VARIATION IN NITROGEN USE EFFICIENCY AMONG
GRAIN SORGHUM GENOTYPES
by
MICHAEL J. LAVELLE, B.S. in Ag.
A THESIS
IN
CROP SCIENCE
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
Accepted
December, 1987
\
ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to Dr. Arthur B. Onken for
serving as chairman of the supervisory committee.
I am thankful for
his patient support and valuable advice throughout the preparation of
this manuscript, and as my supervisor in a professional capacity.
Sincere thanks go to Dr. Daniel R. Krieg and Dr. Richard E.
Zartman for their contribution to this study and their timely review
of this manuscript.
I gratefully acknowledge Dr. Ronald E. Sosebee
for service on the supervisory committee.
I am very grateful to my associates at the Texas Agricultural
Experiment Station, Lubbock, Texas, in particular for the secretarial
assistance of Ida Gonzales and Donna Holdren.
I gratefully acknowledge the tolerance and sacrifices of my wife,
Leticia, and thank her for her encouragement and loving support.
n
CONTENTS
ACKNOWLEDGEMENTS
ii
ABSTRACT
iv
LIST OF TABLES
vi
LIST OF FIGURES
I.
II.
viii
INTRODUCTION
1
LITERATURE REVIEW
3
Approaches to N-Use Efficiency Research
3
Genetic Control and Genotype Differences in N Use ....
5
Yield Components and Their Relationship to N-Use
III.
IV.
V.
Efficiency
9
MATERIALS AND METHODS
13
Field Experiment
13
Sample Collection and Analysis
15
Greenhouse Experiment
17
Sample Digestion Procedure
19
Analysis of Total N
21
Statistical Analysis
21
RESULTS AND DISCUSSION
23
Field Experiment
23
Greenhouse Experiment
52
SUMMARY AND CONCLUSIONS
67
LITERATURE CITED
72
m
n
ABSTRACT
Four grain sorghum genotypes, [Sorghum bicolor (L.) Moench],
differing in morphology and grain yields were evaluated in the field
and greenhouse.
The objective was to identify and assess
physiological and morphological parameters associated with the
efficient use of nitrogen.
The four entries; SC325-12, SC630-11E,
8BH6956, and 77CS1, were grown in a replicated field trial on an Acuff
loam, (fine-loamy, mixed, thermic Aridic Paleustoll), divided into
high N rate (180 kg/ha added N ) , and a low N rate (0 kg/ha added N ) .
Line SC325-12 is a partially converted version of IS 2462.
SC630-11E is a partially converted version of IS 1269C.
is a cross of SC326-^ x SC103-12.
Line
Line 8BH6569
Line 77CS1 has been released by the
Texas Agricultural Experiment Station as TX 2816.
Plant components were sampled throughout two consecutive growing
seasons to determine genotype X nitrogen fertility effects on uptake,
translocation, and deposition of N and dry matter.
The greenhouse
evaluation consisted of the same four entries grown hydroponically
four plants per pot with five N rates set at 100, to 800 mg per pot.
Plants were separated into roots and shoots after being allowed to
grow until deficiencies were observed, approximately 40 days after
germination.
In the field experiment, significant differences were observed on
a per plant basis for grain weight, total aerial plant N at maturity,
N uptake before and after anthesis and N in the grain among the
genotypes.
Significant genotype differences were also found for the
iv
combined components; N-use efficiency (grain wt./N supply), N-uptake
efficiency (N uptake/N supply), metabolic N-use efficiency (grain
wt./N uptake), N-translocation efficiency (N in the grain/N uptake),
grain metabolic N-use efficiency (grain wt./N in the grain).
However, significant year X genotype variability was present for all
these and other parameters measured.
Highly significant correlations were noted across genotypes for N
uptake at maturity and aerial biomass at maturity and between
translocation efficiency and harvest index.
Selection for high
biomass and high harvest index appear the best criteria to select for
high N uptake and translocation.
N-use efficiency was defined as milligrams of dry matter produced
per unit N found in the plant tissue for the greenhouse experiment.
Significant differences were observed at the 200, 600, and 800 mg
N/pot levels for this variable.
Both total shoot N and shoot N
concentration increased in proportion to total root N and root N
concentration as the N/pot rate increased.
Significant differences
were found at the 400, 600, and 800 mg N levels of shoot to root total
N ratios.
LIST OF TABLES
1.
Composition of Nutrient Solution Used in
Greenhouse Experiment
18
2.
Mean Performance of Genotypes for Grain Yield
24
3.
Mean Performance of Genotypes for Grain Yield and
N Accumulations
25
Mean Performance of Genotype for N-Use Efficiency
and Related Components at Both High and Low N
Rates
27
Nitrogen Use Efficiency (Gw/Ns) Adjusted Using
Grain N Concentration (6NC)
29
Mean Dry Matter and N Concentrations at Panicle
Initiation and Anthesis in Vegetative and
Reproductive Tissues of Genotypes at High N
Regimes for 1983 and 1984
30
Mean Dry Matter and N Concentrations at Panicle
Initiation and Anthesis in Vegetative and Reproductive Tissues of Genotypes at Low N Regimes
for 1983 and 1984
31
Mean Dry Matter and N Concentrations at Maturity
in Vegetative and Reproductive Tissues of
Genotypes at High N Regimes for 1983 and 1984
32
Mean Dry Matter and N Concentrations at Maturity
in Vegetative and Reproductive Tissues of Genotypes at Low N Regimes for 1983 and 1984
33
Variability of Morphological and Physiological
Parameters Across Genotypes and Years
35
Linear Correlation Coefficients (r) Between
Agronomic and Nitrogen Physiology Traits in
Four Sorghum Genotypes
36
Linear Correlation (r) of % Leaf Area Reduction
[(LA2-LA3)/LA2]100 to Other Parameters for Both High
and Low N Rates Across Years
37
Linear Correlation (r) of N Accumulation at 50%
Anthesis (Nt2) to Other Parameters at Both High
and Low N Rates Across Years
39
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
VI
M
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Linear Regression of N Accumulation Before
Anthesis on Grain Weight, Grain Weight/N
Supply, and N in the Grain by N Rates Across
Years
40
Linear Correlation (r) of N Accumulation After
Anthesis (Nt-Nb) to Other Parameters at Both
High and Low N Rates Across Years
41
Linear Regression of N Accumulation After Anthesis
on Grain Weight, Grain Weight/N Supply, and N in
the Grain by N Rates Across Years
42
Linear Regression of Total Above-Ground N
Accumulation at Maturity on Grain Weight, Grain
Weight/N Supply and N in the Grain by N Rates Across
Years
44
Linear Correlation (r) of Number of Kernels per
Panicle to Other Parameters at Both High and Low
N Rates Across Years
45
Linear Correlation (r) of Weight of 100 Grains
(grams) to Other Parameters at Both High and Low
N Rates Across Years
46
Mean Performance of Genotypes for Yield
Components
48
Stepwise Linear Regression Analysis of Genotype
Means for Grain Weight, Grain Weight/N Supply and
N in the Grain for High N Rate Over Years
50
Stepwise Linear Regression Analysis of Genotype
Means for Grain Weight, Grain Weight/N Supply and
N in the Grain for Low N Rate Over Years
51
Mean Performance Across Genotypes Grown in
Greenhouse at Different Nitrogen Rates
53
Total N in Shoot and Root Material at Various N
Concentrations
56
vn
V
LIST OF FIGURES
1.
Total Dry Matter Produced at Various N Levels
54
2.
Nitrogen Concentration of Shoots at Various N
Levels
56
3.
Nitrogen Concentration of Roots at Various N
Level s
57
4.
Recovery of Added Solution N
59
5.
Ratio of Shoot Total N to Root Total N at Various
N Levels
Ratio of Shoot to Root N Concentrations at
60
Various N Levels
61
7.
Shoot Dry Matter Production at Various N Levels
63
8.
Root Dry Matter Production at Various N Levels
64
9.
Nitrogen Use Efficiency
65
6.
VI n
'fl
CHAPTER I
INTRODUCTION
It is widely accepted that differences exist both between and
within species to use mineral elements efficiently for growth.
Some
cultivars grow well where others perform poorly or even die when
subjected to mineral stresses.
This differential response may be an
important component of the adaptation complex that could be exploited
in breeding programs to increase nutrient use efficiency, thereby,
making attempts at raising agricultural productivity more specific for
designated areas of the world with their unique associated problems.
Our understanding of genotype X soil fertility interactions
however, is rather limited especially with regard to grain sorghum,
[Sorghum bicolor (L.) Moench] and nitrogen fertility regimes.
Plant
growth and reproduction are not only controlled by inherent genetic
mechanisms, but also by environmental factors that permit the degree
of expression of these genetic capabilities.
Therefore, this
understanding becomes elusive as year to year, soil type to soil type,
geographic region, and other variables presents themself in the
experimental data.
With these environmental factors not easily controllable, the
understanding of physiological and morphological parameters associated
with uptake, assimilation, translocation, and deposition of N and dry
matter in grain sorghum may prove valuable in selecting for genotypes
more efficient in extraction and utilization of N where this nutrient
would ordinarily become limiting.
Because of its transitory nature in
1
V
the soil, it susceptability to leaching, its potential for becoming a
pollutant, and its ever increasing cost as a production input, the
efficient use of applied and residual N should receive more attention
in overall management than any other plant nutrient.
The objectives of these field and greenhouse studies were to
evaluate differential growth responses of selected sorghum genotypes
at both high and low N-fertility rates by quantifying morphological
and physiological growth parameters and establishing their
relationship to N-use efficiency.
This work will eventually lead to
the development of a screening program used to rank genotypes and
hybrids for N-use efficiency as a potential breeding character.
CHAPTER II
LITERATURE REVIEW
Currently, high-yielding grain sorghum varieties managed under
identical N-fertilization regimes do not yield as well as corn, but
take up more total N from the soil.
This disparity is due primarily
to the fact that grain sorghum translocates much less of its N from
vegetative tissue to grain.
This leaves grain sorghum stover with
about 50 percent more total N than corn stover (Perry and Olson,
1975).
Therefore, the possibility exists of developing grain sorghum
hybrids with a propensity to accumulate relatively large quantities of
N and translocate a larger portion of the accumulated N to the grain.
Approaches to N-Use Efficiency Research
The traditional approach to evaluating N utilization efficiency
has been to consider fertilizer N as the input and dry matter
production of the crop as the output.
As applied to grain crops, it
is the average change in grain yield obtained per unit change in the
amount of N applied (Capurro and Voss, 1981).
In plotting this
relationship, yields tend to increase linearly with the first
increments of fertilizer N input until a point is reached where yield
levels tend toward a plateau.
This is considered "the point of
diminishing returns" where each additional increment of output (yield)
requires a corresponding greater incremental increase of input
(fertilizer N ) . Through genetic improvement, yield potential of
cultivars has led to greater fertilizer N efficiency in terms of yield
per unit N supply.
The high yielding cultivars are not only more
responsive to N fertilizer, but many exhibit equal or superior yields
at all levels of N inputs (Fisher, 1981; Sherrard et al., 1984).
An alternative approach in N-use efficiency study examines the
ratio of plant dry matter yield to the concentration of N in the
plant.
Nitrogen absorbed by the plant is considered the input and dry
matter production the output.
The assumption being that genotypes
vary in their ability to metabolize N in relation to dry matter
deposition.
An efficient genotype would produce more dry matter per
unit N absorbed by the plant or would produce equal dry matter with a
lower average tissue N concentration.
Unfortunately these ratios are
not a constant property of a genotype but undergo large changes with N
supply.
Increases in N supply generally decrease the amount of dry
matter produced per unit N absorbed by the plant and visa versa.
In
addition, plants tend to increase the ratio of dry matter produced to
N concentration with time as the proportion of structural material in
the tissue increases (Myers and Asher, 1982).
The efficiency of vegetative tissue dry matter production may not
always be a good indicator of the efficiency of grain production,
which has led to use of grain production per unit of N uptake as an
index of N-use efficiency (Maranville et al., 1980; Rhoads and
Stanley, 1984).
Nutrient use efficiency for N as defined by Rhoads
and Stanley (1984) was grain yield (kg/ha) divided by total nutrient
uptake (kg/ha).
Maranville et al. (1980) approximate that definition
with their NE2 term expressed as g grain/g N.
Further divisions have
been made in an effort to separate acquisition of N from the
rv
rhizosphere "uptake efficiency," from the plants internal economy
which may result from efficient redistribution within the plant and/or
a lower requirement for N at functional sites, "utilization
efficiency" (Moll et al., 1982).
There also exists the evolutionary
adaptive characteristic of growth rate adjustment to make it
compatable with nutrient supply, however, this is more of a survival
mechanism and is of little interest from a production standpoint
(Clarkson and Hanson, 1980).
Genetic Control and Genotype Differences in N Use
Nitrogen and other nutrient elements are transformed into biomass
by crops through sequential chemical reactions eminating from the
element in its ionic form.
These processes of nutrient utilization
may be divided into an uptake and an assimilation metabolic step
mediated by carrier and enzyme proteins, respectively.
Because
proteins are involved in both steps, they are under genetic control.
The degree to which regulation of uptake is coordinated with the
assimilation step remains to be established.
The two steps, however,
can be considered as a consecutive reaction with the total efficiency
controlled by the lower step rate (Cacco et al., 1982; Hageman et al.,
1967).
Different genotypes of the same species have shown variation in
nutrient content when grown under identical conditions, thus
exhibiting genetically controlled mechanisms of mineral nutrition
(Clark and Brown, 1980; Epstein and Jefferies, 1964; Epstein, 1972;
Gerloff, 1963; Jung, 1978; Pollmer et al., 1979; Vose, 1963; Wright,
1976).
These genetic differences that exist for N-use efficiency may
be expressed as differential growth at very low levels of N,
differential growth responses to addition of fertilizer N, and genetic
differences in nutrient levels at which deficiency symptoms are
expressed.
Beauchamp et al. (1976) found corn genotypes differed appreciably
in their ability to translocate N from leaf and stalk material to the
ears during the period following silking.
However, the inbreds tested
varied between years in this ability, leading them to suggest that a
genotype X environment interaction exists. The importance of this
translocated N is evidenced through work by Hanway (1962) when he
showed also with corn, that approximately 50 percent of the total
grain N was translocated from above ground plant parts and that this
transformation occurs only to a significant extent after grain
formation had begun.
In addition to N translocation ability differences among
genotypes of corn.
Chevalier and Schrader (1977) demonstrated that
differences also exist in their ability to absorb and reduce nitrate.
Inbred A632, which took up less N than other inbreds studied, was
found to have more N in the ear fraction while conversely, A632 X
0h43, a large vegatative plant, failed to remobilize to the ear much
of the N stored in the stems and roots. They concluded that total
shoot N does not give an accurate estimate of N absorption as their
study included root analysis where large genotypic differences in N
accumulation were found.
A more desirable method for measuring
genotypic differences in NO^
uptake, in their estimation, would be
to monitor NO^
disappearance from solution during the period from
emergence to eight weeks past emergence.
Reduction of NO^ -N by nitrate reductase and its role in yield
and N-use efficiency have been evaluated (Messmer et al., 1984; Reed
and Hageman, 1980; and Sherrard et al., 1984).
An overall
inconsistency has prevailed in these experiments between nitrate
reductase activity and either grain yield or grain N. The overall
conclusion arises that other N parameters may be more relevant in
estimating N utilization than nitrate reductase activity.
The fact that numerous processes are involved in N-use efficiency
was further postulated by
Moll et al. (1982) with research conducted
using eight corn hybrids grown at two N-fertilizer rates. They
measured grain yield, N accumulation in the plant at silking, and N
accumulation in the grain and stover at harvest.
They concluded that
at the low N rate, efficiency of N use among the hybrids tested was
due primarily to their translocating ability of accumulated N.
However, at the high N rate, N-use efficiency was attributed to
variations in the uptake of N from the soil. They also found that
hybrids with smaller overall levels of N-use efficiency differed
markedly in measured component charateristics.
Nitrogen use
efficiency was defined by them as grain production per unit of N
available in the soil, or grain weight per N supply expressed in the
same units (g/plant).
primary components:
This definition was expanded to incorporate two
Uptake efficiency--the quotient of total N in the
plant at maturity divided by N supplied as fertilizer per plant; and
8
utilization efficiency—the quoient of grain weight divided by total N
in the aerial portion of the plant at maturity.
By contrast, Maranville et al. (1980) working with grain sorghum,
calculated N-use efficiency as:
(1) Total dry matter per unit N
uptake (2) Total grain yield per unit N uptake and (3) The product of
2 and the grain N: stover N ratio.
Nitrogen uptake was defined as the
amount of total N found in the above-ground portion of the plant at
the time of sampling and was not based on the amount of N actually
available to the plant from fertilizer and residual sources.
They
acknowledge that "the factors affecting N efficiency inside the plant
may be markedly different from those that affect N recovery from the
growth medium."
Also evident in their two year study was a
significant hybrid X year interaction that led them to believe three
or more years of data would be needed to establish consistent trends
in N-use efficiency.
The heritability of specific mineral stress characters has been
documented.
Gableman (1976) and Gerloff (1976) studied this
inheritance in relation to the utilization of N, P, and K in tomatoes
and beans and found that the utilization between efficient and
inefficient strains differed by 44 percent for N.
O'Sullivan et al.
(1974) also working with tomatoes, found efficient strains produced as
much as 45 percent more dry weight than inefficient lines under stress
conditions.
Their definition for efficiency of N utilization is the
milligrams of dry weight produced for each mg of N absorbed by the
plant.
They indicated N efficiency at a growth limiting supply of N
was not associated with the root system.
All plants grown in the
nutrient solution removed approximately equal amounts from the
environment and translocated equal amounts from the roots to the tops
of both efficient and inefficient plants.
They suggest that the lower
overall N concentration in the efficient plants indicates they grow
and function more effectively at lower tissue levels of N than do
inefficient plants. They also classified strains as "responders" and
"non-responders" to added increments of N, concluding that crops with
the combined attributes of N efficiency under N stress and
responsiveness to added N would be highly desirable.
Yield Components and Their Relationship
to N-Use Efficiency
Sorghum trials conducted by Alagarswamy and Seetharama (1982) at
the ICRISAT Center in India using 40 elite breeding lines and 49
selected germplasm lines were evaluated for variation in agronomic and
N-physiology traits. These traits included:
Grain yield, biomass,
harvest index percent, days to flower, percent protein in the grain,
total N in the plant, total N in the grain, and N-translocation index
(grain N/total N of the above-ground parts).
Significant genotypic
variations existed for all traits with the germplasm lines accounting
for a greater portion of the variability.
They presumed this was due
to the elite breeding materials adaptability to the post-rainy season,
the time when their trials were conducted.
Strong correlations between total N in the plant and biomass and
between N-harvest index and harvest index percent were found.
These
results indicated to Alagarswamy and Seetharama (1982) that selection
for high biomass and harvest index percent would be sufficient to
10
ensure high N-uptake and translocation. They also concluded that only
parents used in crosses or material in the final stages of a breeding
program need to be analyzed for N to confirm they have an above
average N-uptake and translocation efficiency.
These conclusions are in agreement with those made by Bhatia and
Rabson (1976) who maintain that N uptake and metabolism are energy
dependent and, therefore, require greater photosynthesis to support
this higher uptake, and the determinations of Seetharama (1977) that
later flowering plants have larger leaf areas and possibly deeper
roots.
Such plants are usually larger in size and have a greater
capacity for photosynthesis, N uptake, and assimilation.
Because high protein is an important breeding character,
differences in grain N concentrations have been considered when
evaluating genotypes for differential N uptake and accumulation.
With
wheat, Johnson et al. (1967) found that high protein genotypes overall
had lower stover N concentrations than the low protein genotypes
tested.
The low protein genotypes demonstrated the ability to absorb
more soil N, but were less able to translocate the N to the grain in
comparison to the other genotypes.
The high protein genotypes had
lower concentrations of N in the leaves, but higher N in the grain.
In contrast, McNeal et al. (1968) found that even though a high
protein wheat genotype absorbed about 20 percent more nitrogen than a
low protein genotype, it redistributed about 6 percent less N to the
grain.
Relationships between N allocation to the grain and plant sink
size also appear to exist.
Proposals to increase plant sink size.
11
(dry matter production, grain size, and grain number), through
breeding could lead to improved N efficiency within the plant.
However, plants that respond positively to higher initial levels of
nutrients will, because they are bigger sinks, make larger demands on
other nutrients and water.
These inputs could become limiting,
thereby curtailing the initial response.
In addition, larger plants
will intercept so much light that the lower leaves will receive
suboptimal illumination (Greenwood, 1976).
Although genotypic differences for nutrient use efficiency have
been recognized for some time, it is still not possible to completely
explain how these genotypes can produce an equal amount of growth,
satisfy all their biosynthetic and maintainance needs, but use a
smaller amount of nutrient than required by other genotypes (Clarkson
and Hanson, 1980).
An important step toward explaining N-use
efficency is, therefore, identification of morphological,
physiological, and biochemical parameters associated with genotypes
which differ in N-use efficiency, as these traits are clues to how a
genotype achieves efficiency in its use of N.
Sherrard et al. (1984)
have proposed a "ideotype" corn plant with a greater capacity for
converting N supplied into increased yield with the following
characteristics:
1)
High dry matter and high reduced N accumulated by anthesis,
2)
High stalk NO^*" content at anthesis,
3)
High rate of N uptake and assimilation during grain-filling
period,
4)
High rate of movement to the developing grain.
12
5)
High photosynthetic rates during grain fill and,
6)
Prolonged grain-filling period without a later physiological
maturity date.
In addition to these traits, they propose the possible inclusion
of high harvest index for N as an efficiency improving trait, although
they state that it may not be complementary to increases in yield.
However, Loffler et al. (1985), working with wheat, concluded that
increases in N-harvest index or total N at maturity may increase grain
protein percentage and grain protein yield without reducing yield.
A
model including harvest index alone accounted for 84 percent of the
variation in grain yield, thereby, asserting its importance to grain
production.
However, they state that at a given harvest index a line
with relatively high N-harvest index tends to have a higher grain
protein percentage than a line with the same harvest index but a lower
N-harvest index.
CHAPTER III
MATERIALS AND METHODS
Field Experiment
Four grain sorghum genotypes designated as:
SC325-12, SC630-11E,
8BH6956, and 77CS1, were planted on May 24, 1983 and May 14, 1984, at
the Texas A&M University Agricultural Research and Extension Center at
Lubbock, Texas in field 405 on an Acuff loam (fine-loamy, mixed,
thermic Aridic Paleustoll).
These genotypes were selected because of
their yield ranking in high and low N-fertility trials conducted at
the same location in 1981 and their diverse morphology.
Among the 24
entries in that trial, SC325-12 and 77CS1 were the lowest yielders in
the low N-fertility plots and 8BH6956 and SC630-11E were among the
highest under both high and low N-fertility regimes.
Field selection
was based on three prior years of high/low N-fertility studies
conducted at this site, with the low N half of the field receiving no
added N fertilizer and the stover from the 1982 crop removed to reduce
the residual soil N to the point of substantial yield reduction.
Two levels of N fertilization were utilized.
The "low" growth
limiting rate was 0.0 kg/ha added and the "high" greater than adequate
rate was set at 180 kg/ha supplied as ammonium nitrate in 1983 and
urea in 1984. Urea was used in 1984 due to the unavailability of
ammonium nitrate.
The entire field received phosphorous at the rate
of 20 kg/ha both years to eliminate any possible deficiencies in this
element.
Soil samples were taken to the 90-cm depth prior to
fertilizer application to determine residual soil N levels used in
13
14
calculations of plant available N.
Samples were analyzed using
Technicon's industrial method no. 698-82WF (Anonymous, 1983a).
The experimental design consisted of the entire field being
divided into two equal halves; a high N application rate and low N
application rate with a hybrid sorghum planted between and around the
outside edges as a buffer.
The high N portion of the field was
located closest to the source of irrigation water and the low N
portion located directly behind the high N division.
A randomized
complete block arrangement as described by Snedecor and Cochran (1971)
was imposed on each fertilizer regime with the blocks down the row to
nullify any variation in irrigation.
Blocks were sixteen rows wide
with each genotype appearing once in each of four blocks per
fertilizer regime.
Plot dimensions were eight 101-cm rows wide by 7.6 m in length
with the four inside rows used for data collection to eliminate any
bordering effects.
Of these four rows, one was chosen with the best
representative stand and set aside for final grain yield data while
the other three were sampled throughout the growing season.
The plots
were overplanted and hand-thinned in an attempt to maintain a plant
population of approximately 120,000 plants/ha.
Plots were furrow
irrigated with a pre-plant and subsequent irrigations when necessary
to alleviate any moisture stress. This consisted of a pre-plant plus
six summer irrigations for both years. Weeds were controlled by hand
hoeing.
15
Sample Collection and Analysis
The above-ground portion of two complete plants per plot were
harvested at growth stage 3 (panicle differentiation), growth stage 6
(half-bloom), and growth stage 9 (physiological maturity), as
described by Vanderlip and Reeves (1972) or at the end of GSl, GS2,
and GS3 as described by Eastin (1972).
Plant components were dried
for a minimum of 72 hours at 70 C in a forced-air oven and ground in a
Wiley mill to pass a 20-mesh screen.
Heads from the growth stage 9
sampling were threshed individually and the seed from each sample were
ground in a cyclone laboratory hammer mill (UDY ANALYZER CO.) with a
1-mm holed screen.
All samples were analyzed for total N using a
modified micro-Kjeldahl method in conjunction with a block digester
(Nelson and Sommers, 1973).
The following morphological and physiological measurements were
made:
Designation
1)
NSha
NS
Ntl
Nt2
Nt3
Plant available N (added plus residual):
a) Calculated on a hectare basis.
b) Per plant basis (g/plant).
2) Total aerial plant N (g/plant) sampled at:
a) Panicle initiation - whole plant.
b) 50% anthesis - leaves, stem plus sheaths and
panicles.
c) Physiological maturity - leaves, stems plus
sheaths, glume, rachis and grain.
2
3)
LAI
LA2
LA3
Functional (non-senesced) leaf area of plant (cm )
measured at:
a) Panicle initiation.
b) 50% anthesis.
c) Physiological maturity.
16
4)
Aerial biomass of plant (grams) measured at:
a) Panicle initiation.
b) 50% anthesis.
c) Physiological maturity.
5)
Days from planting to:
a) Panicle initiation.
b) 50% anthesis.
c) Physiological maturity.
Ng
6)
Nitrogen in the grain (g/plant).
Nuta
7)
N taken-up after anthesis (Nt3 - Nt2).
GNC
8)
Grain N concentration, (mg/g).
HI
9)
Harvest Index--grain weight (g/plant), divided by
total aerial biomass at maturity.
LAR
10)
Leaf area reduction--functional leaf area at
anthesis minus functional leaf area at maturity.
%LAR
11)
K/P
12)
Percent leaf area reduction--LAR divided by LA2 and
the quoient multiplied by 100.
Number of kernels per panicle.
wtlOO
13)
Weight per 100 kernels.
14)
Grain yield adjusted to 13% moisture:
a) Per plant basis (g/plant),
b) Per 4.0 meter row, expressed as kg/ha.
BMl
BM2
BM3
Dl
D2
D3
Gw
Gwha
In conjunction with and in addition to these measurements, compounded calculations were made for:
Designation
Nt3/NS
1)
The ratio of total aerial plant N at maturity
(g/plant), divided by N supply (g/plant),
multiplied by 100, "aerial uptake efficiency."
Gw/Nt3
2)
The ratio of grain weight (g/plant), divided by
total aerial plant N at maturity (g/plant),
"metabolic N-use efficiency."
Ng/Nt3
3)
The ratio of N in grain (g/plant), divided by
total aerial plant N at maturity (g/plant),
multiplied by 100, "N-translocation efficiency."
17
Gw/NS
4)
The ratio of grain weight (g/plant), divided by N
supply per plant (g/plant), "N-use efficiency."
Ng/Nuta
5) The ratio of N in the grain (g/plant), divided by
N uptake after anthesis (g/plant), "post anthesis
N-uptake efficiency."
Gw/Ng
6)
The ratio of grain weight (g/plant), divided by N
in the grain (g/plant), "grain metabolic N-use
efficiency."
Nuta/Nt3
7)
The ratio of N taken-up after anthesis (g/plant),
divided by total aerial plant N at maturity
(g/plant), multiplied by 100, "post anthesis
N-uptake contribution."
Greenhouse Experiment
The aforementioned sorghum genotypes were grown hydroponically in
a greenhouse in 12-liter white opaque plastic pots. Seed from each
genotype were sprouted in a controlled environment seed germinator in
paper towels. After four days the seedlings were transferred to a
darkened elongation chamber for several days and then placed four to a
pot in the greenhouse in a randomized complete block design.
tables were employed to support the pots.
Two
Each table contained two
blocks in which each genotype at each N rate appeared once.
The pots contained a modified Hoagland's solution (Hoagland and
Arnon, 1950), that supplied all plant essential nutrients except
nitrogen which was added at a ratio of 5:1, N0^"-N to NH. -N in the
form of potassium nitrate and ammonium nitrate. Table 1.
This ratio
was choosen because some NH- -N is always present in most agricultural
soils and will influence plant growth and metabolism.
rates were: 100, 200, 400, 600, and 800 mg N/pot.
The five N
The solutions were
aerated continuously through the use of an air compressor with
18
Table 1. Composition of Nutrient Solution Used in Greenhouse Experi
ment. Each Experimental Unit Consisted of Four Sorghum
Plants Grown in 10.5 Liters of Solution with N Added as
100, 200, 400, 600, and 800 mg N/pot.
Modified Hoagland's Solution
Compound
CaCl^
KCl
MgS0^-7H20
KH^PO^
Iron chelate**
MnCl2*4H20
*
Amount (mg/1)
Element
Amount (mg/1)
258.43
Ca
93.33
65.04
K
56.87
286.83
Mg
28.30
79.22
P
18.03
S
37.39
59.37
Fe
2.97
1.18
Mn
0.33
CI
196.45
H3BO3
2.94
B
0.51
ZnSO^
0.43
Zn
0.10
CuS0^*5H20
0.11
Cu
0.03
NaMo0g-2H20
0.07
Mo
0.03
Additional K was added as KNO3 with NH- NO3 in the 5:1,
(N03'-N to NH^ -N), mixture.
** Iron chelate derived from hydroxyethlyenediaminetriacetate
(HEDTA) 5% elemental iron
19
individual lines supplied to each pot.
Solution pH was monitored
daily and maintained at 6.0 - 6.5 with either IN sulfuric acid or IN
sodium hydroxide to prevent any iron deficiency symptoms.
Solution
volumes were maintained by additon of nutrient solution without added
nitrogen.
Plants were harvested at approximately 35 days after transfer to
the greenhouse at which time N-deficiency symptoms were evident on
plants grown at lower N rates. The plants were separated into shoots
(leaves and stems) and roots. Harvested samples were dried, weighed,
ground, and analyzed in a manner similar to field samples.
Sample Digestion Procedure
Pretreatment
Dried ground plant material (0,5g) was wrapped in tissue paper
and placed into 250-ml pyrex digestion tubes.
A reference sample, a
blank, a KNO3 spike to check reduction, and a repeat sample were
included per digestion of twenty samples.
Twenty milliliters of a
salicylic acid-sulfuric acid mixture were added, mixed thoroughly, and
allowed to stand overnight at room temperatue.
(2.5g) was then added and mixed.
Sodium thiosulfate
The tubes were cautiously heated in
an aluminum heating block (Technicon BD-20) at 150°C until frothing
ceased.
The tubes were removed from the block and allowed to cool to
room temperature.
This pretreatment, which allows recovery of NO^
and NO3", described by Bremner (1965), converts nitrate to
-2
5-nitrosalicylic acid and S^O^
reduces the nitrogen compound to
20
the corresponding amino compound. Because water has been shown to
interfere with the nitration reaction (Nelson and Sommers, 1973), the
KNO3 spike which was added as a liquid was oven-dried before addition
of the salicylic-sulfuric acid mixture.
Digestion
After cooling, 5.5 grams of salt catalyst mixture--CuS0,'5H20
combined at a rate of 10% w/w with K2S0^--was added along with two
Hengar selenized boiling stones per tube.
The salt addition (K^SO.)
promotes an increase in digestion temperature, ca 40 °C to insure
recovery of N compounds which do not readily decompose at the boiling
point of HpSO- and also reduces total digestion time.
The addition of
copper in the form of CuS0,*5H„0, in conjunction with selenium in the
form of selenized Hengar granules, at the rate of 1% w/w of the amount
of KpSO-, increases the rate of oxidation of organic matter and the
conversion of organic N to ammonium by H^SO,.
The rack of tubes was
then returned to the preheated block set at 400 °C and digested for
two hours beyond the time of clearing, which was ca 45 minutes.
Cooling and Dilution
When the digestions were completed, the rack of tubes was removed
from the block and cooled 10-15 minutes followed by rapid introduction
of 50 ml of deionized H2O.
The contents were mixed thoroughly to
prevent precipitation of salts, allowed to cool to room temperature,
and diluted to 250-ml volume.
21
Analysis of Total N
A 15-ml aliquot of the diluted digestate was analyzed on a
Technicon Autoanalyzer II using industrial method no. 696-82WC, "Total
Kjeldahl Nitrogen" (Anonymous, 1983b).
Total Kjeldahl N is defined as
the sum of free ammonia and organic N compounds which are converted to
(NH^)2S0^ under the conditions of digestion.
For these analyses,
however, the nitrate-nitrite fraction was reduced and included with
the Kjeldahl N and shall be referred to at "Total Nitrogen."
In the Technicon procedure, N is determined colorimetrically
through the development of emerald-green color initiated by the
reaction of ammonia, sodium salicylate, sodium nitroprusside, and
sodium hypochlorite (a chlorine source) in a buffered alkaline medium
at a pH of 12.8-13.0.
Sodium nitroprusside, which increases the
intensity of the color formed, is added to obtain the necessary
sensitivity for measurement of low level N.
solution neutralizes the sample.
The sodium hypochlorite
Absorbance units of the
ammonia-salicylate complex was read at the 660 nanometer wavelength.
Statistical Analysis
The Statistical Analysis Systems (SAS Institute Inc., 1982)
version 4.10 was used for all statistical analyses. Treatment effects
were tested for all observed parameters using the General Linear Model
procedure and genotypes were compared with Duncan's Multiple Range
Test at the 5% significance level.
Pearson correlation coefficients
were calculated for parameters paired in all possible combinations.
Multiple linear and stepwise regressions were utilized to analyze the
22
relationship among traits with genotype means for Gw, Gw/Ns, and Ng as
the dependent variables and genotype means for all other parameters as
the independent variables in the stepwise procedure.
CHAPTER IV
RESULTS AND DISCUSSION
Field Experiment
This experiment was conducted to evaluate morphological and
physiological differences among sorghum genotypes and their
relationships to N utilization grown under high and low N nutrition
regimes for two consecutive years.
Analysis of variance revealed significant (P=0.05) differences
among the four genotypes for grain yield in 1983 and 1984, Table 2,
with their relative ranking remaining similar across years.
It is
interesting to note that although 77CS1 yielded relatively well under
low N it failed to respond to the addition of nitrogen in 1983 as it
did in 1984. This eludes to the possibility that sorghum genotypes
vary not only in their ability to uptake and remobilize nitrogen, but
also in their ability to respond to additions of this nutrient.
This
response may be interrelated with environmental factors as the
analysis of variance showed a significant year X genotype interaction for grain yield as well as most all other measured parameters.
When the genotypes were evaluated on a per plant basis, variability was also evident for grain weight, uptake components, and N in
the grain. Table 3.
The uptake components include only the aerial
portion of the plants and exclude an additional amount of N that will
be found in the roots.
Nitrogen uptake after anthesis was calculated
as the total N in the plant at maturity minus the total N in the plant
at 50% anthesis.
Because this measurement was based on destructive
23
24
Table 2. Mean Performance of Genotypes for Grain Yield.
GRAIN YIELD
Genotype
Low - N
1983
*
(kg/ha)
High - N
1984
1983
1984
8BH6956
3808 ab*
3878 a
6957 a
6940 a
SC630-11E
3900 ab
3900 a
6839 a
6892 a
77CS1
4166 a
3692 ab
5514 b
6643 a
SC325-12
3491 b
3005 b
5059 b
4498 b
Means in the same columns followed by the same letter do not differ significantly according to Duncan's multiple range test
(P=0.05).
25
Table 3.
Mean Performance of Genotypes for Grain Yield and N Accumu
lations (Per Plant Basis).
N
Applied
&
Genotype
Residual
(Ns)
Grain
Weight
(Gw)
Total
N Uptake
at
Maturity
(Nt3)
N
Uptake
at 50%
Anthesis
(Nt2)
N
Uptake
After
Anthesis
(Nuta)
Grain
N
(Ng)
.^4.
y/p 1 an u
1983 (High N)
SC325-12
SC630-11E
8BH6956
77CS1
1.96b*
2.84a
2.57a
2.95a
41.42d
85.52a
73.35b
57.51c
1.02c
2.37a
1.81b
1.87b
0.52b
1.42a
1.32a
1.55a
0.50b
0.95a
0.50b
0.32b
0.70d
1.44a
1.24b
1.06c
1.98b
2.91a
1.77b
2.46a
37.26c
81.82a
63.18b
73.48ab
0.97c
2.07a
1.56b
1.91a
0.87c
1.58a
1.14b
1.51a
0.16a
0.49a
0.42a
0.40a
0.61c
1.28a
1.04b
l.22ab
0.57c
0.80a
0.79ab
0.70b
31.07c
51.79a
40.99b
48.49a
0.53c
1.03a
0.75b
0.94a
0.39b
0.75a
0.69a
0.83a
0.14ab
0.28a
0.06b
O.llab
0.36c
0.66a
0.47b
0.62a
0.35b
0.28c
0.49a
0.37b
31.62c
46.72ab
51.84a
39.00bc
0.51b
0.76a
0.81a
0.56b
0.39c
0.56b
0.71a
0.54b
0.12a
0.18a
0.10a
0.02a
0.35b
0.51a
0.55a
0.32b
1984 (High N)
SC325-12
SC630-11E
8BH6956
77CS1
1983 (Low N)
SC325-12
SC630-11E
8BH6956
77CS1
1984 (Low N)
SC325-12
SC630-11E
8BH6956
77CS1
Means in the same column and group followed by the same letter do
not differ significantly according to Duncan's Multiple Range Test
(P=0.05).
26
is at different morphological stages on different plants, discretion
should be used in its interpretation.
Nitrogen supply was calculated
as the sum of applied N fertilizer and residual N03"-N found in soil
samples taken to a depth of 90 cm prior to planting.
This figure was
divided by the final plant population to determine grams of N
available per plant.
An estimated additional 14 kg of N/ha were
mineralized and made available throughout the growing season, but not
included in the calculations.
Grain weight (Gw) when calculated on a per plant basis, revealed
a ranking slightly dissimilar to grain yield derived from the per
hectare calculations.
This discrepency was attributed to differences
in plant populations and tillering.
SC630-11E exhibited little
propensity for tillering, maintaining its original thinned population
through maturity.
SC325-12, 8BH6956, and 77CS1, however, all tillered
to some degree making the per hectare yield somewhat variable with
respect to the number of heads harvested.
The genotype 77CS1
germinated poorly both years but tillered profusely, perhaps in an
effort to compensate for its original thin stand.
All per plant
measurements were made on main plants that did not have tillers and
that visually represented the average plant in an average population
setting.
Genotype performances for N-efficiency components are listed in
Table 4.
Grain weight produced per unit of N supplied to the plant
(Gw/Ns) reflects efficiency of N in its role in grain production.
Under high N conditions, lines 8BH6956 and SC630-11E produced
significantly more grain dry matter per unit N supply than lines 77CS1
27
Table 4. Mean Performance of Genotypes for N-Use Efficiency and
Related Components at Both High and Low N Rates.
Nt3/Ns
Gw/Nt3
Ng/Nt3
Nuta/Nt3
Gw/Ng
28.49ab**
30.14a
19.47c
23.10bc
73.13ab
84.42a
63.53b
57.70c
39.78a
36.10b
30.69c
41.22a
68.60a
60.83b
56.62c
68.76a
27.43bc
40.10ab
17.29c
47.17a
59.01a
59.35a
54.20b
59.00a
35.73a
28.10b
29.84ab
18.81c
88.02a
70.96a
77.64a
49.19b
40.55a
39.62a
38.47a
38.25a
66.62a
62.13b
63.98ab
62.83b
26.64a
23.73a
20.79a
16.02a
60.87a
63.77a
60.13a
60.88a
129.13a
134.43a
94.30b
93.16b
50.14b
51.53b
54.65ab
58.51a
64.28b
65.57b
63.62b
68.55a
27.11a
11.90a
7.65a
25.80a
78.00a
78.59a
86.48a
85.36a
270.00a
155.35b
164.90b
146.57b
61.80b
69.64a
64.00ab
61.64b
67.04a
69.65a
68.32a
68.23a
23.94a
4.29a
11.76a
23.78a
92.15ab
99.74a
93.91ab
90.34b
Genotype*
Gw/Ns
1983 (High 11
8BH6956
SC630-11E
77CS1
SC325-12
1984 (High 11
8BH6956
SC630-11E
77CS1
SC325-12
1983 (Low
NL
SC630-11E
77CS1
8BH6956
SC325-12
64.89ab
68.86a
52.81b
54-92ab
1984 (Low N)
SC630-11E
77CS1
8BH6956
SC325-12
*
166.32a
106.44b
108.64b
91.47b
Genotypes ranked in order by Gw/Ns averaged over both years.
** Means in the same column and group followed by the same letter do
not differ significantly according to Duncan's multiple range test
(P=0.05).
28
and SC325-12 on a two year average.
Under low N conditions,
variability existed from year to year for Gw/Ns due to a pronounced
reduction in 1984 of the residual N in the soil prior to planting.
The removal of the 1983 crop's stover probably contributed to the
reduction.
With a reduced amount of N made available to the genotypes, i.e.,
grown under a low N regime, they became more efficient in their
utilization.
decreased.
However, N concentration and total grain N (g/plant)
Because graded fertilizer rates were not incorporated into
this experiment, no relationship between N-utilization efficiency and
grain N concentration could be established.
Maintaining high N concentration and high yield levels in
harvested plant material while reducing N inputs or increasing
responses to additions of N are the goals of a N-use efficiency
program.
The use of grain nitrogen concentration (GNC), as a
multipliable component along with the N-use efficiency component
(Gw/Ns) is considered in Table 5.
This adjustment was made in order
to compensate for the reduction of grain N concentration (GNC) with
the improvement in N-use efficiency (Gw/Ns) under low N conditions.
However, this did not radically change the ranking of the genotypes.
Line SC630-11E maintained its dominance especially under low N
fertility.
Mean dry matter and N concentrations of plant components at
panicle initiation, anthesis, and maturity are listed in Tables 6 thru
9.
Because SC325-12
was the earliest maturing genotype, it produced
less dry matter at all stages through to maturity.
SC325-12 also
29
Table 5.
Nitrogen Use Efficiency (Gw/Ns) Adjusted Using Grain N
Concentration (GNC).
(Gw/Ns)(GNC)
Genotype
*
High N
Low N
1983
1984
1983
1984
SC630-11E
51.6a*
44.0b
83.5a
183.6a
8BH6956
49.2ab
58.6a
61.4b
117.2b
77CS1
36.3c
50.4ab
88.5a
108.2b
SC325-12
39.7bc
30.9c
64.4b
100.lb
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple range test (P=0.05).
30
Table 6.
Mean Dry Matter and N Concentrations at Panicle Initiation and Anthesis in Vegetative and Reproductive Tissues
of Genotypes at High N Regimes for 1983 and 1984.
Panicle Initiation
Anthesis
Total Above-Ground Plant
1983
1984
Dry Matter
SC325-12
Leaf
1983
Culm, Sheath, Panicle
1984
g/plant
3.46d* 12.97d
1983
1984
-
•
7.55c
11.90c
20.86b
33.50c
SC630-11E 18.45c
36.94a
24.88b
25.38b
57.04a
66.17a
8BH6956
26.13b
32.53b
31.30a
26.31b
55.77a
52.90b
77CS1
34.65a
25.27c
32.67a
31.08a
66.08a
65.46a
N Concentration
— - g/lOOg DW
-
•
SC325-12
3.41a
2.80a
2.84a
2.74a
1.45a
l-47a
SC630-11E
2.86b
2.46b
2.53b
2.61a
1.38a
1.41ab
8BH6956
2.51bc
2.09c
2.12d
2.04b
1.17b
1.15c
77CS1
2.28c
2.19c
2.30c
2.11b
1.21b
1.31b
*
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple Range Test (P=0.05).
31
Table 7.
Mean Dry Matter and N Concentrations at Panicle Initiation and Anthesis in Vegetative and Reproductive Tissues
of Genotypes at Low N Regimes for 1983 and 1984.
Panicle Initiation
Anthesis
Total Above-Ground Plant
1983
1984
1983
Dry Matter
SC325-12
Culm, Sheath, Panicle
Leaf
1984
1983
1984
27.67b
g/plant --•
3.21c* 11.15c
8.98c
10.67c
25.43c
SC630-11E 16.27b
26.62b
23.80b
17.09b
58.75ab 46.92a
8BH6956
19.95b
35.12a
28.30b
28.49a
51.29b
53.39a
77CS1
34.65a
39.00a
33.18a
20.58b
64.80a
45.93a
N Concentration
—
g/lOOg DW •
SC325-12
2.50a*
1.66a
1.85a
1.57b
0.90b
0.81a
SC630-11E
1.89b
1.28b
1.65b
1.93a
0.61c
0.67b
8BH6956
1.53c
1.03c
1.20c
1.13c
1.15a
0.73ab
77CS1
1.31d
0.90c
1.30bc
1.15c
0.61c
0.65b
*
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple Range Test (P=0.05).
32
Table 8.
Mean Dry Matter and N Concentrations at Maturity in
Vegetative and Reproductive Tissues of Genotypes at
High N Regimes for 1983 and 1984.
Maturity
Leaf
1983
Culm, Sheath, Glume, Rachis
1984
Dry Matter
SC325-12
1983
1984
Grain
1983
1984
•-- g/plant
9.01c*
9.57c
25.77c
27.86d
41.42d
37.26c
SC630-11E 27.33b
21.95b
76.64a
65.43a
85.82a
81.82a
8BH6956
31.73a
26.29a
52.22b
46.58c
73.35b
63.18b
77CS1
28.35ab 28.13a
59.01b
55.00b
57.51c
73.48ab
N Concentration
• g/lOOg DW —•
SC325-12
1.75a
1.94a
0.62a
0.65a
1.67b
1.65a
SC630-11E
1.71a
1.93a
0.60a
0.55b
I.69b
1.57a
8BH6956
1.09c
1.18c
0.51b
0.45c
1.70b
1.64a
77CS1
1.51b
1.37b
0.64a
0.55b
1.85a
1.66a
*
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple Range Test (P=0.05).
33
Table 9. Mean Dry Matter and N Concentrations at Maturity in
Vegetative and Reproductive Tissues of Genotypes at
Low N Regimes for 1983 and 1984.
Maturity
Leaf
1983
Culm, Sheath, Glume, Rachis
1984
Dry Matter
SC325-12
1983
1984
Grain
1983
1984
•-- g/plant
8.70b* 9.91c
24.26d
24-76C
31.07c
31.62c
SC630-11E 22.84a
17.46b
64.77a
49.89a
51.79a
46.72ab
8BH6956
25.58a
25.71a
40.81c
42.13b
40.99b
51.84a
77CS1
24.97a
18.61b
52.61b
37.87b
48.49ab 39.00b
N Concentration
• g/lOOg DW — •
SC325-12
0.84a
0.87a
0.38a
0.32a
1.17a
SC630-11E
0.67b
0.64b
0.31b
0.27ab
1.29a
l.OBab
8BH6956
0.50c
0.54c
0.35a
0.29a
1.19a
1.08ab
77CS1
0.67b
0.49c
0.29b
0.21b
1.28a
*
1.14a
1.00b
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple Range Test (P=0.05).
34
exhibited a higher concentration of N in plant components at panicle
initiation and anthesis at both high and low fertility regimes.
At
physiological maturity however, the other three lines approached or
surpassed SC325-12 in grain N concentrations.
Variability of morphological and physiological parameters across
all genotypes and years is presented in Table 10. Under high N
conditions, ranges are somewhat higher for harvest index however lower
for N-harvest index or N-translocation efficiency (Ng/Nt3).
This
would explain partly why all lines became more efficient under low N
conditions.
Vegetative tissue became a better exporter of N to
reproductive tissue.
Total plant N, biomass, and N in the grain were strongly
correlated (r), with grain weight as well as each other. Table 11.
Because biomass can be measured more easily than total plant N or
grain N this parameter may be useful in attempts at increasing the
amount of harvested grain N, rather than trying to increase grain N
concentrations per se.
Generally biomass production will be
influenced by crop growth duration.
Prolongation (non senescence) of functional leaf area and N
uptake during grain filling have also been considered for increasing
grain N content in sorghum (Rao and Venkateswarlu, 1974).
Percent
leaf area reduction [(LA2-LA3)/LA2]100 correlated in Table 12,
indicates that a reduction in leaf area, "senescence" may be
detrimental to total N uptake after anthesis especially under high N
fertilization.
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37
Table 12.
Linear Correlation (r) of % Leaf Area Reduction
[(LA2-LA3)/LA2]100 to Other Parameters for Both
High and Low N Rates Across Years.
% Leaf Area Reduction (% LAR)
vs.
High N
Low N
1.
Total Above-ground N at
maturity (Nt3), g/pt
-0.13
0.17
2.
Nitrogen in the grain
(Ng) g/pt
-0.11
0.22
3.
Grain wt./N in the grain
(Gw/Ng)
0.10
0.47
4.
Grain wt./N
(Gw/Ns)
0.08
0.41
5.
Grain Yield
(Gw), g/pt
-0.09
0.45
6.
Biomass at Maturity
(BM3)
-0.06
0.44
7.
Grain N Concentration
(GNC)
-0.06
-0.46
8.
N uptake after anthesis
(Nuta)
-0.77*
-0.50
*
P > 0.05
supply
** P > 0.01
*** P > 0.001
38
Under low N conditions a greater amount of lower leaf senescence
occurred from anthesis through maturity.
Overall senescence with N
regimes generally followed a pattern that paralleled the length of
time required by the test genotypes to reach flowering and maturity.
The longer maturing lines had a greater amount of lower leaf
senescence.
Days to 50% anthesis and days to physiological maturity
were both highly correlated, (P > 0.001), to % leaf reduction, 0.86
and 0.84 respectively.
The contributions of pre-anthesis N uptake are presented in Table
13.
Pre-anthesis N uptake, was highly correlated with total above
ground N at maturity, grain yield, biomass at anthesis, N in the grain
and leaf area at anthesis when compared for both high and low N
regimes.
Regression analysis performed on pre-anthesis N uptake is
presented in Table 14. Under both high and low N conditions grain
weight per plant (Gw) and N in the grain (Ng) showed their dependence
upon pre-anthesis N assimilate.
By contrast, post-anthesis N uptake played a minor role when the
data were sorted by N rates. Table 15. Only percent leaf area
reduction at high N showed a significant correlation.
No significance was noted using N accumulation after anthesis as
the Independent variable in regression analysis when the data were
sorted by N rates. Table 16. Again due to the fact that post-anthesis
uptake was determined by subtracting from total N in the plant at
maturity, the total N in the plant at anthesis, these values may not
39
Table 13.
Linear Correlation (r) of N Accumulation at 50%
Anthesis (Nt2) to Other Parameters at Both High
and Low N Rates Across Years.
Nitrogen Accumulation
Before Anthesis (Nt2)
vs.
High N
Low N
Total Above-Ground N at
Maturity (Nt3), g/pt
0.89**
0.92**
Grain N Concentration
(GNC)
0.17
0.49
0.81**
0.88**
Biomass at Anthesis
(BM2)
0.98***
0.98***
Nitrogen in the Grain
(Ng), g/pt
0.84**
0.91**
Grain wt./N supply
(Gw/Ns)
0.39
-0.13
-0.46
-0.06
' Grain Yield
(Gw), g/pt
Grain wt./N in the grain
(Gw/Ng)
Leaf Area at Anthesis
(LA2)
* P > 0.05
** p > 0.01
0.85**
0.92**
*** p > 0.001
40
Table 14.
Linear Regression of N Accumulation Before Anthesis on
Grain Weight, Grain Weight/N Supply, and N in the Grain
by N Rates Across Years.
N Rate
Dependent Variable
Intercept
High N
Grain wt. (g/pt)
17.73
37.73
11.13
Grain wt./N Supply
(Gw/Ns)
18.90
6.14
5.91
0.39
0.29
0.63
0.17
0.84**
15.05
45.31
9.81
0.88**
108.10
-30.14
92.27
0.09
0.66
0.12
N in the Grain
Low N
Grain wt.
Grain wt./N Supply
N in the Grain
* P > 0.05
** P > 0.01
Slope
SE
(slope)
Corre1 at ion
r
0.81**
-0.13
0.91**
*** P > 0.001
41
Table 15. Linear Correlation (r) of N Accumulation After Anthesis
(Nt - Nb) to Other Parameters at Both High and Low N Rates
Across Years.
Nitrogen Accumulation
after Anthesis (Nt3 - Nt2)
vs.
High N
Low N
0.65
0.55
-0.05
0.56
Grain Yield (Gw), g/pt
0.67
0.36
Biomass at Maturity (BM3)
0.63
0.38
Nitrogen in the Grain
(Ng). g/pt
0.68
0.53
Grain wt./N Supply (Gw/Ns)
0.45
0.01
Grain wt./N in the Grain
(Gw/Ng)
0.05
-0.61
Leaf Area Reduction (LA2-LA3)
0.41
0.46
-0.77*
-0.50
Total Above-Ground N at Maturity
(Nt3), g/pt
brain N Concentration (GNC)
% Leaf Area Reduction from
Antheis to Maturity (%LAR)
*
P < 0.05
** P <: 0.01
*** P < 0.001
42
Table 16. Linear Regression of N Accumulation After Anthesis on
Grain Weight, Grain Weight/N Supply, and N in the Grain
by N Rates Across Years.
Intercept
Slope
SE
(slope)
Corre1 ation
r
N Rate
Dependent Variable
High N
Grain wt. (g/pt)
39.73
52.45
23.87
0.67
Grain wt./N Supply
20.84
12.06
9.65
0.45
0.67
0.86
0.38
0.68
Grain wt.
37.82
38.62
40.54
0.36
Grain wt./N Supply
89.03
5.45
193.36
0.11
0.39
0.80
0.51
0.53
(Gw/Ns)
N in the Grain
Low N
N in the Grain
* P < 0.05
** P < 0.01
*** P < 0.001
43
be as valid as the pre-anthesis values because two different plants
were Involved.
Linear regession analysis of total above-ground N accumulation at
maturity as the Independent variable is listed in Table 17.
Grain
weight and N in the grain are shown to be highly dependent on the
total N accumulation at maturity.
From an overall perspective it would appear that pre-anthesis N
accumulation plays a more Important role in grain weight and grain N
accumulation.
This assumption is based on the fact that across lines
a higher percentage of the total N is taken up before anthesis.
Pre-anthesis N uptake as a percent of total N uptake ranged from
67-81% (mean 72%) under high N conditions and 74-92% (mean 83%) under
low N conditions. Table 10. Within genotypes these ranges generally
followed the pattern that the more time needed to reach anthesis and
maturity and the greater the percent of leaf area lost from anthesis
to maturity, the greater the proportion of total N in the plant at
maturity taken up before flowering.
Line SC630-11E varies somewhat
from this pattern in that is reached anthesis and maturity in the
mid-range of the four genotypes yet it accumulated pre-anthesis N as
well as the longer maturing lines. Table 3.
Variation is also noted
from this pattern under high N conditions for percent leaf area
reduction.
Line SC630-11E maintained more of its functional green
leaf area that the earlier maturing line SC325-12.
Sink size, (kernel number per panicle and mass of kernels) and
its relation to agronomic and N-physiology traits is presented in
Tables 18 and 19.
The number of kernels per panicle, when sorted by
44
Table 17.
Linear Regression of Total Above-Ground N Accumulation at
Maturity on Grain Weight, Grain Weight/N Supply and N in
the Grain by N Rates Across Years.
N Rate
Dependent Variable
High N
Grain wt. (g/pt)
Grain wt./N Supply
(Gw/Ns)
N in the Grain
Low N
Grain wt.
Grain wt./N Supply
N in the Grain
* P < 0.05
Correlation
r
Intercept
Slope
SE
(slope)
5.76
34.41
4.89
0.94**
15.66
6.36
4.30
0.52
0.10
0.57
0.05
0.97 * *
13.91
39.11
7.82
0.90 * *
105.04
-20.81
78.57
0.04
0.61
0.02
** P < 0.01
-0.11
0.99**
*** P < 0.001
45
Table 18. Linear Correlation (r) of Number of Kernels per Panicle to
Other Parameters at Both High and Low N Rates Across Years.
High N
Low N
0.61
-0.12
0.67
0.54
Gw/Ng
0.32
-0.14
Nt3
0.50
0.48
Ng
0.64
0.47
Nuta (Nt3 - Nt2)
0.45
0.01
(Nt2)
0.37
0.56
GNC
-0.27
0.19
BM2
0.40
0.51
BM3
0.60
0.49
LA2
0.45
0.36
LA3
0.57
0.51
D2
0.11
0.29
D3
0.17
0.05
Number of Kernels Per Pan icle
vs.
Gw/Ns
Gw (g/pt)
* P < 0.05
** p <c 0.01
*** P < 0.001
46
Table 19. Linear Correlation (r) of Weight of 100 Grains (grams) to
Other Parameters at Both High and Low N Rates Across Years.
Weight of 100 Grains
vs.
Gw/Ns
Gw (g/pt)
Gw/Ng
High N
Low N
0.48
0.38
0.84**
0.55
0.03
-0.07
Nt3
0.90**
0.48
Ng
0.85**
0.52
0.51
0.28
0.85**
0.59
GNC
0.03
0.02
BM2
0.79*
0.48
BM3
0.87**
0.59
LA2
0.60
0.43
LA3
0.70*
D2
0.52
0.39
D3
0.67
0.58
Nuta (Nt3 - Nt2)
Nutb (Nt2)
* P < 0.05
** P > 0.01
-0.05
*** P > 0.001
47
fertilizer regime, revealed no significant correlation with other
variables measured.
However, a high but non-significant relationship
exists at the high N fertility level for N-use efficiency (Gw/Ns),
grain wt./plant, N in the grain, biomass and leaf area at maturity.
It is interesting to note that a relationship was not found with
number of kernels per panicle and the maturity variables, days to 50%
anthesis or days to maturity, within either N-fertility rate.
Weight
per 100 grains was significantly correlated with grain weight, total N
uptake at maturity (Nt3), before anthesis (Nt2) and in the grain,
biomass at anthesis and maturity, and leaf area at maturity. Table 19.
Mean genotype difference for number of kernels per panicle, weight per
one hundred kernels (seed mass) and "Harvest index," which is the
percent of total aerial biomass at maturity occupied by the grain is
listed in Table 20.
Many of the current yield gains made with grain sorghum have been
achieved with the simultaneous Increase in harvest index percentage.
The genotypes tested showed significant positive correlations between
Ng/Nt3, (nitrogen in the grain divided by total N in the aerial
portion of the plant at maturity), "Nitrogen harvest index," and
harvest index at both high and low N supplies. Table 11. Mean values
across genotypes were 63.8% for N-harvest index and 47.2% for harvest
index under high N conditions and 66.9% for N-harvest index and 42.0%
for harvest index under low N conditions.
This would Indicate that
across genotypes tested, they became more efficient at translocating N
to the grain when a scarcity existed for N and less efficient at dry
48
Table 20. Mean Performance of Genotypes for Yield Components.
Genotype
Number of
Kernels per
I^anicle
(K/P)
Weight per
100 kernels
(wtlOO)
(Grams)
"Harvest
Index"
(HI)
"Nitrogen
Harvest
Index"
(Ng/Nt3)
% Leaf Area
Reduction
(%LAR)
1983 (High N)
SC325-12
SC630-11E
8BH6956
77CS1
2120c*
2870b
3376a
2127c
1.95d
2.98a
2.17c
2.71b
54.58a
45.14b
46.62b
39.70c
68.76a
60.83b
68.60a
56.62c
6.88b
0.00c
27.08a
26.10a
2311b
2750a
2664ab
2426ab
1.61c
2.98a
2.38b
3.03a
49.88a
48.36ab
46.44b
46.92ab
62.83b
62.13b
66.62a
63.98ab
30.09b
23.84c
28.17bc
38.45a
1681c
2052b
2444a
1861bc
1.84b
2.52a
1.68b
2.60a
48.95a
37.16b
38.13b
38.45b
68.55a
64.28b
63.62b
65.57b
30.95d
42.13c
50.31b
62.08a
1748b
1851b
2565a
1501b
1.80c
2.52a
2.01b
2.59a
47.70a
40.96b
43.32b
41.05b
68.23a
67.06a
68.32a
69.82a
33.56c
56.43b
60.10b
77.85a
1984 (High N)
SC325-12
SC630-11E
8BH6956
77CS1
1983 (Low N)
SC325-12
SC630-11E
8BH6956
77CS1
1984 (Low N)
SC325-12
SC630-11E
8BH6956
77CS1
Means in the same column followed by the same letter do not differ
significantly according to Duncan's Multiple Range Test (P=0.05).
49
matter transfer.
Lines 8BH6956 and 77CS1 did not follow this pattern
both years in regard to N transfer to the grain.
A high but non-significant negative correlation was found under
high N conditions for harvest index with grain N concentration.
relationship surfaced for low N data.
No
This greater percent carbon
transfer did not result in a dilution of the grain N concentration
apparently due to the higher quantity of total N in the plant under
high N availability.
Nitrogen transfer to the grain Ng/Nt3, was
negatively correlated to grain N concentration under low fertility,
r=-0.77 (P > 0.05).
Harvest Index was also negatively correlated with
days to anthesis.
Stepwise regression analyses of genotype means for grain weight
(g/plant), N-use efficiency (Gw/Ns), and N in the grain as dependent
variables are listed in Tables 21 and 22.
Independent variables are
listed as the best one variable, best two variables model, etc.
the high N analysis with Gw as the dependent variable,
In
the
Independent variable N in the grain accounted for 97% of the
variablility in the best model.
With NUE (Gw/Ns) as the dependent
variable, a two variable model, uptake efficiency (Nt/Ns) and grain N
concentration accounted for 89% of the variability with N uptake after
anthesis improving the model slightly.
Biomass in the aerial portion
of plant at maturity showed its Influence on the dependent variable N
in the grain by accounting for 98% of the variability.
Under the low N-fertility regime, stepwise regression analysis
showed biomass at maturity the best one variable model for the
dependent variable grain weight (g/plant).
Harvest index helped to
50
Table 21.
Stepwise Linear Regression Analysis of Genotype Means for
Grain Weight, Grain Weight/N supply and N in the Grain for
High N Rate Over Years.
Dependent
Variable
Independent
Variable
Constant
in Best Model
Grain Weight
(Gw) g/pt
Grain Weignt/
Ng
Gw/Ng,Ng
Nt3/Ns
Regression Coefficients
bl
b2
b3
b4
-1.33
60.93
-67.09
1.12
1.59
0.26
67.42
0.28
0.97
60.14
Nt3/Ns,GNC
(Gw/Ns)
Nt3/Ns,Nuta,
GNC
70.48
0.38 -10.85
Nt3/Ns,Gw/Ng,
Nuta,GNC
341.87
0.41
BM3
0.13
0.01
-0.38
0.01
(Ng) g/pt
H.I.,BM3
0.99
0.61
N Supply
N in the Grain
R for
Equation
-6.48
0.89
-7.20
0.97
-2.34 -12.49 -19.96
0.99
0.98
0.01
0.99
51
Table 22.
Stepwise Linear Regression Analysis of Genotype Means for
Grain Weight, Grain Weight/N supply and N in the Grain for
Low N Rate Over Years.
Dependent
Variable
Grain Weight
(Gw) g/pt
Independent
Variable
Constant
in Best Model
BM3
N in the
Grain
(Ng) g/pt
2
R for
Equation
11.66
0.30
H.I.,BM3
-38.81
0.89
0.42
H.I.,BM3,D2
-49.84
0.97
0.41
0.25
0.22
-151.86
0.19
1.85
0.98
Nt3/Ns,Gw/Ng,
Nt3/(Nt3/Ns)-222.93
0.22
2.32 9511.93
0.99
Nt3
0.61
Grain weight/ Nt3/Ns
N Supply
(Gw/Ns)
Regression Coefficients
bl
b2
b3
b4
Nt3/Ns,
Gw/Ng
0.04
0.93
0.98
O.IO
0.99
0.86
0.99
52
Improve the model.
N-use efficiency (Gw/Ns) was influenced primarily
by uptake efficiency (Nt3/Ns) and also by the variable grain weight
divided by N in the grain (Gw/Ng).
With N in the grain as the
dependent variable, total N in the plant at maturity (Nt3) accounted
for 99% of the variability.
Greenhouse Experiment
A greenhouse experiment was conducted with the same four lines
that were grown under field conditions in an attempt to compare them
for N-use efficiency and to evaluate the role of roots in the N
economy of the plant at a vegetative stage. The genotypes were grown
hydroponically, four plants per pot, so N availability could be easily
controlled.
The five N treatments of 100 to 800-mg N per pot or 25 to
200-mg N per plant was supplied at the start of the experiment.
This
range of low "growth limiting" supply to more than adequate supply was
provided at a 5:1 ratio of nitrate-N to ammonium-N because plant
growth is often Improved when both forms of N are made available.
The lines were first evaluated across all N treatments for
milligrams of dry matter produced per milligrams of N found in the
plant.
As with the field experiment, metabolic efficiency Improved
with decreasing amounts of N made available to the plant. Table 23.
Total dry matter and N concentration Increased.
The variation in dry matter produced at different N levels is
illustrated in Figure 1.
Line SC630-11E showed a steady increase in
dry matter production with no indication of leveling off at the high N
rate.
Nitrogen concentrations (mg N/gram of tissue) in shoot and
53
Table 23.
N Treatment
mg N/Pot
Mean Performance Across Genotypes Grown in Greenhouse at
Different Nitrogen Rates.
mg Dry Matter/
mg N in Tissue
Dry Matter
Production
N Concentration
mg/g
Roots
Shoots
Total
Roots
Shoots
100
243.83
4.68
11.68
16.35
8.42
8.40
200
214.57
6.43
17.38
23.80
9.24
10.09
400
152.54
7.48
21.68
29.50
12.03
15.19
600
114.81
7.83
22.90
30.73
16.03
20.04
800
104.18
8.13
25.90
34.10
18.40
24.77
54
50T
/
+
¥:
X
o
45--
SC325-12
SC630-11E
8BH6956
77CS1
/
/
/
to
E
ro
SCT)
<
I—
o
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 1. Total Dry Matter Produced at Various N Levels.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
55
roots at various N input levels are shown in Figures 2 and 3.
Shoot N
concentrations showed some significant differences at the 200 and 600
mg-N levels whereas roots varied only slightly at the 200-mg level.
The N concentration in both roots and shoots fall off with line
SC630-11E after 600 mg of N probably because of a greater dilution
with additional dry matter.
With Increasing N additions from 100-mg per pot to 800-mg per
pot, shoot N concentration Increased an average of 297%. SC630-11E
fell below this average at 218%. Root N concentration increased an
average 234% with SC630-11E Increasing only 178%. The lesser N
concentration Increases again can probably be attributed to dilution
with greater dry matter accumulation.
Total N (N concentration X dry weight) also increased with N
additions.
Significant differences (P=0.05) were observed at the
200-mg N level with an evident Inverse relationship between shoot and
root concentrations, Table 24. Root total N differences also appear
at the 400 and 600-mg level. The sum of total shoot and root N was
compared against the amount of N added in the five N treatments to
obtain percent recovery from solution. Figure 4. The resulting
recovery average of all lines was more than 100% for the three lowest
N-solution rates and less than 100% for the two highest N-solution
rate levels. Table 24, indicating some error in the N-concentrat1on
data.
The ratios of shoot total N to root total N and shoot N
concentration to root N concentration are displayed in Figures 5 and
6.
Both total shoot N and shoot N concentration Increased against
56
30T
+ SC325-12
^ SC630-11E
X 8BH6956
25"
cn
cn
o 77CS1
20--
oo
I—
o
o
zcz
oo
o
15"
10"
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 2.
Nitrogen Concentration of Shoots at Various N Levels.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
57
25T
+ SC325-12
^SC630-11E
X 8BH6956
o 77CS1
20-
CD
CD
E
oo
t—
o
o
15"
e_)
:2Z
o
C_)
10"
54
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 3.
Nitrogen Concentration o f Roots at Various N Levels.
Values w i t h i n the same column followed 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 at the 0.05 level of p r o b a b i l i t y .
58
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cn
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cn
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cn
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59
140T
+ SC325-12
¥: SC630-11E
130"
X
8BH6956
o
77CS1
120"
Q
<:
a:.
1 10"
o
LU
100"
90"
80
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 4. Recovery of Added Solution N.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
60
5.5T
5.0"
•e^^
-0'
-
/
o
o
4.5"
I—
o
4.0"
o
o
31
OO
3.5"
<:
I—
o
hU-
o
CD
3.0"
<
cc
2.5"
2.0
0
100
200
300
400
500
600
-f-
SC325-12
¥:
SC630-11E
X
8BH6956
o
77CS1
700
800
900
MG N/POT
Figure 5. Ratio of Shoot Total N to Root Total N at Various N
Levels.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
61
1.6T
1.5"
C_5
O
C_)
1.4 -
O
O
az
1.3"
C_)
o
C_)
1.2"
o
o
zr.
oo
o
o
1. 1 "
•a:
az
+ SC325-12
¥: SC630-11E
1.0"
X 8BH6956
o 77CS1
.9
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 6. Ratio of Shoot to Root N Concentrations at Various N
Levels.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
A
I
62
total root N and root N concentration as the solution N rate Increased
Indicating an improvement in translocation efficiency.
Significant
differences existed among the lines for their ratio of shoot to root
total N at the 200, 400 and 600-mg N solution levels. Line 77CS1
showed a propensity for maintaining a significantly higher proportion
of its total N in shoot material at the three N solution levels.
At
levels 400, 600, and 800-mg added N it maintained a ratio of
approximately 5:1.
Shoot N concentration to root N concentration also
varied with the lines across the solution N levels. Once again line
77CS1 maintained a higher N concentration in shoot material in
relation to root material.
However, after the 400-mg N level this
ratio diminished in line 77CS1 as if the shoot portion increased
disporprotionally to the roots in dry matter.
Dry matter production when viewed as shoot dry matter and root
dry matter production also produced variability between the lines at
the various N rates. Figures 7 and 8.
A greater variablity was noted
In root materials at the different N input levels than in shoot
material.
These differences along with the N concentration and total
N shoot to root ratio differences elude to a major drawback of
screening genotypes for N-use efficiency in the field where only the
aerial portion of the plant is evaluated.
Variablility between
genotypes for root N content could obscure their actual N requirements
and, therefore, obscure their true ability to use N efficiently.
Nitrogen use efficiency (mg dry matter produced/mg N in the
tissue) is Illustrated in Figure 9.
The total dry weight of the
shoots In milligrams was added to the total dry weight of the roots in
63
40T
+ SC325-12
^SC630-11E
35 -
X8BH6956
/
o 77CS1
/
/
30"
/
/
to
E
ro
iCT)
25 •
o
o
3:
oo
20 -
15 •
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 7. Shoot Dry Matter Production at Various N Levels
Values within the same column followed by the same letter arp nnt
significantly different at the 0.05 level of probability.
64
12.5T
/
+ SC325-12
11.5"
/
¥: SC630-11E
/
X 8BH6956
o
10.5"
/
77CS1
/
9.5"
to
E
ro
as
o
o
8.5"
7.5"
Q:
6.5"
5.5"
4.5"
3.54
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 8. Root Dry Matter Production at Various N Levels.
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
Bs
65
130T
+ SC325-12
120"
¥: SC630-11E
X 8BH6956
1 10"
o 77CS1
100"
e3
90
az
LU
80"
>-
oz
CD
70
t-D
60"
50"
40"
30
0
100
200
300
400
500
600
700
800
900
MG N/POT
Figure 9. Nitrogen Use Efficiency (mg Dry Matter Produced per
mg N in Tissue).
Values within the same column followed by the same letter are not
significantly different at the 0.05 level of probability.
Kv
66
milligrams.
This sum was then divided by the sum of total shoot N
(shoot dry weight X shoot N concentration) and total root N (root dry
weight X root N concentration). Differences were noted at the 200-mg,
600-mg, and 800-mg N solution rates, decreasing with increasing N
rate.
i_..^is^is'
CHAPTER V
SUMMARY AND CONCLUSIONS
The efficiency of N utilization by grain sorghum [Sorghum bicolor
(L.) Moench] and its relationship to selected morphological and
physiological parameters were evaluated for two consecutive years in a
field environment.
A greenhouse experiment was also conducted to
evaluate responses with the same material grown hydroponically.
Under field conditions all of the four test lines became more
efficient in N use (Gw/Ns) when grown under low N conditions.
However, grain N concentration and total grain N decreased.
When
evaluated under high N fertilization, uptake efficiency (Nt3/Ns) was
positively correlated with total N in the plant at maturity, N in the
grain, leaf area at maturity, and biomass at maturity.
The low N
evaluation revealed a negative correlation between translocation
efficiency (Ng/Nt3) and total N in the aerial plant at maturity, N in
the grain and leaves at maturity.
Consistent with previous research (Alagarswany and Seethararma,
1982), the uptake component, N in the aerial portion of the plant at
maturity, was highly correlated with biomass in the aerial portion of
the plant at maturity.
However, the early maturing, small biomass
line SC325-12 which was the poorest yielder showed superior
translocation and harvest index under both high and low N regimes.
This would Indicate that high biomass alone would not insure selection
for the translocation component of the N-use efficiency equation.
Therefore, since harvest index correlated well with translocation
67
i^
68
efficiency (Ng/Nt) under both high and low N conditions, both high
biomass and high harvest index appear the best criteria to insure
efficient uptake and translocation In the selection process.
Significant year X genotype varability was present under both
high and low N rates for; weight/100 kernels, biomass and N
concentration of vegetative tissue at all growth stages, harvest
index, grain weight, N supply, N in the grain, N uptake at anthesis,
and the combined components Gw/Ns, Nt3/Ns, and Gw/Nt3.
Under high N
conditions, significant year X genotype variability was noted for;
number of kernels/panicle, and the compounded components Ng/Nt,
Nuta/Nt3, and Ng/Nuta.
Low N conditions revealed significant year X
genotype varibility for; N uptake at maturity (Nt3) and the combined
component Gw/Ng.
Grain N concentration was the only parameter
measured that showed no line variability.
year to year variability.
However, it showed strong
This information confirms the strong
Influence environment has on uptake, assimilation, translocation, and
deposition of N and dry matter.
Overall, the lines showed higher harvest index percentages under
high N conditions indicating a more efficient carbon transfer to the
grain.
Whereas, under low N a higher percent N transfer to the grain
as observed.
A negative correlation between harvest index and grain
weight was observed under low N conditions.
Nitrogen taken up prior to the 50% anthesis sampling appeared
more Important to total uptake at maturity than that taken up after
anthesis especially under low N availability.
Of the total aerial
plant N taken up by maturity, uptake by the lines at anthesis ranged
y"-^
69
from 67-81% under high N and 75-92% under low N conditions.
Regres-
sion analysis bore this out with highly significant correlations found
between pre-anthesis N uptake and N in the grain and N in the mature
plant under both high and low conditions.
Regression analyses of
post-anthesis N uptake showed no significanct relationship at either
high or low N availability for these variables, however, the
correlation was high with the high N rate.
Confounding these results
in the selection process is evidence that the more N taken up before
anthesis, the smaller the harvest index.
As the percentage of functional leaf area lost to senescence
after anthesis increased, the amount of N taken up after anthesis
decreased to the point of significance under the high N fertility
regime.
Under low N, this decrease was high but non-significant.
An associated problem with selection of high harvest index to
improve N translocation efficiency is its negative relation to grain
protein concentration which, in this experiment, had a high but
non-significant relationship under high N conditions.
Significance
was shown in the research conducted by Alagarswamy and Seetharama
(1982).
Overall the improvement in grain yield by selecting for high
biomass at maturity should allow for a greater protein harvest per
unit area.
Under high N conditions, stepwise regression considered N in the
grain the best one variable model for grain weight, uptake efficiency
(Nt3/Ns) the best one variable model for N-use efficiency (Gw/Ns) and
biomass at maturity the best one variable model for N in the grain as
the dependent variable.
Under low N conditions biomass at maturity
70
was the best one variable for grain weight, uptake efficiency (Nt3/Ns)
the best one variable model for N-use efficiency (Gw/Ns), and total N
In the plant at maturity was the best one variable model for the
dependent variable N in the grain.
In the greenhouse evaluation, N-use efficiency was considered as
milligrams of dry matter produced per unit of N found in the plant.
As with the field experiment, the lines demonstrated Improved
efficiency with decreasing amounts of N made available per plant.
Total shoot N varied significantly only at the 200 mg N per pot
level, whereas, root total N varied significantly at the 200, 400, and
600 mg N per pot rates.
Perhaps of more Importance are the
differences in total shoot to root N and shoot N concentration to root
N concentration ratios between the lines at the five different N
rates.
Both total shoot N and shoot N concentration Increased in
proportion to total root N and root N concentration as the N rates
increased.
Significant differences were noted at the 400, 600, and
800 mg N levels of shoot to root total N ratios.
Because of these differences between the four test lines in
shoot to root ratio for total N and N concentration as well as
differences in root dry matter production, consideration should be
given to roots in their role of N extraction from the soil and
remobilization within the plant.
Greenhouse screening can be a valuable tool in evaluating the
role of roots in N-use efficiency work.
Hydroponically grown plants,
where nutrient Inputs can be completely controlled, allow for the
recovery of the root system to be used in evaluation of nutrient needs
^
71
and morphology.
However, plants should be grown to maturity perhaps
one plant per pot before any valid comparsion to field grown material
can be made because of the disparity that exists between field and
greenhouse data collected at panicle initiation.
Parameters measured
at panicle initiation in the field also did not correlate well to
yield components measured at maturity in the field indicating that
early sampling may be eliminated.
A more desirable continued approach to N-use efficiency screening
could be to Isolate lines in a field situation, within the same
maturity group, which differ in total aerial biomass and harvest
index.
These parameters are easily measured and correlate well to
total N uptake and N translocation to the grain, the components of
N-use efficiency.
Having test lines within the same maturity group
would allow them similar exposure to environmental conditions at the
same physiological growth stages.
Once lines are isolated for superiority and inferiority of
biomass and harvest index, greenhouse screening under controlled
environmental and nutrient availability conditions could further
elucidate morphological and physiological parameters accociated with
N-use efficiency.
l•P^PM^v
LITERATURE CITED
Alagarswamy, G. and N. Seetharama. 1982. Biomass and harvest index as
indicators of nitrogen uptake and translocation to the grain in
sorghum genotypes, p. 423-427. J_n_ M.R. Saric and B.C. Longhman
(eds.). Genetic aspects of plant nutrition. Martinus Nijhoff/Dr.
W. Junk Pulb. The Hague, Netherlands.
Anonymous. 1983a. Technicon Auto Analyzers II Method No. 696-82WF.
Nitrate. Technicon Industrial Systems, Tarrytown, N.Y.
Anonymous. 1983b. Technicon Auto Analyzers II Method No. 696-82WC.
Total Kjeldahl Nitrogen. Technicon Industrial Systems, Tarrytown,
N.Y.
Beauchamp, E.G., L.W. Kannenberg, and R.B. Hunter. 1976. Nitrogen
accumulation and translocation in corn genotypes following silking.
Agron. J. 68:418-422.
Bhatia, C.R. and R. Rabson. 1976. Bioenergetic consideration in cereal
breeding for protein improvement. Science. 194:1418-1421.
Bremner, J.M. 1965. Total nitrogen. Jj^ C A . Black, D.D. Evans, J.L.
White, L.E. Ensminger, and F.E. Clark (eds.). Methods of soil
analysis. Am. Soc. Agron. Madison, Wis.
Cacco, G., G. Ferrari, and M. Jacconmani. 1982. J[ji^M.R. Saric and B.C.
Loughnan (eds.). Genetic aspects of plant nutrition. Martinus
Nijhoff/Dr. W. Junk Publ. The Hague, Netherlands.
Capurro, Eduardo and Regis Voss. 1981. An index of nutrient
efficiency and its application to corn yield response to fertilizer
N. I. Derivation, estimation and application. Agron. J.
73:128-135.
Chevalier, P. and L.E. Schrader. 1977. Genotypic differences in
nitrate absorption and partioning of N among plant parts in maize.
Crop Sci. 17:897-901.
Clark, R.B. and J.C. Brown. 1980. Role of the plant in mineral
nutrition as related to breeding and genetics, p. 45-70. In^
Matthais Stelly (ed.). Moving up the yield curve: Advances and
obstacles. ASA Special Publication Number 39. Madison, Wi.
Clarkson, D.T. and J.B. Hanson. 1980. The mineral nutrition of higher
plants. *Ann. Rev. Plant Physiol. 31:239-298.
72
73
Eastin, J.D. 1972. Photosynthesis and translocation in relation to
plant development, p. 214-246. 2ll N.G.P. Rao and L.R. House
(eds.). Sorghum in the seventies. Int. Crop Res. Inst. Semi-arid
Trop. Hyderabad, India.
Epstein, Emanuel. 1972. Mineral nutrition of plants:
perspectives. John Wiley and Sons, New York.
Principles and
Epstein, E. and R.L. Jeffries. 1964. The genetic basis of selective
ion transport in plants. Ann. Rev. Plant Physiol. 15:169-184.
Fisher, R.A. 1981. Optimizing the use of water and nitrogen through
breeding of crops, p. 249-278. ]_n^ J. Monteaith and C. Webb (eds.).
Soil water and nitrogen in mediterranean-type environment.
Martinus Nijhoff/Dr. W. Junk Publ. The Hague, Netherlands.
Gableman, W.H. 1976. Genetic potentials in nitrogen, phosphorous and
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