So i f Advv Servic

B o ,,,v a n a

PHYSICAL PROPERTiES, MOISTURE REGIME

AND CROi;. MUCTION

STUDY LUVISOL IN SFBELE

AC

PHYSICAL PROPERTIES, MOISTUI

AND CROP PRODUCTION

A CASE STUDY ON A LUVISOL iN SEBELE

By

Willie D. Joshua

Soil Physicist

'2ood Fuld griculture Organization of United NationsUnited Nati Develoment PrognmmeRepubliz of Botsana

Gaborone, 1991

Tb. e

t h

' I I Fhra,

4

CC)

on ic sol, Sebele..

43

.19

ir

S

o o o e eso o o o o o 6 o o ato o*0000 fteoego o woo 466

2.44430** 4

o

" .10

V

`'Y'000 ' ,o , oo ..13

4b i...fall, i ; -: .." d 33 , , a idl3 in 33,1, -0 3;0-, 3a, ,,; cr, 1,3; ,, ....14

.15

5bo ';',- -,3 iii N 6 6

i 6 i i i, Li L :L6'LLI . . . 16

6a ic r ,; d," 3 3-, -3 -73 k 166 6", -"S,

6 L iL°6 O:, i) °:6 F66 :1, iL C.26 . . 17

°- o o 'OU:, oìolo, 'o" ,` '; ^ !ro

, ". (o- -.. I:k r. k

7

8 \do " Cq tr.....249;, L6 6 ", 6 LiiiL::666 i$ (o '1 12,1( CY f

U.o,. oor,o .

10 ; ;ooko'000- oo O°. oo-oo.F000 °. .;rc different1kaan,;,'3;a3, A

11 ;30, ;;;; 303 ;,;

Lii L 6 ii°6 k k k 6o6o66.66630

12 ; on, ;;,"C';',3 2- s " .:(P, oU-..) , ^o,

' os, ra , - ol 4 . UkSVLS So o. ,,; ?, °S

13 "vi2iU1 "o°oo: ' oov o OU, 'ou2Uo.lo rainfall330 3,3-3-din, n3-33 ;..3.-;;0 o .03-0 o.3;.;. kk k k,k kao

LIST OF URES Con

16'i. ',

,4

o

4 4 0 . . 0 0 . 4 434

0 0 (4 0 0 0 0 0 4 0 .

m 0 0

;T OF TABLES

Aele Jistribution - c Lar. . . 2

2 o 4,4 41', 4,111 44 4 ,L

11.4LL,jtL , H.L 'r5 4

0 0 a, 4

4 ,a4 oo 4: no4,40 7

5

6 11J .,,' s , H. ..4),', ' ,i'., .1'1, L ; ' ,,

H.c. ,, '. '., .38

o t

41') 4e '11),

), Os* `,%1 ...40

1. INTRODUCTION

priyz.5j '101 Atri.du,!.eur,1.1 Rosea rch-;. r jtnterprtznq

r"'Y? 3 r.:1,r, Th rC-= ki:( St C ' I ',3(

r o t j--..11:" C (.1-? A

t- 1sttU avr-,.1 , ° 3

L'e)1V:Ine.-1..;ttr.e.,',1 ,ïI ph.ys ccJpr t,",J r ) r t t-pr o oL Were lased t o i-( p t-

wn al Itmovtant L riculture, in as-A7iTtm,Eitte ir, the Luv:..c;,:,%ls

tU7 cNaL?( L 'Ly v i-;:rt p iT11.-: data was u..sr-d t k

tc, prodict- bat(s, soliovapo.',:at'l.on and F.ollDiLavL,:ic», natural r,:eAndit:ic,n Th. m°,1,,,:

wi,!-..11 0 year's rainfall recrd,splohtac: opp:,,rt.unities based nso'' m: tThmnd.l. for response to moistu,:e wuitimated 5\7..) moisture storage in plantinq

in ord,:,:r o ong rang.-tun,' rtress on scrqhum yield ir thes..7i L7,

The imviE07.,1E LI-1 the hardveid regAous La .1::3."3H,:WcriTh vAk4 'propertaet) depend::ng on the nature (-J-f polcr roctc::.

17, opOqraphJ C pos LtI On riWhi ch (.:(1V

Resear,,A, Statiol: Sb:Ae;flO)US no !;rtr-t. amorph ic r0C7 .NOS

dez-_"-rIced as moderatoLy cieep coarse san,-.); Tr,1oams, The fir7-1,1s on the upper p:-.)siti.r...)n5 of 1

topoqrJphy are we,,1 ilra,ned and ora1ual)7drained in thc.2 1(,Aver po Tn(,!sE-,

Forlsiu HP;the Crar and Ckr11". ,,02.

t 11 C. 41 Ca.orrLJ S , '4,:

Wit it rnar .(:(°(k/ C.:eh UOT tJ y 4- \,°

''srer y tnt.. 1.6 r _ ir it kt ` -

17, °,)11)sririon j(-.ke Ferric: "L"-. I. .wo/ LOL' thc-Y.wo ictuto and (...-kpa wi cïwo

tLi1lor the mr.:?,-71.s',1,,eoltt'7. C'i Y .P rg,,--)s o ,

,),t-,..)1,14)(-, it 2 reor;

o roc)Lmi, 1 oN°"3nkd

rtnt h. i apo Tno moistuze atly1:". (o 1 i hO o LMC,If3 7'. 7.1r 4":-.).S/.1. I 'Li rOni

31-( 3, 'L.-.&3 te,rlìnco 'tw'rer I o 1. a cr:' t-!,(1" 11 ,1 t

on nc di Li t Ork,j,a'

*);1O,c' F Y'0t- 1,1 . ;0` ,

z.`leLj

3ilt2

18 9

18 8 2 2

21 13 3 2

Ito e

SOIL PHYSICAL PROPERTIES

2.1. Particle size distribution

6116J y i 6 L o ne t prpc rt i.t-,n,L, c1 1,a y-ano L: I ay Wa u1 by 3 i; ,q1bií' bu L) In thf., 31.1.11ac,,2. thc

L'O" Plv101:11n.--1L, -111A

,7`.V J d, )4

I f ' +111JPJ L ;

r.111'lk , n L an L iti L-01: ghu h prc:i e

horjAolls with cLay contEtnt are ccollmon ti-1(2wine.ralLy c:hankle trom loamy ,-,and tt.; anc taLos LO z...,..31.10 clay

depth

Thr, vory tt)w WAth c:Jay cl-Jntent 1.731,1t, -oorK.ohL dowear to hc.' Lhe typaì parts ci iXf1,

Ai;, arid hard seLnoI: the

uoc?r,pr--To

Table 1: Particle size distribution - Ferric Luvisol,

9 ..,, 21

6 6 12 17

rt.

t

Pht''

(-0 Ì ,.,1 , C16-1\41 1 t Leï...)(1 1.

t t. t. LOP. I.,- ,=1 LViiCiL I )1' z:`,

-'15 LLi411 :1". '4,-1,',

2.2 Bulk density and total porosity0.s I,

r ;

rto '; , , v

17»';, tTh"L;,c me '."1.^3 .17

Ctt? tr°' l Pr! 1.1.1' (4." ° '1,+^

ii', 4,1.5 1.1ìch Lif0C.0"

,t f:

!LOslt:=1-1:c

1 . L. 5çii

th6 rat4r,pe..r c.: Lht: in ial porosi t ìe t i l

(1:1, t"'

4 L Thesr.) valuca for ttve or till z. 50 t eXt Ora I c: .

2.3. Infiltration characteristics

tro TLe n t _1 t'rJrc)Lori1 'l)

(1 5 t: C t rot--;

Ori . A

3te fl

1,

i

1 L-

,11C-' ,

o

'

C. + 1. 1_ al- 1...G: 7 ',11.,d f;r",» /0. ^ ''r*`;\'trrl,rr', r.1 , ^' L..1.1:1 al 7,

t o"

I

r '

"

"I

P ' h"Ph.LH, .."t! ,1;

á. t

tUtt

ILï rj),,.:71' a

I

h.Ikt")

jr,

'

, hir

Tab ezolla of

;1)

6., - 8 1.

Table 3. Ynfilt,yeton characteristics of Ferric Lu

Jaf;Ce,,

-t)s

"a"

F

9.2 1 30

13.80 10.21 7.93 6.80 5.60 6.20 6.00

17. 15.51 13.43 11.18 8.90 7.40 6.90 6.40

_s cm/hr

--tion, t -

4

41,I

" value

C

'I" ear-L t ,,+aa 1.

6C t f.q", 4i. 4::

4 ne3 ;;L 'a0 a, , laa,Htaa s '

a Ta arh,i A.Tata",:aCta'al.t,, )1t,E

t ,,tH it a ^ 15,1 e H ; »,14( 1a

t, 7!(,. "Lt.: 3 Lov, is typical"", "O° o "^°, , 7)7110 ,

".

;

o.o

o ,

,

5

ata

,

,

t

(1' °moo, o "o , o o (1, t t,? :(:)11(10 1:9'rt

t kn1 1114., t )

, Lt-'7` o `," OF-1 0000-Et.2v o:" oo O1

o'; O. do o oo'o° O.O,173

2.4.1 Moisture availak and aerat

3

3 0

5

0 ^±

0 15

0 - 33

-

N

s NN

N

,

o ,LY

e

DE Frn-f

o - 33

:33 89

- 138

RAINACIE C,F COVERED SATI H WANA)

2 mm !re used for the measurement. The structural stability in-dices vary between 1 and U corresponding to roxnp1ete1y stable andcdmpletely unstable aggregateF. respectivel. ! In general, struc-tura4 stability index ls measured only on ::urface soils becauseol theLr siTt,ticant intiut-mce on surfacH Ling roson and

dlt:thu rainfallThe ,tr.ructuraL Jo.ability moasure6 4bove petnod1-,1 i_ntcrpcetd ir t t proporth tsinq qrauswhi,!!!, !IQ nt rq ditinto;,..qratior. on Fast wett,inq.

t,end luct<-?as t- V!AkUE' 1-!neAnOW tbaf, wha ftu I

mn(! ki!ructur,a1 aiï l itV .nd.olr; ot the Lo,v1oJ. ,tryi11!: ra!;:tion dbOUZ. 70 percent r.hre ;: iIst,T:uctuc, r:he o i tiggrdatt, murti 'wet

;,00r stability. 't'huì tros J 1,Lt5'!W.) Lnduce r17n-o{t and eroon unde:!.vrrntr!!!. ,

2.6e Hydraulic conductivityNott-,!fir, ,i.,on, 71ki1J,! H? tiio!.. '!a-r-i!r-éln-W, hOl!tuli- !.'.ofIclu,,;'!n!as ,,,-.n! t.nT:.-!t:i.H !--J,,,-;..uro,1,.L" .i.,.! (!nl.! an_ (v-.-,1:!,..;(v1,;,:s t! IT, ;. - 1 ! . , !. ,...!, i. _,-,!!!,!.,, is:,!,4, VP ' r , ì :' r,!3!:., ,' `1 ,'.!,'¡"-! ..'!,

h!./!4,1iiv y,,)flf!!;,:..1.tv n:a!, ,1;9.1.".1>Hni-1,-, !. !.-- L t

1 /!,{!

'

al"p'1r'',1 !PP ! Pt !! P-c"!!!'"U'L..!.,Th!A L1:l r

Peo,!,,P! 1' 3 !P'.:PP'10,'' P`p h,!!!! th!.n !

ron..>.i.\ .1 .1 .,3!" f- .!".t t1 L Y i iL k,N"

piony !-;henot;!!: At(!,7! !!!,v)i.; :3

lilYevapofn!!tYcinp(yfi!! (1(,\Jr!n:!

,; V .1 , ! 91" 33/t " 3'

M!.,33 L!, JP-7.11f,..IP 1:3'.)3n `p)!

Th,, wt-4,.,i.iuremen",. wove mad J: 4 nowt nLyrv ì at tile! boo;,anio,,2!and :,!o\-1(tcd ts.7, 12 hou/ interval:, ,iftet 3 6ayi", When d,catno!.,) ratf,

meciuremen t wetc macl!,_ at 7,-- day Lnt7!tvals. !1:1

ca L cit al. tnq thQ tydraulic conclucciyitv, tho hydrault gradl,en,be unitA,: .i t t is usually th;!:, case du/Hug

drainage,

Th ceutu indicate that the soil profile can be grouped t;;1-.!three layers namely 0-45cm, 15-75cm and 75-120cm according tc, toe

ir, the hydraullcJ conductivities, Figure 3 show t,nevarLtion In hydraulic conductivities with molsture ,,nntent to

dt:bth interval, At high moisture content between 0.20 ancJO. cc per cc, thc hydraulic conduLzkivitLes for all deptim aresimliAl, varying 1)etween Q.L and lcm per hr, As moisture content

th'irop in hydraulLc conducti,vity is higher Cor theJowel J-1.pth:.4 which hove higho cfav 7.ontent flonversely, for ar-I

9

*(3

lo

90-105 -cms

:7-

90,;\A44NO

26

S.01- STURE REGI2

11

chane s i s miii.a.r-s.." tans% wet artaf d:' q :'st ,""-Sss

11, gho.st t ;to:- nurz 1 Itst ,ts st.ts ,tispssil 1.13 ., ',le "set t i r se,s I la, Ls' ras."-Ncy"sas -

up ta 4 5. al, Ofain css lass". Fima.1.1 intssyrni istasnt. ra.`..11F Tss,' 2: esst,"T ".sis rany ins :ta f ssirr,s., s "7- s :77 l'assy <Ls ". ;la r,

per i.t-Ttift ts '1tIttsstit Tbess sma tar'. fitTss "ttzt ti ' t t2- bsst ssct tstsilsstIs oss st , , I'fl..." 7 49999' 1'

s (Pi s a. s, l'a:" ra, 'say zs a t kl3 Es s : ts,t1.1",s st tot t,s"Is ss-s.st st .pir'nTtEa,".3 ,) Lna sa,,4 4? ì../ V'C. 999/ 999 M49:4 Cs.s Tss ty,st ss tie s,s

st, I t st, 4, " htt (to sass laps( a 7 snr" S %Ns a

SSSS r ft'f ff 12.0f"'''Cf srs, - ".1 fro:7 s' a a ,

t 4 r94 9 s S za': i V4494'4;9994

54'0)4, 59/494 , 4/4,999494,999,9 51, /t9 949999

3. is stss 9949./ r P1999T s,"1 t s tivists t s !St! st.s . ITsts, t ts I'st"

sat' "tt,',"t 1.15r r tn's prof 7 NON- ,

"aaars,Tsa twiNs1s.a.p aNsa.""enlas 3,121), t "I' fcsa"

Ittso,s1171Itilts.ts sti tts 1 4ss ftt st). .,:ttilrs is, sss,

estr-Lsti'.

INTs s ",'" is sis s tt. ",, t ' ss Ts s.s,'" , ' "'s stt ts"""T.T. st t '):. /9.9 N " . -ass , '' a .. si ,,,,,,, , Sa.:Ns;,....,N sassa any , su-ssaa7 Na .1, s , ,..-,-- ",,'",.. N s . '5 7.a. sa 4 In, as» sass') .,., ., J.'

:, ,- .,- 1, , a ' ; ,,,,,, s , s

.o ' ' ," a sy 1--San ; cr.y.r.',',..:- ? rrs. y ,,,:. ! 1, 1\ ',:r ' ,,-4-r,' ,,..--, '

1-_' imf ,.6 ,,y,,,,-1, t ; g,'..,,, .- r '''., " v; f',, '..'' ,,. , 1,,

ly,,," - :11, 7 a 9 7, ' i' :' '", r I '. ' r 4., , 5 :, r 'ff' ,1 f(If .1,, ,

eiss ,,'', TOT'," , , d, ; 6ritls,

st,:sst r", ,""" sS 1S5N hi5 " sso,TItr 55

Isso Ss s, s tts h -

9 49 9 9 .1:199,49 /99 ; /49999' ' t

',.' 144;4 99

/ ' 44 4 9'94

.N 'tss , '9499 ''11

.5s Istst T.s. st/tt,'Is siTIS

12

sss

11

9 995'

,

9;9' 44W9,499 9*H C9 P999-4,

9 5'19 '994,9 s f

;' cW,1 ' sarrs, 'as J°. ' t

49 S, 9/4 9 9r4 4 4, 9 5 49,i 4 99,

55r. t55 j;tS hi.L'its

S.S S5t r:y,,,,, ?A,

sstt s sts .11 t.> Isss; sts (T, TT), 4,2"stt "Ls, -"t ".stOt

" ,`, t, :Tat ' \ ss ti -1 4 f'ff no, sSs."" ,rN5.5,sos1 As' S

SS

L S ca. 'k i 55 f s5.SSJYSThfff -fffS tf if? t;f.Y02''./ His Tli", Z.

1 ff. i`9, 4 !9

A 1°- ',1 e tui ; .) tQ'; t ht.?, 'Lis, J5 s,h,S4-11t: trz.14., 1 L"ItsItj, S:s h

, ,'inui n t ron.) Ina v:1;111.13'0 3 7 'ir Lwdr., ,-)rf

0- I

A3,4

08 -S

L

SL-09

09 - So-

SP - OC

Of - S I

51 -0

1,-u3)Pild30

111,1A

MC

22

1

20 14

4,4

V

201

t

Fig

. 5a-

4.--

a fo

r pr

ofiie

and

Yy.

,

"M

AY

th`l

- -

I 5 15 -

30

7590

20

4444

444

1A

llri

NU

;

22 70--

50 50 10

tJ

JUN

E 8

9T

RY

AC

CS

EP

OC

TN

OV

MO

NT

HS

Fig

. 5b:

Rai

nfal

l, so

I m

oist

ure

for

prof

ile a

nd 1

5 cm

dep

th in

crem

ents

for

perio

d 19

89/ 9

0 -

Site

2 (

Seb

ele)

KE

Y

DE

PTH

(cm

)

0-15

1530

3045

4580

80 7

575

90

OE

- 9

- 0- -

A3>

1

.bli

5,4

alG

AG

SE

P

f,- p

erio

d 19

89/ 9

0 -

Site

4 (

Seb

e!e)

Ay

KE

Y

---

15

15 -

30 45 90

OISTURE BALANCE AND CROP PRODUCTION

9rA0 11,YK virz, of rai,rto_ cy0TD aff,1Y7t. Wid

;,Jcsoors caadat2i.t var;.ai-clwAotiy docra,s; ;o

-.z/e 6 1-H,. s;':ss ;17o,6insimgo0(! -);C'1

Jr, watoy supply, ,bi*k!- actuadeleils on. the piantin4 Td°;:t

i'A1 the- subsequsnt grcwinJI period. Tr. F7,rediv BocBis nocsaary to stlidy the moisr:ur baianr,e Yar-

piantind to obtain optial plantinq Moistur7pscud's! oi a ,'ropoed soit for each plaritinc.!tn7,3ued a I e pot,Antil yìe ,7e-7(:)un,t.

-ieducinn tn moisturo ntres, ThuP, hert,T,T !-.4,T.VE! a estimali spLL ea,Bad)--e

,,orC7' methodclow,, to nrod. ).rzT'e1cU7 urIc

(.°t reo.liitLrsk cso ('managemorl-.TBeI pav., !>f ctkaptA41: t,poeseo-ps o !Juac!t.',Tro

PP-;:7C !Vt.° Citra r.-tera r

0J3 ng phySTk(i! rpW:h0d0.LOly aleip A.accporates 8vaporati-)noi4servd i6borat-.orv experiments simulatir

Wet The model waSr.,f rainfall.; reoc,-1 :flyCrk 7,

t1011; 1->are and: sruTzip,oThe .71-JdL:1.; t).rediciioTlz; ¡Ao..roed

Tr LT,,,ies011.part, .BAO .iaieth3S!lodogy d) (orwas psec) 1.p pre:Ltd' saJnied sop-3-s 'd '$Pess Pds »a-tv

perpfi, Piard,laa ap70000lo:,neo ss,ar pac-o<1.PJCV do1B\npopo ,pcp

i« E.1 TOCKfC.. BBocenPLal aorghtla >-2peLds wa.ps eStdriapP .J lc PTs

cliprons plantirig upportunitls Caar ocausl-P,P cocPat=';r rsah ''as, Based. P the r=n, ait:v ;.1d

as-a7ei:jes aso, di.scussd.

4.1 Evaporation rom bare soiidr7it9 of 17,ure 60LI obE:erer3 tr; oCkr in throo recoynal)1(,,

sta9e{:, In the Lirsi- stage, the si)il 4krIL water moves fJsoli surface to match che evaporatton potential of the atmosphere.The evaporation rate at this stage is therefore controlled byatmospheri conditions The second stage begins when the moisturecontemt oi the surface soil layers decreases to a point when watercann;.-,t move to the surface fast enough ro meet the evaporative

u, j;. .t I 41 N"N1," 0,4 , .' It t

NN 21:71N1', n

' tA,s- "t I rA h,I .° ......'33YiIr)r"./ r73 32"

3' '1 3 S: ea 'Ç Tr"; 1I Çn )11",td,

- t° C- ' t q'

h333, ',;13; f+ilY1"-13;? YY tAar10.1..c..1 A;1°,0).

"r. A °, . All .5 ,c4

'J-Yik(11hTt 1;,s Y7k A

,T" ""-'333-", n's, ;."1"),0? 333:1 Yv;;IY,Y,,t-" ;71133,C2 "31(Yctit,

'IA It' A 3 r31,-"Y?t" -"Xu..;`,Y,7"3 1.3,Y)Yt ab, st YT". 1 ''7-"," 3,-1"73Y.31:3"3.7 s7-?..Y. ' f

, 5';' NO ' ' a'1N4 '316,1 .1'.S 1.1),1tN NINNY

,t IT^ T' TT ',, Yt,t -0; 3 4`1,,tkt.'1'Nq 1NN

3 37," ""; 3 3333 ,, 1, ;". 1,

S S '

( ' t' 343 ;;YY-3;.

I ,»43,9343, )1 .0 ), "Y,, !,

110 "I;L3'.; ""'1 (1`"33 -o`"Ylí",3

733 3,3"

, 3 55, f,

; 3,7 ' 17'1» 33 3,7'A " \ c't ;t3"24 33:A)4 "

3,t 431', " 0^,

° t- " a" ".'"" Y.'I t- 3' J sYt,1,, qt; 3 41

",St

" , 1'1.'1,

11

4 ^.5 :5:,.IN` 11'1I I," +, 4 y 4, or,s3 I,; I,

rrll 554

"t N

,

I n

412 ; " , )k ^,

'11

,.` "-;"-i

20

Isotheimal unsaturated water flow for bare soil has been shown toobey the partial differential equation

0/6t ,v6x[o(e). -(1)

EquatIon 1 can be solved analytically assumi¡Lq soil of infinitodepth at uniform initial moisture content, ond infivitoly highatmospheric evaporation potential. integrating thn u LiCO wiLhrespect Lo x gives the cumulative evaporation L as Eollow..; (Crank,1956; Black et al., 1969)

E=2 (ei-00)(ät/iov2 -(2)

WhereE = cumulative evaporation in stage 2 (1.,

t = elapsed time (t)D = Weighted mean diffusivity (L'it(9= initial moisture content00= air dry moisture content

Equation 2 can be written as:

E = Ct"2

where C is constant for a given soil.

Equatior states that dumulative evaporation is dis:ec,tlyproportional to the square root of elaT.:a6 t3me, fi,mover,experiments have shown that this relationship holds only durimginitial period of stage 2 evaporation and tna constant tor agiven soil depends on the depth of wetting and the ambionttemperature.

Gardner and Gardner (1969) have shown that ,

in a dimensionless form and E/M, plotted against (Dot7L, theresulting curve is applicable to any depth of wetting. M; is thetotal initial amount of water present for stage 2 evaporation, Dois the diffusivity of air dry soil, L is the depth of wetting andt is the elapsed time after onset'of stage 2 evaporation. Thisapproach gave reliable estimates of evaporation from bare soilduring a single drying cycle from an ini,ia:ly wet soil of anydepth. However, in the field the soil is wetted by rains of variousmagnitudes and frequencies. Modifications are necessary to adaptthe above results to field situations.

21

where9 = volumetric moisture content (1,3,'7,',

x = distance (1-.

00)=. soil water diffusivity (1,7t )

t - time (t)

4.1.3 Experiment: A field exprimnt to wea&;orE:evaporation was catriod ow,- on a Ferric Luvisol at the AgrirulalResearch Station at Sebele, Botswana, Relevant soilcharacteristics are given in Table 5. A square plot of si.,Ao 2fuwith a neutron access tube at the centre was wetted to tJ.eidcapacity to a depth of about 105 cm. The profile moisture wasperiodically monitored with a neutron moisture probe and w;Iteradded necessary to wet the profile to the required depth. The plotwas covered with plastic sheet to prevent evaporation and mc,isturwas allowed to redistribute in the profile. When the profilereached field capacity, as ascertained by ileutron orol'eobsoLvations, the plastic covering was removed and the profil w3sallowed to dry under natural atmospheric conditions. Soil Triist,ls-ewas monitored with the neutron moisture probe at 15cm Jepthincrements, Initially, measurement were made at 1-day inteyalF,and latt-!r increasod Lo 2 and 3-day intE:vals as the ovapor,JLio.1rates decreased. Thu length of the drying cycle was 22 days,

4.1.4 Models and computatiJna The procedures and calcul,adeTted in the models are g5,ven balow. The moisture ';ntent

all c:al'ulations ere e..xpr(--,d in depth uAits. All 3ymbf.,1

oKpLi j_ne u th i L atLoc.hed.

1. For each measurem t of profile moisture content,volumetric moisture content w4:.s plotted against d6Ttll 7,The cumulativo evaporation was ealcnlated with thLs data. M_L3plotted along with petential ev,ipottanspil:ation (FAO L977) a,latnsL

sed time (FicTuLe 'a). Using Figure S, the maximum Ilrl1ua:11j,evaportion in stage 1 i. e- U was estimated Flg the cutfllof:veev,To;atiQn up to 1Tho pOitit WiteVC the cumulativr2 E,vapratloprudpartc from thc cumulative pote7qial evapot'fanspirau cu vuTttdel:,th LC 1_') which mt:>it,ure depletion tks plctccevaporaLion 1 ; rketelmine,:t frocr4 Fjçiuto 7 Prrm Figure:, 7 Fs Lc:-- 45cm. and 11 = 1,65cm,

Values of E and t wore read oft rom E tcjulu e potthu diew,ionless cnrve E/Mi versus (Dnt/L2)'" ta.kIng E-0 JOlor begini,Lnq of stage 2 evaporation. For simplfficcitin I

N, since the ch-pth uf v7etting i s closely TeJat-oHtothr- initi;.1 amount of water, 00 is l so assumed to 1-,o equal-i ncc dit'isAvities oecrasc- to 1,ntweet, 1 an

(771-:da\,, the lower limit of wetnoss arri tn,2 L,wost.pr;-)1?abl . ,,c('ars At air-dry moi3ture (ILL1 lei 1Lflfl . Fijui(2 1 j+low'sLltei iwnc i orti sr cm-ye of 1,/M, versus (t/Mi:) " tor the Jo ríeovJ.Flo.

Moistur ,.,',,hterits at saruration. capar:tr-N,p(--nt. 7i)oil,ture rotent_,-,r

thi:A slo;:iyo fitild wos 111

I 10 Jiold t fcr !.F)3 catt dori,h\ ;. ;1.F.4.--°irn:-Jd Ihgr-

22

Tab e 5. Properties of Ferric Luvisol-Sebele,

Depth Bulk density Moi5tur:e retention PD.rtl,c7,10 stze'cm) (gicc.) (vol

Coa.1.3mS -

vf5 - ',Tory tjin sand-

f3t. Fi.no

23

.1.bar That 5bar mS fSi C

)-3 1.66 15.4 12.0 6.5 28 21 21 11 2 3

33-69 L.55 15,8 12.29 9.3 32 21 ' 8 2 269-139 1.54 20.6 17,2 9.8 18 7- 3 2

,leasured field capaci. 3-1

30 80

X) 90

'108

120

/30

04

73

45

87

89

10r

oL

o

o

I,..

.III2

1,11

[

191)

45 L

mj

4A A

, fU

33

AL

;T

I

f,40

¡219

1920

5

o

KE

Y

oP

OT

EN

TIA

L E

T(4

2.80

,087

1 01

2000

11

AC

TU

AL

EV

AP

OR

AT

ION

(C

UM

)

230

o o

29

-

2024

2212

2425

2524

2929

7034

11

1-t

9L

33

E

O1

43

05

97

99

1011

1213

14ro

1718

1

100s

Ill;

O:[

''

;11

1 89

0 PO

I'0

1f1A

.NSP

IRA

TIO

H

25

mrt o

',r,\t`t , Tho ,F,Nra r,t3,t, ,

J t U h pLtOT L

to,Pt IlAlloti 5 1. , 44\ 43.1 N't 4: 1 43,44.3 3'" I

It444,4I"4i111",

L ^ - '

f ; 114 0,4 i bt,» , 1°\-1 t y tt ^

DLo .tro °

143 443t43441. 4444 , tAP,'

klr','07);

o 44:4,41 °°4 '3 34 'it43'1;4.44

I'd 14.4444444' 4It'' 44' 4I44" t. 44:41 /, 4.4-33 1°3'4 '44 43'4 "43 43° °0 t, '47 3,4). i43 vd 4,-dd , " ,

6(41' , d t2,1.1 F)k-4i4. 4. '0

at-ti J

t 40'4' 3 II 443' ' 4,-0144 t 444 44.°3 d 416 d 4I""'

;,..4 1.1, t.. tki VY C",L..00:LI

" 1 ,

t tt,' tt'tt tttt :,;ttt 'tt , r ; .11 ,' 0,20

^ ; '

. t I 3 I

t:, eVr:1

,r re.t: clvt t 1. Lo,d

TM

4 I 431*t 4, 4 '444, 044744.4 » S .kk; .3t I.4344S..°4 I.143Iit,' 444

; " '7'1! *OTTr TO. 44431 V434 d y Itq,:01.r.ctt : t

t = lo (U mi. U

Ok; " tittxtt,t1

::: :h '...,'-'71, 3, '4',-.» 4:43 3 4. °. ,' 444)43 ' 'I "r.ii: i : , , -

4', ' ,, .,V.:',,:..t.tre ot-1 IL,' t» J' , H ,f, ?, d; lc! '' ,-,;;;t '1's t,t""ottt ;,,t'!,,,, 't ' ' :t;:,-.; 1.",, ''',,;,, '_. t..., 'r,i k

tC,' ' ,'. *:. t h(' ,,)1.'--",!'..tIli.,l'L M' ,..k-Ot k''' ,,,'`'I'r,1°,,,,,: ' . "',..t..,t trS.:tt.s,' t- J mt,. t. , , '..:',,,,,,,,

.i. !,1 !-,),, c..' day,t-7 -;.,i; , ;-i, 1, i.i:i Lai, 0, ;,, inii:e.w li i '',i 4, ' 4, Y33 I.;44,4 III s°4 '4 , _a ' :1 j ^ ,

ttat.1A.-', ef, ( t;71; new 7. /11, t'' or t. '-',c 1,7.' 4 '4 414.4'4, 14' '43' '44 43.; '44r434 4 : i ,,U.

2V-, fi.:, 1,'0,, d,i,,:i,273;1,2 -,-., t_1,-,..L

AE

26

[Lril Hav.Lnu estimated thc, evaporati.nn LOI the decade with norainfall, the model then consident the toi rainfall P for thedecade az3 if a.LI fe i. on the first day ot he dec.ade. The rainfaliamount is spar_ateu luto four categories.

The rainfall P is ).arde enough Lo replenish tnepa717,i.ally or fully in tha total dopth to bring the

profile to st.?. 1 evaporar ion i,e, P > TiS - U. (Figure 10a) Int.hi;:ase, the calculation '..1n0 NACk to .itop ril to (7sTirila-to,

evaporation for the new amount. ot s;.?2 tc i ml discards thecalcuLations of the eariter case with rainfall,

The rainfall ? is large ellou:lh (.)nJy to replen731! fhrde 1(..'it in depth LC to bring it back -cc tEqe L Avporation i.e,P > TESC - U where TESC MXMC IMC, ;Figure 10b,. In such a case,the calculation goes back to step [I but considers the profiLe ,Asof depth LC, so that Mi -.-- nxmc-ti,

The rainfall P is small but cannot be evaporated in2 days so that moisture penetrates io deeper layers (Figuro 10c).The increased evaporation due to the wet surface soil layers isloss than the rainfall (Gardner and Gardner, 1962: Ritchie, l9721.The evaporation in such cases varies from .6P to .9P and in thismodel it is taken as .6P based on actual observation. Tr thi:i

amount is added the evaporation from the profile caiculaterd bystep3 [I.) or [III for the no-rainfall case to obtain the totalevaporation fpr the decade.

The rainfall P so small suc:h th7.t :1P i Ie IanPEr".z 3,e r Ali tl)i7.evapte tn evap=;tion.n-iinf,--111 as steps W or tij

Trtor oi T.)! .

HE'c"-f dent-r, clo1n.1.)ci1tc., V1L1u, LK,!ten 11 5 07.'.

0',*31/t Ot S17,1; 11.1 crìo int ' '

0 7.3 3 1.Toftiuo'2 L L L H (

Wa t 7 t. on rpr-

tra o"n!

ciec,A0ctalt1,1t. '

rosp, :7)y 1-Jtt-, Tscrii tfte.,1 surocte.', ficm thce

,Ln the deuv.hs anA"tjm-11 Cr.PLCCT±C totI o r L ! y 1 E.t Oct -1 h. °

t , ",0,1

27

1

1//1

1IN

G I1

0:51

1111

1 11

.011

11:II

BA

K S

011

AI

t

CA

SI (

. WIN

ill I

,.

30 90 13,!

:

1.1

Mr.

9151

1111

a.1

t.!

67

b9

0II

tit13

14ri

10it

rar

r4

6E46

R06 3 11

0

CA

SI R

!11/

1/41

1iill

rit1

11S

111

S U

1110

1 P

0111

1011

Y il

l11

451_

14

10: 1

1111

101W

I 111

11 1

1111

1111

51

1

f1

1)1(

1111

31M

AC

NIIU

DE

1.1

;6

.64/

3 14

4110

111

6t

139

1'$3

1446

le11

I.106

1011

E C

ON

1EN

T 1

61%

66

76

910

II13

i34

16la

i7rr

rT-r

--1

Itt

CA

SE

WI F

AIN

tilp

Ulil

Silt

S D

IFIC

II'--

. ;-H

111

13C

l WA

Y

lb 30

A i 1 imi 0 TrtoiLLUÏ MNNC iS i n t. roduccsd Îor riepth'.,t-sCS,.11? '6` Çr." ).-...7ty,,,L; 66)"\ '? th a nto i

y -1 3c..) 3.7, (13-y

, .

ss crst" // ,."s",/s s";s°' /Ss' C's"'

sCs° ,,sssssi s ://sss Sr. rs /1/F 'f1,1) t ,11-;'`';

r, *(1" 6 :r 661, 6-6" rh 1 6 6:: 6 ^H:r '6, 2 016"666: '')" t ;6'66 1.7(.:20.66".

CI 0 rPri rr Fr rqrq/

Y :" ' : //,./ °

°/,.S , ss.3 ; ss s , "," s " r's", rsr 66r,hK -61h "rs h' '06" h 6 ".06''

, hh h h6"rhr `hrir;;:, I 6 ' 1r' Y1 ; 1'

,..;1"1 VC: ; qrqqqAT.,1,;-; ; , ; "1, , ",q. F; c; 11;

Lir ts/t.'s

q.s./°' /1°/s"q r

1 ' , 1

:tn

, "CS/s "/s. sC °

1,")'I 1'k !Po. sSs ".."/." Ss , S ss" ' ss, s

s°-"/," ss"../HS'r.' 1"'s's" °,sd-Ss: /,

tt iLtr ?ti ". °

r Frh, 61161kr,,hr 666,1 hr'h6"-.6 2 6 66'`'hrhr h6' 6 '6 6hi rr" °

u.0

.

,/, e" 1

'

29

S

s s://. s

s

,, 6 ;,

,

r, It , II

,

, ,r)

' C/ 3 S/

s'osSs' s ' 2`,Ss's," '7,"^

/./..,31/111-s",/ ,s s

Va3/

( IR

IIS'plA

;Alq 3)0Pli

EZ

EZ

qI

tt

£-

r,A

aa

Et

AA

A

L,

12 o7

.

M12X

MnR

21 1H12: D

PP! YA

W' "-A

a

2A

1

Pl11211,11.

FIG Lib:CUMULATIVE EVAPOR.ATION WEEKLY RAINFALL TOTALS L., SURE

02,20,32

444

0

32

3nou1:3 fi)11z..,.tr the same t nd withoul much deviations. Figures IA,

and 15 show the predicted and measured weekly variations of soLmoisture content in the 0 - 45 cm and 0 - 105 cm depth for the twoprof,i116 ±or which evapora!Lor, was t.,11Qu1ated The :greomenL isgec.J.or pract-L?z-1: pi,;rpose,s, This apprh ur 4iso be 17,,aa*Li.y

t.v.otiturr? ,anyprOg re;.- JaLI y 0.3: i. .a in IfL 1 t 11F.: arc-1 uf

n,rofilu otT,a-t Tkia , (

':)Ìr

bt"' th 0 V e ^ fï:o. ,

hT& ,, f Yd.!: P'Y a _Hp, -40,

`,),a 1E,:kr pit:olh" ti- Jtott, t.

t / r ni k` Uri P 0) ; 1)...tt,R)r 7-17.t 11 Ai

`14.12(4,:3Y e L r"LW),crtt,,h/it" t,

ytt. --_, tit ti/ t./ mitat,itlirc.:°111C-J,) 1);)t. tt.),..k t ft,

diiubit t; tti ciens 1.y fi iid tro)

One Lid'.-fi:Aional mca3u--ment ,)f evivoration. ca',1 a p,1 ti/tr t,it,,,./A? bu:7. 9T bL 1 raw Ctt Pci LI. rrYtT1.7 _

OS fteri ItAttlY1 LY-it ,)`¡ YY

rT ff,t)6,'," .Y et:" tt /7t, -Eitt -. .

: t it/ttt ',,` r-, -

drd ,t1 7*, . ,

../u 17,t/ti,tt-t..iftctY it,» ; 1.1.3 itn(.7 "Y., ' d

potranspir defj, iuc

t r,f n'n ,

, n ,. I

"

,,

L:p ,;, , 1

r "p T '3 ,

Cr.)

Ti) roipi.la po1,7t::), 4) 1.. n92.: , 1)-IrK- Y.)) PA, 9

Whi'fa actual harvested yield (M)

33

9 9 IC 12 13 1 a

, - 45. c_frq

:0

's2

ion 0/88

35

2,C1I'59

KEY

TO T6

Level 1 Eguivaleni to 50 percent or more of totalavailable moisture of O- 45 crn depth of

MTh ,

Equivaien t(7, '.5U percent or moro of -(70T

available moisture of O - 30 cm depth of

36

Y, = maximum harvested yield (M)

Ky = yield response factor (dimensicTET = actual evapotranspiration (L)ET. = maximum evapotranspirati.on (L)

The Ae of yield response factor Ky ì specific [o rbevo.and its stdqe oi growtn development. Moisture stress o.E a givenmagnitud may occur in any of the crops growing peri.W.relative magnitude oi tne Ky tactors reflec.ts the sensitiatythe q-owth per.lod to moisture stress in reducing yiald.

Equa'.ioD 4 Lihowb rhr.! tne atua evapotranspLratIQnmoisLun, can by estimatAid, anJ it ET, aW a;c )kwci

tnou top pot,enta no U y readiv ostImated a

of meximom

4.2l Modela and computations

Re 31) .t or A-, clo kthZtttOfl of E,, and ET, It av

deve,lopea anc,' pub i.sti.e.a by PAU i 9 , 3 9 9 These, pubUtiono noessary iputs ).uciuding R, values tux rilttrer,17

proceouro:, aro iet,cribed to e,:,timatIno4

,.-apotranspir;Aion Tn-1979'! for estimtilly, yLeLd

p< t oefcr oro jdictj t CT cP' r

, , Maxiwtmì, L.: A C,r

ov .4c./ r

"t)11Ma.:C' ITV-J11(,»,

, )1I'Ll :10,R

d v ; ?,0L C , L`u { ,

mo Lu''oV ';-` 1.1 eftic. r", C). .12j ,1 N

..10:1Auc. " , , s Ita k

,ak n c.; {%701.1fl L a 3.s.r io.11,1k:mot.sc.ur(..,t.oLi.ij -Apacity may,trtimt

' The oppori,unities w rc do utldtodsu on tho am)uut sc,(1 w6F!luro

layor cat In Ferric Luv;sot

37

(50 - 56 mm.)

Level 3 Equivalent to 50 peicent or more of totalavailable moisture of 0 - 15 cm depth of soil.(44 -50 mm.)

TheL.E'' Ilroo 1 nt moIST.U1:0 t() cage 11 tt.71t. I .4 sh a fai imurn ttaqe tha L, .-`7, -

t u r.th in.() ro inf. all reg. I 111,71 'J t., ofoLc) o s T'd9L-,..? asrnos ufff Inc, 5.. (idLLQ1.. er .:_tto. 1 t SUtc1fl(leccb:ícu w_L t h E, r,

rue I Luu up tur+& +1 +tu22'22 2222,221 +Ki T 4n L ' ,

C-v2s u au (Li t L i L urc, t; 7!-tttt (100', 41 tt,ta Lt °PLL. i nt12. ,"ug t

tt7;tt c) Ctt r"Vii

e.",,'"4.2t .,11c. ,, r:H'd L0.1',,1.1p, ton f.,

tt- 4,

t31:ttj ct tit, 1, é 4' Z éé

t 1s4:t/_,J 1,4,c L " z

4.2.2 Results and discussions:é

,, t 1\',

, é" N t'é;' L-' t-'1 i" ' t'

,0 ""

(tr'rHHmcé.," ' rI'{ 4¡"'"

vs-,)

/b;.,2c, °P"' "-e r . 001:U , 9

kLitre a r1 té, f

!LIc,Li.N.L:2,,,,yr, a :

rrvi !TrLrCk t::)71)¡:.)012c".:,- +11'-$r ia»ta aLe L y-Luivt1Lic,,;-; 11103 t at t ha Lac acH

no As1::p1-1,r1- Or-Li L,h ta 71d, r-r

(,4 e y L;:371.r.1,31 avid Lnt:c.:rroj

av aìì iLe L iu1u: tyt ewrn aLarja o 1,,)p/_.ant:7; underqc, no i. ttestnss iLmportrmt in

th d.--(1,re,r.:i of_ ykelr] ciopresLon, ;-3ome yrawth stawL%'5: ot ti 'ir.)pmoco a t-J) mni.s,:ura t.Le LAhGrs.octhumrof, t otc,st t i.ve por3 ho f

Tabl e

Feb

6 .

'

jJ

23

23

1

23

1

2

3

23

>

>

p),,J)(,

it'

t i

o

o

i- 't9

8

LitP J I

0

33

4

3

3

.1

2

22

1I2

'p" "isj

31

2

3

o

3

47,

23

6

7

6

3

4

42

,"1 IJ I

3

25

1110

131713

161619

18141. 6

161513

- o

for.'1Gt(1,:j Thi"..)F;(,,,s; ;:i(?1 I z3 1. -` h ct.ynnuL-nce't C,L i Lor Li:h-r ();;

4N ; (7ta(,.re t))11H 1..1 t '

",- ," s'h

'

,

P,t tit

o

t

39

1

" Itzh t 'tL, (.Th hz-' ;0.Ly` 'i CY3.

t.

'n-rx i t 'E s L jtrt)riQt, riii);."2:','T'L. t elt.r-:"s.

40

1 S 3 348 57 63

51/52 S 3 3

42

3 1 2 350 34 47 41

54/5 1 3 2 1

37. 31 27 35

1 2 1

47 27 27 25 20

56/57 S 3 1 3

Y 48 53 31

57/5- 1 2

2

35 25

30 S25

ti S 1 1 1 "

52 52 44 53 63

61/62 S

2 2

24

Table 7. i i flittt, (Ind ,..,-.\,;:r.e.S111/4_111til.11(.1

(7? 2'. CI t.7 ; t-1 t t IT\L ',11J "

'tts ,

,

Cont.7. ,e

wLt.fl p!-1.nr,417,;777)177,:H: Cc:'n'Cq,-;ry ?.7,49-19)

. .

- - ,o

N, ,7"

.*7

63/64

6 1 3 2

29 6 22 21

Y

66/67 S 1 1 1 1

Y 72 74 72 62

Y

Y

69/70

70/71 S 2 2 1 1

41 40 37 31

71/72 S i 1 2 1 1

51 40 40 24 23

72/73

73/74 S 1 1 2

78 71 58 - 41 27

74/75 S 1 1 1 1 3 i 2

Y 64 64 66 70 79 80 75

75/76 3 3 1 1 1 1 1 1

73 69 71 72 65 52 51 42

1 2 1 1 3Y 37 656 49 36

t;2

3

30

8 S 2

Y

3

43

1 1 1 1 2

Y 51 47 45 39 41

44

7" 1 1 1 3

31 27 26 24

78/79 S 3

19 21

3 3 1 1 1 1

67 44 38 31 24 19

31 2 2 1 1

Y 68 70 30 24

1 3

Y 32 33

33 s 3 1 1 1

Y 34 25 26 22 .

Y

84/85

Cont.e soil fl S t L t rnd

e.to

cioLi oL, `8

3,;roy,7 1,0t/

-

, , )

, Suss

°

The results t Table #.; can i \JillIt jt t r , t >f

1-.(.. 111int, toi. xampio, moisture s'r,resi3 durio,k,( CiL. OWe:C.111.0y i.e or-min.9 stages shoui d he zn.i. u Piltra 'Ca t) Le 6proba i. tio or obta in ir..g iqute oì inotu s orptantiu.1ai:i4 between the secDnd decado Ot Liec,eint).--. 1' (awl t

a. L

r(,-. two Li , ortc?. , ì;.fanuary ",c)

rry, 7.,tt S fi. t. t?

t tt /LA t 1 \L a ttr `tt^CI'C' tt>

rittLt: F.; 1'

4.3 Conclusions

In areas 'Df 'limited rainfall ti e use of Tile metile,(1+g,..rorow bro iiiwoyks

or titro rk,i)senLiutL con t ,),f..1Sr LOO increaF.-ie n rpoil.,,turr? ',I ton. r°

1:1:1 pr, 1_1 agon 1 t}:

IJ.CenDi.:1-. plot .7)f Eitfi.,v ( ) 1- 1-, .1 ts,otvp,- of

'Clus mu- i.cuTj S rs is ;us's:suss s`; ',:sufetS,,su, sulsSL-S, , usu

uSS, s.sz.sos, ,

oyt't. .1", t h -S S; ,

Itt6 tOsu'is r S

US oo.1.1-.1o, 'coo, Oo or:o

su,-,susnn

loo, to e achiITV:" : .11 1,11.v

-

U

' ?; / -//Dr/

/,` //,/

/.' ///:

45

in depth units.

5

6.

9

11

o M;-r

A

'o? Nooy

14, or

46

and W.D.Pruit

0:

2 of

- use. Calro:FAO13

15 .

47

Ap

0 -

A11

BU

33-

51 c

m

BU

51 -

97 c

m

Bt3

97 -

180

cm cm

fez

42'6

:"

tt'--

B

t

2_12

22"

me

cc, t

s.dt

:a'a

.s

-

-:6.

0,

12 -

C:

50D

:55

-95

G:

155

))7 ,,ved D; inatinAltr.iry of Agrica!ture

Prite Bog 0,03 C,iborone, B6bwar:;,4