An agronomic and nutritional evaluation of maize (Zea mays L.) in a Mediterranean-type environment

I

_AN AGRONO!{IC AND NUTRTTIONAL EVALUATION OF ^MAIZE

(Zea mags

¿./ IN

A MEDITERRA¡\¡EAI{-TYPE ENvlRoiu4utlt _'

A thesis

submitted by¡

WAYNE ALLAN HA$ITHORNE

B.Agr.Sci.

r

^(Ade1aide)

to

the

TTNIVERSITY OF ADELAIDE

for the

degree

of

MASTER OF AGRICULTUR,AL SCIENCE

Department

of

^Agronony

WAITE AGRICULTURAL RESE,ARCH INSTITUTE September 1982

(ii)

TABLE OF CONTENTS

Headinq

List of tables.

List of figures.

List of

appendices.

Sumrnary.

Declaration.

Acknowledgements .

1.

INTRODUCTION

2.

LITERATURE REVIEW OF MAIZE

2.I Introduction

Page

vi vii i

x

xii xviii

xix I

2 2 2 2

6

I I

9

IO L2

L2

T7 19

I9

2.2

The development

of the

maize

plant with

time

2.2.L Defining

growth stages and

maturity 2.2.2

Growth

of the

maize

plant

2.3 Predicting

maize growth stages

2.3.L

Thermal

units 2.3.2 Leaf

number

2.4 Effects of ensilinq

maize

plants at different

srowth stages

2.5 Effects of plant

^growth sÈage on maize

silage

2.5.L Effects of plant

growth stage ^{on maize}

silage

composition

2.5.2 Effects of plant

^growth stage

on the

voluntary

drymatter intake of

maize

2.5.3 Effect of plant

^growth stage

on the digest- ibility of

maize silage

2.5.4 Effects of plant

stage on

the

animal ^production from maize

silage

2.6

Maize qenotypes

2.6.L Traditional varieties

2.6.L.I Effects

on

plant production of

^harvesting

maize

varieties on the

same

day

¹⁹

12

15

2.6.L.2 Effects

on

plant production of

harvesting maize

varieties at the

same drymatter

content 20

(iii)

2.6.I.3

Feeding

value of

maize

varieties

ensiled

on the

same day

2.6.L.4

Feeding

value of

maize

varieties

ensiled

at the

same

drymatter

content

2L

22

- :

^;.

2.6.2

Other Genotypes

2.6.2.I

High

grain

types

2.6.2.2

Low

grain

types

2.6.2.3

Improved

quality

types

2.6.3

Conclusions about genotype

3.

THE LOCALITY AND THE OB.]ECTIVES OF THE ^RESEARCH

4.

AGRONOMIC EXPERIMENTS

4.1

^AgÉonomic experiment

I 4.1.1 Introduction

4.I.2 Materials

and Methods

4.1.3

Results and Discussion

24 24 25 27 30

2.7

fnfluence of

^{o'l a}

nt

rJpnsi l-v at harvest 30

2.7.1 Influence of density

on

yield

and

plant

components 30

2.7.2 fnfluence of crop density

on animaf

production

33

2.8 Influence of

row

spacing

³⁵

2.9 Influence of time of seedins

36

2.10 RoIe

of the

cob

in the nutritive value of

maize

silage

³⁷

2.L0.I

A

physiological

model

2.10.2 Agrononic assessments

2.10.3 Nutritional

assessments

2.ll

^The

addition of nitrogen to

maize

silage

38 39 40 43

2.12 The

addition of grain to

maize

silage

⁴⁴ 2.13 Maize

silage

compared

with

hay

plus grain rations

49

2.14 Summary

of

conclusions from

the literature

review 50

5I

s4 54 54 54 57

(

iv) 4.2

Agronomic experiment 2

4.2.L fntroduction

4.2.2

lr,laterials and Methods

4.2.3

Results and Discussion

4.3

Agronomic experiment 3

4.3.1 fntroduction

4.3.2 Materials

and Methods

4.3.3

Results and Discussion

4.4

Combininq agronomic experiments

5 FEEDING EXPERIMENT

5.1 fntroduction

5.2

l4aÈerials _and Methods

5.2.L

Crop production

5.2.2 Plant

sampling

5.2.3 Silage

production

5.2.4

Forage sampling

5.2.5

Feeding

facilities 5.2.6

Animal management

5.2.6

Rations

5.2.8

Animal measurements

5.2.9

Sarnples and chemical analyses

5,2,10 Metabolisable energy

density calculations 5.2.II StatÍstical

analyses

5.3

Results and Discussion

5.3.1

Crop characÈeristics

5.3.2 Effects of ensiling 5.3.3 Ration

^components

5.3.4

^Animal performance

5.3.5 Relating

animal performance

to crop

^production

5.3.6 Practical significance of feeding results

76 76 76 78 89 89 90 93 l-20 L32 L32 133 r33 134 135 135 136 136

t37

138 139 140 141

14I

141 L42 L42 148 r65 I68

(v)

6.

PRACTICAL SIGNIFICAI,ICE OF ^RESULTS

7.

^APPENDICES

g.

BIBLIOGR,APHY

r7t

r80 204

3.1 4.1

s2

55

4.2 The

total

plant, drymatter

content, total

drymatter

yieldr

and

proportion of

cob

in the total

^drymatt'er

of

17 maize

varieties at the fína1 harvest in

experiment

l.

⁷⁵

4.3

Characteristics of

maize

varieties

^sown

in

^exPeriment

2

and harvested 57 days post-anthesis. ⁷⁹ 4.4

Influence of density on the variety

^xL-45

in

experiment

2. ⁸⁶

2.2

4.5 ^Mean

value

^and

its

associated

variation for total dry- matter content

and

proportion of

cob

in the drlmatter

when assessed from

the

mean

of individuat

^{whole maize}

plants.

4.6 The number

of

harvests

out of five per

^{treatment r'rhen}

density

responses were

significant for

^maize

variety

and

time of

seeding treatments

in

experiment 3.

4.7 Mean

drymatter content, total drymatter yietd'

^propor-

tion of

cob

in the

drymatter,

in vitro

^d

igestibility

^and

digestible dfymatter'yield'of mai'ze'varieties

^{sown on}

different dates

and harvestedon

lst

May

in

experiment

3. It3

Table 2.L

4.8

4.9

4. r0

(vi ₎ LIST OF TABLES

TitIe

Mean composition and range

of

values

of

maize silages

ensiled at various

^{growth stages}

of the

crop.

In vivo drymatter digestibilities of

^rnaize

silage ensiled at various

^{growth stages}

of the

^crop.

Meteorological

data for the region near

^Struan.

Information

about

the hybrid

and open

potlinated varíeties

^{of, maize sowh}

in the

experiments.

Mean drlzmatter

content, total drymatter yield,

^propor-

tion of

cob

in the drymatter, in vitro

^drymatter

dÍgestibility,

and

digestible drymatter yield of

maize

varieties

^{sown at.}

d.ifferent dates

and harvested

at dÍfferent times so that drymatter

content was

constant

at

about 26

per cent in

exPeriment 3.

Corn Heat

Units

and number

of

^{days from seeding Èo}

mid-anthesis

for

selected maize

varieties

^{sown on one}

date in

experiment

2,

and

on three dates in

experiment 3.

Corn HeaÈ

Units required

by maize

varieties to

achieve

a

30

per cent

drymatter

content,

and

to

achieve ^a

I.0 percentage unit

increase

in

drlzmatter content.

Dr]¡matter

yield,

comPonent

proportionsr

and

in vitro digestibilities of the

two maize

varieties

ensiled

in the feeding

experiment.

Page

13

16

92

94

114

L23

L27

5.I

143

Table 5.2

5.3

5.4

5.5

5.6

5.7

(vii) Title

The

drymatter

^contents

of the

^maize

varieties

^before

and

afler ensiling,

^and

the losses

^due

to ensiling in the feeding

exPeriment.

Dr!¡matter

content,

chemical

composition,

^and

in vitrq

drymatter

digestibility of the ration

components ^used

in the feeding

exPeríment.

The ¡netabotisabte energy

densities of the ration

components as

calculated

^by

various

^methods

in

^the

f,eeding exPeriment.

Mean

proportion of

components

, the

metabolisable

"rr.tgy dãnsitÍes,

and crude

protein

contents

of

^the

rations

^consumed

ín the

112 days

of the

^feeding

exper iment.

Liveweight

gain'

carcase

characteristics,

^{and feed}

consumptÍon

of steers

f,ed

rations of either

^xL-8I

maize

ãifuge (high cob),

^{GM-21I maize}

silage

^{(low cob),}

or lucerne

^hay

with several levels of

^{added barley}

grain.

Drlrmatter

fed

and

rejected per steer, plus

^steer

paafot*att"a, feed

requiremenÈs, and

steer

^numbers

per

hectare

of

maize Produced.

Page

144

146

r47

r49

150

l-67

(viii

)

LIST OF FIGURES

TitIe

The

total drymatter content of 5

selected ^maize

varieties

^harvested

at 5 times in

experiment

I.

The

total

forage

drymatter yield of 5

selected

maize

varieties

^harvested

at 5 times in

experiment

l.

The

totat

forage drymatter

yield of 5

selected maize

varieties plotted against the total

drymatter content

in

experiment

l.

The

proportion of

cob

in the drymatter of 5

selected maize

varietíes

^harvested

at 5 times in

experiment

l'

The

proportion of

cob

in the total

^drymatter

of

⁵

selected maize

varieties plotted against the total drymatter content in

experiment

I.

The

yield of stover

drymatter

of 5

selected ^maize

varieties

^harvested

at 5 times in

experiment

I.

The

yield of stover drymatter of 5

selected maize

varieties ptotted against the total

^drymatter

content in

experiment

I.

The number

of

leaves Per

plant of 3I

maize

varieties plotted against the time for

each

variety to

^reach

mid-anthesis in

experiment 2.

The

drymatter content of 3I

^maize

varieties

^when harvested 57 days

post-anthesis, plotted

against

the time for

each

variety to

reach

mid-anthesis in

experiment 2.

The

influence of plant density on the total

drymatter

yield of 3

maize

varieties

^sown

at different

^times

and harvested

at a drymatter content of

about 26 per

cent in

experiment 3.

The

influence of plant density on the total

drymatter

yield of 5

maize

varieties

^{sown on 15th November}

in

experiment

3,

and harvested

on the one

^day.

The

influence of prant density

^on

the drymatter

content

of

5 maize

varieties

^{so$tn on 15th November}

in experi-

ment

3

and harvested

on the one

day.

The

influence of plant density

^on

the proportion of

cob

in the total drymatter of 5

^maize

varieties

^sown on

l5th

^November

in

experiment

3

and harvested

on

the

one

day.

The

influence of plant density on the $i!gg dry- matter digestibility of

3 maize

varieties

^{sown aÈ}

different times in

experiment

3

and harvested

on

the

one

day.

Page

58

60

62

64

66

68

7A

81

83

95

97

99

rI

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4 .10

4

.II

4.L2

4.r3

r01

l

:t rl

4.L4

103

(

ix) TitIe

The

influence of plant density on the digestible

drymatter

yietd oi

3

naize varietíes

^sown

at different

times and harvested

on tþg one

daY'

The

effects of several

systems

of

maize production achieved by

variety

^and

time of

^{seeding changes'}

The

effects of several

^systems

of

maize production achieved by

variety

^and

time of

^{seeding changes'}

The

relationship

^between

the

^mean

proportion of

^cob

ín the total

drlzmatter and

the

^mean

total plant dry- matter content of all harvests

^from

aIl

experiments' The mean

total drymatter

^contenÈ

of

an

early

^maturing

maize

variety (XL-45), a

^{medium maturing}

variety

(Q-739), and two

late

maturing

varieties

^{(Q-I280 and}

cH-128)

ptotted against the

Corn Heat

Units

accumul-

ated

from ^seeding

to

^harvest.

Regression

of steer liveweight gain

versus 9?ifV

drymatter intake for aII rations in the

feeding experiment.

Carcase

weight

and

backfat thickness (1I - I2th rib) of steers

versus

steer Iiveweight

^increase

for aII rations in the

feeding experinent'

Mean

calculated

metabolisable ^energy

density of

^the

rations fed in

^Èhe

feeding

experÍment

versus

^(a)

mean

daily drymatter intake (b)

^{mean feed conversion}

ratio (c)

^mean

daily liveweight gain'

Actual

means, and

predicted daily Iiveweight

^gain

versus mean

daily intake of

metabotisable ^energy

for

treatments

in the feeding

experiment'

Page

r05

r09

IlI

L2L

L25

r56

ì6+

r6o

158 4.16

4.L7

4. 18

4.L9

5.1

5.,+

5.3

s.2

(x)

LIST OF ^APPENDICES

TiÈIe

Assessment

of the period required for

oven drying

at

87oC, and

the variation in drlmatter

^content

between

individual plants

from

a

^row

of

maize.

The forage

drymatter yield per

hectare

of

17 maize

varieties

harvested

ot dif,ferent dates in experi-

ment 1.

The

total

drymatter

content

of. L7 maize varieEies harvested

qt different dates in

experiment

I.

The

proportion of

cob

in the total drymatter of

¹⁷

maize

varieties

harvested

at different dates in

experiment 1.

The drymatter

content of the

cob

of

17 maize

varieties

^harvested

at different dates in

experirnent

I.

The drymatter

yield per

hectare

of

cob

of

^{17 maize}

varieties

harvested

at different dates in

experimenÈ 1.

The

drymatter content of the stover of

L7 maize

varid,ies

^harvested

at different dates in

experiment

I.

The drymatter

yield of stover of

17 maize

varieties

harvested

at different dates in

experiment 1.

Mean forage

drymatter content of

13 maize

varieties

which were sown

at 3

seeding dates and harvested when Èhe cobs were

visually

assessed

to be in

the

dent stage in a preliminary

unpublished experiment

in

L97L/72.

Attributes related to the

whole

plant of the

32

maize

varieties Ín

experiment 2.

Attributes of the

cob and

stover of the

32 maize

varieties in

experiment 2.

Attributes related to the in vitro

drymatter

digest- ibilities

and

nitrogen

contents

of the

32 maize

varieties in

experiment 2.

Page

172

L73

L74

r75

L76

L77

L78

L79

180

181

L82

183

184

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4 .10

4

.II

4.L2

4 .13

Attributes of the cob, tillers

maize

varieties in

experiment

and leaves

of the

³²

, 2

An assessment

of the variation

between

individual plants

from

a

densely planted, row

of

maize

in

experiment 2.

4.L4

r85

(xi ₎

Title

The mean

density

and

density

^range

of varietyr tine of

seeding rand

date of harvest

treatments

in

experiment 3.

The

lnfluence of density on the toÈal

drymatter

yietd of

^maize

varíeties,

ExPeri¡nent 3.

The

ínfluence of density on the total drymatter

^content

of

maize

varieties,

ExPeriment 3.

The inf,luence

of density on the proportion of

cob

present in the total drymatter production of

^maize

varieties,

Experiment 3.

The

influence of densitll on the in vitro

^drymatter

digestibitity of

^naÍze

varieties,

Experiment 3.

The

influence of density on the in vitro digestible

drymatter

yield of

^maize

varieties,

Experiment 3' 4.2L

Publication.

Page

186

t88

190

l-92

194

195 196

L97

198

199

200

20L

202

203 4. 16

4.r7

4.18

4. r9

4.20

5.1

5.2

5.3

5.4

5.5

s.6

5.7

Calculation of ration proPortions to feed in

the

feeding

experíment.

Energy values

of feedstuffs

^and

rations fed in

^the

feeding

experiment as

calculated

from published feed-

ing

standards and from

the

measurements recorded'

Analysis

^on

the label of mineral blocks

^supplied ad

libitum to steers in the feeding

exPeriment.

The metabolisable ^energy

densities of the rations

as

predicted

by

various calculatíon

methods

in

^the

feeding

experiment.

The

relationships

^between

steer

1íveweight

9ain, dry- matter intake,

and

ration

metabolisable ^energy density

when

calculated for all

treatments

by various

^methods.

Actual

and

predicted liveweight

gains obtained ^by

various calculation

methods which

utilize the

data recorded

in the feeding

experiment.

Publication.

(xii)

SUMMARY

Three ajronomic experiments and one

feeding

experiment were conduc-

ted wÍth irrigated

^{maize (Zea mavs}

L)

^grown

for silage in the

mediter- ranean

- type climate of the

^{South East}

of

South

Australia.

^Agronomic

evaluationwagbasedondrymatteryieldperhectareandonforagequality

as assessed by drymatter contenÈr cob

proportion,

and sometimes

in vitro-

drymatter

digestibility.

In the fÍrst

agronomic experiment, 17

varieties of different maturit- ies

were compared

for their

^{growLh and}

theír

development by

harvesting

^on

five occasions.

Conclusions from

this

experirnent were:

-

^increases

in the

forage and cob

drymatter yields per

hectare

'

^cob

content,

and drlrmatter

content of the

^maize

varieties with

^harvesÈ

delays were as expectedrbased on

similar

comparisons

in other

areas.

Stover

yield per hectare

increased

initially, but

decreased again once

a

^forage

drymatter content of

19 ^{Lo 24}

per cent

was exceeded.

-

^{when harvested on}

the

^same

dayr early

^maturing

varieties

had ^a

significantly (p<0.05) higher drymatter content

^and

higher

Propor-

tion of

cob

in the total drymatter

^compared

with late

maturing

varieties.

-

^when

the varieties

^{were harvested}

on the

^same

day,

^{forage drYmatter}

yields per

hectare were

highest for the early

maturing

varieties

PX-50 and PX-52r and

the

^medium maturing

variety

^Ds-8054.

-

^when

the varieties

were compared

at the

same

drymatter

^content,

drymatter yield per

hectare

of the late

maturing

varieties

Q-500 ^and

Q-I280,

^and

the

^medium maturing

variety

Q-739rtended

to

be highest.

Thus

the later

maturing

varieties

^had

the Pot'entiar to

^be

the

^high-

est yíelding varieties if conditions permitted

^them

to

develop beyond

the

24

per cent drymatter content

^achieved'

-theproportionofcobinthetotaldrlrmatterwasgenerallysimilar

for the different

^maize

varieties

when compared

at the

same

total

(xiíi)

forage

drymatter content,

although

the late

maturing

varieties

Q-500 and Q-1280 had

significant (P<0.05)

lower

Proportions of

cob than

did the majoritY.

In the

second agronomic experiment,

all of the 3l

commercially

avail- able

maize

varieties

^{$rere evaluated}

at a fixed

growth stage

selected as

⁵⁷ days

post-anthesÍs.

conclusions from

this

experiment were:

-thematuritydescrÍptions(e.g.earlyrlate)suppliedbytheseed

companies

rated their

^own

varieties, but the descriptions did

^not

reliably

^equate

the anthesis

^dates

of varieties

^from

different

companies whích had

the

same

maturity description'

-

^{when harvested 57 days}

post-anthesis, the total

^{drYmatter contents}

of the varieties

^were

negatively related to the

number

of

^days

taken

to

reach

mid-anthesis.

^Thus

late

^maturing

varieties

^tasselled

later

than

early

maturing

varieties,

^and

also

developed more slowly post-anthesis.

- leaf

^number

post-anthesis could

^be used

as a

reasonable

guide

to

the maturity rating of

a maize

variety'

systems

of

maize production lñIere examined

in the third

^agronomic

experíment. Five varieties of different maturity ratings

^{$'ere sown}

at three

seedÍng dates and 15

densities in

an incomplete

factorial

^design'

Each

of the nine variety

^and

time of

seeding treatments were harvested

post- anthesis

^on

five occasions.

Conclusions from

this

experiment were:

- early

^{and medium maturing}

varieties

^sown

in nid

^{November were the}

only

treatments

to

achieve

the

33

to

37

per cent drymatter

^content considered

the

optinum

for

maximum

drymatter yield

and forage

quality.

-

^a

nid

^{November sowing}

of the

early-medium maturing

variety

^xL-81

was

selected as the best

maize

production systen for both

single and consecutive

harvests.

^DrymaÈter

yield per hectaret

^drymatter

contentr

and

proportion of

cob

all

^increased

to

^be

optinal at

^the

(xÍv)

final

harvest.

- alternative

maize

production

systems based on

other varieties

^and

time of

seeding co¡nbinations

usually

had lower drymatter

yierds'

drlzmatter contentsr and

proportions of

cob than

did the

XL-8I system.

- for

^those systems aimed

at

^producing

consistent silage quality,

as

indicated

by

a

constant drymatter

content of

about ²⁶

per cent at

harvest,, drlzmatter

yield per

hectare and cob

proportion

decreased

as the harvest period

Progressed.

-whereassessed,@dr1rmatterdÍ9estibiIitiesdidnotaffect the

choice

of the

maize

production

system.

- significant

^responses

to plant density (P<0.05)

^{were most frequent}

for

forage

drymatter yield per hectare

(23

out of

45 assessments).

A

plant density of

10

to

¹⁵

plants

Per ^square metre seemed

to

maximize forage

yield per

hectare

without greatly affecting

the

drymatter content,

cob

proportior¡

and forage

digestibility.

!{hen

data

from

the three

agronomic experiments were combined, the conclusions obtained were:

- the

^number

of

days and Corn Heat

Units reguired

^{by each}

variety

^to

reach míd-anthesis was

relatively constant,

and were 83 and 1670

for

XL-45

(ear1y);

94 and 1903

for

Q-739 (medium); and 107 ^and 2208

for

GH-I28

(Iate) respectively.

-

^drymatter

content

^increased

linearly as the

number

of

Corn ^Heat

Units

accumulated post-seeding

increased, but the rate of

increase depended on

the maturity rating of the variety.

For each 1.0

percentage

unit

increase

in

drlzmatter

content, xL-45

^(earIy)

,

^Q-739

(medium), and GH-128

(Iate) required 60,

^'17,and

I28

Corn Heat Units

respectively.

^To

attain a drymatter content of

30 Per

cent'

^xL-45

required

2700

corn

^Heat

units,

Q-739

required

3L02, and ^GH-128 would have

required

3?13 Corn Heat

Units.

Thus,

late,

maturing

(xv)

varieties tasselled late,

^developed

slowly Post-anthesis,

^and

in the

South East

of

^South

Australia

^{would never} achieve more than 30

per cent drymatter

^content.

- the proportion (t) of the

^cob

in the total drymatter (y)

^was

related to the total drymatter content (8) at harvest (x):

y =

9.33x

-

^o.L22x2

- 113.0

^(ro0r2

=

^{92.2) .}

Cob

proportion

plateaued,

with little variationrat

^{about 64}

per

^cent

cob when forage

drymatter

contents were

higher

than about 32 per

cent. At drymatter contents lower than

³²

per cent, variation in

cob

proportion

r.ras

greater,

and

the selection of varieties with

extreme

proportions of

cob was possible.

In the

feeding experiment¡

silage of

a ^maize

variety (xL-8I) with

^a

high proportion of

cob

in the drymatter (45'4 + 4'42)

was compared

with silage of a variety

^(GM-2I])

with a

^low

proportion of

cob

in the

drymatter

(34.3

+ 4.88).

^Both

varieties

^were

ensiled at a

drymatter

content of

²²

per cent.

^The

silages

^were

fed with

^{urea and}

either 0r25tor

⁴⁵

per

cent added

barley in the ration

^drlmatter

r

^{and were}

also

^compared

with

^lucerne

bay

plus barley grain rations calculated to

be near comparable

in

metabolisable energy

densities per unit drlrmatter.

Conclusions from the feeding experiment were:

- steers fed

GM-211 (Iow

cob) silage

^grew

significantly

(P<0.05) slower

than

those

fed xL-81 (high cob) sitage

when no

barley

^was

added

(0.60;

0.71 kg/head/day

respectively),

^{and when 25}

per

cent

oftherationdrlrmatterwasbarley(0.90;I.03kg/head/dayrespect- ively) .

^vlhen

barley

^was

fed at

45 Per

cent of the ration

drymatter '

steer Iiveweight

^{gaíns r,Yere}

not signif icantly dif ferent

(P>0.05) between GM-2II and

XL-8I silages (I.3'5;

1.03 kg/head/day respect-

ively)

.

-

^added

barley grain significantly (P<0.05)

increased

liveweight

gains

above those ^achieved on

silage alone, but the

^highesÈ

live-

(xvi ₎

weight

gains

achieved were obtained

with

GM-2I1

plus

45

per

cent

barley,

^xL-81

plus

25

per cent barley,

and xL-81

plus

45

per

cent

barley.

- a

^{lucerne hay}

plus

⁴⁵

per cent barley ration

had

a slightly

^higher

metabolisable energy

density per unit drymatter

than

did either of the silage-only rations,

and gave

sígnificantly (P<0.05) better liveweight gains

(0.89 versus ^mean

of

O.66 kg/head,/day

respectively)

because

of a higher drymatter intake.

- a

^{lucerne hay}

plus

⁶⁹ Per

cent barley ration

^had

a sinilar

^metabol-

isable

energy

density per unit drymatter to both of the silage

^plus

45

per cent barley rations, but

^gave

significantly Poorer

(P<0.05)

liveweight gains

^{(0.89 versus mean}

of

L.O4 kg/head/day

respectively)

because

drymatter

inÈake was lower

possibly

because

of D-lactic

acidosis

- for aII rations ( n =8), liveweight gains

were

linearly related to voluntarydr}rmatterintake,metabolisableenergyintakerand

¡netabolisable energy

density

⁽¹⁰⁰¹²

= 95.g, 92.7r

^and

72.2

^tespect-'

ively). In the

^absence

of D-lactic acidosls ( n = 7), the relatÍon- ship

between

liveweight gain

and metabolisable energy

density

^{t^tas}

quadratic

and

less variable

⁽¹⁰⁰¹²

= 95.6).

GM-21I (}ow

cob) silage

f,ed

without bartey

was

the only ration with a significantly

Poorer

(P<0.05)

feed. conversion

ratio

than

the others (1I.4

versus a ^mean

of 9.3).

- the

metabotisable energy

density of

GM-2I1

silage

^(9.84

MJ/kg),

^as

calculated

from

the

Rostock

equation

was

significantly

(P<

0.00I) lower than that of

^XL-81

silage (I0'20

^tE/kSl

'

- overall, i!

^seems

that

^maize

varieties

^can

influence steer liveweight gain by increasÍng the

metabolisable energy

density of the silage,

hence

increasing the voluntary drymatter

^and metabolisable ^energy

intakes.

^The

Broportion of

cob

in the

forage

drlmatter

^{may be}

, involved in

determining

the

metabolisable ^energy densít'y

of

^maize

(xvii

)

silage.

In placing the

agronomic and feeding experiment

results into perspective, the practical

conclusions Ì.tere made

that:

- the best varieties to

^grovr

for either sitage or

greenchop were

the

ones which would achieve

a drymatter content of

33

to

^{37 per}

cent.

^Thus

early to

^{medium maturing}

varieties

need

to

be ^grown

in the

South East

of

South

Australia.

- the variety

should be selected on

digestible

drymatter

yield of silage, with consideration also for a high proportion of

cob

in the

forage

drymatter

being

ensiled.

- the

^apparent

high yield potential of late maturity varieties

could

not

be

exploited

because

the

dr1'matter

contents they

^achieved

(maximum

of

30

per cent)

were

too low. Insufficient

Corn Heat Units accumulate

in the

growing season

to

enable

the late

maturing

variet- ies to

achieve

their

maximum drymatter

yierd'

- the proportion of

cob

in the

f,orage

drymatter

was

often

lower with

Iate

maturing

varieties

^compared

with earlier

^maturing

varieties.

A low cob

proportion

may

limit

animal performance because

of

^low

drymatter and metabolisable energy

intakes.

-

^{a mid November sowing}

of

^Èhe

variety

XL-81 was selected as

being

the most

suitable

maize

production

system

for either a single harvest

or

for

consecutive harvests.

- varieties

^vrere

guantitated f,or Èheir

Corn Heat

Unit.requirements to

^\

achíeve mid-anthesis and

a drymatter content of

³⁰

per cent.

^The

appropriate varieties can, therefore,

be

selected for

^other

locations

which have

guantitated theír

maize growing season using Corn Heat

Units.

(xviii)

DECLARATION

The work

reported in this thesÍs

^{was conducted}

by the

^author

whilst at the

Struan Research

Centre,

Department

of Agriculture,

Naracoorte, ^South

Australia.

This thesis contains

^no

material

which has been submitted

for the

^award

of

any

other

degree

or

diploma

in

any

University.

To

the best of the authorrs belief,

^no

material previously

^{published by} another ^person

is included in the thesis unless specifically

acknowledged

in the text

^and

in the alphabetical list of

^such

publication included as

^a

bibliography.

A

portion of this

^{work has been published:}

HAI{THORNETW.

A.

⁽¹⁹⁷⁸⁾

-,The

^feeding

value of

^maize

silage for cattle'r.

Proceed

inqs of the Australian

^SobIE

of

Animal Production l.2zL7L (Abstract)

(w.

A.

^HAWTHORNE)

I

(xi x)

ACKNOWLEDGEMENTS

The author wishes

to

^express

his sincere

thanks

to the following:

My

wife Jane, for the lonely

hours she spent

during the

^progress

of this project.

2.

Dr. !{.

G.

Allden for

permissíon

to

undertake

the project in his

department, and

the help

he gave

as initiat

supervisor

of this project.

3

Dr. A. R.

^Egan

for

undertaking

the role of project supervisor

during

the thesis

preparation.

4. R.

W. McNeiI as

Officer-in-Charge of the

Struan Research Centre

for stimulation

and assÍstance

during the project.

5.

B. Glaetzer for

assistance

ín statistically analysing the

^data;

E. A.

Dunstan

for

arranging and

assisting with

chemical analysesi and

A. D.

Hughes

for

chemical analyses and advice.

C. Billing¡ A. Dolting. G.

^Fromm¡

R.

Ross and

A.

Zerk

for

^assistance

ín the fietdi

^and

R.

^Stacey

for

assistance

with the

data.

7 G. Davies and

C,

Pahl

for tlping this thesis.

6

The

Australian

lvleat Research Committee

for providing financial assis-

tance

for this project.

8