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8126567

W in slo w , M ark D a v id

NITROGEN UTILIZATION IN MICHIGAN WHEAT CULTIVARS, AS
RELATED TO GENOTYPE X ENVIRONMENT INTERACTION

Ph.D. 1981

Michigan S tate University

University
Microfilms
International

300 N. Zeeb Road, Ann Arbor, M I 48106

NITROGEN UTILIZATION IN MICHIGAN WHEAT CULTIVARS,
AS RELATED TO GENOTYPE X ENVIRONMENT INTERACTION

By

Mark David Winslow

A THESIS

Submitted to
Michigan St at e U n i v e r s i t y
i n p a r t i a l f u l f i l l m e n t o f the requirements
f o r the degree o f

DOCTOR OF PHILOSOPHY

Department o f Crop and Soil Sciences

1981

ABSTRACT
NITROGEN UTILIZATION IN MICHIGAN WHEAT CULTIVARS,
AS RELATED TO GENOTYPE X ENVIRONMENT INTERACTION
By
Mark David Winslow

The s o f t white w i n t e r wheat { T r i t i c u m aestivum L. ) cul t i v a r
'Tecumseh'

i s h i g h l y responsive t o heavy a p p l i c a t i o n s

f e r t i l i z e r , but is l o w - y i e l d i n g i f N is not a p p l i e d .
inc re as in g cost o f f e r t i l i z e r ,
t h a t use N e f f i c i e n t l y .

it

is

important

of nitrogen
With

(H)

the

to develop cul t i v a r s

This research was conducted t o examine

the

basis o f Tecumseh's high N requirement and hi gh N responsiveness.
Data were c o l l e c t e d on the seasonal accumulation and st r aw grain p a r t i t i o n i n g o f reduced N in the above-ground portions o f
cultivars

('Tecumseh',

'Io n ia ',

'Y o r k s t a r ' , and 'Augu st a' ) ,

fun ct io n o f three r a t e s o f N topdressing ( 0 ,
three l o c a t io n s in 1980.

four

as a

45, and 90 k g / h a ) ,

at

The e f f e c t of N topdressing on y i e l d , y i e l d

components, and ha r v e s t i n de x, was also measured,
over t hr ee years and th r e e l o c a t i o n s .
the e f f e c t s o f o t h e r environmental

i n e i g h t experiments

To compare the e f - f e c t o f N w i t h

variables, yield

and yield-component

responses to improvement in s i t e y i e l d p o t e n t i a l were measured,

in

f i f t e e n s i t e s over two y e a r s .
Tecumseh was as high o r h i g h e r than the e t h e r c u l t i v a r s i n N
accumulation per h e c t a r e , a t a l l
growing season.

r a t e s o f app lied

N, by the end of

Tecumseh took up approximately twice as much soil

the
N

a f t e r an th es is as the o t h e r c u l t i v a r s , and maintained a h i g h e r who!ep l a n t con cen tr ati on o f N a t a l l

growth s t a g e s .

I t i s concluded t h a t

. Mark David Winslow
Tecumseh's high N requirement i s not caused by a d e f i c i e n c y in capa city
f o r uptake o f soi l

N.

The high y i e l d responsiveness of Tecumseh to N was associated
with a high responsiveness o f the y i e l d component heads/m

2

(X).

Tecumseh was also more y i e l d - r e s p o n s i v e than ot her c u l t i v a r s to
improvements in s i t e y i e l d p o t e n t i a l , and t h is was also associated with
a high X-responsiveness.

Thus, genotype x environment i n t e r a c t i o n f o r

Tecumseh r e s u l t s from an unusually high X-responsiveness; t h i s is a
general

response to improved environments, r a t h e r than a s p e c i f i c

response to N.
Tecumseh's high y i e l d response t o N was achieved with a p p l i c ­
a t i o n o f N a t any time up u n t i l
stage.

the crop reached the f u l l y - t i l l e r e d

In c o n t r a s t , a high y i e l d response t o N f o r Io n ia was achieved

only when N was a p p li e d a t the f u l l y - t i l l e r e d stage .

This is i n t e r p ­

re t ed as i n d i c a t i n g an i n h e r e n t l y lower l e v e l o f i n t e r - t i l l e r
competition in Tecumseh than in I o n i a .

Thus, Tecumseh's high

X-responsiveness to improvements i n the environment may be a r e s u l t
o f a low l e v e l

of i n t e r - t i l l e r com pe tit io n, which allows t h i s c u l t i v a r

to achieve a high X d es p it e the seasonal f l u c t u a t i o n s
environmental

in the supply o f

resources t h a t commonly occur in production s i t u a t i o n s .

ACKNOWLEDGMENTS

I would l i k e to thank Dr. E v e r e t t H. Everson f o r p r ov id in g the
op p or tu ni ty f o r me to perform t h i s research.

Dr.

Russell

given generously o f his time in reviewing the manuscript.
Adams, St anley K. Ries, Andrew D. Hanson, and David A.

D. Freed has
Drs. M. Wayne

Reicosky have

also given valua ble c r i t i c i s m s .
This research could not have been done w it h o u t the superb a s s i s t ­
ance o f Mr. Le s te r E. Morrison in p l a n t i n g , m a i n t a in i n g , and ha rv es tin g
the f i e l d p l o t s .

I t has been a real

pleasure to work with L e s t e r these

f o u r y ea r s.
I am also indebted to Ms. Pamela Hulse, Mr. Rick Blakeney, and
Mr. Geoffrey Heinr ich f o r assistance with the f i e l d w o r k and f o r t h e i r
support and f r i e n d s h i p .
I would l i k e to make a spe cial acknowledgment to the c o n t r i b u t i o n
which the l a t e Dr. John E. Gra fius has made to t h i s research.

The

approach which I took in ana ly zi ng t h i s problem was g r e a t l y i n fl u e n c e d
by the ideas o f t h i s outstanding s c i e n t i s t .

I consider myself very

f o r t u n a t e to have been exposed to Dr. G r a f i u s 1 rigorous but pragmat ic
philosophy o f research.

TABLE OF CONTENTS
Page
LIST OF TABLES................................................................................................................... i v

LIST OF F IG U R E S .............................................................................................. vi
I N T R O D U C T I O N ............................................................................................................. 1
REVIEW OF LITERATURE............................................................................................... 3

MATERIALS AND METHODS................................................................................. 16
RESULTS AND D I S C U S S I O N .............................................................................................. 21
SUMMARY AND CONCLUSIONS.............................................................................................. 40
APPENDIX A, EFFECT OF N TOPDRESSING ON DRY MATTER AND N
ACCUMULATION AT THREE GROWTH STAGES, FOR FOUR WHEAT
CULTIVARS: DATA FROM SPECIFIC LOCATIONS, IN 1980..........................
APPENDIX B, EFFECT OF LATE-SEASON N SUPPLEMENTS ON
GRAIN N AND YIELD VARIABLES OF THREE WHEAT CULTIVARS

.

.

42

.

.

45

APPENDIX C, EFFECT OF N TOPDRESSING ON YIELD VARIABLES OF
SEVERAL WHEAT CULTIVARS: DATA FROM SPECIFIC LOCATION-YEARS

.

.

47

APPENDIX D, EFFECT OF INCREASING SITE YIELD POTENTIAL ON
THE YIELD AND YIELD COMPONENTS OF SEVERAL WHEAT CULTIVARS.

.

.

53

LITERATURE C I T E D .................................................................................................... 57

LIST OF TABLES

Table
1.

Page
Crop N st atus and y i e l d performance a t t h r ee l o ca tio ns
in 1980 .......................................................................................................

21

Pre- and p o s t- an t h es is accumulation o f N, and g r a i n straw p a r t i t i o n i n g o f N, f o r f o u r wheat c u l t i v a r s

.

25

Relat io nsh ip between gr ai n N and y i e l d f o r f o u r wheat
c u l t i v a r s ................................................................................................

25

E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f two
wheat c u l t i v a r s ..................................................................................

28

E f f e c t o f N topdressing on dry m a t t e r production and
N accumulation a t three growth stages in f o u r
wheat c u l t i v a r s , a t Mendon..............................................................

42

A2. E f f e c t o f N topdressing on dry m a t t e r production and
N accumulation a t three growth stages in f o u r
wheat c u l t i v a r s , a t East Lan sin g................................................

43

A3. E f f e c t o f N topdressing on dry m a t t e r production and
N accumulation a t three growth stages in f o u r
wheat c u l t i v a r s , a t S a r a n a c .......................................................

44

2.

3.

4.

A l.

B l.

.

E f f e c t o f la te -s e as on f o l i a r and s o i l N a p p l i c a t i o n s
on grain N and y i e l d v a r i a b l e s o f three wheat
cultivars.
Saranac, 1980 ..............................................................

Cl. E f f e c t of N topdressing on y i e l d v a r i a b l e s o f two
wheat c u l t i v a r s . Saranac, 1978, experiment 1

46

.

47

C2. E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f four
wheat c u l t i v a r s . Saranac, 1978, experiment 2 .

48

C3. E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f three
wheat c u l t i v a r s . Saranac, 1979 .................................................

49

C4. E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f fou r
wheat c u l t i v a r s . Mendon, 1980.......................................................

50

C5. E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f fo ur
wheat c u l t i v a r s . East Lansing, 1980

51

iv

Table

Page

C6. E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f fo ur
wheat c u l t i v a r s .
Saranac, 1980..................................

v

52

LIST OF FIGURES

F ig u re

Page

1.

E f f e c t o f N topdressing on dry m at ter production
and N accumulation in f o u r wheat c u l t i v a r s ,
a t m a t u r i t y ...................................................................................... 23

2.

Dry matter production and N accumulation over three
growth stages, f o r fo ur wheat c u l t i v a r s
. . .

.

24

3.

E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the
y i e l d and y i e l d components o f Tecumseh wheat,
r e l a t i v e to the gene pool m e a n ...................................... 31

4.

E f f e c t o f seeding r a t e on y i e l d v a r i a b l e s in wheat .

5.

V a r i a t i o n o f y i e l d components across s i t e s of
d i f f e r i n g y i e l d p o t e n t i a l .................................................... 34

6.

E f f e c t o f d i f f e r e n t dates o f a p p l i c a t i o n o f N
topdressing on y i e l d and y i e l d components

.

33

o f two wheat c u l t i v a r s ................................................... 36
Dl. E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the
y i e l d and y i e l d components o f I o n i a wheat,
r e l a t i v e t o the gene pool m e a n .................................................53
D2. E f f e c t o f in c r e a s i n g s i t e y i e l d p o t e n t i a l on the
y i e l d and y i e l d components o f York sta r wheat,
r e l a t i v e t o th e gene pool mean . . . . . .

.

54

D3. E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the
y i e l d and y i e l d components o f Augusta wheat,
r e l a t i v e t o the gene pool m e a n .................................................55
D4. E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the
y i e l d and y i e l d components o f Frankenmuth
wheat, r e l a t i v e t o the gene pool m e a n ................................... 56

vi

INTRODUCTION

Soon a f t e r i t s r e l e a s e in 1974, i t was no ti ced t h a t the Michigan
s o f t white w in t e r wheat ( T r i ti c u m aestivum L . ) c u l t i v a r
required he a vi e r sp r in g topdressings o f n itr og en

'Tecumseh'

(N) f e r t i l i z e r than

o th er c u l t i v a r s , i n o r d e r to achieve s a t i s f a c t o r y y i e l d s .
fe rtiliz e r

Since N

is an expensive production i n p u t , i t would be d e s ir e a b le to

develop c u l t i v a r s

th a t have low N requirements.

This research was

conducted t o di s c o v e r the reasons f o r Tecumseh's high N requirement
and high

response to supplemental N.

This in fo rm at io n could be h e l p f u l

in designing breeding s t r a t e g i e s to improve the e f f i c i e n c y o f N use
in f u t u r e c u l t i v a r s .
Tecumseh's high N requirement might be caused by a d e f i c i e n c y
in ca p a c i ty f o r uptake o f soi l

N.

To t e s t t h i s hyp othesis, data were

c o l l e c t e d on N accumulation in above-ground parts o f f o u r c u l t i v a r s ,
as a fu nction
ments.

o f d i f f e r e n t r a t e s o f N topdressing, in th ree e n v i r o n ­

Other f e a t u r e s of N accumulation and p a r t i t i o n i n g were also

measured, t o see i f d i f f e r e n c e s in u t i l i z a t i o n o f N occurred among
cu ltiv a rs .
Since N a p p l i c a t i o n increases y i e l d by inc re as in g the values o f
the y i e l d components, c u l t i v a r d i ff e r e n c e s in y i e l d component response
to N might e x p la i n

d i ff e r e n c e s in y i e l d response to N.

To t e s t t h i s

hypothesis, y i e l d and y i e l d component responses to N were measured over
several years and l o c a t i o n s .

1

I t was recognized t h a t there may be s i m i l a r i t i e s

between crop

response to N and crop response to o t h e r growth-promoting f a c t o r s ,
such as moisture and cool

t em pe r at ur es , which cause much o f the d i f f e r ­

ences in s i t e y i e l d p o t e n t i a l
o f Michigan.

among s i t e s in the wheat-producing areas

Thus, d i f f e r e n t i a l

same basis as d i f f e r e n t i a l
y ie ld potential,

c u l t i v a r response to N may have the

c u l t i v a r response to improvements in s i t e

and may t h e r e f o r e be a model system in which t o study

"genotype x environment i n t e r a c t i o n . "

To examine these id e a s , y i e l d

and yield-component performance across a s e t o f s i t e s o f d i f f e r i n g
y i e l d p o t e n t i a l , were measured.

REVIEW OF LITERATURE

The i n t e n s i v e c u l t i v a t i o n o f cropland has reduced s o i l
(N) f e r t i l i t y

nitrogen

to such a degree t h a t the use o f supplemental N f e r t i l i z e r

is necessary f o r high y i e l d s and p r o f i t a b l e farming ( 4 5 ) .
use o f chemical N f e r t i l i z e r s

has several

drawbacks.

However, the

I t i s expensi ve,

accounting f o r approximately 10% o f a f a r m e r 's production costs in
Michigan ( 5 8 ) .

I t is e n e r g y - i n t e n s i v e ; o n e - t h i r d o f the energy

r eq ui r ed to produce a corn crop in the United States goes toward the
manufacture, d i s t r i b u t i o n , and a p p l i c a t i o n o f f e r t i l i z e r N ( 8 6 ) .

Much'

o f the f e r t i l i z e r a p p l i e d i s l o s t through le ach in g or d e n i t r i f i c a t i o n ,
which can cause serious environmental problems ( 8 8 ) .
Despite these drawbacks, increased use o f N f e r t i l i z e r i s
essential
(105).

i f food production is to keep pace w ith population growth

Thus, agronomists are faced with the challenge o f developing

e f f i c i e n t systems o f s o i l
cultivars.

Vose ( 9 9 ,

N f e r t i l i t y management and e f f i c i e n t crop

100) and Epstein (20) argue t h a t gr eat p o t e n t i a l

e x i s t s f o r improving the e f f i c i e n c y o f n u t r i e n t use in crops, by g e n e ti c
means.
Evidence f o r g e n e ti c v a r i a b i l i t y in N use e f f i c i e n c y has been
rep ort ed in the l i t e r a t u r e .

Ch e v a l ie r and Schrader (13) measured the

amount o f n i t r a t e and reduced N accumulated ( p e r p l a n t )
and hybrids in s o l u t i o n c u l t u r e .
in the amount o f n i t r a t e

by corn inbreds

They found d i f f e r e n c e s among genotypes

taken up from s o l u t i o n and in the p a r t i t i o n i n g

3

o f reduced N among p l a n t p a r t s .
ol d pl ant s in s o l u t i o n c u l t u r e ,
(which has the same parentage

disappeared

a l . ( 7 1 ) , using 28-day

found t h a t the wheat c u l t i v a r

' A r th u r '

as Tecumseh) took up more n i t r a t e from

the s o l u t io n than did ' A t l a s 66'
the s o l u t io n was low.

Mugwira e t .

when the con centration o f n i t r a t e in

However, the d i f f e r e n c e between c u l t i v a r s

when con cen tr ati on of n i t r a t e was high in the s o l u t i o n .

Thus, A t l a s 66 was more responsive than A r t h u r ,
uptake per p l a n t ,

to increases i n n i t r a t e

in terms o f n i t r a t e

supply.

This group of

workers also found d i f f e r e n c e s among c u l t i v a r s o f t r i t i c a l e
in n i t r a t e uptake per p l a n t .

Lai e t .

al.

(57)

and r y e ,

found t h a t t r i t i c a l e

c u l t i v a r s accumulated more N per hectare than did wheat c u l t i v a r s ,
but considerable w i t h i n - s p e c i e s v a r i a t i o n occurred f o r both crops.
Harvey ( 4 4 ) ,

in s o l u t io n c u l t u r e stu die s w it h corn and tomatoes, found

c u l t i v a r d i f f e r e n c e s in dry matter production per p l a n t , as a fun ct i on
o f s o l u t io n n i t r a t e co n c e n t r a ti o n .

He re po rt ed t h a t c u l t i v a r s t h a t

were low in dry m a t t e r production a t low n i t r a t e l e v e l s were more
responsive ( i n terms o f dry matter production)
nitrate

to increases in the

level.
G e r l o f f (3 2) advocates- the use o f the v a r i a b l e "N e f f i c i e n c y

ratio"

(mg dry wt per plant/mg N absorbed per p l a n t )

as a measure of

p l a n t e f f i c i e n c y in the use of accumulated N f o r dry m a t te r production.
Using t h i s c r i t e r i o n ,

c u l t i v a r d i f f e r e n c e s were found in tomato (74)

and ryegrass ( 1 0 1 ) , on a p e r - p l a n t basis, in s o l u t io n c u l t u r e
experiments.
The f i n d i n g t h a t c u l t i v a r s can d i f f e r in dry m a t t e r production
per u n i t N absorbed implies
o f N in p h y s io lo g i c a l

t h a t they d i f f e r in the e f f i c i e n c y o f use

processes.

One e x p la n at io n f o r t h i s could be t h a t

c u l t i v a r s d i f f e r in t h e i r ca pa ci ty to convert the absorbed inorganic

n i t r a t e i n t o useful organic forms o f N.

The r a t e - l i m i t i n g step in t h i s

process i s the reduction o f n i t r a t e to n i t r i t e
reductase ( 1 6 ) .

Genetic d i f f e r e n c e s in n i t r a t e

have been reported ( 1 6 , 17, 3 0 ) .

by the enzyme n i t r a t e
reductase a c t i v i t y (NRA)

I t was hoped t h a t g e n e ti c d i f f e r e n c e s

in NRA would c o r r e l a t e with d i f f e r e n c e s in p l a n t v i g o r , gr ai n y i e l d ,
and grain p r o t e i n , and would t h e r e f o r e would provide a basis f o r
s e l e c t i o n in breeding programs.
have been weak ( 1 4 ,

U n f o r t u n a t e l y , however, the c o r r e l a t i o n s

16, 17, 8 2 ) .

I t appears t h a t i n e f f i c i e n c i e s in ot her

N use processes, such as uptake and t r a n s l o c a t i o n , compensate f o r high
NRA, so t h a t gain in economic t r a i t s would not be achieved by s e l e c t i n g
f o r high NRA alone ( 1 6 , 17, 8 2 ) .
The r e l a t i o n s h i p o f g e n e ti c v a r i a t i o n in the e f f i c i e n c y o f
the various N use processes among c u l t i v a r s ,
has recieved considerable a t t e n t i o n .

to gr ai n p r o t e i n produ ction,

Studies in wheat (70) and corn (47)

i n d i c a t e t h a t c e r t a i n h i g h - p r o t e i n c u l t i v a r s accumulate more N from the
soil

( pe r hectare.) or from s o l u t i o n c u l t u r e

than do l o w - p r o t e in c u l t i v a r s .
conducted by Cataldo e t .

(per p l a n t ) ,

respectively,

However, a growth-chamber pot study

a l . (1 1)

revealed t h a t a h i g h - p r o t e i n oat

c u l t i v a r accumulated no more N than a l o w - p r o t e in c u l t i v a r ;

rather,

high g r ai n percent p r o t e i n r e s u l t e d from a lower accumulation o f carbo­
hydrate in the h i g h - p r o t e i n c u l t i v a r .
There does not appear t o be any co n s is te n t as s o c i a ti o n between
gr ai n percent p r o t e i n and l e a f N c o n ce nt r at io n.

High-protein c u ltiv a rs

have been found to have l e a f reduced N concentrations hi gh er ( 7 9 ) ,
lower ( 5 4 ) ,

and equal

(87)

to those

o f l o w e r - p r o t e i n c u l t i v a r s . One

study advocated the

use o f seedling reduced N con centration as a

screening c r i t e r i o n

f o r id e n tify in g high-protein lines

The study o f

Cataldo e t .

(48).

a l . mentioned above found t h a t the

high

p r o t e i n oat c u l t i v a r continued to accumulate N from the pot a f t e r
a n t h e s is , whil e the low p r o t e i n c u l t i v a r did not.
study using s i x oat c u l t i v a r s ,
a l .,

However, in a f i e l d

i n c l u d in g the two studied by Cataldo e t .

another group (79) obtained the opposite r e s u l t s f o r these two

c u l t i v a r s ; the l o w - p r o t e in c u l t i v a r took up more N a f t e r anthesis than
did the h i g h - p r o t e i n c u l t i v a r ,

per he c ta re .

Thus, caution must be

ex er cis ed in extending conclusions deriv ed from growth-chamber pot
experiments on s i n g l e plants to make inferen ces about crop performance
in the f i e l d .

Among the s i x c u l t i v a r s in the l a t t e r study, no c o r r e l ­

at io n was found between po s t- a n t h e s i s N accumulation and gr ain percent
protein.

In a f i e l d experiment using c u l t i v a r s o f wheat studied in

the present rese arch , Heinr ich

(46) found t h a t Tecumseh (which has a

high g r ai n percent p r o t e i n ) was g r e a t e r in p o s t-a nt he si s N uptake than
lower-protein c u ltiv a rs .
H i g h - p r o t e i n c u l t i v a r s o f wheat ( 5 3 , 55, 8 7 ) , oats ( 7 9 ) , and
r i c e (7 8) were found to t r a n s l o c a t e more N from the v e g e t a t i v e parts
i n t o the g r a i n ,

than l o w - p r o t e in c u l t i v a r s .

wheat found no such r e l a t i o n s h i p

(70).

However, another study in

The study o f Cataldo e t .

a l.

mentioned above found t h a t the h i g h - p r o t e i n c u l t i v a r a c t u a l l y t r a n s l o c ­
ated less N from the v e g e t a t i v e part s to the g r a i n , than did the lowprotein c u l t iv a r .
Thus, i t

seems t h a t there is no s i ng le ph ys io lo gi cal

t r a i t that

can be used to p r e d i c t o r s e l e c t f o r high grain percent p r o t e i n .

Rather,

gra in percent p r o t e i n is the r e s u l t o f the i n t e r a c t i o n o f many processes
t h a t may show compensatory s h i f t s when one p a r t i c u l a r process is
increased or decreased.
individual

I d e n t i f i c a t i o n o f genotypes su p e r io r f o r

processes may be valua ble in c o l l e c t i n g parents f o r high-

p r o t e i n breeding programs, even i f these parents are not p a r t i c u l a r l y

high in grain percent p r o t e i n themselves; "p h y s io lo g ic a l
(102)

complementation"

o f these processes in segregating generations may lead t o hi gh-

p ro te in l i n e s among the progeny.

This idea o f using p ar en ta l

component

complementation to achieve progress in s e l e c t i o n f o r complex t r a i t s was
used su c ce s s fu l ly by Gra fiu s e t .

a l . (40).

Many breeders have n ot ic ed a ne g at iv e c o r r e l a t i o n beween y i e l d
and grain percent p r o t e i n in segre gat ing populations ( 8 , 66, 77,
This c o r r e l a t i o n f i t s
( 9 , 81) .

95).

the e x p e c t a t io n from a b i o e n e r g e t i c p o i n t o f view

Approximately twice as much glucose is re q u i r e d to synthesize

one gram o f p r o t e i n as compared to one gram o f carbohydrate ( 9 ) .
i f the pool o f a s s im i la t e s is f i x e d ,

Hence,

and i f i t l i m i t s gr ain pr odu ction,

any increase in p r o t e i n production w i l l

be accompanied by a decrease in

carbohydrate production ( t h e r e f o r e y i e l d w i l l

dec re ase ).

However, by

increasing the ca pa ci ty o f a c u l t i v a r to a s s i m i l a t e s o l a r energy in
useful forms, gains in both y i e l d and p r o t e i n could be achieved ( 8 1 ) .
In actual

breeding programs, simultaneous increases in y i e l d and pr ot ei n

have been achieved ( 5 4 ) .

Thus, gr ai n percent p r o t e i n and y i e l d can be

increased simultaneously , i f both are se le c t e d f o r , but because o f the
negative c o r r e l a t i o n , progress w i l l

be slower than i f j u s t one or the

oth er t r a i t was emphasized in s e l e c t i o n .
Although s e l e c t i o n f o r hi g h er g r a i n percent p r o t e i n slows progress
for y ie ld ,

cultural

p r a c t i c e s e x i s t which can g r e a t l y increase p r o t e i n ,

withou t s a c r i f i c i n g y i e l d .

(Th is observation casts doubt on the assumpt­

ion underlying the b i o e n e r g e t i c argument described above, i . e .

th a t

a s s im i la t e supply l i m i t s y i e l d and p r o t e i n production in c u r r e n t l y
grown c u l t i v a r s , since c u l t u r a l N amendments also r e q u i r e p l a n t energy
f o r reduction and in c o r p o r a t i o n i n t o p r o t e i n ) .

Late season N su p p le ­

ments, app lie d to the s o i l o r f o l i a g e , boost g r a i n percent p r o t e i n ( 2 3 ,

33, 50, 69, 83, 8 5 ) .

The leaves play an important ro l e in late -se aso n

N uptake and t r a n s l o c a t i o n t o the g r a i n , as demonstrated in le af-removal
experiments ( 7 0 ,
n i t r a t e reduction

73).

The f l a g l e a f is p a r t i c u l a r l y important in

( 41 ,

uptake from the s o i l

7 0) .

i s soil

A very important f a c t o r determining N
a v a i l a b l e mois tu re ; drouthy conditions

reduce N uptake markedly ( 1 9 , 89,
te n s i o n ,

96).

Drouth increases s o i l water

reducing mass flow of n u t r i e n t s to the roots ( 9 8 ) .

Thus,

adequate s o i l moisture i s necessary f o r high p r o t e i n production per
hec tare.
An i n t e r e s t i n g aspect o f crop N use is the phenomenon of
v o la tiliza tio n

losses o f N.

S i g n i f i c a n t amounts o f N are l o s t from

the st ra w, p r i m a r i l y as ammonia ( 1 5 , 4 9 ) , in a maturing wheat crop.
Presumably, the ammonia is a product o f p r o t e i n catabolism during
r e m o b i l i z a t i o n o f amino acids to the developing g r a i n .

V o latilization

losses are g r e a t e r a t high temperatures ( 9 4 ) .
The breeding o f c u l t i v a r s with g r e a t e r y i e l d responsiveness to
heavy a p p l i c a t i o n s o f f e r t i l i z e r N, was a key f a c t o r in the spe ct a cu la r
y i e l d increases achieved during the "Green Revolution" o f the e a r l y
I 9 6 0 ' s.

The new s h o rt -s tr aw ed c u l t i v a r s withstood the increased growth

s t im u l a t e d by N w i t h o u t lodging ( 1 2 ) .

These c u l t i v a r s had s m a l l e r ,

more e r e c t le a v e s , so t h a t the increased l e a f area r e s u l t i n g from N
a p p l i c a t i o n did not cause as much mutual shading as in t r a d i t i o n a l
cultivars

(5,

12,

18, 1 0 8 ) .

Mutual shading reduces net photosynthesis

in the lower l e v e l s o f the canopy, thus reducing net a s s i m i l a t i o n ra te

( 12).
Donald and Hamblin (18) po in t out t h a t the s h o r t e r straw and
s m a l le r leaves o f modern c u l t i v a r s cause them to have a hi gh er har ve st
index (HI=wt o f g r a i n / w t o f whole p l a n t ) .

Thus, modern c u l t i v a r s are

more N-responsive because they are less competitive

(l e s s mutual shading),

and t h i s is r e f l e c t e d in a hi g h er H I. They propose s e l e c t i n g

f o r HI to

continue inc re as in g N responsiveness.
Well hausen (104) describes the g r e a t e r N responsiveness o f modern
corn c u l t i v a r s developed in Mexico.
se le ct ed to give r e l i a b l e ,
land near the v i l l a g e s .
itional

agricultural

Traditional

cultivars

had been

but low, y i e l d s on the continuously cropped

No types o f f e r t i l i z e r s

were used in the t r a d ­

systems, so the s o i l s were ve r y low in f e r t i l i t y .

The modern c u l t i v a r s were s e l e c t e d from land races t h a t had evolved
in the few h i g h l y - f e r t i l e

lakebottom ar ea s.

When grown in the n u t r i e n t -

depleted areas, these modern c u l t i v a r s y i e l d e d no more (and sometimes
l e s s ) than the t r a d i t i o n a l

cu ltivars.

When f e r t i l i z e r was supplied,

however, the modern c u l t i v a r s y i e l d e d twice as much as the t r a d i t i o n a l
c u l t i v a r s , and ap pro ximately seven times as much as when not f e r t i l i z e d .
Hence, the use o f f e r t i l i z e r N and the breeding o f c u l t i v a r s more
responsive to i t

have been

inc re as in g y i e l d s in g r a i n

i ns epa ra ble components o f

the s t r a te g y

for

crops in modern times.

In the United S t a t e s , corn production u t i l i z e s hyb rid c u l t i v a r s
r a t h e r than the o p e n - p o l l i n a t e d c u l t i v a r s and syn th e tic s

o f Mexico.

There are d i f f e r e n c e s among corn inbred l i n e s in y i e l d

responsiveness

to N ( 6 ) .

( 10 , 9 3 ) .

Hybrids may be more responsive than inbreds

I t is accepted t h a t modern s m a l l - g r a i n c u l t i v a r s ar e more y i e l d responsive to N than are t r a d i t i o n a l

cultiva rs .

Are t h er e d i ff e r e n c e s

among modern c u l t i v a r s themselves, with regard to N responsiveness?
Several

studies have come to d i f f e r e n t conclusions.

Two studies found

no d i f f e r e n c e s in y i e l d responsiveness to N among diverse c o l l e c t i o n s
o f wheat c u l t i v a r s

(76, 84).

Two o t h e r re por ts ( 6 7 , 92)

demonstrated

s i g n i f i c a n t d i f f e r e n c e s among c u l t i v a r s in response of the y i e l d

10
components to N, but not o f y i e l d i t s e l f .
ical

Despite the lack o f s t a t i s t ­

s i g n i f i c a n c e , however, th ere was a tendency f o r the more y i e l d -

responsive c u l t i v a r s

to be those which were more responsive in the

y i e l d component heads per u n i t area ( X ) , in one o f the re ports

(92).

In e i g h t s t u d i e s , s i g n i f i c a n t d i f f e r e n c e s in y i e l d response to N
among s m a l l - g r a i n c u l t i v a r s were r epo rt ed ( 2 5 , 42, 58, 65, 72,
107).

103,

106,

In f o u r o f these s t u d i e s - - one with wheat ( 7 2 ) , one w it h b a r l e y

( 1 0 3 ) , one w ith oats
were measured.

( 2 5 ) , and one with r i c e

In a l l

( 1 0 7 ) - - the y i e l d components

f o u r , the c u l t i v a r with the hi ghest y i e l d response

to N was the one t h a t e x h i b i t e d the hi ghest X response to N.

Thus, high

X-responsiveness seems to be important in causing high y i e l d - r e s p o n s i v e ness to N, in modern s m a l l - g r a i n c u l t i v a r s .
Since X is the r e s u l t o f the growth and development o f t i l l e r s ,
i t i s necessary to understand the processes c o n t r o l l i n g t i l l e r develop­
ment in order to understand X-response to N.

T i l l e r s are e s s e n t i a l l y

branches, a r i s i n g from a x i l l a r y buds in the basal

leaves o f a grass culm.

Conditions which f a v o r p l a n t growth as a whole, such as adequate m oi st u re ,
fe rtility ,

and tem per at ur e, fa v o r t i l l e r i n g

(60).

Active t i l l e r i n g

is

a process occ ur ring in the v e g e t a t i v e stage o f p l a n t growth; once the
api cal meristem begins to d i f f e r e n t i a t e i n t o a re pr oductive s t r u c t u r e
(s pike in w h e a t ), t i l l e r i n g
60).

from the base o f t h a t culm is i n h i b i t e d ( 3 ,

This i n h i b i t i o n i s hormonal in nature ( a u x i n ) , r a t h e r than being

due to competition f o r n u t r i e n t s among t i l l e r s

(51 , 52, 62, 63 , 6 4 ) .

T i l l e r s which have begun t o e l o n g a t e , but have not y e t begun to d i f f e r ­
e n tia te t h e i r spike, w il l

senesce and die i f t h e i r parent culm is

d i f f e r e n t i a t i n g i t s spike ( 3 , 6 3 ) .
Asp in all

(3),

in a greenhouse pot experiment with b a r l e y , found

t h a t a p p l i c a t i o n o f a n u t r i e n t s o l u t io n reduced t h i s i n h i b i t i o n ;

tille r

bud elo ng at io n was again s t im u l a t e d , and senescence o f s m a l le r t i l l e r s
prevented.

In a subsequent experiment ( 4 ) ,

he compared two c u l t i v a r s ,

a h i g h - t i l l e r i n g type and a l o w - t i l l e r i n g t yp e, with regard to the degree
o f rel eas e o f i n h i b i t i o n
ation.

Apex removal

fo ll o w in g apex removal

and n u t r i e n t supplement­

caused a g r e a t e r in crease in number o f f e r t i l e

heads in the l o w - t i l l e r i n g c u l t i v a r than in the h i g h - t i l l e r i n g c u l t i v a r .
N u t r i e n t supplementation gave the same r e s u l t .

He concluded t h a t , since

rel eas e from i n h i b i t i o n was g r e a t e r in the l o w - t i l l e r i n g c u l t i v a r , t h i s
c u l t i v a r must have a g r e a t e r degree o f ap ic al
situation

dominance in the normal

( w i th o u t supplementation o r apex removal).

Note t h a t t h i s

study was conducted during the heading stage o f growth, which is l a t e r
than the stage in which senescence o f s m a l le r t i l l e r s

occurs,

in f i e l d

situations.
The p o i n t a t which spike d i f f e r e n t i a t i o n begins (and hence
tille rin g
(59)

ceases), i s c a l l e d the f u l l y - t i l l e r e d stage.

Lang and Holmes

found t h a t a p p l i c a t i o n o f N f e r t i l i z e r a t t h i s time gave the g r e a t e s t

y i e l d response.
much t i l l e r i n g ,
bear seed.

They commented t h a t e a r l i e r a p p l i c a t i o n s s t i m u l a t e d too
and t h a t many o f these t i l l e r s would not survive to

They did not s p e c i f i c a l l y say whether the N a p p l i c a t i o n

the f u l l y - t i l l e r e d stage s t im ul at ed new t i l l e r i n g ,
senescence, or both.

Gericke (31)

reduced t i l l e r

found t h a t delayed a p p l i c a t i o n (by

two to f o u r weeks) o f IN gave the maximum number o f f e r t i l e
oat p la nt s in greenhouse pots.

at

In f i e l d stud ies with o a t s ,

tille rs

in

Frey (27)

and Frey and Wiggans (28) found t h a t a two-week delay in N a p p l i c a t i o n
maximized y i e l d , as a r e s u l t o f maximizing X.

The f u l l y - t i l l e r e d st age

occurs approximately two to f o u r weeks a f t e r the beginning o f spring
growth in small grains (personal o b s e r v a t i o n s ) .
delay o f n u t r i e n t a p p l i c a t i o n u n t i l

Thus, i t appears t h a t

the f u l l y - t i l l e r e d stage maximizes

12
X-response to N, although genotypic d i f f e r e n c e s f o r t h i s

response may

exist.
The a p p l i c a t i o n o f N f e r t i l i z e r st im ul at es an increase in the
y i e l d components heads/m

2

(X) and seeds/head ( Y ) , although c u l t i v a r s

d i f f e r as to which component is s t im ul at ed the most ( 2 5 , 67, 72, 92,
107).

103,

In c o n t r a s t , the seed weight component (Z) is r e l a t i v e l y

unaff ect ed by N supplementation.
To some e x t e n t , the response o f Y to N supplementation is reduced
as a r e s u l t o f the a l lo m e tr y o f y i e l d component development ( 3 7 , 4 3 ) .
All ome try r e f e r s to the r e l a t i o n s h i p o f the siz e o f d i f f e r e n t p l a n t
p art s to one another.

The concept arose from the observation o f S i n n o t t

(90) t h a t "the size o f any organ depends upon the siz e o f the growing
p o i n t out o f which i t has developed".
A grass p l a n t begins shoot growth a t a s i n g l e ap ic al meristem.
As t h i s meristem develops, l e a f buds appear with small
meristems in t h e i r a x i l s .

t i l l e r bud

Since these t i l l e r buds are s m a l le r than the

apical meristem o f t h e i r parent culm, the culms which are e v e n t u a l l y
d erived from these t i l l e r buds w i l l
per S i n n o t t 1s law.

be s m al le r than the pa re nt culm, as

Thus, more d i s t a l

culms w i l l

be p r o g r e s s iv e ly

s m al le r.
The spike a r i s e s from the apical meristem o f a culm.

The apical

meristem a r i s e s from the t i l l e r bud meristem, from which t h a t culm
originated.

Since more d i s t a l

t i l l e r buds are s m a l l e r ,

t h e i r culm

apices are also s m a l l e r , and thus they give r i s e to s m a l le r spikes.
Thus, more d i s t a l

tille rs

have sm a l le r spik es , with fewer seeds.

T h e r e fo r e , as N f e r t i l i z e r s t im u la t es t i l l e r i n g ,

it

increases the

production o f sm al le r culms, with sm al le r spi kes, bearing fewer seeds.
This i s not to say t h a t N causes a decrease in average Y; on the c o n t r a r y ,

13
N u s u a ll y causes an in crease in Y, as a r e s u l t o f b e t t e r p l a n t n u t r i t i o n .
However, t h i s increase would probably be g r e a t e r i f not f o r the dampening
e f f e c t o f allometry.
Seed s i z e is q u i t e d i f f e r e n t from the o t h e r y i e l d components, in
terms o f response to changes in resource supply.

Many p l a n t species,

when coping with a l i m i t e d resource supply, s a c r i f i c e seed number ( X- Y)
but conserve seed size

(Z)

(91).

Cereal

crops appear to have evolved

compensatory mechanisms to insure proper development o f Z in the face
o f considerable s t r e s s .

Pinthus and Sa r-S ha lo m, (80) found t h a t l a t e

p l a n t i n g o f a wheat crop reduced the seed f i l l
seed f i l l
achieved.

p e r i o d , but the ra t e o f

increased t o compensate, with the r e s u l t t h a t normal
G al la g h e r e t .

Z was

a l . ( 2 9 ) , working w it h b a r l e y , found t h a t stem

carbohydrate reserves were m o b i li z e d to the g r ai n to a g r e a t e r degree in
years o f poor c l im a t e and in s t r e s s f u l environments, again as a compens­
a t o r y mechanism to complete s e e d - f i l l i n g .

Fi scher (24) found t h a t

shading o f wheat pl a n t s during the g r a i n - f i l l
little

e f f e c t on y i e l d ;

period had remarkably

presumably, stem reserves were m o b i li z e d to the

gr ai n to compensate f o r the reduction in c u r r e n t ph o to sy nt ha te .
Stebbins (91) o f f e r e d an e v o l u t i o n a r y j u s t i f i c a t i o n f o r the con­
stancy o f Z .
life

The se e dl in g stage i s the most vulnera ble stage in the

cycle o f the growing p l a n t .

An optimum seed s iz e probably e x i s t s

f o r a given sp ec ie s, in i t s ecosystem.

Any sm a l le r seeds w i l l

enough carbohydrate reserves to survive t h i s stage.

not have

Larger seeds

c a r r y unecessary carbohydrate t h a t could have been used to increase the
number o f seeds produced by the parent p l a n t .

Thus, t her e may be a

strong s e l e c t i o n pressure towards the e v o l u t i o n o f mechanisms t h a t
maintain Z a t a f a i r l y preci se val ue.
N is j u s t one o f many environmental

factors a ffe ctin g y ie ld .

The

e f f e c t o f environmental

f a c t o r s on y i e l d can be c l a r i f i e d by examining

t h e i r e f f e c t on the y i e l d components ( 6 1 ) .

Optimum balances among the

y i e l d components may e x i s t f o r maximizing y i e l d , and these optima are
probably d i f f e r e n t in d i f f e r e n t environments ( 3 5 , 3 8) .

Thus, i t appears

p l a u s i b l e t h a t c u l t i v a r d i f f e r e n c e s in y i e l d response to improvements
in s i t e y i e l d p o t e n t i a l ,

described by the phrase "genotype x environment

i n t e r a c t i o n " , may be caused by d i f f e r e n c e s in y i e l d component response
(26).
I f the y i e l d components are important in determining y i e l d and
y i e l d response to environmental

v a r i a b l e s , then breeders should be

i n t e r e s t e d in changing the y i e l d components to maximize y i e l d .
However, because o f t h e i r developmental

interdependency, the expression

o f the y i e l d components in segregating populations e x h i b i t
(compensatory) c o r r e l a t i o n s

(1).

negative

Se le c ti o n to increase one component

r e s u l t s in a decrease in the ot he rs .

There does appear to be some

amount o f u n c o r re la t e d v a r i a n c e , however; the d i f f i c u l t task is to f i n d
and u t i l i z e

t h i s v ar ia nc e .

Since Z i s r e l a t i v e l y i s o l a t e d from the compensatory f l u c t u a t i o n s
t h a t c h a r a c t e r i z e X and Y, i t has been the e a s i e s t to work w i t h .

Knott

and Talukdar (56) were able to c a p i t a l i z e on the u n c or re la te d variance
f o r t h i s component in t h e i r gene pool.

By backcrossing a high Z parent

i n t o an adapted c u l t i v a r and s e l e c t i n g f o r high Z, they e v e n t u a l l y
i s o l a t e d li n e s which had the high X-Y (seeds per h e c ta r e ) o f the adapted
r e c u r r e n t p a r e n t , but had the high Z o f the donor p a r e n t , and thus were
higher y i e l d i n g .
Gra fius e t .

a l . (40) were able to f i n d unc or re la te d variance f o r

Y in t h e i r p o p u la t i o n , and by making the proper cross, obtained a progeny
whose mean y i e l d

( u ns el ec te d) was highe r than t h a t o f the h i g h e r - y i e l d i n g

15
pa ren t .

This is a c h a r a c t e r i s t i c o f h e t e r o s i s , but t h i s was not t ru e

h e t e r o s i s , since these progeny were homozygous (F^ g e n e r a t i o n ) .

The

apparent h e t e r o s i s was a t t r i b u t e d to "component complementation", which
is a r e s u l t o f the m u l t i p l i c a t i v e i n t e r a c t i o n o f component t r a i t s
described by G ra fiu s ( 3 4 ) and Adams and Duarte ( 2 ) .

MATERIALS AND METHODS

The e f f e c t o f spring n itr og en

(N) topdressing on reduced N

accumulation and on y i e l d components o f f o u r s o f t white w i n t e r wheat
c u l t i v a r s adapted to Michigan, was measured in e i g h t f i e l d experiments,
over three years (1978-1980) and in t h r ee environments (Mendon, East
Lansing, and Saranac).

In a d d i t i o n , y i e l d component responses across

a s et o f environments o f d i f f e r i n g y i e l d p o t e n t i a l , were measured in
f i f t e e n s i t e s , over two yea rs.
N accumulation was measured in t h r ee o f the experiments o nl y.
The experiments were a t th re e d i f f e r e n t s i t e s chosen to present a range
o f con ditio ns o f N a v a i l a b i l i t y

and y i e l d p o t e n t i a l .

Mendon is in southwest lower

Michigan

(St.

Joseph Co.)

I t i s the

wannest s i t e , with an average o f 2800 growing-degree days ( 4 0 ° base)
between A p r i l

1 and Ju ly 31.

This causes e a r l y m a t u r i t y o f the crop.

The experiment was on a Nottawa sandy loam s o i l
is a w e l l - d r a i n e d s o i l , and i t s

(Typic A r g i u d o l l ) .

low w a t e r - h o l d i n g ca p ac ity

the high temperatures r e s u l t in drouthy con ditio ns a t t h i s

site.

This

combined with
Drouth

stress combined with the e a r l y matu ration make t h i s s i t e low in y i e l d
potential.

The previous crop was corn, which had been supplied with

f e r t il izer.
East Lansing is in s o u th - c e n tr a l

lower Michigan (Ingham Co.)

The

climate is c o o l e r , with an average o f 2400 growing-degree days between
April

1 and Ju ly 31.

Crop maturation is about ten days l a t e r than a t

16

17
Mendon.

The experiment was on a Capac loam s o i l

( A e r i e O ch r aq u a lf ),

4

which i s somewhat poo rly dr ai ne d.
adequate throughout the season.

Moisture supply to the crop seemed
The combination o f . t h e co o le r temp­

e r a t u r e s and adequate moisture supply make t h i s a s i t e of high y i e l d
potential.

In an attempt to reduce s o i l N f e r t i l i t y

p r i o r to the

experiment, a corn crop was grown the previous summer.
fe rtilize d ,
m icro bial

I t was not

and the s t a l k s were incor pora ted i n t o the s o i l

to s t im ul at e

im m o b il iz a t i o n o f N.

Saranac is l o c a t e d in w e s t - c e n t r a l
I t is in te rm e d ia t e in temperature

lower Michigan ( I o n i a Co.)

(2600 growing-degree days).

matures approximately seven days l a t e r than a t Mendon.
was on a Miami loam s o i l

(Typic H a p l u d a l f ) .

The experiment

This s o i l

is w el 1- d r a i n e d ,

but moisture supply seemed adequate throughout the season.
s oi l moisture but s l i g h t l y high temperatures cause t h i s
in te rm e d ia t e in y i e l d p o t e n t i a l .

For a l l

as a green manure.

The adequate

s i t e to be

experiments a t t h i s

previous crop was soybeans inc or po ra te d i n t o the s o i l

The crop

s i t e , the

before f l o w e r i n g ,

Thus, s o i l N f e r t i l i t y was probably high a t t h i s s i t e

before the experiments.
In t h i s research, f a c t o r i a l
block design, were used.

The number o f r e p l i c a t i o n s v a r i e d from three to

n i n e , depending on the experiment.
six re p lic a tio n s .
apart.

experiments with a randomized complete-

All

N accumulation experiments used

Pl ot s were 3. 7 m long, w it h e i g h t rows spaced 30 cm

Only the c e n t e r f o u r rows were harvested f o r gra in y i e l d , to

avoid border e f f e c t s .
N t opd res si ng , in the form of urea or ammonium n i t r a t e , was a p p lie d
w i t h i n the f i r s t two weeks o f spring regrowth, using a mechanical
spreader.

This is the period o f t i l l e r

in itia tio n .

Later soil a p p lic ­

at io ns were made by hand; f o l i a r a p p l i c a t i o n s were made using a hand-

18
held sprayer.
In the N accumulation experiments, a l l
surface roots)

p l a n t m a t e r ia l

( i n c lu d i n g

in a 30 cm section o f row (randomly chosen from w it h in

the second row o f the p l o t ) was harvested f o r N and y i e l d component
a n a l y s i s , a t each o f th ree growth stages ( f u l l y
m aturity).
48 hours.

The samples were rin sed f r e e o f s o i l
At the f u l l y - t i l l e r e d

was weighed f o r use in t o t a l
the N de t e r m in a ti o n .

t i l l e r e d , a n t h e s is ,
and d r ie d a t 706C f o r

and ant hesis stages, the e n t i r e sample

dry m a t t e r c a l c u l a t i o n s , and then used in

At the m a t u r i t y st age , ten culms were randomly

s el ec te d from the sample, and used f o r the N de t e r m in a ti o n .

Grain samples

were drawn from the p l o t y i e l d bag f o r N de t e r m in a ti o n .
Samples f o r N det erm in ati ons were ground in a Wiley m i l l
through a screen with 0. 5 mm hole diam eter .

t o pass

The powder was s t i r r e d

t houroughly, and a 30 mg po r t io n taken f o r the N measurement.
N was measured using an automated m i c r o - k j e l d a h l

Reduced

apparatus (the

Technicon Auto A n al y ze r ; Technicon C o rp ., Tarrytown, NY) ( 2 1 ) .

This

procedure uses a c o l o r i m e t r i c assay f o r ammonia-- the B e r t h e ! o t r ea c ti o n
(97).

Addition o f n i t r a t e

ments ( 4 6 ) ,

to p l a n t samples did not change the measure­

i n d i c a t i n g t h a t only reduced forms o f N are measured in t h i s

procedure.
Y i e l d components and ha rv es t index were measured in the fo ll o w in g
manner.

A f t e r removing the ten culms f o r the N de t e r m in a ti o n ,

the number

o f heads in the remaining po rt io n o f the sample was counted (ranging
around 40 heads).

The po r t io n was weighed and th reshed, and the number

o f heads di vi de d i n t o th e weight o f threshed g r a i n , to obtain the average
head weight.

Harvest index was c a l c u l a t e d by d i v i d i n g the weight o f the

threshed grain by the weight o f the po r t io n before th re sh in g.

Total

m at ter f o r the p l o t was c a l c u l a t e d by d i v i d i n g the harve st index i n t o

dry

the p l o t gr ai n y i e l d .

Seed weight was determined by counting the number

o f seeds in a f i v e g sample taken randomly from the p l o t y i e l d bag.

The

number o f seeds per head was c a l c u l a t e d by d i v i d i n g the average head
weight by the average seed weight.
Y i e l d and yield-component data were also c o l l e c t e d from the MSU
Regional-Advanced Win ter Wheat Nurseries (01 s e r i e s ) in 1979 and 1980.
These t r i a l s

t e s t 30 e n t r i e s

(adapted c u l t i v a r s and advanced l i n e s )

using a 5 x 6 r e c t a n g u l a r l a t t i c e design with three r e p l i c a t i o n s .
were 3 . 7 m lon g, with fo ur rows spaced 30 cm a p a r t .
were used at a l l

Plots

The same e n t r i e s

s i t e s w i t h i n a y e a r , and 26 o f the 30 e n t r i e s were the

same in both yea rs.

Data were c o l l e c t e d a t e i g h t s i t e s in 1979 and a t

seven s i t e s in 1980.
A ll

f o u r rows were harvested f o r gr ai n y i e l d .

Before h a r v e s t , a

random sample o f ten heads was c o l l e c t e d from each p l o t .

The average

head weight c a l c u l a t e d from t h i s sample was div id ed i n t o the p l o t gr ai n
yield,

to get the number o f heads per p l o t .

Seed weight and number o f

seeds per head were determined as in the N accumulation experiments
described above.
Four c u l t i v a r s were studi ed in the N accumulation experiments.
These c u l t i v a r s are adapted to Michigan and are o f con sid er abl e economic
importance in the s t a t e .
Ionia was the f i r s t c u l t i v a r re leased from the MSU breeding
program ( 1 97 2 ).

I t s pedigree is Redcoat/3*Genesee.

o f the wheat acreage in 1978.

I t is t a l l

I t was grown on 15%

and l o w - t i T i e r i n g , w ith l a r g e

seeds.
Tecumseh was the next MSU re lease ( 1 9 7 4 ) , and was the most w id e ly
grown c u l t i v a r in Michigan in 1978 (30% o f the acre age ).

I t s g e n e ti c

background i s q u i t e d i f f e r e n t from t h a t o f the o t h e r c u l t i v a r s .

I t has

20
the same complex parentage as ' A r t h u r '

(a popular Purdue r e l e a s e ) .

Tecumseh matures approximately seven days e a r l i e r than the o t h e r c u l t ­
i v a r s , which may account f o r i t s
h ig h -tillerin g ,

lower y i e l d .

I t is s h o rt - s tr a w e d ,

and high in g r ai n percent p r o t e i n .

Yo rk st a r is a 1967 re le as e from C o r n e l l .
Norin 10 /B re v o r // Y o r k w i n /3 /3 * G e n e s e e .

I t s pedigree is

I t y i e l d s well

was grown on 13% o f the wheat acreage in 1978.

in Michigan, and

I t is in te rm e d ia t e in

y i e l d components and h ei g h t .
Augusta i s a new rel ea se from the MSU program ( 1 9 8 0 ) .
pedigree i s 6 e n e s e e /R e d c o a t/ /Y o r k s t a r .
y i e l d components to Y o r k s ta r .

Its

I t is s i m i l a r in h e i g h t and

RESULTS AND DISCUSSION

Data des cr ib in g the crop N s ta tu s a t the th ree s i t e s used f o r the
N accumulation exp eriments, are presented in Table 1.

At Mendon, the

crop was lowest in N accumulation per h e c t a r e , p l a n t N co n c e n t r a ti o n ,
and y i e l d .

Moisture st r e s s probably l i m i t e d N uptake and g r ai n y i e l d

at this s ite .
for y ie ld ,

East Lansing was in te r m e d ia t e f o r the N v a r i a b l e s and

but showed the g r e a t e s t y i e l d response to N.

r e f l e c t i o n o f the low s o i l

N fe rtility

This is a

a t the beginning o f t h i s exp er ­

iment (see M a t e r i a l s and Methods), combined with adequate m oistu re,
which promotes uptake o f N.

Table 1 . - -

The g r e a t e s t N accumulation, p l a n t N

Crop N s t a t u s and y i e l d performance a t three l o c a t io n s in 1980.

Meanf
Location

N
accumulated
in crop

Wh ole-plant N
conc'n. a t
anthesi s

kg/ha
Mendon

q/ha

%

1.23 a

33.6 a

42

%

84 a *

Grai n
yiel d

Mean*
yiel d
response
to N

East Lansing

146 b

1.52 b

43 .3 b

69

Saranac

187 c

1.82 c

46.9 c

12

*Means w i t h i n a column follow ed by d i f f e r e n t l e t t e r s are s i g n i f i c a n t l y
d i f f e r e n t a t the 5 * l e v e l , by Duncan's M u l t i p l e Range T es t.
'•'Experiment grand means (averages o f 72 o b s e r v a t io n s , over f o u r c u l t ­
i va r s and three ra t e s o f N t o p d r e s s in g .)
*Mean response o f f o u r c u l t i v a r s .

21

22
co n c e n t r a ti o n , and y i e l d occurred a t Saranac.
high N f e r t i l i t y

st at us o f the s o i l

Because o f the high s o i l

This r e s u l t e d from the

a t the beginning o f the experiment.

N f e r t i l i t y , y i e l d response to supplemental N

was low a t t h i s s i t e .
Thus, the th ree s i t e s e x h i b i t e d a range o f conditions o f N supply
and y i e l d p o t e n t i a l .

Despite the d i s s i m i l a r i t y o f the environments,

however, the c u l t i v a r p a t t e r n s o f N accumulation and dry m at te r prod­
uction were remarkably c o n s is t e n t over experiments.

For t h i s reason,

the data were averaged over s i t e s , and are presented in Figures 1 and 2.
Data f o r the i n d i v i d u a l experiments can be found in Appendix A.
Figure 1 shows t h a t , despite being the lowest in dry m at te r
accumulation per h e c t a r e , Tecumseh was as high or higher than the o t h e r
c u l t i v a r s in N accumulation per h e c t a r e , a t m a t u r i t y .

I t is seen from

Figure 2 t h a t Tecumseh lags s l i g h t l y behind the o th er c u l t i v a r s in N
accumulation a t a n t h e s i s , but the d i f f e r e n c e s among c u l t i v a r s f o r N
accumulation are much less than the d i f f e r e n c e s in dry m at te r accum­
ulation.

In o th er words, Tecumseh maintained a s i g n i f i c a n t l y hi gh er

w h o le - p l a n t N conc entr ation than the o t h e r c u l t i v a r s , a t a l l
stages.

growth

The values f o r w h o le -p l a n t N concentration a t anthesis were

1.60 $,

1.53%,

1.52%, and 1.44%, f o r Tecumseh, Augusta, Y o rk s ta r , and

Ionia,

r e s p e c t i v e l y (LSD

q ^=

0.05%).

Tecumseh also took up approxim­

a t e l y twice as much N a f t e r a n t h e s i s , as did the o th er c u l t i v a r s
below).

(see

Based on these o b s e r v a t io n s , i t i s concluded t h a t Tecumseh's

high N requirement i s not a r e s u l t o f a d e f i c i e n c y in c ap ac ity f o r
uptake o f s o i l N.

Tecumseh appears to be a t l e a s t as ( i f not more)

capable o f N uptake as the o th er c u l t i v a r s , which nevetheless y i e l d
con side ra bly more than Tecumseh, in conditions o f low s oi l N f e r t i l i t y .

23

y

crop
dry
matter

10 -

be*
b

<o

crop

de

>
be

e

d

fg

jc

-200

g

<o

ef

4->
£

a

CD

o '

>-

5-

a

a

a

a

Y

A

o.
o
on

-100

o

cc

□

Q.

O

CtL

O

r

T

RATE OF N TOPDRESSING ( k g / h a )
Figure 1 . — E f f e c t o f N to pdress ing on dry m a t t e r pr odu ction and N
accumulation in f o u r wheat c u l t i v a r s , a t m a t u r i t y .
* For a given v a r i a b l e (crop dry m a t t e r or crop N ) , bars topped by the
same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t a t the 5 % l e v e l , by Duncan's
M u l t i p l e Range T e s t.
Data are means o f 18 o b s e r v a t io n s , over th ree
locations.
+I = I o n i a , T=Tecumseh, Y = Y or ks ta r, A=Augusta.

24

tO

10

-

a

}

b

O

c

c

b

CO
-

a

200

-C
CD

5 c

be

a.

o
C£

b

crop

1=I o n i a
T=Tecumseh
Y=Yorkstar
A=Augusta

cn
LU

>OC
o

crop
dry
matter

b* „
B m

b

Q_

100

b

§

H h

! T Y A
FULLY TILLERED

I

T

Y

ANTHESIS

A

I

T

Y

A

MATURITY

Figure 2 . — Dry m a t t e r production and N accumulation over t h r e e growth
s t ag es , f o r f o u r wheat c u l t i v a r s .
* W it h i n growth s t ag es , bars topped by the same l e t t e r are n o t s i g n i f i c a n t l y
d i f f e r e n t a t the 5% l e v e l , by Duncan's M u l t i p l e Range T e s t.
Data are means
o f 18 o b s e r v a t io n s , ov er t h r ee l o c a t i o n s and t h r ee r a t e s o f N to p d r e s s in g .

25
The h i g h e s t - y i e l d i n g c u l t i v a r s were Augusta and Yo rk s ta r ; however,
it

i s seen in Figures 1 and 2 t h a t these c u l t i v a r s were no higher in N

accumulation per hectare than the l o w e r - y i e l d i n g c u l t i v a r s
Tecumseh.

Thus, i t

Io n ia and

seems t h a t the breeding o f h i g h e r - y i e l d i n g c u l t i v a r s

does not r e q u i r e g en et ic advance in ca pa ci ty f o r N uptake.

However,

these h i g h e r - y i e l d i n g c u l t i v a r s were lower in gr ai n percent p r o t e i n (see
below).
Several

f e a t u r e s o f seasonal accumulation and s t r a w - g r a i n

p a r t i t i o n i n g o f N f o r these fo ur c u l t i v a r s , are presented in Table 2.
Tecumseh accumulated approximately twice as much N a f t e r anthesis as did
the o t h e r c u l t i v a r s .

This l at e -s e as o n surge o f N uptake caused Tecumseh

to have the h ig h es t t o t a l
2, m a t u r i t y s t a g e ) .
soil

seasonal

accumulation o f N a t m a t u r i t y (Figure

In an experiment with la te -s e as on f o l i a r and /or

N supplements, Tecumseh a l s o showed a high ca p ac ity f o r l a t e N

Table 2 . - Pre- and p o s t-a nt he si s accumulation o f N, and g r a i n - s t r a w
p a r t i t i o n i n g o f N, f o r four wheat c u l t i v a r s .
N accumulated by crop:
prean t h es is

Veg etati ve
ANr

po s tanthesis

Ky/na

Grai n
N

N
harvest
in d e x *

..............

111

42

-60

102

0.7 0 b*

Tecumseh

98

70

-30

100

0.63 a

Yo rk st a r

117

32

-62

95

0 . 6 7 ab

Augusta

108

40

-60

100

0.70 b

Io n ia

*Means fo llo w ed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t a t
the 5% l e v e l , by Duncan's M u l t i p l e Range Tes t.
A l l data are means
based on 54 o b s er va t io n s, over two loc at io ns and three rates o f N
topdressing.
+Net change in N content of non-grain po rt io n o f crop a f t e r an th es is .
*N in gr ai n ( kg /h a) di vi de d by t o t a l

crop N ( k g / h a ) .

26
uptake (Appendix B).

Despite being the hi gh es t in t o t a l

seasonal N

accumulation, Tecumseh accumulated no more N in the grain po rt io n o f the
crop, than the o t h e r c u l t i v a r s

(Table 2 ) .

This was a r e s u l t o f a lower

net t r a n s l o c a t i o n o f N from the v e g et a ti ve p l a n t parts i n t o the g r a i n ,
for this c u ltiv a r.

Tecumseh's low e f f i c i e n c y o f t r a n s l o c a t i o n is

r e f l e c t e d in a low N ha r v e s t index.

Thus, Tecumseh's high ca p ac ity f o r

N uptake is negated ( i n terms o f gr ai n p r o t e i n production per hec tar e)
by a compensating i n e f f i c i e n c y in i t s c a p a c i ty to t r a n s l o c a t e N i n t o
the gr ai n port io n o f the crop.
The r e l a t i o n s h i p between grain p r o t e i n production and y i e l d f o r
the f o u r c u l t i v a r s , i s i l l u s t r a t e d in Table 3.

The c u l t i v a r s accum­

ulated remarkably s i m i l a r amounts o f N in the g r a i n port io n o f the crop,
per hectare.

However, they d i f f e r e d in g r ai n y i e l d .

Thus, d i f f e r e n c e s

in gr ai n percent p r o t e i n among c u l t i v a r s was p r i m a r i l y a r e s u l t of
d i f f e r e n c e s in carbohydrate accumulation per h e c t a r e , r a t h e r than in

Table 3 . - -

Re la t i o n s h i p between grain N and y i e l d f o r four wheat c u l t i v a r s .

Grain
N

Grain
yiel d

kg/ha

q/ha

Augusta

88 b*

44.7 d

9.8 a

Yo rk st a r

84 a

42.9 c

9.9 a

Io n ia

88 b

40.8 b

10.8 b

Tecumseh

88 b

36 .7 a

12.1 c

C u l t i var

Grain
proteinr
%

*Means w i t h i n a column fo llowed by d i f f e r e n t l e t t e r s are s i g n i f i c a n t l y
d i f f e r e n t a t the 5% l e v e l , by Duncan's M u l t i p l e Range Test.
Data are
means o f 54 o bs er va tio n s, over three lo c a t io n s and three rat es o f N
topdressing.
A d j u s t e d to 14% moisture.

27

N accumulation.

This conclusion was reached in a study o f oat c u l t i v a r s

d i f f e r i n g in gr oat percent p r o t e i n , as well

(11).

Using the data o f

Table 3, the c o r r e l a t i o n between gr ai n percent p r o t e i n and g r a i n y i e l d
is s t r on gl y negative ( r = - 0 . 9 8 4 * , p < 0 . 0 5 ) .
fits

the t re nd seen in the l i t e r a t u r e

This neg ati ve c o r r e l a t i o n

(see L i t e r a t u r e Review).

Data showing the e f f e c t o f ea rl y- sea so n N topdressing on y i e l d ,
y i e l d components, and ha rv es t in dex, are averaged over s i x experiments
and presented in Table 4 , f o r two c u l t i v a r s .
l o c a t i o n - y e a r s can be found in Appendix C.

Data f o r the s p e c i f i c
In a l l

s i x experiments,

Tecumseh showed the g r e a t e s t y i e l d response to N.

In f i v e o f the

experiments, t h i s was associated with the l a r g e s t increas e in the y i e l d
component heads/m

2

(X) f o r Tecumseh, as compared to the o t h e r c u l t i v a r s .

I o n i a , on the o th er hand, had the l a r g e s t response of a l l

cultivars for

the y i e l d component seeds/head ( Y ) , in t h r ee o f the s i x experiments.
Seed weight (Z) was . r e l a t i v e l y unaff ect ed by N t op dr ess ing .

Thus, the

two c u l t i v a r s have d i f f e r e n t s t r a t e g i e s o f N response: Tecumseh is more
X responsive (and most y i e l d - r e s p o n s i v e ) , w hi le
sive.

Io n ia i s more Y-respon-

Augusta and Y o rk s ta r seem to have more "balanced" responses than

these two.
The asso ci ati on between high head-number (X)
high y i e l d responsiveness to N f o r Tecumseh, f i t s
ature (see L i t e r a t u r e Review).

responsiveness and

a t re nd in the l i t e r ­

Why should X-responsiveness be more

important than Y-responsiveness, as a mechanism f o r high y i e l d respons­
iveness to N?

Three possible reasons are o f f e r e d below.

F i r s t , the ontogeny o f y i e l d component development is in the order
X, Y, Z.
optimal

Since N is u s u a ll y a p p li e d e a r l y in the season, N supply is
f o r s t i m u l a t i n g an increase in X.

The Y component response must

28
T

Table 4 . - cultivars.

E f f e c t o f N topdressing on y i e l d

v a r i a b l e s o f two wheat

Topdressi ng
r a t e , kg/ha
Variable

Cultivar

0

90

LSD*
0.05

response to
topdressing
%

Y i e l d , q/ha

I o n ia

33.1

42.4

28
1.6

Heads/m2

Tecumseh

27.3

38.8

Ionia

304

349

42

15
24

Seeds/head

Tecumseh

388

494

I o n ia

26 .2

29.7

27

13
1.4

Seed wt, mg

Tecumseh

21.2

23.0

I on i a

44.4

44 .2

8

0
0.51

Tecumseh

Harvest Index

Ionia

35 .7

35 .8

0.368

0.379

0

3
0.008

Tecumseh

0.37 2

0.390

5

*Le as t s i g n i f i c a n t d i f f e r e n c e f o r comparison of i n d i v i d u a l means.
Data
are means o f 60 o b s e r v a t io n s , over three years and three l o c a t i o n s .

29

u t i l i z e what l i t t l e

N may be remaining, or what can be m o b i li z e d from

the t i l l e r v e g e t a t i v e t is s u e s .

Hence, N supply is more r e s t r i c t e d to

the developing s p i k e , than i t is to the t i l l e r .
A second reason is t h a t Y is r e s t r i c t e d by developmental

controls.

X r e s u l t s from a v e g e ta ti v e process ( t i l l e r i n g ) , wh ile Y r e s u l t s from a
reproductive process (spike d i f f e r e n t i a t i o n ) .

Ve ge ta tiv e processes are

p r i m a r i l y c o n t r o l l e d by n u t r i e n t supply, w hi le r epr odu cti ve processes
( i n determinate i n fl o r e s c e n c e s ) are c o n t r o l l e d by developmental l i m i t s ,
such as photoperiod and temperature.

These l i m i t s dampen the ca p a c i ty

o f Y to respond to increases in the supply o f n u t r i e n t s .
A t h i r d reason is the dampening i n fl u e n c e o f a l l o m e t r y , as
described in the L i t e r a t u r e Review.
more d i s t a l
w ill

N st im u l a t e s the development o f

culms, but because they a r i s e from sm a l le r meristems, they

have s m al le r sp ik es , and hence a sm al le r Y.

This reduces the

magnitude o f the Y response to N.
Table 4 shows t h a t N topdressing did not have a g r e a t e f f e c t on
the har ve st index ( H I ) .
significant)
ars.

N caused only a s l i g h t ( bu t s t a t i s t i c a l l y

increase in H I ; t h i s increase was s i m i l a r f o r both c u l t i v ­

Thus, N does not a f f e c t the p a r t i t i o n i n g o f dry m at te r between

g rai n and straw d i f f e r e n t y f o r these c u l t i v a r s .

These f in d in g s are

somewhat a t odds w ith those o f Donald and Hamblin ( 1 8 ) .
t h a t N c o n s i s t e n t l y decreased H I , though s l i g h t l y .

They report ed

They al so found

t h a t t h i s de c lin e was less in more N-responsive c u l t i v a r s .

These

modern c u l t i v a r s were less c o m p e ti ti v e , hence v e g e t a t i v e growth s t i m u l ­
ated by N did not cr ea te d e l e t e r i o u s l e v e l s o f mutual
L i t e r a t u r e Review).

shading (see

Perhaps the d i f f e r e n t p l a n t types and more ample

moisture supply in Michigan crea te an ecosystem o f lower co m pe tit io n,
as compared to the s i t u a t i o n in A u s t r a l i a .

I f t h i s is t r u e , the

30
increased v e g e ta ti v e growth in response to N would not n e c e s s a r i l y
cause a de c lin e in HI.

Increased number o f seeds per head (as a r e s u l t

o f both increased number o f s p i k e l e t s per head and seeds per s p i k e l e t )
seem to cause the increase in HI in the Michigan s i t u a t i o n

(personal

observations).
Does Tecumseh respond to increases in s i t e y i e l d p o t e n t i a l
across a range o f production environments, in a fashion s i m i l a r to i t s
response to N, i . e .

by a large X-response?

To answer t h i s q ue st io n,

y i e l d and yield-component data were p l o t t e d as a f u n ct io n o f l o c a t io n
mean y i e l d , over the set o f t e s t s i t e s used in the MSU wheat breeding
program.

These data are shown in Figure 3.

v a r i a b l e s ( y i e l d and i t s

The values o f the dependent

components) are p l o t t e d as a percentage o f the

mean value a t a p a r t i c u l a r l o c a t i o n - y e a r .

This allows p r e s e n ta ti o n o f

the data f o r y i e l d and i t s components on a s in g le graph.
d e v ia t i o n o f a po in t above or below the 100% l e v e l

In t h i s f i g u r e ,

i n d i c a t e s a value

g r e a t e r o r less than t h a t o f the "average c u l t i v a r " ,

respectively.

A

regression l i n e slope s i g n i f i c a n t l y d i f f e r e n t from zero i n d i c a t e s
"genotype x environment i n t e r a c t i o n " ,

i.e .

t h a t the p a r t i c u l a r c u l t i v a r

is responding d i f f e r e n t l y than the average c u l t i v a r to increases in
s ite y ie ld potential.
Figure 3 shows the data f o r Tecumseh; several o t h e r c u l t i v a r s
are shown in Appendix D.

Tecumseh expressed s i g n i f i c a n t genotype x

environment i n t e r a c t i o n f o r y i e l d ; and t h i s i s seen to have been caused
by an unusually high X response.

The o t h e r two y i e l d components behave

s i m i l a r l y to those o f the average c u l t i v a r .

No s i g n i f i c a n t genotype x

environment i n t e r a c t i o n was found f o r the other c u l t i v a r s
Thus, i t

(Appendix D ) .

is concluded t h a t Tecumseh's high y i e l d response to improve­

ments in s i t e y i e l d p o t e n t i a l ,

like its

response to N, is caused by

31

LO

TECUMSEH

o

o
CO

r-J o
Qi 2
O

X

o

UJ o

s: 5

+ +■

o

O
o
CO
o

W=YIELD
B= 0 .5 7 * *
X=HEADS/M2 B= 0 .8 6 * *
Y=SEEDS/HEAD B= 0 .0 3 NS
Z=SEED WT
B = -0 .0 8 ns
30'. 0

35.0

40.0

45.0

LOCATION MEAN YIELD (

50.0
Q /

55 .0

ha)

Figure 3 . - E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the y i e l d
and y i e l d components o f Tecumseh wheat, r e l a t i v e to the gene pool mean.
**Slope s i g n i f i c a n t l y d i f f e r e n t from zero a t the
NS= slope not s i g n i f i c a n t l y d i f f e r e n t from zero.

1%

probability level.

32
an unusual

cap acity f o r X response.

seems to be a general

Thus, X-responsiveness f o r Tecumseh

growth response to improvements in environmental

resource supply, r a t h e r than a s p e c i f i c response to N.

(The main f a c t o r s

b el i e v e d to d i f f e r e n t i a t e s i t e s in Michigan with regard to y i e l d p o t e n t i a l
are moisture supply and temp er at ur e) .
Since X-responsiveness i s important in e x p l a i n i n g Tecumseh's
high y i e l d responsiveness, experiments were conducted to examine some o f
the f ea t u r es o f y i e l d component response in these c u l t i v a r s .

The e f f e c t

o f varying p l a n t population le v e l on y i e l d and y i e l d components is shown
in Figure 4.

With in cr e a s i n g seeding r a t e , X increased d r a m a t i c a l l y ,

but a compensating d e c li n e in Y (and to a l e s s e r e x t e n t Z) kept y i e l d
almost constant.

Thus, the increase in i n t e r p l a n t competition brought

about by a s i x t e e n - f o l d increase in seeding r a t e causes compensatory
adjustments in X and Y, such t h a t Z is almost un a ffe ct ed .
almost unaff ect ed.

HI was also

This i n d ic a t e s t h a t the pr opo rtion o f grain to culm

dry m a t te r remained c on st a nt , despite l a r g e declines in the dry weight
o f both these two components.

This is an e x c e l l e n t example o f the

importance o f a l lo m e t r y in crop development.

Since both the v e g e ta ti v e

and spike portions o f the culm a r i s e from the same o r i g i n a l
meristem, reduction in growth o f both due to crowding w i l l
correlated.

apical
be h i g h l y

The near constancy o f HI in the N experiments reported

e a r l i e r was also a r e f l e c t i o n o f t h i s growth c o r r e l a t i o n .
The e f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l
components o f the "average c u l t i v a r "
years,

is presented in Figure 5.

on the y i e l d

(means o f 30 e n t r i e s ) , f o r two

X and Y f l u c t u a t e in a compensatory

manner across s i t e s , w h il e Z is almost un a ff e c t e d .

The y i e l d and y i e l d

component balances o f p a r t i c u l a r l o c a t io n s change from y e a r to y e a r .
For example, Tuscola was the t h i r d - l o w e s t y i e l d i n g s i t e in 1979,

33

ELD

SEED WT

Li_1
UJ

oo

HEADS

600

LU
OO

Q
UJ
UJ 2
oo
•s

0

-

HARV.

INDEX

<

fio>-

100

300

200

SEEDING RATE

(

400

500

kg/ h a )

Figure 4 . - E f f e c t o f seeding ra t e on y i e l d v a r i a b l e s in wheat.
Saranac, 1980.
+Means o f 24 o b s er va t io n s, over t hre e N rates and t hr ee c u l t i v a r s .

1980

50-

------------

----------

40 1
HEADS

CD

s e e d s 7 head

30

25

I—
S

20

ea

UJ
LU
00
Cd

X
Q_
LU

0
0

N
<

10

LU
UJ
s
<
X
LU
—I

CO

O
-j

<
-

o

<
x:

1
—

CO

<

X

LU
O

0

Cd

X
O
*—

CtC
X)
X

X
O
SI

<
_J
O
u
CO

X
1
—

ca
<c

75

35

45

"

00

LOCATION MEAN YIELD

ea
uj

"5?"

55"
( q/

60

ha)

UJ
c o

979

50
CD
1—I
X

Csl

SEED WT
/

40

---------

—

s e e d s / head

CO

§

30

/

20

\

' x

Q.

O
O

LU
CO

O
“5

10

-

1—

HEADS

LU
LU
s
<
X
LU

< N
—1<

O 21

CJ <
CO —I
x <
1- X

CO

<c

LU
O

0

0

*—« cc
X
X

<

X

O
QC

X

C3

X
X

X
M

•—> 2

—r

35

40

45

LOCATION MEAN YIELD

50
( q/

55
ha)

Figure 5 . - V a r i a t i o n o f y i e l d components across s i t e s o f d i f f e r i n g
y ie ld potential.
+ Means o f 90 obse rva tion s (30 genotypes x 3 r e p l i c a t i o n s ) .

60

35

and was c h a r a c t e r i z e d by a low X and moderate Y.

In1980, i t

h i g h e s t - y i e l d i n g s i t e , with a high X and moderate Y.

was the

Lenawee

was a

low-X, high-Y s i t e in 1979, but i t was hi gh- X, low-Y in 1980.
The compensatory f l u c t u a t i o n s in X and Y across s i t e s and across
y e a r s , probably r e f l e c t v a r i a t i o n in the s e a s o n a l i t y o f a l l o c a t i o n o f
growth-promoting environmental
temperatures.
seasonal

resources such as moisture and cool

Since the y i e l d components develop s e q u e n t i a l l y ,

v a r i a t i o n in resource a l l o c a t i o n w i l l

components

differen tly,

promote the d i f f e r e n t

depending on how c l o s e l y the period o f

ample resource a v a i l a b i l i t y coincides with the period o f growth o f
the p a r t i c u l a r components ( 1 ) .
the season, X w i l l
be promoted; i f
X and Y w i l l

I f resources are a v a i l a b l e e a r l y in

be promoted; i f

they are a v a i l a b l e l a t e r ,

resources are eve nly d i s t r i b u t e d over

Y w ill

the season,

be r e l a t i v e l y balanced.

Z is seen to be r e l a t i v e l y i s o l a t e d from component compensation
f o r v a r i a t i o n in s i t e y i e l d p o t e n t i a l

( Fig ur e 5 ) .

I t was al so found to

be r e l a t i v e l y u na ffe ct ed by N topdressing (Table 4) and a l t e r i n g the
p l a n t population l e v e l

(F igure 4 ) .

Small grains have developed

b u f f e r i n g systems to maintain Z a t an optimum l e v e l
Review).

(see L i t e r a t u r e

Thus, v a r i a t i o n in t h i s component is not l i k e l y to be import­

ant in e x p l a i n i n g genotype x environment i n t e r a c t i o n .
Do genotypes wit h i n h e r e n t l y d i f f e r e n t balances o f the y i e l d
components d i f f e r in t h e i r a b i l i t y to compensate f o r seasonal f l u c t ­
uations in resource supply?

Gra fius

( 35 , 3 6 ) , Gra fiu s and Okoli

(38)

and Grafius and Thomas (39) argue t h a t y i e l d component optima e x i s t
f o r d i f f e r e n t environments, which supports t h i s p o s s i b i l i t y .

An

experiment was conducted in which N was supplied a t d i f f e r e n t dates,
f o r Ionia and Tecumseh ( Fig ur e 6 ) .

Y i e l d response to N was maximum f o r

36

50i

r-H

IONIA

50-i

TECUMSEH

SEED WT

O

4-

rH

x

YIELD

CD

s:

HEADS
y ie l

OO
Q
<C
UJ

Q
UJ
UJ
OO

S

ACh'

'

S^ED WT

ce:

■> o

30-

30

s e e d s / head

N HEADS
Q OO
— I Q
UJ UJ
UJ

204-

CO

T IM E

t im e

WEEKS

WEEKS

WEEKS

WEEKS

WEEKS

WEEKS

Figure 6 . - E f f e c t o f d i f f e r e n t dates o f a p p l i c a t i o n o f N topdressing
on y i e l d and y i e l d components o f two wheat c u l t i v a r s .
r Means o f s i x obse rvat ions ; Saranac, 1979.
^130 kg/ha N as ammonium n i t r a t e a p p li e d a t time 0 (beginning o f spring
r egr ow th ), +2 weeks, +4 weeks ( f u l l y t i l l e r e d s t a g e ) , or +6 weeks
(hea ding ).

37
Io n ia when the N was a p p li e d a t the f u l l y - t i l l e r e d stage ( f o u r weeks
a f t e r the beginning o f spr in g regro wth ).
dates markedly reduced the response.

A p p l i c a t i o n o f N a t the ot her

In c o n t r a s t , a p p l i c a t i o n o f N any

time in the f i r s t f o u r weeks caused an i d e n t i c a l y i e l d response, in
Tecumseh.
in X.

These response v a r i a t i o n s were caused by response v a r i a t i o n s

Y changed l e s s ,

d ifferential

in compensation f o r the change in X.

Thus,

X response to date o f N a p p l i c a t i o n caused d i f f e r e n t i a l

y i e l d response,

in the h i g h - t i l l e r i n g

c u l t i v a r Tecumseh, as compared to

the l o w - t i l l e r i n g c u l t i v a r I o n i a .
These d i f f e r e n c e s can be i n t e r p r e t e d in terms o f the d i f f e r e n t
levels of apical

i n h i b i t i o n in low- and h i g h - t i l l e r i n g c u l t i v a r s ,

suggested by As pin all

(4)

(see L i t e r a t u r e Review).

stage i s the po in t o f maximum i n t e r - t i l l e r
t im e,

older t i l l e r s

younger t i l l e r s .

assume ap ic al

Any t i l l e r

The f u l l y - t i l l e r e d

com pe tit io n, since a t t h i s

dominance, i n h i b i t i n g growth of

t h a t survives t h i s compe tit iv e "bottlen ec k"

has a high p r o b a b i l i t y o f s u r v i v i n g to produce seed.
supplementation reduces apic al
of i n t e r - t i l l e r

com pe tit io n,

inhibition ( 4 ),

it

and t h i s e f f e c t w i l l

Since n u t r i e n t

reduces the amount
be maximal

if

the

n u t r i e n t s are supplied a t the time o f maximum competition ( f u l l y - t i l l e r e d
stage).
I f l o w - t i l l e r i n g c u l t i v a r s have a g r e a t e r degree o f apical
dominance, as As pinall

argued ( 4 ) , then i n t e r - t i l l e r competition a t the

f u l l y - t i l l e r e d stage is probably g r e a t e r f o r these types.

Aspinall

also found t h a t n u t r i e n t supplementation released t h i s apical

dominance

to a g r e a t e r e x t e n t in the l o w - t i l l e r i n g c u l t i v a r , presumably because
o f the g r e a t e r degree o f dominance t h a t e x i s t e d before the n u t r i e n t
t re a tm e n t.

I f these conclusions can be extended to the present study,

the f o l l o w i n g

e x p la n at io n o f the d i f f e r e n t responses o f I o n ia and

38

Tecumseh to d i f f e r e n t dates o f N a p p l i c a t i o n seem p l a u s i b l e .
E a rl y a p p l i c a t i o n o f N st im u l a t e s t i l l e r i n g

in I o n i a , but because

o f the higher le v e l o f i n t e r - t i l l e r co m p e ti ti o n , few o f these t i l l e r s
survive through the comp et itiv e bot tle n ec k o f the f u l l y - t i l l e r e d stage.
Ap p lic a t io n o f N a t the f u l l y - t i l l e r e d stage r e l i e v e s t h i s co m p e ti ti o n ,
al lo wi ng many t i l l e r s
X response.

to survive and bear seed, which appears as a la rge

E a rl y a p p l i c a t i o n o f N s t im ul at es t i l l e r i n g

in Tecumseh as

w e l l , but since i n t e r - t i l l e r competition i s l e s s , the com petitive
bot tle ne ck o f the f u l l y - t i l l e r e d stage is less r e s t r i c t i v e , and a high
proportion o f these t i l l e r s
response o f Tecumseh w i l l

survi ve to m a t u r i t y .

Thus, the larg e X

occur over a range o f dates o f N a p p l i c a t i o n .

I f these hypotheses are t r u e , then the low y i e l d responsiveness
o f Io n ia to N may be an a r t i f a c t o f the e a r l y date o f a p p l i c a t i o n o f N
commonly used in commercial production.

I t is more convenient to apply

N e a r l y in the season, because spring rain s may make f i e l d w o r k impossible
f o r considerable periods o f time.

However, these data and conclusions

suggest t h a t producers o f Io nia wheat may be s a c r i f i c i n g y i e l d with
this practice.
The high responsiveness o f Tecumseh to N and to improvements in
o t h e r environmental f a c t o r s may be a r e s u l t o f the f l e x i b i l i t y o f i t s
tille rin g

response t o seasonal

v a r i a t i o n s in resource supply.

Tecumseh

can increase X despite d i f f e r e n c e s in the date o f maximum resource
a l l o c a t i o n in d i f f e r e n t environments.

Thus, on the average, i t appears

to be more responsive to improvements in the environment.
Y i e l d component balance and response may thus be an important
f a c t o r in e x p l a i n i n g genotype x environment i n t e r a c t i o n .
as a "model" environmental

v a r i a b l e which can reveal

N may serve

such i n t e r a c t i o n s .

Y i e l d components are e a s i l y measured, and t h e i r response t o N may simul­
ate t h e i r response to environments, e s p e c i a l l y i f date o f a p p l i c a t i o n
is used as an independent v a r i a b l e

(along with r a t e o f a p p l i c a t i o n ) .

D i f f e r e n t dates o f a p p l i c a t i o n simulate the seasonal v a r i a t i o n

of resource

a l l o c a t i o n t h a t occurs in production environments, and hence model an
important f a c t o r i n f l u e n c i n g genotype x environment i n t e r a c t i o n .

SUMMARY AND CONCLUSIONS

1.

Tecumseh's high N requirement does not r e s u l t from a d e f i c i e n c y in
ca p a c i ty f o r N uptake.

2.

Tecumseh accumulates approximately twice as much N a f t e r anthesis as
several

3.

o th er c u l t i v a r s , , which are more t y p i c a l

o f the MSU gene pool.

Tecumseh is less e f f i c i e n t in t r a n s l o c a t i n g N from v e g e ta ti v e p l a n t
p ar t s i n t o the g r a i n , than several o t h e r c u l t i v a r s .

4.

Di ff e r e n c e s in g r a i n percent p r o t e i n among f o u r c u l t i v a r s

(Ion ia,

Tecumseh, Y o r k s t a r , and Augusta) are due to d i f f e r e n c e s in carbo­
hydrate accumulation in the g r a i n , r a t h e r than N accumulation.

5.

Tecumseh's high y i e l d responsiveness to N is caused by a high response
o f the y i e l d component heads/m

6.

2

(X).

Tecumseh's high y i e l d response to improvements in s i t e y i e l d p o t e n t i a l
i s al so caused by a high X response.

7.

The seed weight component (Z)
in the supply o f environmental

is r e l a t i v e l y una ffected by f l u c t u a t i o n s
resources.

X and Y (seeds/head) a d j u s t

in a compensatory fashion to l i m i t a t i o n s in resource supply.

8.

The l o w - t i l l e r i n g

c u l t i v a r I o n ia is very s e n s i t i v e to the s e a s o n a l i t y

o f resource a l l o c a t i o n .

N u t r i e n t supplements app lie d a t the

40

41

f u l l y - t i l l e r e d stage cause a maximum y i e l d response in t h i s c u l t i v a r .
This observation i s i n t e r p r e t e d as i n d i c a t i n g a high l e v e l o f
i n t e r - t i l l e r competition in t h i s c u l t i v a r .

9.

The h i g h - t i l l e r i n g c u l t i v a r Tecumseh is less s e n s i t i v e to the season­
a l i t y o f resource a l l o c a t i o n .
time up u n t i l

N u t r i e n t supplements a p p lie d a t any

the f u l l y - t i l l e r e d

in t h i s c u l t i v a r .

stage cause a s i m i l a r y i e l d response

This observation i s i n t e r p r e t e d as i n d i c a t i n g a

low l e v e l o f i n t e r - t i l l e r competition in t h i s c u l t i v a r .

10. The low le v e l

o f i n t e r - t i l l e r competition in Tecumseh, which allows

i t to u t i l i z e n u t r i e n t s or o t h e r environmental

resources across a

range o f dates, may thus e x p l a i n the high X-responsiveness o f t h i s
c u l t i v a r , both in terms o f response to N and t o v a r i a t i o n s in s i t e
y ie ld potential.

This low l e v e l

thus be the cause

of genotype x environment i n t e r a c t i o n f o r

Tecumseh.

o f i n t e r - t i l l e r competition may

APPENDICES

APPENDIX A

EFFECT OF N TOPDRESSING ON DRY MATTER AND N ACCUMULATION AT THREE GROWTH
STAGES, FOR FOUR WHEAT CULTIVARS: DATA FROM SPECIFIC LOCATIONS, IN 1980

42

APPENDIX A

Table A l . - E f f e c t o f N topdressing on dry m a t te r production and N
accumulation a t three growth stages in f o u r wheat c u l t i v a r s , at Mendon.

Variable

Dry
matter,
mt/ha

Growth
stage

Fully
tille re d

Anthesis

Maturity

Topdressing
r a t e , kg/ha

Fully
t i l lered

Anthesis

3.84

2.98

3.18

3.53

45

3.6 8

3.03

3.53

3. 7 7

90

4.2 1

3.27

3.95

3. 52

0

6.81

4.90

6.82

5.9 6

45

6.58

6.17

7.84

7.43

90

8.00

6. 37

7.43

7. 50

0

7.79

6.67

7.86

7.96

45

9.18

7.98

9.38

9.44

10.3

8.56

10.6

52 .9

43.4

46.0

49.0

45

53.8

50 .2

59 .7

57.6

90

75.0

61.0

65.6

62.5

0

69.5

55.3

75.8

62.3

45

72.3

79.5

97.6

90.9

91.0

98.1

111

65. 2

57 .6

58 . 9

66. 1

45

70.7

96.1

89 . 9

78.9

104

107

91.7

0.57

1.19

0. 94

10

18

110

0

90

LSD*
0.05

10.1

0

90

Maturity

Augusta

0

90

N
accumul­
a te d,
kg/ha

Io nia

C u l t i var
Tecumseh Yorks t a r

16

101

* L e a s t s i g n i f i c a n t d if f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f s i x o b s e r v a tio n s .

Data

43
APPENDIX A

Table A 2 . - E f f e c t o f N topdressing on dry m a t t e r production and N
accumulation a t th ree growth stages in f o u r wheat c u l t i v a r s , a t East
Lansing.

Variable

Dry
matter,
mt/ha

Growth Topdressing
stage
r a t e , kg/ha

Fully
tille re d

Anthesis

Maturi t y

N
accumul­
a te d,
kg/ha

Fully
t i l lered

Anthesis

Maturity

Io n ia

Cul t i var
Tecumseh V o rk st a r

Augusta

0

1.78

1.60

1.87

1.61

45

1.76

1.79

1.94

1.97

90

1.96

1.74

1.76

1.76

0

5. 60

4.16

5.74

5.96

45

8. 63

5.45

8.67

6.51

90

9.22

6.89

8. 2 3

7.82

0

7. 5 8

6. 64

7.8 8

7.66

45

11.2

10.1

12.0

11.0

90

13.1

1 1 .8

1 2.0

12.7

0

30.4

28.9

33.4

29 .0

45

46.7

53.4

60.3

52 .4

90

61.7

61.0

55 .3

62.8

0

62.3

52.4

64 .2

6 6 .6

45

120

90

160

0

94.3

8 6 .0
147

98.0

141
144

92.0

89.6

LSD*
0. 05

0.39

1.4

1 .2

10

29

163

91.4

45

133

147

170

*I! jon
j

90

193

212

172

210

* L e a s t s i g n i f i c a n t d if f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f s i x o b s e rv a tio n s .

26

Data

44
APPENDIX A

Table A 3 . - E f f e c t o f N topdressing on dry m at te r production and N
accumulation a t t hr ee growth stages in fou r wheat c u l t i v a r s , a t Saranac.

Variable
Dry
m a t te r ,
mt/ha

Growth Topdressing
stage r a t e , kg/ha
Fully
t i l i e red

Anthesi s

M aturity

N
accumulated,
kg/ha

Fully
t i 1l e r e d

Anthesis

Maturity

Io nia

Cultivar
Tecumseh York sta r

Augusta

0

3. 0 7

2.55

3.21

2.86

45

2.59

2.76

2.6 4

2. 62

90

2.89

2.76

2.66

2.78

0

6.17

4.79

7.16

5. 94

45

8.16

7.19

8.40

6.85-

90

8.14

7.53

7.82

8.22

0

12.9

10.1

11.2

1 1.8

45

14.2

11.4

12.3

11.9

90

14.5

12.1

1 2.0

12.6

0

55.0

52 .0

62.5

57.7

45

85.0

84.7

82 .8

83.1

90

96.4

97.2

95 .1

96.1

0

74.8

68.5

94.3

75.9

45

148

126

144

129

90

182

178

194

187

0

144

164

147

140

45

199

214

182

174

90

240

240

210

197

* L e a s t s i g n i f i c a n t d i f f e r e n c e f o r comparison o f i n d i v i d u a l means,
are means o f s i x o b s e r v a t i o n s .

LSD*
0.05

0.61

1.4

1.4

16

10

27

Data

APPENDIX B

EFFECT OF LATE-SEASON N SUPPLEMENTS ON GRAIN N AND YIELD VARIABLES OF
THREE WHEAT CULTIVARS

45
APPENDIX B

C u l t i v a r d i f f e r e n c e s in ca p a c i ty to accumulate N l a t e in the
season were i n v e s t i g a t e d in an experiment t e s t i n g the e f f e c t o f l a t e season f o l i a r and /o r s o i l N a p p l i c a t i o n s on N accumulation in the grain
(Table B l ) .

Both s oi l

and f o l i a r N treatments increased N accumulation

in the g r a i n , although the e f f e c t was g r e a t e r f o r the s o i l tre a tm e n t.
The f o l i a r trea tme nt caused a s l i g h t amount o f l e a f burn, r e s u l t i n g in
reduced seed weight and lowered y i e l d s .

The increase in gr ai n percent

p r o t e i n f o l l o w i n g f o l i a r N a p p l i c a t i o n was thus p a r t i a l l y a r e s u l t of
lower carbohydrate accumulation in the g r ai n po rt io n o f the crop.

N

accumulation i n the g r a i n f o l l o w i n g the combined s o i l and f o l i a r
treatments was less than t h a t f o l l o w i n g s o i l

trea tme nt a l o n e , suggesting

t h a t f o l i a r damage reduced the crop's a b i l i t y to take up N from the s o i l .
This supports the f i n d i n g s o f Mik e se ll
al.

(73)

and Paulsen (70) and Neales e t .

t h a t the leaves are important in uptake o f s oi l N.

Tecumseh showed the g r e a t e s t increas e in N accumulation ( d i f f e r ­
ence between t r e a t e d and unt re at ed p l o t s )

f o r both the s o i l

and f o l i a r

t r e at m e nt s , although c u l t i v a r d i f f e r e n c e s were not s i g n i f i c a n t .
showed very l i t t l e

Augusta

in crease in N accumulation from e i t h e r t r e at m e nt .

46

APPENDIX B

Table B l . — E f f e c t o f la te -se aso n f o l i a r and s o i l N a p p l i c a t i o n s on
gr ai n N and y i e l d v a r i a b l e s of t h r ee wheat c u l t i v a r s .
Saranac, 1980.

N tre a tm e n t 1"
Parameter

none

soil

fo lia r

soil +
fo lia r

Ionia

92

120

95

114

Tecumseh

85

116

98

112

Augusta

93

110

93

112

I o n ia

1 0 .8

14.4

12.2

14.4

Tecumseh

1 2.2

14.9

13.8

15.2

9.6

11.5

11.6

12.3

C u l t i var

N accumulated in
the g r a i n , kg/ha

Grain percent
protein*

Augusta

LSD
0.05

11

0.57

Seed w e ig h t, mg

Averaged over
cul t i vars

41 .1

41.5

39.2

39.8

1.1

Grain y i e l d ,

Averaged over
cul t i vars

44.0

44.4

39.7

42 .3

2.5

kg/ha

t Soil t rea tm en t: 90 kg/ha N as ammonium n i t r a t e sidedressed a t an th es is .
F o l i a r treatm en t: app roximately 170 kg/ha N a p p li e d as a f o l i a r spray
( 12% urea s o l u t i o n ) f o u r days a f t e r ant hes is.
^Adjusted to 14% moisture.

APPENDIX C

EFFECT OF N TOPDRESSING ON YIELD VARIABLES OF SEVERAL WHEAT CULTIVARS
DATA FROM SPECIFIC LOCATION-YEARS

47
APPENDIX C

Table C l . - cu ltivars.

E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f two wheat
Saranac, 1978, experiment 1.

Topdressing
r a t e , kq/ha
Variable

Cul t i var

0

90

LSD*
0.05

response to
topdressing
%

Y i e l d , q/ha

I o n ia

31.7

35.0

10
3.1

Heads/m

2

Tecumseh

23 .6

26.9

Io n ia

238

229

14

-4
35

Seeds/head

Tecumseh

243

291

I o n ia

31 .5

36.2

20

15
3. 5

Seed w t , mg

Tecumseh

26.7

26.5

I o n ia

41. 1

40.9

-1

-1
1 .1

Harvest
Index

Tecumseh

35.1

34.3

Ioni a

0. 395

0.401

-2

2
0.011

Tecumseh

0.369

0.377

* L e a s t s i g n i f i c a n t d i f f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f 24 obse rv at ion s.

2
Data

48

APPENDIX C

Table C 2 . - E f f e c t o f ' N topdressing on y i e l d v a r i a b l e s o f f o u r wheat
cu ltivars.
Saranac, 1978, experiment 2.

Topdre ssing
r a t e , kg/ha
Variable

Cul t i var

0

LSD*
0.05

90

response to
topdressing
%

Y i e l d , q/ha

Heads/m

2

Seeds/head

Seed w t, mg

Ion ia

2 2 .2

30 .3

Tecumseh

21.6

33.6

Yo rk st a r

24.1

32.1

Frankenmuth

28.2

37.2

Io n ia

170

201

Tecumseh

242

333

Yo rk st a r

211

263

25

Frankenmuth

241

286

19

Io n ia

30.9

36.6

Tecumseh

25.9

28.3

19
9

Y o rk st a r

32.7

35 .8

10

Frankenmuth

33.0

35.0

6

Io nia

41.8

41.1

-2

Tecumseh

34.0

35.2

Y o rk st a r

34.9

32.2

-8

Frankenmuth

36.0

34 .4

-4

36
4.4

56
33
32

'

18
60

4. 6

38

4

1.2

* L e a s t s i g n i f i c a n t d i f f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f nine o bs er va tio n s.

Data

49

APPENDIX C

Table C 3 . - E f f e c t o f N topdressing on y i e l d v a r i a b l e s o f t hr ee wheat
cultivars.
Saranac, 1979.
Topdressing
r a t e , kg/ha
Va ria bl e

Cultivar

0

90

LSD*
0.05

response to
topdressing
to

Y i e l d , q/ha

Heads/m

2

Seeds/head

Seed w t , mg

Ionia

45.0

48 .6

Tecumseh

32.3

45.0

Yo rk st a r

42.4

48.0

13

Io n ia

255

265

4

Tecumseh

312

419

Yo rk st a r

238

288

Io nia

35 .7

37.4

Tecumseh

24.0

25.8

Y o rk s ta r

39 .9

38.6

-3

Io n ia

47.7

47 .2

-1

Tecumseh

42.0

40.0

Yo rk st a r

43.0

41.8

8
5.0

39

39

34
21

5
2 .1

1-4

7

-5
-3

*Least s i g n i f i c a n t d i f f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f nine obs ervations.

Data

50

APPENDIX C

Table C 4 .-- E f f e c t o f N to p d r e s s in g on y i e l d
c u ltiv a r s .
Mendon, 1980.

v a r ia b le s o f f o u r wheat

Topdressing
r a t e , kg/ha
Variable

Cul t i va r

0

90

LSD*
0.05

response to
topdressing
%

Y i e l d , q/ha

Heads/m

2

<

Seeds/head

Seed w t , mg

Harvest
Index

Ionia

26.0

35.4

Tecumseh

23.8

34.5

Yo rk st a r

29.4

41.5

41

Augusta

29.5

42.6

44

Ionia

288

343

19

Tecumseh

498

529

Yo rkstar

331

387

17

Augusta

421

424

1

Ionia

21.4

23.0

7

Tecumseh

14.1

18.1

York sta r

22.6

25.5

8

Augusta

18.3

24.6

34

Ionia

43.1

46.2

8

Tecumseh

34.9

36.8

Yo rk st a r

40.1

42.1

5

Augusta

39 .3

41.1

5

I o n ia

0. 335

0.353

5

Tecumseh

0. 359

0.403

York sta r

0. 378

0.394

4

Augusta

0. 373

0.422

13

*L e a s t s i g n i f i c a n t d i f f e r e n c e f o r
are means o f s i x o b s e r v a tio n s .

40
2. 5

45

6

64

3. 0

28

5

0.87

0.024

12

comparison o f i n d i v i d u a l means.

Data

51
APPENDIX C

Table C 5 . ~
c u ltiv a r s .

E f f e c t o f N to p d re s s in g on y i e l d v a r ia b le s o f f o u r wheat
East L a n sin g , 1980.
Topdressing
r a t e , kg/ha

Va ria bl e

Cultivar

0

90

LSD*
0.0 5

response to
topdressing
"

Yield,

Heads/m

q/ha

?

Seeds/head

Seed w t, mg

Harvest
Index

%

Ionia

30.2

53.5

Tecumseh

26.5

47.5

Yorkstar

33.7

51.3

52

Augusta

33.2

56.4

70

Ionia

355

533

50

Tecumseh

420

680

Yorkstar

382

546

Augusta

389

556

43

Ionia

19.3

22.9

19

Tecumseh

19.6

2 0.1

Yorkstar

382

546

43

Augusta

2 1 .8

26.4

21

Ionia

45.1

44 .6

-1

Tecumseh

32.9

35.2

Yorkstar

39.0

38.6

-1

Augusta

39.6

38.8

-2

I onia

0. 398

0.408

Tecumseh

0.399

0.405

Yorkstar

0.428

0. 430

0

Augusta

0.43 3

0. 443

2

11

4.3

QG
yt)

79

62
43

3

3.8

7

1.4

3
0 .0 16

*L e a s t s i g n i f i c a n t d if f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f s i x o b s e r v a tio n s .

2

Data

52
APPENDIX C

Table C 6 .- - E f f e c t o f N to p d re s s in g on y i e l d v a r ia b le s o f f o u r wheat
c u ltiv a r s .
Saranac, 1980.
Topdressing
r a t e , kg/ha
Variable

Cul t i var

0

90

LSD*
0.05
-

Y i e l d , q/ha

Heads/m^

Seeds/head

Seed w t , mg

Harvest
Index

response to
topdressing
%

Io n ia

43.7

50 . 8

Tecumseh

35.9

45 .4

Y o rk s ta r

44. 9

46.2

3

Augusta

49. 3

51 . 8

5

Io n ia

519

520

0

Tecumseh

610

710

Y o rk st a r

471

509

8

Augusta

452

513

13

I o n ia

18.2

22 .3

23

Tecumseh

16.9

19.2

Yo rk st a r

25.1

25 .3

1

Augusta

27.5

28.0

2

Io nia

47.5

45. 1

-5

Tecumseh

35.3

33.4

Yo rk st a r

39.8

36.0

-10

Augusta

40.4

36.7

-9

Io n ia

0.342

0.352

Tecumseh

0.360

0.373

Yo rk st a r

0. 403

0. 387

-4

Augusta

0.419

0.414

-1

16
4.3

96

3.4

1 .8

26

16

14

-5

3
4

0. 026

* L e a s t s i g n i f i c a n t d i f f e r e n c e f o r comparison o f i n d i v i d u a l means.
are means o f s i x o b s e rv a tio n s .

Data

APPENDIX D

EFFECT OF INCREASING SITE YIELD POTENTIAL ON THE YIELD AND YIELD
COMPONENTS OF SEVERAL WHEAT CULTIVARS

53

APPENDIX D

ID

I ONI A
O
<0

^

cr:

CJ

d

CD

■>

^
x

_L

i

■oT

2

s

s:

2

„

-s-

B E T D ;—
"T"

□

Y

A

v
A

a

P

□

_________ □

n

uj

t

□
a

A

y
n

a

&

a
A

/ j.

0
1 ®
__
<c
c_) O
S
CD

□

1

‘

V

+

x

? n r

^

y=r
CD O.

X

I— °
S
00
LU
t_>
Qi Q
L_l I

.

O

O
CO

V H IE L D
X=HEADS/M2
Y=SEEDS/HEAD
2= SEED WT

B= - 0 . 0 5 ns
B= 0 .0 6 NS
B= - 0 . 0 5 NS
B= - 0 . 0 5 NS

o

LD

I

30'.0

3 5 .0

40.0

45.0

LOCATION MEAN YIELD

50.0

55.0

60'.0

(q/ha)

Figure D l . - E f f e c t o f inc re as in g s i t e y i e l d p o t e n t i a l on the y i e l d
and y i e l d components o f I o n i a wheat, r e l a t i v e to the gene pool mean.
*NS= slope not s i g n i f i c a n t l y d i f f e r e n t from zero.

54

APPENDIX D

ID

YORKSTAR
o
CO

o

X

L-U

CD

o
o

O
CO

W=YIELD
X=HEADS/R
Y=SEEDS/HEAD B= - 0 .1 0
Z=SEED WT
B= 0 .1 8

o
o

U3

30'. 0

40.0

45.0

LOCATION MEAN YIELD

SO.O

SS.O

60.0

(q /h a )

Figure D 2 . - E f f e c t o f inc re asi ng s i t e y i e l d p o t e n t i a l on the y i e l d
and y i e l d components o f Yo rkstar wheat, r e l a t i v e to the gene pool mean.

*NS= slope n o t s i g n i f i c a n t l y d i f f e r e n t from ze ro .

55

APPENDIX D
ID

AUGUSTA
O
CO

r-vj

o

os
o

22

>■n o
X
^

w
z

1A
#

<c
•
LU O
s: o

o
>1

A
------------A----------------------------------------I
1
-I
B A

"|

<c
•
t_D O
o
O)

X

□

n n

□

X

□

-L
-Y

X *

X +

X
X

X

LL.
CD O

"f
□n,

V

i

I— o

------------------------

X
X

±.____
D

X

X
X

•

I— o
2S

CO

UJ
C_>
c n
LU O
Q•

o

W=YIELD

o

Z=SEED WT

r*

co

o
to

B= - 0 . 1 3 n s *
B= - 0 . 02 ns
B= - 0 , 0 5 ns
B= 0 .0 2 ns

J_ _ _ _ _ _ _ I_ _ _ _ _ _ _ L
30*. 0

35.0

40.0

45.0

LOCATION MEAN YIELD

50.0

55.0

60'.0

(q /h a )

Figure D3.—
E f f e c t o f i n cr ea si ng s i t e y i e l d p o t e n t i a l on the y i e l d
and y i e l d components o f Augusta wheat, r e l a t i v e to the gene pool mean.
*NS= slope not s i g n i f i c a n t l y d i f f e r e n t from zero.

56

APPENDIX D
in

FRANKENMUTH
o
CD

O
X

o

£
s

°
°

o

05

LL. O
O
o
00

( >
Q_

0

o

o

W=YIELD:
X=HEADS/M2 :
Y=SEEDS/HEAD
Z=SEED WT

B= -0.01NS
B= 0 .2 3 ns
NS
B=
B=

(p

o
o
la

30'. 0

35.0

40.0

45.0

LOCATION MEAN YIELD ( Q /

50.0

55.0

60'. 0

ha)

Figure D 4 . - - E f f e c t o f i n c r e a s i n g s i t e y i e l d p o t e n t i a l on the y i e l d
and y i e l d components of Frankenmuth wheat, r e l a t i v e to the gene pool
mean.

*NS= slope n o t s i g n i f i c a n t l y d i f f e r e n t from zero.

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