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Copyright is owned by the Author of the thesis. Permission is given for

a copy to be downloaded by an individual for the purpose of research and

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the permission of the Author.

ASPECTS OF THE WATER BALANCE OF AN OATS CROP GROWN ON A LAYERED SOIL

A the s i s presented in partial fulfilment o f the requirements for the Degree of

Doctor of Philosophy in Soil Science at

Ma ssey University

BRENT EUAN CLOTHIER 1 9 7 7

ABSTRACT

The increasing pressure on our water r esources, for irrigation in particular, has resulted in a growing

awareness of the importance of water balance studies.

In this thesis three aspects of the field \>later balance are investigated� evapotranspiration (ET) from well-watered crops, the upper l imit of soil water storage in the field, and drainage.

Daily ET values, measured by the Bowen ratio-energy balance method, are presented for an oats crop grown in winter and also for a number of e.urruner crops, all of which were \\1ell-watered. ET measurements w ere also made over longer periods using a drainage lysimeter. It was found that the Penman, and Priestley and Taylor ET

estimation procedures predicted ET with an accuracy of 15-20% and _8% for daily _and weekly periods, respective^ly6 The Priestley and Taylor method is simpler _{to u}se but requires an empirical constant ·to relate the 1 equilibriura

ET' to ET. This constant was found to be 1.21 for winter, spring and summer over a range of crops in the _Hanawatu.

Net radiation data on a dayl ight basis were used to evaluate th is constant, as seasonal variations in the constant were introduced when 24-hour data were used _..

Also it is easier to empirically estimate daylight than 24-hour net radiation. Long term E'I' estimates using the Priestley and Taylor method with net radiation calculated from incoming solar radiation, were in reasonable agree­

ment with the drainage l ysimeter measurements of ET for the oats crop.

A theoretical development is presented that describes water retention in soils underlain by a coarse-textured stratum. rrhis development accounts for the physical character of the overlying soil, the depth to the coarse layer, and the coarseness of the underlay. F'ield data are presented for the Manawatu fine sandy loam, a soil with a coarse-textured layer at ·90 cm. For this soil the layering resulted in an additional 55 mm of water

storage at the ces sation of drait-lage, an increa se of 31% over a similar hypothetical soil with the coarse stratum absent.

iii

Drainage from a permeable soil underla in by a coarse­

textured layer is investigated. Simplified theory is used to develop a model relating the drainage flux at the ba se of the soil to the water stored in the over­

lying soil. Despite sign ificant hy steresis in both the water retentivity curve of the overlying so il and the hydraulic conductivity-pre ssure potential relation­

ship of the coarse layer, hystere sis had little effect on the storage-flux relation. The model simulated

both the field drainage in the Manawatu fine s andy loa1n measured by a lysimeter, and field profile water storage

found by neutron probe mo i sture mea surements. The model indicates that only simple field measurements are

needed to find the storage-flux relationship.

The components of the water balance of an autumn­

so'Ym oats crop grown in the Hanawatu are resolved ..

Drainage lo s s was found to con stitute _60% of _the rainfall, with the remaining amount being lost as _ET.

ACKNOWLEDGEMENTS

I expres s my sincere thanks to my supervisor s, Dr s. Dave Scotter, Jim Kerr and Max Turner for their direction, encouragement and friendship during all the stage s of my work. I would al so like to thank

Prof. Keith Syer s and Dr Ken Mitchell for making it all po ssible. This work wa s carried out whil st I held

a U. G. C. Po stgraduate Scholarship and the 1 9 7 4 B. P.

( N . Z . ) Postgraduate Scholar ship, for which I am grateful.

To the D^.S.I. R. I am grateful for the help that enabled me to do this work.

Thank s al so to John Talbot, Peter Menalda,

Peter Rollinson and Jim Gordon for a s sistance both in the field and laboratory.

To Penny Clothier, thanks for the continual encouragement and warm under standing.

For much typing I wish to thank Erin Temperton.

TABLE OF CONTENTS

Page

Abs�ract . .. . . • . . .. . . • • • . • • • • . • • • . • • . • • . . • . ii

Ac)<:now 1 edg em en t s • • • • .. • • • • • • • • • • • • • • • • • • .. • • • i v

Table of Contents • • • • • • • • • • • • • • • • • • • • • • • • • • v List of Figures • • • • • • • • • • • • • • • • e • • • • • • • • • • •

List of Tables ^• • • • • e • • •• • • • • • • • • • • • • • • • • • • •

List of S)"'"riJ:>^{ols • • • • •}• • • • • • • • • • • • •

·

• • • • • • • • • •

CBAPTER 1

viTA'rER BALANCE STUDIES • • • • • • • • • • • • •• • • • • • • • •

1 . 1 IJ:\TTRODUCTION • • • • • • • • • • • • • • • • • • • • • e • • • •

1. 2 THE FIELD WATER BALANCE EQUATION ... . 1 . 2 . 1 EVAPOTRANSPIRATION (ET) ... ..

1 . 2 . 2 MAXIMUM PROFILE WATER STORAGE

viii XV xvi

1 2 2 3

( , ... 7max) ^{• • • • • •} • • • • • • 0 • C" • • • • • • • e • 8 1 . 2. 3 PROFILE DRAINAGE ( J) • ., • • • • • • • • 12 1 . 2. _LJ. SU�1A.RY ^&: • • • • • • • • • • • • .., ^• • • • • • • • • 15 1. 3 MATERIALS _A-� METHODS • • • • • •• • • • • • • • • • • 17

CHAPTER 2

!-1EASURED M'D PREDICTED EVAPOTRANSPIRA'I'ION

FROM WELL-vll'.TERED CROPS • • • • • • • • • •• • • • o • • • •

2 . 1 INTRODUCTION •• • • • • • • • • • • • • •• • • • • • • • • •

2 . 2 EXPERIMENTAL METHODS AND ^{MATERIALS • • •}

2 . 3 RESULTS ^• • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

2 . 4 CONCLUSIONS _AND SDr�'iMARY • • • • • • • •• • • • • •

CHAPTER 3

WATER RETENTION IN SOIL UNDERLAIN BY

A COARSE-TEXTURE!D LAYER ^{• • •} • • • • • • • • • • • • •• • •

3.1 IJ:\TTRODUCTION ^{• • • • •} • • • • • • • • • • • • • • • • • • � •

3 . 2 3.3 3.4 3.,5

TfiEORY . ..^{. . .. .}. ^o • • • • • • • • &; . . . .. . . . .

EXPERIMENTAL METHODS AND MATERIALS • • •

RESULTS • • • • • • • • • • • • • • • • • • • ., ^e • • • • • • o • •

SUi-".J\·IARY AND CONCLUSIONS � o • o • � e • • • • • • •

19 2 0 2 2 2 6 39

40 41 43 5 3 5 7 6 1

CHAPTER 4

DRAINAGE FLUX IN PERHEABLE SOIL UNDERLAIN BY A COARSE-'l'BX'I'URED LAYER ... ... .

4.1 INTRODUCTION .. ... .. ... .

4 . 2 ^{THEORY • •• • • • • • • • • • • • •• • • • • •• • • • •• •• •} 4. 3 !1ATERIALS AND Mr:::'I'HODS • • • • •• • •• • • • • ••

4.4 RESULTS AND DISCUSSION • • • • • • • • •• •• ••

4.5 CONCLUSION • • •• • • • • • ^{• • ••• • •• • • • •• • •••}

CI-IAPTER 5

CONCLUSIONS AND SUMMARY • •• • • • • • • • • • • •• • • •

5.1 THE OVERALL WATER BALANCE ._.......... . 5.2 SUMMARY OF RESULTS • • • • • •• • • • • • •• • • ••

APPENDIX I

ERROR ANALYSIS OF THE B OWEN RATIO-ENERGY B ALANCE HETHOD OF ET ESTIMATION • •• • • • • • ••

Al.l INTRODUCTION • •• • •• • •• • • • • • • • • • • • • •• •

Al. 2 TI-IEORY ... . . Al.3 RESULTS

Al.3.1

1\1.3.2 Al.3.3

• • • • • • ^{• • • • • • • • • • • •} • • • 0 • • • • u • •

. ERROR CONTRIBUTION DUE TO THE PSYCHROI1ETER CONSTANT • • • • • •

TEMPERATURE MEASUREMENT ERROR NET RADIATION MEASURE�SNT

�Ftf<()�. ^{• •• • • • • • •• • • • • • • •• • • • •} Al. 4 DETER..�INATION OF THE ERROR IN ET ...

APPENDIX II

NEUTRON PROBE CALIBRATION • • • • • • •• • • • • • • ••

A2.1 INTRODUCTION • • • • •• • • • • • • • • •� • • • • • • ••

A2. 2 ^{THEORY • • •• • • • • ., o •• • • e • • • • • •• • • • • • •• •} A2 .. 3 EXPERU.1E:t-1TAL . . _{. . .} . . . . ^. . . . . . . . . . ^. . . . .

Page

63 64 65 66 71 84

87 88 91

94 95 96 97

97 100

lOO 102

103 104

104

106

vi

APPENDIX III

SCIL PROFILE DESCRIPTION ^{• • • • • • • • •• • • • • • •} A3.1 SPATIAL VARIATION ^{• • • • • • • • • • • • • • • • • •} A3. 2 PROFILE DESCRIPTION ^{• • • • • • • • • • • • • • • •}

APPEJ\TJ)IX . IV

CROP DESCRIPTION • • •• ••• • • • • • • • • • • • • • • • • •

A4 . 1 IN�RODUCTION ^{• • • •• • • • • • • •• • • • • • • • • • •} A4. 2 CROP AGRONOMY ^{• • • • • • • • • • •• • • • • • • • • • •}

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . .

vii Page

109 110 110

114 115 115

118

Fig.l.l

Fig.l.2

Fig.l.3

Fig.2.1

Fig.2.2

Fig . • 2 . 3

LIST OF FIGURES

PeP�an and Thornthwaite esti�ates of weekly ET for Palrnerston North over the suwmer of 197 4/75 compared to

est.imat es using Priestley and Taylor's method ( ET ( P _& T ) ) (After Clothier ll al . 1975 ) . • • • . • • • . • . . . • . • • . • • • . . . •

Water content at 30 cm depth in uniform soil , and the same soil underlain by sand at 61 cm and 1 2 2 cm depths and by gravel at 12 2 cm,as affected by the time after irrigation . Surface evaporation

Page

7

prevented ( After Miller , 1969 ) • • • • • • • 14

Comparison of predicted drainage flux ( Eq. 1.6 ) with that measured for the Yolo loam, Hiller silty clay and Cobb

loamy sand {After Davidson et al. 1969 ) . 16

Comparison of measured evapotranspiration ( ET} against computed Penman estima·tes ( ET )p , for oats. The correlation

coefficient (R) and S yx applu to the - .I

linear regression equation�c••••••••••

Comparison of measured ET against the

24 hour value of the equilibrium evaporat­

ion rate ( ET eq ) for oats , S yx calculated for the regression line constrained

through the origin • • • • • • • • • • • • • • • • • •

Comparison of measured ET against the daylight ET eq , for oats • • • • • • • • • • • • •

27

2 8

30

Fig . 2 . 4

Fig.2 . 5

Fig.2.6

Fig . 2.7

Fig.3.1

Fig.3 . 2

Fig.3 . 3

Regression of incoming solar radiation (K-!< ) against the net radiation (Rn) measured over oats . Both the 24 hour and daylight regressions are shown • •

Ratio of daylight ET/E'Feq(i . e. o<} for oats from winter to early summer.

Days when free water was· noted on the crop are indicated ( o ^{) • The mean} monthly temperature is sho\m . The limits on 0< o f 1 and ( s + � ) ^{/ s} suggested by Eq . 2 . 3 are also shown

(---) • . . • • . . . • . • . . . • • . . • . • • . . • . . . .

Predicted ET (1.2 2 ET ) for selected eq periods against the _ET measured from a water balance applied to the lysimeter growing oats. The error band is ± 0.05

ix Page

3 2

3 3

(rainfall) over the period • • • • o • • • • • • • 35

Comparison of measured ET over oats ( 0 ) and lucerne , paspalum or pasture (0} against the daylight ETeq • • • • • $ c � ·

Variation in the water retentivity curve due to changing the value of the pore

38

size distribution index A

.,

^•

..

^{• •} • • • • • • • • 44

The pressure potential profile in

a layered soil and in a uniform soil at the cessation of drainage • • • • • • • • • • • • •

The increase in storage _6W 1 as

a function of the pore size distribution index A. , for varying

-y}

^{i 1} the cut-off potential in the underlay . Inset.

The increase in storage as a function

46

of

y,.,

₁ ^for

A

^{= A} _max • • • • • • • • • • • • • • • 49

Fig.3 .4

Fig.3 .5

Fig . 3 .6

Fig.3 .7

Fig .. 3 .8

The increase in storage Aw, as a function of the pore size

distribution index A ^, for varying z. the soil depth. Inset. The

l. .

increase in storage a s a function of z . for 1.

A

⁼

A

max . . . . • • . • . . . • .

The increase in storage _�W, in a soil with secondary layering a t depth zL.

The subscript '11 refers to the soil zL _< z � ^{zi and 1 2 1} to the soil

0 � ^z � zL. Inset. The increase in storage as a function of

.A

^{2 for}

A

¹

=

Almax.

^{• • • •} • • • • • • • • • • • • • • • • • • • • • • •

Drying water retentivity curves for the three profile elements of a Manawatu fine sandy loam • • • • • • • • • • • • • • • • • • • •

Hydraulic conductivity curves for two of the profile elements of a Manawatu . fine sandy loam. Drainage is considered

X

Page

50

52

negligible wl1en K < 10 -l cm/day e • • · · · 56

Field tensiometer pressure potential

data showing the decline in potential for a Manawatu fine sandy loam following

a heavy w�nter rainfall of 2 9 mm . Over the subsequent 35 day period evapo­

transpiration losses o f 70.5 mm were offset by 19 small rainfalls totalling

6 6.2 rmn. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 58

Fig. 3. 9a Predicted prof iles of v1ator con·tent in a Manav>Tatu fine sandy loam, with and without the gravelly coarse sand layer

xi

Page Fig.3.9b Field neutron probe data for

Pig.4.1

Fig.4.2

Fig.4.3

Fig.4.4

a .Hanawatu sandy loam compared with the predicted profile of

water content • • • • • • • • • • • • • • • • � • • •

The -.-vater retentivity curves for the three profile elements of a Manawatu fine sandy loam. Mea sured hysteresis loops ( + ⁾ and compu·ted scanning

curves (·�·) are shown for the gravelly coarse sand and fine sand. The

scanning loops for various soil

profile depths are shown for the fine sand. Field data for the fine sand

( ^l!l ) and fine sandy loam ( 0 ) are also presented . ^{. .} . ^{. .} . . ^{. .} . ^{. . .} . ^. . ^{. . . .} . ^. . ^{. . .} .

Hydraulic conductivity curves for all three profile elements of a Manawatu

60

68

fine sandy loam • • • • • • • • • • • • • • • • • • • • • • 69

Predicted wettest and driest profiles ( ignoring evapotranspiration ) of

water content in a Manawatu fine sandy loam. The two wettest and driest water content profiles

recorded between May and September

1975 are also shown · • • • • • • • • • • • • •• • 7 3

Measured tensiometer pressure potential in the gravelly coarse sand at 100 cm depth during the winter of 197 5, and predicted tensiometer pressure

potential in comparison with field measurements at depths of 40 cm and

60 cm in the soil profile.,., • • o • • • • • • 7 5

Fig . 4 . 5

Fig . 4 . 6

Fig. 4 . 7

Fig . 4 . 8

Fig.4 . 9

Predicted wetting and drying drainage flux - profile water storage .relatio�

xii Page

ships for a Manawatu f ine sandy loam ^••• 7 6

Predicted decline in profile water storage with time in comparison with that measured by the neutron probe at two sites following two heavy winter

rainfalls ^{• ee •• •• • • •• • o• •• •• • •• o• • ••• ••} 7 8

Predicted decline in drainage flux with time in comparison to the drainage flux computed from the neutron probe data in Fig.4 . 6 , and the mean of that measured by the lysimeter over four drainage events . . . . . . . . . . . . . . . . . . . .

Neutron probe profile water content data at two sites , in comparison with that predicted for 1 9 7 4 and 1975.

Also , the drainage flux predicted , in comparison with that measured by the

7 9

lysimeter in 197 4 and 19 75. . . .. . . 81

Predicted drainage in relation to that measured by the lysimeter , for both

1974 and 1975 ^{• • • • •• • • ••• •• • • • •• • • • • • •} 82

Fig . 4 . 10 The decline in profile water storage for a uniform soil o f fine sand , predicted using the model of Black et al . ( 1969 ) , in comparison to the decline predicted for a fine sand

underlain by a layer of gravelly coarse sand using Eq . 4 . 6 ^{• • • •• • • • • • •• • • •• •• •}

Fig.Al. l Ratio of the psychrometer to the

psychrometric constunt as a function o f the aspiration flow _rate for four

85

different experimental runs .. . .. . . . .. •.. 99

Fig.Al.2 Comparison of daily net radiation measured by t\"lo different net

radiometers. The daily total of one found by integration of 1 minute sampling on a data logger and the other by analogue integrationo•••

Fig.A2.1 Soil moisture content ( cm3/cm3 ) in comparison with the count ratio . ­ Also sho\v.n is the calibration curve

xiii Page

101

supplied by Troxler • • • • • • • • • • • • • • • • 108 Fig.A3 . 1 The profile of Hanawatu fine sandy

loam ^{• • .} ft e . . . 112 Fig.A3.2 The interface between the fine sand

and gravelly coarse sand of Manawatu fine sandy loam. The range.in height

of the interface in this photo is

10

^{cm . 113}

Fig.A4 . 1 Seasonal changes in yield components and dry matter ^{% (Dm)} of total forage for the 1974 oats crop ( After Kerr

and Menalda , 1976 ) • • • • • • • • • • • • • • • • • • 116 Fig.A4.2 Seasonal changes in the height and

leaf area index ^{( LAI)} of the 1974 oats

crop ^. • . . . • . . . • • . . • . • . . . • . . . • 117

Table 1 . 1

Table 2 . 1

Table 3 . 1

Table 5 . 1

LIST OF TABLES

Page

Estimates of the available water storage based on \'1 max at a pressure potential of -340 cm, in relation to that observed in the field, for

4 soils underlain by a coarse layer.

(Miller, 1969 ) • • • • • • • • • • • • • • • • • • • • • 11 Comparison of monthly values of 1.22

ET eq and Penman estimates of evapo­

transpiration ( ET p ) for Palmerston

North • . . . • • • . • • . • . . • • • • . . . • • • • . • • . • 3 6 Physical characteristics of Manawatu

fine sandy loam • • • • e • • • • • • • • • • • • • • • 55

Estimates of the components of the water balance of oats grown

in the Manawatu during 1974 and 1975 . The figures in brackets are the values of the components in terms of %

rainfall. Also shown is the mean rainfall { 1941-1970 ) . All values

1.n nun • • • • • • • • • • • • • • ., • • • • • • • 0 • • • • • • 89 Table A3.1 Profile description of the Manawatu

fine sandy loam • • • • • • • • • • • • • • • • • • • 111

a b

c C. R .

e .Ae

ET" _eq f(u) f(w}

G H

J J, l.

LIST ^OF SW.LBOLS

empirical constant in Eq. 1.3 exponent in Eq. 1.3

convective term in the combination evaporation equation

counts per second in soil/counts per second in neutron probe radiation shield

specific heat capacity of air soil depth

soil water diffusivity plant dry matter %

change in surface water detention vapour pressure

difference in vapour pressure betwe.en two levels above crop

saturated vapour pressure evapotranspiration

Penman's evapotranspiration estimate·

equilibrium evapotranspiration rate daylight equilibrium evapotrans­

piration rate

nocturnal equilibrium evapotrans­

piration rate

wind function in Penman's equation

drainage flux-profile storage - relationship

soil heat flux sensible heat flux

drainage flux

drainage flux in coarse underlay

UNITS

dimensioriless

mm day -1

dimensionless

�1 -1·

J g c cm 2 ^_, cm day - dimensionless

mm

mb

mb mb

mm day -1 or

\''lm -2

mm day-l

mm day-l

rnrn day -1

mm day -1

mm day-l

mb-1

mm day -1

mm day-1 Wm-2

mm day -] -

\!Jm - 2

mm day-l

mm day-l or

or

K

I<. _�

Kf

K s K-!-

L LAI Ll'

m

p

Ph

r s

R n

RO RF R S. D ..

s

-T Tma::x:

L2

Tmin Td,TW ATd'

ATW

hydraulic conductivity

hydraulic conductivity of the coarse underlay

hydraulic conductivity of the over­

lying soil

saturated hydraulic conductivity incoming solar radiation

latent heat of vapourization leaf area index

characteristic length of soil particles

slope of the K-loge(S) curve atmospheric pressure

energy used in co2 fixation by photosynthesis

crop resistance to water vapour net radiation

run off rainfall

simple correlation coefficient standard deviation

crop hea·t storage change

slope of the saturated vapour pressure-temperature curve

standard error of the regression estimate

mean daily temperature maximum daily temperature minimum daily temperature

dry bulb, wet bulb temperature dry bulb, wet bulb temperature

difference betvveen two levels above crop

xvi

UNITS cm day -1 cm day -1

cm day-l cm day -1

mm day -1 or

\'lrn-2 Wm -3

dimensionless

mm

mb

mm day -1 or YVm-2

sec cm -1

mm day -1 or

Wm -2 ^. mm

mm

dimensionless

mm day -1 or 'Nm-2

c c c c

c

t

u

Vl max

w . m1n

z z. 1

0(

time

wind speed

saturation vapour pressure deficit profile soil water storage

profilG soil v1ater storage at time t uniform soil profile water storage layered soil profile water storage WL - Wu

maximum profile soil water storage minimum profile soil water storage soil cl�pth measured from soil surface soil depth to coarse layer interface soil depth to secondary layering aerodynamic surface roughness depth defined by Eq. 3.8

empirical constant, ET/ETeq Bowen ratio

psychrometric constant psychrometer constant error operator

slope of the log K- loge curve volumetric soil v1ater content volumetric soil ,.,ater content at time t

saturated volumetric water content difference between

�*

^and

�

(Eq.Al.l2) pore size distribution index

pore size distribution index when d ( AVJ) /dA. =

0

xvii

UNI'rS

day

-1

m sec or

k.rn

^day

-1

mb cm cm cm cm cm cm cm cm cm cm cm cm

dimensionless dimensionless

mb c-1 mb c-

1

cm3 cm-3 3 -3 cm cm

3 -3 cm cm

dimensionless dimensionless

'

ratio of the molecular weight of water to air

soil bulk density time

tensiometer pressure potantial air entry pressure potential

pressure potential when J = 1 mm day -1

' -1

pressure potent�al when Ji = 1 mm day

xviii UNI'l.'S

dirnensionless g ern -3

day ern ern ern ern