

is

::LJe gr·

vj

_tat

io:

··...,l

'~

tsr.

le ·

o

· th.

t

vhen

t:t

water content of t:1

.. soil n

... ss is

i

.creaGe

beyon

-::h

:~.t

of

t,·

8

capillm·

y

volur:e,

s

Jr,e point

ill be

rea~he

1 re the concentr.:.<.tion of

r

oi t-..rre is sufJ

·

ciF.nt

to

<-t::_

:--pe~:r

as

~-r

e vatn ·,

or

th:.tt

~la.ts-~

in

t

10

soil

-·~1ich

is

regulated

by

tbf,

force

of

gravi

t.

r

or

th

tt

v"·ich

1

as a

tr-ndc!J

cy

to

perc ol t

thru

t11e

s

oi

1

mass

to tht'

lo

.Ter

1ept:bs.

.e .o ·

hc~ve

m1

ide-::. of th s

three

r;o

itions

0.1.

t1•r;

oist

Ie

o-r

v~ater

-.-·itl:

-i

soi1s

•

.-:'ror a pr cti-;al stu

'Ji

,

as

wGll

a:;

·o

r

3Cic

1ti~i0

n;..rposo.:>,

£rust

have

sor c

r

.:~.s·

r /

o-::

the

.., _

o·.n

t

of r.

oisturc

i.J.

th

s

il.

Cor

reonly,

tl'

is

i

r;

exp!'e

s

~,er

as

. e

•

i

stur

ace

011

dr;:T

the

r.:·

o

st

co1

ron

.~ c2.s

ure

~:

ht -

to

br:

r-

,

ti0.

..,

ly

TL'I'J.i ·

ers

...

Howe7er,

it

i.: ob ions

t"h

...

t ...

c·1-bic unit

of

coil

1.7 be

su.i

'co ,ont,.dn ·

(tefinit fr..,.-:til"'1 ..

'1.l

p ... rt

of this

vol· re

of

fr e

··at r;

or

,

'6

11.:_Lt

S:...v;; t1,~t t"

e

s1'l cont ins

per urit o.£0

e"'?f, :...so

f

foot,

:i

certai11

~Gnti:

o

free

vater

,

or

a

ce

~t~lin volm.~.e

o·

i

nt..u,it

voluLt:; of

s

il.

It

i5

to

b6 ~- --r

rcico.ted

in

this

CU-86

r.

t i, is

~if

·c·

lt

t')

de

E

-per

unit

volu e,

s a c Jic foot.

Let

1_1S s~~i _tba

t

_{.:...11 c.L.,}

_0l.:ty

_{so i 1"" ... 1}

carr

~red

on

a

vol~e

basis.

~or

the

s

n

-ples "'

1

::.1

r,

).ve

_"IDeq··

_l volm··e;

th·

t

is

,

_t:t8

\·'oic--.,t:;

pr:;r

cu

ic

=oot u.re

not L

_{c s;;:.r}

e

•

..:'ris

~eans

tl.,at

fo1

clu~•

huv:il10'

·t

efi""'itf

per86

1

1t

of

_l"Oi .... turc

·o ·:

co ·1t

,Jn

7

:pou.nAs

of watc ..

or

3~

liters

p·-r

cubic foot,

where

the

S8.ndy

s

i1 for

tl1

sar

· e

centa~e

wo1.Jl

co

;.tai·1

9

poun._

01" 4~

liters

por

cubic

foot

,

··n

(~re

the . ...

;r

:.>oil

i::

t

'"C:"

at

?2

lbs

.

TIF;r·

cubic

foot

a:.Yl

thn

S9.Yl'1

:r

soil

_

t

93

lbs

.

ner C<1uic

foot

,

v~"'ltiDb.

tC"r"J. '

u .,

..loll~

f"Y'OTI

200

Lo [') rrrn-: s

,

or

1/2 to 1

_..OUll( & ~-

is

f)~.UI n~

r

is

ir_

e

jute

-~or-e

a1

thnri

ti•s

recor.,..

n

th ..

t

tbo y·eigni11:_rs be

n arlc

in

thr

ficl

.

'""'t

a

t

crrnc :ra tuJ'A

of' 110 or llC degrees

c

.

fo:r

_;., su:fil1i

ent r.erio

of tire to

c

1

_rive

_off

_a

₁

_{tf:tc n·oi s}

-t

r .•

_'or

accurL te deterrrd-

ations

of

sojl

}Tnist-~lr€

it

;j_ll

be

necesca!""r

to test

o

cas ionall v to

fi

ncl

ov t

'b:n

our

sam')le h

~

reachc

a c

mE

tan

t

v1ei~}1

t

.

~re r

o:re

r-Ji::>t<re

th=;

S3JT"f)le cont

ins

,

that

is

for

clay,

n.1.1ck

,

.:r

othe

Y'J..V"'"f

soil.:.

o~

tbis

nature,

t

"C

lonrrc!"

it

will

be

necossar to

bu1~e

the . atcrial

.

ho ... ,

e.;.cJ·e

a

constd:1t ..

i_

ht

,

tho

trur

wei,...}"t

is

c1..

terr-.:<ined

,

this

latter

,~ei

:rht

beir

.. :_-

less t=-:d.r

U1e

fiJT ...

"r weighing CJ.nd

the

0.ifferencc

re _a.·esonti.·1g

the

a!.Dunt

of

rroistur·~

coJtc..:..h_ec

i:r

our

sa1·~1.e.

ror

c:xsrnle

,

if

the

oveL

-

ried

.~aterial

be

JOO

gra!".s

and t~lE. · i

fferencc

bet

reen

the

first

_n

..

s

co ... d we·

r:l i1:v

has bP-en

foun

to 1;e

20

grarr.s,

t1 r:n

this loss

,

jvi

e

ly

the

oven-dried

·1ci

ht

or

20/200

eives

10/100

or

0

.

10

.

I'llis

,

as us1Ja .. 1.;.

exprc:

ssed

,

ro,_:tld

be

10 pe ··cent,

or

e 7ou:

~

sc..y

the

.. i:stur

of

this

sa. :ile

v.r~s

10

p.rcent

..

This is

thc;

FOSt

prfl.ctical

-vvay

of

a.--r1ving

1~0

1

t u.:J t,

~our

att ntion to

so~~:

o."'

th

otbr:;:vo

irr1?ort~

t tl i11t_n,s

i

o•Jt

soil

Let

,

~

fir.;t get so!.,.

i ea

s to

t

. " r<:. e of

.c>; '!'I

n s s of

rt

~

es

of

soil.

•11

is is

it

ort

n~

i

1

order

th

t

con, i

ti

1ns of ... ois tur·

.... 'l.

s

ph

r e

1

in eh

i

71

a

i.

a e

t

e

·~

as """ cnrf_ ee

area of

~.142

sa1-·e

i~c~es.

If

we ar- no'll; to il,· ginf:

bo:~

12

inehes sq'

...

t·

a..nd

12

il

c'hes de -;, it •;i_l be

ossi,

lA

fo

us to put o·,

thP

l.,r1tto.

o-P

thi

a

1~.-

cr

oft"

es

S}c1herc:;,

1...,

e c

'tay

.

Or

,

for

tl

e c l

·

c .oot

lP • Ot.11

be ·-

1

to

l)Ut

in

1~::28.

.~:~o·, let

us irr-"'·r.e

that our

snhPres

b

':ade

/10

of ,n

i

chin

ia

-rr ..

t

r; then

0.-

v oul

tai-

ed

1

11_

it

S I(TG,

10

00

Of

t

be SF .3! :..¥

1

~-p}'lc,y Co

surface

- ie"

·

oul' lJave: a

tot

.. 1

_,.,

areC~.

of

31

.

42

sr~u

(

inv!cs.

If

o -·

ophcre be rc;d· cec

to

1/100

i

~cJ1,

then t1• ·

to

tal

31.ll

-of

t

e

1

,

000,000

r

·ire to

f'i,

1

one

Cll

ic:

i1

c1

·;ou

.1

be

rz142 squ

rE

i

~J~

-es or

~1.

ut

2'2

-,:..tr

feet

.

o .rs

san

1 i

1

t 1o· r·

.,lay

4 0

lZ,~O

2.000

40

,

bno

10·1,

000

142,000

It

is to bf-

ob.:Jfrve

th-tt

i

n

t1F:

o1e

c·l>ic-f"'ot

of clay, tl-:!e'e is ·n

aggrea-ate

~:re~

of

t!·,

infinite nur1)el of

p--rtj_cles

of

-bout ....

.

7

o.o.c'~'·es.

It

is

~~·o ~n th~t

th, hog o

-sco··ric

o i rt· rc

i

tl

c

clc .... ;;

o

ils

is

r

-:J 1~

grr-

ter

t1 :....n

tl1c...

t

i ""

tr

sw1r,. sr)

11_ ,

•

,.,ror

t· E d

ta

just

aiven,

- see th_

t

t·

oreo.

0-!'

t1

6

1."):.1rtic1ef.J

i;!

the

S'lr

S

Jj

ls

i .. ,

!

llCh

... ss

t-

a

in

t"

a

:lS

the

hygxo

o

ic

:r.1oL .. tur

is

i1

s1rfuces,

it

is

obvio,~

t

e~

t a t

1

o

_ oi stu!,

of' t:i1i

natur

ri

1

b

-;. 1

1JY

th

~luy

c.oil....J

eco..-130 of

this greater

:::~.rea.

'r:ren, too

,

·, se.

that becausG of t'.,e

.gr at r uY~-l>t:r

of

c:.o:..t·,

AS

i•

t

c1c...

aoi ls

t.1f,

ca

j_1lo.r'r

·

ssa-2'

,,

ys aro

r

u ,h

s. aller in diarre ter,

thus,

s s 0'.'71

'Ly

exper

i

ent s

it"

tubes~

tb·

t

t

1e

totu.l

,ise

10

-is

ver.,.r

'UCh

gre~ter i J

t

~ore

con

...

t

Sf)ils.

~berc- ~J

G ot·

er

coe:ficient un

const

nts

h,vj1~

to

c

lith

soil !"'oisture

tho.t

will

be useful in

etLi

1

correct conce·ntion of soil r oist11

e.

~'i

t,

have

hygr

s,onic

~oisture. ·~his

l s U')a

t

fo rrn

u.

; cb ·

s

an

O}

t

rer

l;r

thin

fi

1" held

fir!Ily

b~

attraction to the

su.rf'9..c,

of

t:Pe s il pa,...tiGles

.

If

t:ris .:.oil

filn be

increc.ser i

thic~mesR

to

a !)Oint at

ihiJ··

plants

are

.iu~t

ab16

to

rae

:c.se o: it,

we no\

i·~B.ve

a

co·

i

ti on

ln1

as

t',E

vriltirg point,

or

t·r6

\Jilting co· f'ciP:nt

.

cOUC

hly

,

t i s

is

1~-

times

the

hygrOSC01JiC

!l')iSture

OI'

a sorption coefi'jciont, to

whic

,

r

f

rred e rJie in t1"is

disc1ssi01

.

s we

rocced

I'urtJ!

cr

it" tho in

-crease in the thic'kne ss of t1'e rroi st 1re fi 1 .. , we reach a poj_nt Jmo-ro; n as the len to

ca

ni llary point

.

l'l1is con i tion

is ·where the moistlU'e film has inc:rease

to such

thickness as

to perrr·it

t

e plant

to more reo.dily secure moisture

.

l.,nto

-·w

1eneve~

th c

soil r.oisturc is aaove the

capillar:r point

,

tJ1e plants secure this vn.ter ·.vith the

A

least

effo:rt

.

r:

the rEoisture content is near this I>Oint

,

tl•o e:ro,dn-"' pl nts in

-die- te

b~r .h(

ir a

!_JJ:L

raY' ce

tl

e need of water;

howevr;r,

they

rr:a.y

not b8

i!l

a 'l.ni lted

con~it· o

•

Obviously thi;::; poi

.t

is

rorewhat greater than the iltinrt -poil"t

.

On

18

to 20 percent

.

I

t is fou,ld in co:;:mecti.on :j_th the

:r

rl tion of tr

ieln

ss of

moisturE.

fil.

to

ianeter

of

-part

·

~le

that nhe., the:r

is

5 ·oo- ce·

1

t

oisture,

this filrr

is

.

02

of

this

i

r-et

or

10

II f

_.

04-"

fl

')0

It

"

,,

,f II

.

os

"

If

0

,,

H .t

'

.1m

II II II

40

or

sa t·n·d.

ti

01•, It n

"

.

lll

I

_tHe

It

It is believed that we have nowdiscussed in sufficient detail the matters

pertaining to the physical conditions of moisture and soil.

Let us now turn our

attention to the practical side of our problem.

Water in the soil is absolutely essential to tbe growth and development of

plants.

This water reaches the soil thru the air to some extent, but the chief

source is precipitation and application by irrigation or rise of the ground water

table.

This water in eontaat with the organic, as well as the inorganic,

mater-ials of the soil mass will dissolve these substances in a greater or less degree,

thus putting into solution certain elements that are absorbed thru the root system

as plant food.

What are some of the practical methods of

gettir~

the moisture into the soil,

and what are some of the

ways

of retaining it when once established?

We will not

touch upon the application of water to soil

by

the various methods of irrigation

only in so far as they bear upon our subject.

It was thought, however, in this

connection that the diagram here shown would be of interest in picturing the

capill-ar,y movement of moisture thru a soil ae affected by a shallow and deep furrow.

This is conclusive, that to obtain the greatest spread of the moisture within a

cer-tain time the deep furrow is muoh more effective.

In the preparation of the soil for producing a crop, let us start at the

bot-tom and see what e

.

ffect subsoiling has on our problem.

Subsoiling increases the

percentage capacity for water of the soil stirred. Subsoiling decrease• the

ca-pillary oonducting power of the soil stirred and suosoiling increases the rate of

percolation thru the soil stirred.

The soil forming the surface foot constitutes that layer which, from a

prac-tical standpoint, we are able to manipulate to the advantage of reception of

mois-ture to the soil as well as some control of its wasteful es9ape, due to evaporation.

12-The top soil must be kept in such a state as to decrease the ease of

movement

of

moisture from the lower soil mass.

All cultivated fields, that is cropped area,

are not possible of periodic stirring of the soil surface

by

cultivators or harrow

because of the nature of the crop.

From the standpoint of the conservation of

moisture in the soil we may, therefore, conclude that the cultivator operated at

&

comparatively shallow depth, so as not to cut off the top feeding roots of the

plants, is considered to be one of the most important methods of retaining the

mois-ture for the use of the plants.

Tests have been conducted to show the ra. te of

loss of moisture from soils.

King has found that under very favorable conditions

as to sunshine, wind and condition of soil that the loss is from 2, 3 or even 4

pounds of water per day per second-feet, v.hich amounts to 40, 60 and 100 tons of

water per acre.

Other observations have shown that a fine sand lost 2.37 pounds

per sq. ft. per day and a clay loam 2.05 pounds per sq. ft. per day.

These rates

are exceptions rather than the rule.

At Fort Collins, the annual rate of

evap-oration from a free water surface is about 41 inches per year. Recent tests

con-conducted on moist soil surfaces show that these soils lose at the rate of about

75% of that from a free water surface; or, in other words, the loss from a moist

field would be at least 50 percent or approximately 20 inches ner year.

If this

relation be true, it is seen that our total rainfall is used to

com~ensate

for

evaporation losses.

Ho~ver,

since all the soil surfaces are not moist, the

act-ual loss is, therefore,

~ess

than this amount but may on the average be as much as

25 pereent, or approxirr

.

a tely 10 inches per year.

Let us irrigate less and run

the cultivator more.

Numerous experiments have been conducted to see the effect of rise of soil

moisture by capillary action due to application of water on the soil surface.

This

by the

a~plied

water.

This in turn reduces the interior temperature, thus causing

increased action of the capillary movement.

A rainfall on a f

i

eld which would have

little or no effect in adding moisture to

.

the ground

w~~ld

have a tendency to raise

the soil moisture, which might be looked upon as a means of depletion of moisture

rather than an addition.

Tests show that a sandy loam soil will yield about 14 pounds of water per

cu

b

ic foot, while a clay soil

~11

yield only

12t

pounds

n

er cubic foot.

It is

evi-dent that while the precentage cap

a

city of the sandy soil is much below that of the

·

olay, it has greater weight of water available to the plant, and the greater

free-dom with which it yields this water makes it more nearly equal to that of the loamy

clay than at first

~~uld

be supposed.

It is on this account that a sandy soil

kept well fertilized has

~any

advantages over the colder,less perfectly aerated and

mo~e

obstinate cold ones which crack badly in dry weather and become over-saturated

in wet seasons.

Clear water will penetrate into the soil at a much faster rate than when

carry-ing silt or collodial matter.

I am going to recommend to you to conduct the

fol-loWing simple experiment on the pen

e

tr

a

tion of water in soils as a means of

creat-ing more interest, as well as gettcreat-ing a pers

J

nal contact with the problem of soils

and water.

(Describe the experiment)

.

We know that the movement of water into

or thru soils on an irrigated field is

largel~

influenced by the character of the

material in solution in the water.

This point will, then, introduce further

in-terest.

Not being beyond our means, Why not conduct the

e~eriment

in two parts,

using distilled water in one case and ordinary ditch water in the other, or same

water known to contain a liberal amount of salts in solution.

The percolation or penetration of water in soils may be

SQ~ed

up, in

14-1- Downward most ra,idly in the soils where capillary is quickets,

2- The rapidity of percolation decreases materially as the wetted

soil column increases in length.

Storing water in soils: The storing of water in soils consists, first, in

getting the water into the soil, and, secondly, preventing its escape.

Of these,

we are concerned largely with those principles and methods which are under our

con-trol.

Getting water into the soil depends first upon the condition of the

sur-face soil at the time of rain or application of irrigation,

the character and

amount of the application, and amount of water already in the soil. Keeping it

there for the use of the plant has been briefly touched

u~on

in our previous

dis-cussion.

\Vater

capacity

measurerr

.

ents made

by

various investigators on 20 different

classes of soil show th

a

t the amount of water absorbed by the soil, when in need

of irrigation, varies from 1/2 inch of water to 1 foot of soil in depth, for sand,

to

2t

inches of water to 1

foot

in a clay loamy soil.

That is, for a depth of 6

feet we could expect 3 inches for the sandy soil and 13t inches for the lo

a

my soil.

As an average of nearly 3000 trials, it was found in Utah that the Greenville

lOam soil retained a little more than 1 inch of water for each foot of soil about

24 hours after irrigation.

Other tests s

h

ow that 10 days after heavy irrigations

were applied, about

lt

inches of water per foot in the u-pper six feet of soil was

retained.

When irrigation water is anplied to the soil, it penetrates in part by

flow-ing into cracl<s and also by

way

of small spaces bet·ween the :particles of' soil.

The rate of penetration of water into a dry soil is

i~fluenced

not only b

y

the

gen-eral texture of

t~e

soil, but even more by the physical reactions of the soil

rr.a-terial to water.

In a

dry

soil, more or less compact, the ra.te of penetration is

greatly influenced by the air

~thin

the small cavaties within the soil. The

water cannot wholly occupy these spaces until the air is driven out, and because

of internal resistance the escape is

ve~J

slow.

Let us now, in conclusion, briefly review some of the various points

mentioned in the discussion, as enumerated in these sheets.

S 0 I L

M 0 I 8 T U R E

Soil, air and water are indispensible to all forms of life •

.

The sell is a great water reservoir in which the rains are caught

and held, as well as a laboratory to make the essential plant foods.

W

ater in soil in different forms,

Hygroscopic

Capillary

Free water

All moisture percentages are calculated

on

the basis of the dry soi

}

weight.

Plants

c~1not

use hygroscopic moisture, butfuis moisture is thou

g

ht

to be beneficial in bringing into solution plant food material held

in the soil.

Ordinary plants get their water supply from the capillary form.

Capillary movement of moisture is slow and little is brought up fro

m

the sub-root zone.

Capillarity is a force which helps to distributeabiequalize the moi

s-ture.

·:

Silt in

beco~ing

wet does not change in size. Clay particles swell,

causin

g

an increase in resistance to capillary movement.

Chemic

e.

ls affect the rate of capillary action.

Where irrigation is applied in amounts greater than the power of

retention, the excess is wasted as deep percolation and joins the

water table b

·

elow as seepage. The passage of this water carries

down plant food.

Barometric pressure changes soil water below surface.

Optimum moisture.

For optimum conditions the soil should contain

about one-half water and one-half air of the pore space.

vTI1en the pore space has more than

60%

of water, the plants are unabl

l

to get sufficient oxygen, dilutes the plant food and also causes

excessive transpiration.

When less than

40%,

the plant has difficulty in securing moisture

an

:1

plant food.

Brin

g

the water content to the highest optimum and then irrigate ju

st

sufficient to keep the content within this

range~

-Optimum at a

·

pofnt about

1/2

maximum hei

g

ht to which the water can

rise by c

a

pillarity from the water level,-a

.

principle in drainage.

It is known with reasonable certainty that the rate and extent of

movement of soil moisture is gre

a

ter

w

ith temperatures above but ne

a

l

"'

Water :r.-:oves do

w

nw

a

rd, but the greater portion remains near the top

or surface where the plants can use it.

A

feeding plant withdraws the moisture which is renlaced by capillar

:

movement.

Water capacity of soils is an important factor in land values.

In

general, the finer

th~

soil grain the more

wa

ter the soil will

hold, and the greater the number of spaces which are larger than

capillary size, the less it will

hold~

The

water~holding

.

capacity

of the soil decreases as the temperature

increases.

From

30

to

40

percent of. th

.

e saturation runount must be drained a,:vay

before the soil ccn contain enough air for the plant.

In order

th~t

maximum yields may result the water content should not fall far bel

(.

··.

these amounts.

T~"'e

total quantity of water which can be retained by a soil column

b:,

··

capillarity in the absence of grourid water is much less than capill

Ql

saturation.

The percentage of moisture held in field soils to a depth of g to 10

fe~,

when the top foot is saturated; may be called the field water

capacity of

c.

soil. This is about the optimum water content for

plant growth.

Soils retain from 1 to 3 inches of water; sandy soils less, heavy

soils more.

Adding water

to

the surface of the soil causes moisture to rise from

below; that is, increases the capillary movement--decrease in

temper~

ature.

Subs-oil

Ol!"

water at greater depths supplies

by

the tap root the chief

supply.

Root penetration in clayey soils less than in sandy soils.

The roots of our cereal plants, if kept submerged for a period of

on

c

week, will c

2.

use injury.

How

~ater

enters into life stream--

The amount of water used

by'

plants in general ls.about 325

.

tons per ton of dry matter, roots,

stems, leaves and

fruit~

When plants

gro~,

they use water,

King has found that a single cor

n

plant during the first week of August used

1t

quarts of water per d

£7

Plants are said to be wasteful of water when the moisture content i

n

the soil is low.

Water require

me

nts vary during the gro

w

in

g

season and most durin

g

t

he

3.

For like conditions of development, the water requirements vary with

the leaf area.

Transpiration is a maximum

during

Ju~y

and August •

.

Soil kept moist absorbs moisture more readily •

.

Prevent the soil from completely drying out.

Evaporation is one of the

.

rfactors that controls the extent and rate

of movement of soil moisture by capillarity.

Too much water does not pay.

Time of irrigation; Dark green, need; light green, too much.

·

Irrigate frequently with small application.

The

percentage~

irrigation should vary with the development of the

crop.

Fall irrigation and fall plowing conserve the ooason' s moisture.

The crop should have sufficient moisture to germinate the seed.

Save the soil moisture by cultivation.

Rolling the land brings up the soil moisture from below.

Freezing shatters the soil mass.

REFERENCES TO

LITERATURE

Soils--Hilgard

The Soil--King

Soils--Lyon

&

Fippin

Irrigation and Drainage--King

Use of Water in Irrigation--Fortier

Elements of Hydrology--Meyer

Soils and Fertilizers--Snyder

Irrigation Farming--Wilcox

Soil

Alkali~-Harris

Principles of Irrigation Practice--Widtsoe

Capillary Movement of Soil Moisture.

U.S •

.

Dept. Agr. Bu ..

S35,

McLaughlin.

Capillary Distribution of Moisture in Soils Columns of Small

Storage and Use of Soil Moisture. Univ. of Neb. Bul. 140

1

Burr.

Irrigation Practice and Water Requirements for Crops in Alberta.

Dept. of the Interior, Canada,

Irr-ig.

Series No,

6._

Snelsonf

.

Movement of Water

in

Irrigated

Soils.

Journal of Agr. Research,

Vo.

XXVII, No.

9,

March,

1924,

Scafield-Effectiveness of Mulches in preserving Soil Moisture.

Journal

A

g

r.

Research, Vol XXIII, No. 0, March, 1$23, Harris and Yao.

l4ovement of Water

in Irrigated Soils

't

Utah

Ex

-

pt. Sta.

Bul. 115,

Widtsoe

and

McLaughlii.n.

__

Water~Holding Capacity of Irrigated Soi~s~

Utah Expt.

Sta. Bul.

1~3

lsrealsen and West.

Management of

Sandy

Soils under

Irrigation.

,

Oregon

Expt •

.

Sta. Bul

177,

Dean.

Controlling

Soil

Moisture for Vegetable Crops in Missouri. Mo. Expt.

Sta~

Bul. 204, Rosa.

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