Carbohydrate reserves of green needlegrass (Stipa viridula Trin.) as affected by clipping and
fertilization
by Larry Melvin White
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY in Crop and Soil Science
Montana State University
© Copyright by Larry Melvin White (1972)
Abstract:
Nitrogen (N) fertilization and frequent clipping have sometimes reduced grass stands by reducing the
carbohydrate reserves. We applied N and imposed clipping treatments to determine their effect on the
seasonal variation of total nohstructural carbohydrates (TNC) in stem bases of dryland green
needlegrass (Stipa viridula Trin.) during 1969. Ammonium nitrate was broadcast at 0, 70, and 140 kg
of N/ha in November 1968. Green needlegrass was either left unclipped in 1969 or clipped to a 5-cm
height five times — May 7 and 28, June 17, July 8 and 29 — at approximately 21-day intervals.
A preliminary study showed that live stem bases of green needlegrass contained twice as much TNC as
live roots. The coefficient of variation of TNC in live stem bases from individual plants was 20%
compared to 37% for live roots.
Seasonal variation of TNC in stem bases of clipped and unclipped plants were similar, but clipped
plants had a lower TNC content at all sampling dates. The TNC in non-fertilized, unclipped plants
decreased from 18 to l4% from growth initiation after winter dormancy (April 5) until after second leaf
formation (April 28). The TNC increased after second leaf formation to 19% on May 20 just before
boot stage, decreased slightly at heading (May 29) then increased to 18% at first anthesis (June 9).
Following first anthesis, TNC decreased to 9% on July 22 just prior to completion of seed
dissemination, increased to 19% in late September, decreased to 16% by November. The percentage of
TNC in clipped plants was 3 to 5 units lower at all sampling dates and the terminal value in November
was 13%. Clipping in 1969 reduced yields significantly in 1970 and tended to reduce yields in 1971Nitrogen increased TNC content of stem bases during mid-July and again in late autumn, apparently as
a result of new tiller development and increased photosynthesis. Nitrogen decreased the TNC only
from growth initiation until the second leaf formation. Application of N in November 1968 increased
yields in 1969, 1970, and 1971. CARBOHYDRATE RESERVES OF GREEN NEEDEEGRASS (Stipa viridula TRIN.)
AS AFFECTED BY CLIPPING AND FERTILIZATION
by
LARRY MELVIN WHITE
K'
A thesis submitted to the Graduate Faculty in partial
fulfillment of the requirements for the degree
of
DOCTOR OF PHILOSOPHY
in
Crop and Soil Science
Approved:
Head, Major Department
Cochairman, Examininj^Jbmmittee
CocK&irman, Examining Committee
Graduate vDean
MONTANA STATE UNIVERSITY
Bozeman, Montana
June 1972
-iii- ACKNOWLEDGMENTS
The author would like to express sincere thanks to Drs, Ce, S 0
Cooper and J0 H 9 Brown for their assistance in planning and reviewing
this project and for the help of the other committee members, Drs0
I9. K 9 Mills, G 9 F 0 Payne, and E 9 O 9 Shogley0
Special thanks are
offered to the Agricultural Research Service team, Drs9 A 9 R 9 Grable,
F 9 H 9 Siddoway, J9 R 9 Wight, and Mr9 A 9 L9 Black, for their assistance
and suggestions in planning and reviewing this work=
The author also
wishes to thank the Northern Plains Soil and Water Research Center,
Agricultural Research Service, USBA, Soil and Water Conservation
Research Division for providing the funds to conduct this project.
author would like to thank especially his patient and understanding
wife, Gail M 9 White, for typing and correcting this thesis=
r
r
The
-iv-
TABLE OF' CONTENTS
Page
VITA e e e e e e e e e e p e e o e e e p e e e e
ACKNOWLEDGEMENTS ..................
, ........
e
•
e
•
e
e
.
ii
.
iii
iv
TABLE OF CONTENTS
............................
®
LIST OF TABLES
e e e p e e ® e a o o » ® e e
. 'vii
■»
LIST OF FIGURES
. viii
ABSTRACT . . , ........
. . . . . . . . . .
INTRODUCTION.............. .. . . .............
LITERATURE REVIEW
..............
............
•
ix
®
I
3
Importance of Carbohydrate Reserves . . , . <
3
Reserve Constituents
4
Storage Organs of Perennial Grasses 4
„
7
8
Variation of Carbohydrate Reserves
Diurnal and seasonal
8
Temperature
o o ® ® a o o ® ® ® ® a ® a o
9
a # ® ® ® ® * ® ® ® ® ® ® ® ® ® ® ®
12
Nitrogen ® o ® ® ® ® ® ® o ® ® ® ® @ ® @ ®
13
Wat er
Regrowth After Partial Herbage Removal
® ® .
®
e
e
e
e
@
o
e
16
Clipping e ® o e ® ® ® e o o o o e e e ® e
16
Grazing versus clipping
................
19
. . . . . . . . . .
21
Management Implications
-V -
Table of Contents— continued
STUDY AREA
METHODS e o o e e o o e o i o e t f C i e e y o o o e o
Experimental Design and Treatments
Total Nonstructural Carbohydrates . . . . . .
Other Analyses
. . . . . . . . . . . . . . .
Statistical Analyses
. . . . . . .
........
RESULTS. . . . . . . . . . . . . . . . . . . . .
Preliminary Study . ................
....
Plant G r o w t h ........ ..
Analysis of TNC Data
. . . . . . . . . . . .
Seasonal Variation of TNC . . . . . . . . . .
Effects of Clipping . . . . . . . . . . . . .
Effects of N Fertilization
....
......
U n d i p p e d plants . . . . . . . . . . . . .
Clipped plants . . . . . . . . . . . . . .
Total Nitrogen
. . . . . . . . . . . . . . .
DISCUSSION . . . . . . . . . . . . . . . . . . .
Seasonal Variation of TNC . . . . . . . . . .
Effects of Clipping . . . . . . . . . . . . .
Effects, of N Fertilization
. . . . . . . . .
Table of Contents— continued
Total Nitrogen . . . = =
SUMMARY AND CONCLUSIONS . .
REFERENCES
..............
-vii-
LIST OF TABLES
Page ■
I.
2-
3=
4.
5-
Summary of soil analysis data (July 1968) before
application of N-P fertilizer-
25
Analysis of variance of percent TNG in stem bases of
green needlegrass during October 1968. - - - . -
32
The date unclipped autumn-initiated (1968.) floral
tillers of green needlegrass reached successive
developmental stages during 1969 (White et al.,
1972)
34
Analysis of variance of percentage of TNG in'stem bases
of green needlegrass from April 8 through May 8,
I969 - O ^ - - O - O -
-
38
Analysis of variance of percentage of TNG in stem bases
of green needlegrass from May 20 through November 8,
1989 * o-**--'---
-
39
6 - Eepidual effects of'N fertilization in November 1968
and clipping in 1969 on dry matter yield of green
needlegrass during 1970 and 1971»
44
-viii-
LIST OF FIGURES
Page
1.
2,
3»
4.
5.
6.
7.
Total fructose in the stem bases of orchardgrass
plants grown in Massachusetts, USA, and Hokkaido,
Japan (Colby et al., 1966). . . . . . . . . . . . . . . .
11
Weight of stem bases (averaged over N levels) from
ten green needlegrass plants during 1969 when
clipped five times from May through July 1969
or left unclipped. . . . . . . . . . . . . . . . . . . . .
35
Five-day mean air temperatures and mean soil water
content in the 0- to 30- and 30- to 60-cm depths
during 19^9 ® . . . . . . . . . . . . . o o e e q . . . .
3^
Perceptage of TNC in stem bases of unclipped green
needlegrass during 1969 with and without N
fertilization during 1968. . . . . . . . . . . . . . . .
40
Mean percentage of TNC (averaged over N levels) in
stem bases of green needlegrass during 1969
when clipped five times from May through July
1969 or left unclipped. . . . . . . . . . . . . . . . . .
42
Weight of stem bases from ten undipped green
needlegrass plants during 1969 with and without
N fertilization during 1968. . . . . . . . . . . . . . .
45
Percentage of TNC in stem bases of frequently
clipped green needlegrass during 1969 with and
without N fertilization during 1968. . . . . . . . . . .
4?
8.
Weight of stem bases from ten frequently clipped
green needlegrass plants during 1969 with and
without N fertilization during 1968. . . . . . . . . . . . 4 9
9.
Percentage of N in stem bases of unclipped green
needlegrass during 1969 with and without N
fertilization during 1968. . . . . . . . . . . . . . . .
51
Mean percentage of N (averaged over N levels) in
stem bases of green needlegrass during 1969 when
clipped five times from May through July 1969 or
I ©f*"fc "Un.CIIjDjp6Cle o e c e o e e e e e o e e o e e p e e o e
^2
10.
— i - X ”*
ABSTEACTNitrogen (N) fertilization and frequent clipping have sometimes
reduced grass stands by reducing the carbohydrate reserves. We applied
N and imposed clipping treatments to determine their effect on the
seasonal variation of total nohstructural carbohydrates (TNG) in stem
bases of dryland green needlegrass '('Stipa viridula Trin.) during 1969«
Ammonium nitrate was broadcast at 0, 70, and 140 kg of N/ha in November
1968. Green needlegrass was either left unclipped in 1969 or clipped
to a 5-cm height five times — May 7 and 28, June 17, July 8 and 29 —
at approximately 2I-day intervals.
A preliminary .study
grass contained twice as
variation of TNC in live
compared to 37% for live
showed 'that live stem bases of green needle­
much TNC as live roots. The coefficient of
stem bases from individual plants was 20%
roots.
Seasonal variation of TNC in stem bases of clipped and unclipped
plants were similar, but clipped plants had a lower TNC content- at all
sampling dates. The' TNC in non-fertilizedj,unclipped plants decreased
from 18 to l4% from growth initiation after winter dormancy (April 5)
until after second leaf formation (April 28). The TNC increased after
second leaf formation to 19% on May 20 just before boot stage, decreased
slightly at heading (May 29) then increased to l8% at first anthesis
(June 9)• Following first anthesis, TNC decreased to 9% ©n July 22 just
prior to completion of seed dissemination, increased to 19% in late
September, decreased to l6% b y ;November. The percentage of TNC in
clipped plants was 3 to 5 units lower at all sampling dates and the
terminal value in November was 13%. Clipping in 1969 reduced yields
significantly in 1970 and tended to reduce yields.in 1971Nitrogen increased TNC content of stem bases.during mid-July and
again in .late autumn, apparently as a result of new tiller development
and increased photosynthesis. . Nitrogen decreased the TNC only from
growth initiation until the second leaf formation. Application of N in
November 1968 increased yields in 1969, 1970, and 1971-
INTE0BUGTI0N
Green needlegrass (Stipa viridula) is a palatable, productive range
grass (Bubbs, 1966) and constitutes an important component of climax
■vegetation on many sites in the northern Great Plains.
Improper grazing
has reduced the population of this species on millions of hectares and
has concomitantly reduced forage production on these ranges.
Informa-"
tion about the effects of nitrogen (N) fertilization and clipping on
carbohydrate reserves of green needlegrass is needed to improve its
management.
Adequate carbohydrate reserves are important in perennial plants
for winter survival, initiation of early spring growth, and initiation
of regrowth after herbage removal until photosynthesis is adequate to
meet plant needs.
Low carbohydrate reserves limit plant growth during
the first 2 to 7 days following herbage removal and this slower recovery
lowers production during subsequent exponential growth (Bavidson and
Milthorpe, 1966b).
Furthermore, tillers will die if carbohydrate
reserves are decreased below the critical level (Alberda, 1966).
Although N fertilization of grasslands in the northern Great Plains
generally increases forage production, it sometimes decreases production.
Applications of 5© to 200 kg of N/ha on grasslands in the northern
Great Plains during some drought years or frequent herbage removal
reduced stands of native grasses (Klipple and Eetzer, 1959), crested
—2—
wheatgrass (Agrepyron desertorum) (Eogler and Lorenz, 1969; Seamands and
Lang, i960), and intermediate wheatgrass .(Agropyron intermedium)
.(■Lawrence, 1963).
These stand reductions were attributed to exhaustion
of carbohydrate reserves.
High rates of N (200 to 4-00 kg of N/ha) on
grasslands in the eastern United States in conjunction with frequent
clipping, low soil water, and high temperature reduced stands and
carbohydrate reserves'of 0rchardgrass (Dactylis glomeralfa) (Drake et al.,
1963; Colby et al., 1965) an^ tall fescue (Festuca arundinacea) (Hallock
et al., 1965).
This study was initiated during the autumn of 1968 to determine the
effects of N fertilization and clipping of green needlegrass.
"This
thesis reports the effects of these treatments on the seasonal variation
of carbohydrate reserves.
White et al. (1972) reported the effects of
the treatments on the development, growth, dry matter yield, and forage
quality of green needlegrass and-White and Brown (1972) reported the
effects on the seasonal variation of evapotranspiration, water-use
efficiency, and fertilizer N recovery.
LITERATURE REVIEW
Importance of Carbohydrate Reserves
Carbohydrate reserves are thought to be used by plants as substrate
for growth and respiration.
Adequate carbohydrate reserves are
important in perennial plants for winter survival, early spring growth
initiation, and regrowth initiation after herbage removal, when the
photosynthetic production is'inadequate to meet these demands.
Many
pasture and range management practices are based upon knowledge of how
various environmental factors and herbage removal treatments affect
carbohydrate reserves,
This understanding helps managers to maintain
high yields of desirable species and to control undesirable species.
May and Davidson (1958) and May (i960) questioned the importance
of carbohydrate reserves in controlling herbage regrowth rate because
only indirect evidence supported the role' of reserves.
However,
research has shown recently that, under certain conditions, the herbage
regrowth rate depends on the level of carbohydrate reserves.
The
following is a review of the functions of carbohydrate reserves in
grasses with emphasis on recent findings.
summarized in the following reviews:
Earlier findings were
Graber et al. (1927)5 Graber
(1931)5 Weinmann (1948, 1961), Troughton (1957)5 May (i960), Priestley
(1962), Jameson (1963)9 Cook (1966), and McIlroy (1967) •'
-4-
Eeserve Constituents
Graber et al. (192?) first defined reserve energy constituents as
. . those carbohydrates and nitrogen compounds elaborated, stored,
and utilized by the plant itself as food for maintenance and for the
development of future top and root growth."
These carbohydrates,
termed total available carbohydrates, are those available as energy to
the plant (Veinmann, 1947).
Smith (1969) suggested that the term
total nonstructural carbohydrates (TNG) be used, because it is more
applicable to both animal and plant investigations;
Nonstructural carbohydrates--reducing sugars (glucose and
fructose), nonreducing sugar (sucrose), fructosans, and starches— are
the major reserve constituents.
Structural carbohydrates— hemicellulose
(pentosans and hexosans) and cellulose— are not considered to provide
significant reserves (McCarty, 1938; Sullivan and Sprague, 1943;
Weinmann, 1948).
Type, distribution in the plant and relative
proportions of individual carbohydrate reserve components vary among
and within grass species and under various climatic conditions during
the growth season.
Predominant carbohydrate reserves stored by
temperate-origin grasses are sucrose and fructosans, whereas those of
subtropical- or tropical-origin grasses are sucrose and starch (Cugnac,
1931; Weinmann and Reinhold, 1946; Smith, 1968; and Ojima and Isawa,
1968)»
The Hordeae, Aveneae, and Festuceae grass tribes store
fructosan as shorts or long-chain units.
0 ■
Genera of the Hordeae and
-5-
Aveneae tribes stere predominantly short- and long-chained fructosans,
respectively, while some genera of Festuceae tribe characteristically
store long-chained fructosans and others store short-chained fructosans
(Smith, 1968).
Although Graber et al. (1927) originally defined reserve
constituents as including nitrogenous compounds, most investigators
have only considered carbohydrates.
proteins may be involved.
Recent studies indicate that
Bavidson and Milthorpe (1966b) concluded
that nonstructural carbohydrates formed only a part of the labile pool
which provided substrates for respiration and new growth of orchardgrass in a growth chamber during the first 2 to 4 days following
severe herbage removal. ,They suggested that other labile substance,
presumably proteins, must have remobilized because the amount of
nonstructural carbohydrates was inadequate to account for the
respiration and new growth of roots and shoots.
Bilz (1966). in
studying perennial ryegrass (Lolium perenne) concluded that
proteinaceous material should be regarded as reserve constituents.
Most investigators generally have found that proteins are used in
respiration but there is not a net utilization (Hackett, 1959).
Proteinaceous sources accounted for 27 percent of the CG^ released by
respiration in phloem explants from the storage root of a carrot
(Daucus carota var. sativa) (Steward et al., 195§; Bidwell et at.,
1964).
Breakdown products from protein turnover contributed to the
storage pool of amino acids and supplied carbon products for direct
used in respiration, but carbohydrates were used preferentially ever
stored amino acids in synthesizing new proteins.
Studies show that even though nitrogenous compounds are
used in respiration they still are not as important as carbohydrate
reserves in supporting regrowth.
Smith and Silva (1969) found that
proportionally less nitrogenous compounds than TNG (I;l8) were
translocated from the roots of alfalfa (Medicage sativa) for production
of new top growth after cutting in greenhouse trials.
Alberda (1966)
pretreated perennial ryegrass for a short period to change the plant's
level of reserves.
Plants with low TNG were obtained by placing them
in a nutrient solution in the dark at 30 C 5 and plants with high TNG
were obtained by placing them in water at 15 C in continuous light.
The pretreatment changed the amount of nonstructural carbohydrates,
but did not change the amount of organic nitrogenous compounds.
In summary, reserve constituents are those nonstructural carbo­
hydrates which include reducing sugars, nonreducing sugars, fructosan,
and starch.
The predominant reserve constituents of temperate-origin
grasses are sucrose and fructosan; of tropical-origin grasses, sucrose
and starch.
Nitrogenous compounds are used in respiration, but are
not alternately stored and utilized as are carbohydrate reserves.
Storage Organs ef Perennial Grasses
Nonstructural carbohydrates may be stored temporarily in all plant
parts.
Mdny scientists in the past concluded that underground organs
were the major storage begion for carbohydrate reserves (Weinmann5 1948;
Troughton5 1957)•
Many other studies, however, have shown that the
major storage region is generally in the stem bases (which includes
stolons, corms, and rhizomes), not in the roots per se (Sampson and
McCarty, 1930; Smelev and Morazov, 1939; Sullivan and Sprague, 1943;
Baker and.Garwood, 1961).
The decrease of carbohydrate reserves- In the roots of orchardgrass, grown in growth chambers, after severe herbage removal only
accounted for less than one-tenth of root respiration (Davidson and
Milthorpe, 1966b).
They concluded that transfer of carbohydrate
reserves from the shoots, remob'ilization of other substances in the
roots, or both, must have occurred to account for root respiration,
Marshall and Sagar (1965), using autoradiographs and labeled CO^5
found that nonstructural carbohydrates in the roots of Italian ryegrass
1
(LoIium multi'florum) were not mobilized to the shoots to support
regrowth following herbage removal, nor were labeled compounds
translocated to the roots from the shoots when a part of the herbage
was removed from all tillers.
They concluded that "The classical
view of a transference of compounds from the root to shoot following
-8-
dgfoliation. (Troughton, 1957) • • « seems unlikely . . . in perennial
grasses without special storage organs."
In summary, the major storage areas of carbohydrate reserves are
usually the lower regions of the stems— stem bases, stolons, corms, and
rhizomes.
These reserves are used as an energy source to initiate new
growth until photosynthesis is sufficient to sustain plant respiration.
Nonstructural carbohydrates in the roots of grasses are probably not
used directly in herbage regrowth following herbage removal.
However,
more research using labeled carbon is needed to determine if nonstructural carbohydrates in the roots are translocated aboveground for
respiration or as structural components of regrowth following herbage
removal.
Variation of Carbohydrate Reserves
Diurnal and seasonal. The accumulation of carbohydrate reserves
in plant tissue is a dynamic system of energy balance.
The level of
carbohydrate reserves (hexoses and sucrose) of four grasses at Ayr of
Scotland showed marked diurnal variation (Waite and Boyd, 1955)-
In
Indiana, bromegrass (Bromus inermis) utilized almost one-third of the
TNC in the herbage during the night, but diurnal fluctuations for other
grass species were less (Holt and Hilst, 1969).
For the grass species
studied, TNC concentration in the herbage was lowest at 6 AM and
increased linearly to a high at 6 PM.
-9-
The seasonal variation of carbohydrate reserves differs among grass
species.
In many grass species, the reserve level is lowest when the
second or third leaf emerges (about one month after the start of plant
growth), but in other species, the reserve level is lowest after seed
ripening (Jameson, 1963).
Carbohydrate reserves of Colorado wildrye
(Elymus ambiguus) and mountain muhly (Muhlenbergia montana) in Colorado
decreased during fast growth and increased during slow growth (McCarty,
1935)-
However, temperature and the availability of water and nutrients
also affect the seasonal variation of carbohydrate reserves.
The accumulation of carbohydrate reserves in plant tissue is
dependent upon the balance between photosynthesis and respiration.
The
carbohydrate reserves of orchardgrass and bermudagrass (Cynodon dactylon)
grown in growth chambers decreased when growth and respiration demands
were greater than photosynthetic rate and increased when growth and
respiration demands were less than photosynthetic rate (Blaser et al.,
1966).
The level of reserves in determined by growth rate, plant
development stage (Hyder and Sneva, 1959) "and environment (Troughton,
1957) .
Temperature.
The effect of temperature on the percentage of carbo­
hydrate reserves in the stem bases is influenced by the origin of grass
species.
Optimum temperatures for growth and net photosynthesis by
temperate-origin grasses are about 20 to 25 C, whereas those for tropicalorigin grasses are about 30 to 55*0 (Evans et al., 1964; Treharne and
-10-
Cooper, 1969)=
This difference in temperature optima for growth of two
temperate'species (oat (Avena sativa) and perennial ryegrass) and two
tropical species (maize (Zea mays) and buffelgrass (Cenchrus ciliaris))
resulted from differences in temperature optima of the major OO^-fixing
enzymes (Treharne and Cooper, 1969).
The activity of ribulose-1,5-
diphosphate carboxylase is higher in temperate-origin grasses while the
activity of phosphoenoIpyruvate carboxylase is higher in tropicalorigin grasses.
Temperate-origin grasses contain only the Calvin (C^)
photosynthetic pathway, while tropical-origin grasses contain both the
C^ (Hatch and Siack) and C^ photosynthetic pathways.
In tropical-origin
grasses, the C^ pathway is located in chloroplasts of mesophyll tissue,
whereas the C^ pathway is located in chloroplasts of bundle sheath
tissue (Berry et al., 1970;'Kortschak and Nickell, 1970).
Temperature markedly affects the seasonal variation of carbohydrate
reserves.
Seasonal variation of total- fructose in stem bases of
orchardgrass (Fig. I) was different when grown in Massachusetts, USA,
than in Hokkaido, Japan (Colby et al., 1966).
The total fructose level
of orchardgrass grown in Hokkaido increased following heading, whereas
in Massachusetts, it decreased.
High June temperatures in
Massachusetts apparently caused the decrease following heading.
Smith
and Jewiss (1966) showed that high day and night temperatures decreased
the percentage of water-soluble carbohydrates in the stem bases of
timothy throughout a growing season.■
, Smith (1970) showed that changing
Heading
Flowering
Mature S e e d
-5 20
JAPAN
UNITED
STATES
A ugust
TIME OF SAMPLING
Fig. I.
Total fructose in the stem bases of orchardgrass plants grown in
Massachusetts, USA, and Hokkaido, Japan (Colby et al., 1966).
-12-
timothy plants at inflorescence emergence from a cool to a warm regime
decreased water-soluble carbohydrate content in the stem bases at early
anthesis.
The effect of high day temperatures is different from that of
high night temperatures.
High night temperatures in a growth chamber
decreased reserves of temperate-origin grasses, such as timothy (Phleum
pratense), bromegrass, orchardgrass, and Kentucky bluegrass (Poa
pratepsis), more than high day temperatures (Baker and Jung,? 1968).Increasing the day temperature, if below optimum, increases both
respiration and net photosynthesis; whereas increasing the night
temperature increases only the respiration rate and, thereby, decreases
the reserve level.
The level of carbohydrate reserves during the
season may be more characteristic of climatic factors than of
individual species.
Water.
Eaton and Ergle (1948) in a review article noted that the
effect of water stress on carbohydrate reserves varies.
Some scientists
have reported that drought increased the carbohydrate reserves in
several grass species (inlander, 194$; Brown and Blaser, 196$; Blaser
et al., 1966); others have reported that drought decreased carbohydrate
reserves (Bukey and Weaver, 1939; Brown, 194$).
The degree of water stress and the plant growth stage during which
it occurs will variably affect carbohydrate reserve levels.
Orchard-
grass under increasing water stress in a growth chamber showed a
-13-
decrease in, both net photosynthetic and respiration rjates (Murata and
Iyama, 1963).
The photosynthetic rate, however, decreased much more
rapidby than respiration, thus lowering carbohydrate reserves.
If
water stress stops stem elongation and has only minor effects on
photosynthesis, as reported by Wardlaw (1968), carbohydrate reserves
would then increase.
Brown and Blaser (1970) suggested (that the build­
up of carbohydrate reserves and inorganic nitrogen in plants under
water stress results from the transformation of carbon-containing
nitrogenous substances.
Nitrogen.
The effects of N fertilization on carbohydrate reserves
are complex and variable.
Weinmann (1948) in a review article noted
cases where N fertilization caused no effect, increased, or decreased
carbohydrate reserves.
Generally, N applied at low to moderate rates
increases carbohydrate reserves.
Nitrogen applied at high rates
decreases carbohydrate reserves (Adegbola and McKell, 1966).
The
physiological reasons why N variably affects carbohydrate reserves are
not well understood.
Jf N is deficient, application of moderate amounts of N can
increase plant growth when carbohydrates, water, and other nutrients
are available and environmental conditions are favorable.
Increased
plant growth from N application was associated with increased leaf area,
chloroplast protein, and chlorophyll content which increased photo­
synthesis. (Murata, 1969).
The increased photosynthetic activity can
then, theoretically, increase carbohydrate reserves.
Excess N tends to decrease carbohydrate reserves when other
nutrients and environment do not limit plant growth.
In this case, N
fertilization stimulates the synthesis of amino acids and amide
compounds to the. detriment of carbohydrate reserves (Prianishnikov,
1951)•
Carbohydrate reserves are used as the carbon-skeleton for
protein synthesis (Prianishnikov, 1951)•
Application of high rates of N fertilizer (200 to 400 kg N/ha)
in conjunction with frequent clipping, low soil water, and high
temperatures reduced stands and carbohydrate reserves of orchardgrass
in Massachusetts (Drake et al., 1963; Colby et al., 1965) and tall
fescue in Virginia (Hallock et al., 1965).
Applications of. high rates
of N also reduced stands of orchardgrass and tall fescue in Maryland
(Alexander and McCloud, 1962).
Scientists also reported that application of 50 to 200 kg N/ha
reduced severely the grass stand, especially when associated with
drought or frequent herbage removal on native range in Colorado
(Klipple and Retzer, 1959) on crested wheatgrass in Wyoming (Seamands
and Lang, i960) and North Dakota (Rogler and Lorenz, 1969), and on
intermediate wheatgrass in Saskatchewan (Lawrence, 1963).
scientists assumed that carbohydrate reserves were reduced.
These
Frequent
clipping, with or without N fertilization, decreased the percentage
basal ground cover of non-irrigated green needlegrass in Saskatchewan
-15'
(Heinrichs•and Clark, 1961).
In contrast, N fertilization (0 to 375 kg
N/ha) did not increase the winter-kill of intermediate wheatgrass under
irrigation in Saskatchewan, although frequent and close clipping did
(Lawrence and Ashford, 1969).
High rates of N should not be applied under the combined conditions
of drought and high temperatures.
Under these conditions, clipping or
grazing could deplete carbohydrate reserves below a critical level, and
cause stand reduction and poor growth recovery.
In summary, the interaction of the plant with the environment and
the balance between photosynthesis and respiration determine the
variation of carbohydrate reserves during the growing season.
In some
grass species, a low reserve occurs when the second or third leaf
emerges; in other grasses, it may occur just before or after seed
ripening.
The seasonal variation of carbohydrate reserves can differ
for the same species grown in different environments.
Above-optimum
temperatures, especially during the night, decrease carbohydrate re­
serves; wtierpas water stress can either increase or decrease reserves,
.depending on the degree of stress and stage- of plant growth.
Studies to date generally show that N applied at low to moderate
rates increases carbohydrate reserves, but that N at moderate to high
rates decreases reserves.
Excess N applied during periods of water
stress and high temperatures, coupled with frequent herbage removal,
often reduces stands and growth rate.
More research is needed to
- 16-
fully understand the effects of N fertilization on carbohydrate
reserves.
Regrowth After Partial Herbage Bemovai
Clipping.
The effect of herbage removal on plant regrowth has been
classified into three simplified categories.
Herbage removal reduces
(I) amount of carbohydrate reserves, (2) root growth, and (3) leaf area
(Alcock, 1964).
Many other factors, however, also affect the regrowth
rate of a sward following herbage removal (Jameson, 1963).
The importance of carbohydrate reserves in controlling regrowth
rate following herbage removal is a controversial topic in grassland
management.
The results of many field studies show that carbohydrate
reserves decreased in both stem bases and roots of grasses after
cutting (Graber et al., 1927; Troughton, 1957) until sufficient leaf
area developed that carbohydrates produced in photosynthesis equaled
those used in respiration and growth.
This observation led to the
general belief that, following herbage removal, some reserves are
converted to structural components of the new and expanding cells, and
thus the reserve level affects the regrowth rate.
stated that the
However, May (i960)
. . specific role for carbohydrate reserves in
initiating regrowth, and in determing the rate or ultimate extent of
regrowth,, cannot yet be considered as firmly established."
Since May's (i960) conclusion, new research techniques have
-17-
provided evidence that carbohydrate reserves are used for regrowth
following herbage removal.
Carbohydrate reserves, assimilated as
labeled CO^ by bahiagrass (Paspalum notatum) were used to help form
leaves for 6 days after herbage removal (Ehara et al., 1966).
nonstructural carbohydrates in alfalfa (labeled by
lh
Those
CO,, assimilation)
which were initially stored in the root and crown were utilized after
herbage removal as substrate for respiration of both roots and tops and
as structural components for top growth (Pearce et al., 1969; Smith and
Marten, 1970).
The dry weight of perennial ryegrass with high carbohydrate reserves
did not increase for 4 days following clipping because respirational
losses exceeded photosynthetic gain but the weight of plants with low
carbohydrate reserves did not increase for 7 days (Alberda, 1966).
Davidson and Milthorpe (1,96$;. 1966a, 1966b) after measuring both
respiration and photosynthetic rates of or'chardgrass grown in growth
chambers, concluded that regrowth following clipping depended upon
carbohydrate reserves for only the first 2 to 4 days.
During this
period, stored carbohydrates were used for regrowth and respiration.
Afterwards, regrowth depended on other factors, such as photosynthetic
rate and nutrient uptake.
Milthorpe' and Davidson (1966) demonstrated
that, even though carbohydrate reserves influenced the regrowth rate
for only the first few days, the initial stimulus due to the level of
reserves was maintained during subsequent exponential growth.
Measure­
- 18-
ment of the initial response attributable to the level of carbohydrate
reserves during the exponential phase of orchardgrass regrowth is
difficult because complex interrelationships frequently obscure the
response (Davidson and Milthorpe, 1966b).
Ward and Blaser (1961) concluded that carbohydrate reserves of
orchardgrass in Virginia-stimulated dry matter production for the first
25 days after partial or complete herbage removal; thereafter, regrowth
rates were dependent on leaf area.
Davidson and Milthorpe (1966b)
re-examined Ward and Blaser1s data and concluded that the relative
rate of leaf expansion of plants with high and low levels of carbo­
hydrate reserves was the same and the effect of carbohydrate,reserve
levels was confined only to the initial stage of regrowth.
Weinmann (1948) stated that clipping does not always reduce
carbohydrate reserves, and Jameson (1963) stated that regrowth rate
does not always depend upon the level of carbohydrate reserves.
discrepancies may be due to any of the following factors:
Such
(I) Variation
in amount or capacity of photosynthetic tissue remaining after herbage
removal; (2) sampling for reserves too late after clipping, When the
reserves have already been restored; and (3) sampling the wrong plant ;
part.
Photosynthetic capacity remaining after herbage removal depends on
height of cutting, growth habit of the plant, and age of remaining
leaves.
The photosynthetic rate of the sheath of young orchardgrass
-19-
tillers grown in growth chambers was about one-third of the rate of the
blades (Davidson,and Milthorpe, 1966b)„
The maximum photosynthetic rate
of a leaf occurred when the leaf blade first emerged from the sheath
and this rate then decreased with age in tall fescue (Jewiss and Woledge,
1967) and orchardgrass (Treharne et al., I968).
The life span of an
orchardgrass leaf in Kentucky, after it reached full extension,, was
only about'28 days (Taylor and Templeton, 1966).
Thus leaf blades about
28 days after full extension would be of little value in maintaining the
photosynthetic rate of a sward.
In summary, the level of carbohydrate reserves in the lower
regions of the stems apparently affects the regrowth rate for 2 to 7
days after herbage removal; but this initial support from carbohydrate
reserves can be maintained during subsequent exponential growth.
After
the initial period, plant regrowth rate depends on other factors, such
as leaf area and nutrient uptake.
Grazing versus clipping.
similar, but not identical.
The effects of grazing and clipping are
Clipping removes all herbage above a given
height from all plants, whereas grazing removes herbage at heights vary­
ing from plant to plant and even within the same plant.
Hormay and
Talbot (1961) reported that grazing of Idaho fescue (Festuca idahoensis)
by cows in an opening of ponderosa pine (Pinus ponderosa) in California
was not uniform from plant to plant.
When the overall utilization of
Idaho fescue herbage was 43%, 40% of the plants were grazed to a 2.5-cm
-20-
stubble height; 29%, to 5 .1-cm; 13%, to' 7 „6-cm; and 3%, to 10.2-cm or
taller; and 13% were not grazed at all.
Grazing reduces plant vigor more than clipping at the same degree
of herbage removal because grazing often removes herbage from one plant
and not from the surrounding vegetation.
In Montana, clipping of
individual Idaho fescue plants and not the surrounding vegetation
reduced yields of clipped; plants more the following year than when the
surrounding vegetation was also clipped (Mueggler, 1970).
Undipped
plants competed advantageously with clipped plants for nutrients and
water.
Grazing, however, can be less detrimental to plant vigor than
clipping by leaving ungrazed tillers in a plant.
Carbohydrate reserves
of tall fescue in Missouri (as indicated by greater etiolated regrowth)
increased as the percentage of unclipped tillers per plant increased
from 0 to 30% (Matches, 1966).
Carbohydrate reserves of dallisgrass
(Paspalum dilatatum) in Mississippi also increased as the percentage of
unclipped tillers increased from 0 to 10% (Watson and Ward, 1970).
Carbohydrate compounds are transferred from unclipped to clipped
tillers only for the first few days following cutting and only in small
plants.
When a single unclipped tiller remained, it initially trans­
ported labeled carbon products to defoliated tillers within the same
plant (Marshall and Sagar, 1963)0
However, transfer of assimilates from
an unclipped tiller to clipped tillers did not occur beyond the third
-21-
day after cutting. More, mature tillers of Italian ryegrass were
independent because leaf blades fed labeled CO^ transported labeled
assimilates only to the root system of that tiller (Marshall and
Sagar, 196$).
Tillers of large plants of weeping lovegrass (Eragrostis
curvula) in Maryland apparently were not completely connected together
by vascular connections at the crown because partial clipping of a
group of tillers stopped root growth only of clipped tillers (Crider,
1955)•
Leaving unclipped tillers not only increased production because
of the transfer of carbohydrates but alsp because of feaving photo­
synthetic tissue and carbohydrate reserves stored in the stems.
In summary, the effect of grazing on herbage regrowth rate can be
more or less detrimental than clipping, depending oh circumstances.
Grazing may be more detrimental than clipping if grazing removes all
herbage from some planfs and not others, because ungrazed plants take
available nutrients and water away from grazed plants.
However,
grazing may be less detrimental than clipping if grazing leaves
ungrazed tillers on a plant while removing others, thus allowing for the
transfer of carbohydrates from ungrazed to grazed tillers.
Management Implications
Various management practices,— range readiness, season of use,
degree of utilization, and grazing systems— are partially based upon
how they affect carbohydrate reserves of grasses (National Research
-22-
Council, 1962).
Effects of a particular management practice often can
be evaluated in a single year by observing carbohydrate reserve levels
and variation.
The effects of various management practices on plant
vigor can be partially measured objectively and quantitatively with the
percentage of TNC (Cook, 1966; National Research Council, 1962).
The seasonal variation of carbohydrate reserves of many grasses has
not been determined.
Knowledge of the seasonal variation of carbo­
hydrate reserves and the effects of climate and management practices on
them will help pasture and range managers improve.present management
practices.
Factors other than carbohydrate reserves-^-leaf area, light
interception, root area, nutrient uptake, competition and other
morphological and physiological factbrs— also influence the effects of
herbage removal.
Cook (1966) stated that "Proper management . . . does not
necessarily imply that a maximum level of carbohydrate reserves be
maintained, but care must be taken . . . that these reserves do not
fall below a critical level" or tillers will die.
More research is
needed to determine critical levels of carbohydrate reserves at which
some tillers die.
Perennial ryegrass grown in growth qhambers was
unable to use carbohydrate reserves below 6% of dry weight, the amount
required for normal cell function; and at the G°/o level, reserves
inadequately supported the existing tiller population and some tillers
-23-
died (Alberda, 1966; del Pozo, 1963)•
The critical level of carbo­
hydrate reserves can be different among grass varieties (Davies, 1965)
and species and is probably affected by fertility, management,
environment, and season.
STUDY AREA
This study was conducted'from 1968 through 1971 on a solid stand
of green needlegrass seeded in 1961.
The site is 11 km north of
Culbertson, Mont, on the Soil and Water Conservation District
Research Farm.
The soil is a Williams loam (sandy loam) derived from
glacial till, sloping from 4 to 6% to the south.
In July 1968, 44.8 kg
of phosphorus/ha was boradcast uniformly, since the soil is normally
deficient in phosphorus.
After application of phosphorus, the soil
contained over 5 ppm of available phosphorus to a depth of 30 cm (White,
1971)»
Table I.
The results of chemical analysis of this soil are shown in
The study area is classified as a sandy 25.4- to 35-6-cm
precipitation zone range site.
•
Prior to 1969, green needlegrass
herbage was harvested annually for hay when the first seeds ripened.
Weeds in the stand, primarily volunteer alfalfa, were controlled
by spraying with 1.1 kg/ha of active ingredient 2,4-D amine on May 12,
1969. From 1969 through 19711 leaf spot disease, Alternaria tenuis,
infected the entire second leaf and the distal half of the third leaf
during the middle of May causing light to moderate damage.
Subsequent
infections did not occur during the growing season of any year.
The experimental site normally receives 32.6 cm of precipitation
annually, 26.0 cm of precipitation during the growing season (April
Depth
Summary of soil analysis data (July 1968) before applications of N-P fertilizer.
Soil
Con- '
texture. ductivity
pH
cm
mmhos/ cm
0 - 7.5
7.4
.
ppm
390
1-3
0.7
1-5
6
250
1.4
0.7
1.2
' 6
160
■ 1.2
1.1 ■
1.1
'4 ■
130
1.1
■ 7-2
si
: S'
.ppm
23
15-30
I
ppm
' 2.1
si
-
sl-clt
..
■
*Average of values measured in May and August 1969 (nonfertilized plots).
*fSandy loam-clay loam.
Available
nitrate*
0.8
7.1'
:'a
%
Avail­
able K
si
7-5 - 15
7-7
Organic Available P
■matter (Bray-HCL)
-GE-
Table I.
- 26-
to September), 114 frost-free days, and tb,e mean annual air temperature
is 5-2 C.
During the 1969 growing season, above-normal precipitation
supplied adequate soil water from August 1968 through April 1969, and
from June 25 through early August 1969•
However, below-nqrmal
precipitation and above-normal temperatures caused drought stress which
retarded the growth rate in plants from, the last of May through June 24
and again from mid-August through mid-September 1969 (White, and Brown,
1972).' Precipitation during the 1970 growing season was above normal
except for the last three weeks of May and first two weeks of June.
Precipitation during the 1971 growing season was below normal and
herbage production was only about one-third of normal.
1
METHODS
Experimental Design and Treatments
Factorial combinations of three levels of N and two levels of •
clipping were assigned, to plots in a completely randomized split-plot
design with four replications.
Ammopium nitrate was broadcast on main
plots (17 by 5 m) in November '1968 at 0, 70, and 140 kg of N/ha.
two clipping treatments applied on subplots (8.5 by 5
The
were (A) plants
undisturbed until sampled (unclipped) and (B) plants clipped to a 5-cm
height at about. 21-day intervals on May 7 and 28, June 17, July 8 and
29, 1969.
Total Nonstructural Carbohydrates
A preliminary study was conducted during October 1968, to determine
the plant part and number of samples required to adequately determine
the percentage of TNG in green needlegrass.
Samples included-stem bases
to a 5-cm height aboveground and roots in a 15-cm diameter by 15-cm deep
core.
Individual cores were washed free of soil and the plant material
was separated as stem bases or roots and as either live or dead.
Material from 35 individual plants was analyzed for TNG to determine the
variability among plants.
Also, ten plants from each subplot were
composited and analyzed for TNG to determine the variability of
composited samples.
r-28-
Only live stem bases .were sampled for TNG in 1969.
A sample of 10
plants from each subplot was taken for analysis at about 10-day
intervals from April 8.through August 12, on September 2 and 27, and
on November 8, 1969.
From April 8 through May 8 (four sampling dates),
only the plants on unclipped subplots were sampled, since clipping did
not begin until May ?•
Herbage above 5 cm was clipped and discarded.
Blasts of air were used to remove soil from the stem bases.
Within
one-half hour after sampling, samples were placed in a forced-air oven
at 90 C for one hour to stop enzymatic action and were then dried at
70 C to constant weight.
Hoots and all dead leaf sheaths (dead at the
time of sampling) were removed.
Dry stem bases were weighed to the
nearest tenth of a gram and ground to pass a 40-mesh screen, then
redried at 70 C and stored in glass jars for. subsequent analysis.
The stem bases were analyzed for TNG following the procedure
described by Smith (1969).
The TNG was extracted and hydrolysed with
takadiastase enzyme solution (Clarase 900, Miles Laboratories, Inc.,
Elkhart,' Ind.) because green needlegrass, stores some starch (Smith,
1968).
Reducing power was measured by the Shaeffer-Somogyi copper-
iodometric titration method as described by Heipze and Murneek (19^0).
Results were reported as a percentage of dry weight using a glucose
standard.
-29-
Other Analyses''
Stem bases were also analyzed for total N by the Kjeldahl procedure
(Jackson, 1958).
The residual effects of N fertilization in November
1968 and clipping in 1969 upon dry matter yield in 1970 and 1971 were
determined from samples harvested"when seed was ripe.
Dry matter was
harvested from two permanent 1
A- by 4-m areas by clipping plants to a
5-cm height.
Mithin treatment A, samples were collected from subplots ■
which had not been clipped in 1969.
Within treatment B, samples were
collected from the same permanent plots used in 1969.
Soil water content (0- to 120-cm depth) was determined approximately
every 10 days from April through August 1969 as previously described
(White and Brown, 1972).
Minimum and maximum daily air temperatures
were measured :at a standard weather station adjacent to the plots.
Statistical Analyses
Standard analysis of variance was used to determine if treatment
differences were significant.
When the F-test for N means was
significant at the 5% probability level, Duncan's Multiple Range test
was used to determine which differences among N means were significant.
All differences discussed are significant at the 5% probability unless
stated otherwise.
When subsequent measurements were made over a period of time,
time was considered an additional variable; therefore, data were
-30-
analyzed as split In time.
When date by clipping or date by N inter­
action was significant at the 3% level, analysis of variance was made
for each date.
When error (B) was larger than error (A), the two error
terms were pooled before the F-tests were made (Steel and Torrie, i960).
RESULTS
Preliminary Study
The preliminary study conducted during October 1968 showed that
live stem bases contained 13»9^ TNG and dead stem bases only 3 .4% TNG.
The TNG in material designated as dead stems..was'disproportionately
high due to the inclusion of some current year's spring tillers which
were difficult.to distinguish from dead stems.
Live roots contained
6 .7% and dead roots only 0.9% TNG.
Analysis of individual plants for TNG showed that the coefficient
of variation for live stem bases was 20% and'for live roots,37%.
It
was estimated that 16 individual plants were.needed in a sample for
live stem bases and 52 individual plants for live roots to obtain a
sample mean within' 10% of. the population mean at the 95% probability
level,.
When plots were arranged in a completely randomized design with
four replications and 10 plants were composited per sample, the
coefficient of variation' was 16.5% for live stem bases (Table 2) and
21.7% for live .roots.
From information obtained in the preliminary study, 10 individual
plants were composited per sample from each subplot in 1969.
Composit­
ing 10 plants per subplot, when main plots were arranged in a completely
randomized design with four replications, resulted in coefficients of
variation for the percentage of TNG in live stem bases at individual
sampling dates ranging from 7 to 16% for both N and clipping treatments.
-32-
Table 2.
Analysis of variance of percent TNC in stem bases of green
needlegrass during October 1968.
Source of Variance
df
SS.
MS
F Value
Nitrogen
2
9.&3
4.91
.94n s
Clipping
I
14,73
14.73
2.SlNS
Nitrogen x Clipping
2
9.59
4.79
.9INS
Error
18
94.30
5.24
Total
23
128.45
C,V. - 16 . %
-33-
Plant Growth
Growth of the 1969 .crop of green needlegrass started in late
August 1968 after the heavy mid-August j-ains.
White et al. (1972)
estimated that two-thirds of the floral tillers present in July 1969
were initiated the previous autumn.
Tiller initiation which started in
the autumn pf 1968 continued during the spring of 1969 after the spring
thaw (Aphil 5 )•
Table 3 shows average dates when green needlegrass
reached given stages of development.
The growth of green needlegrass during 1969 is illustrated by
changes in the weight of stem bases per 10 plants (Fig. 2).
Limited
soil water from late May through mid-June (Fig. 3) probably stopped ,
tiller initiation during this period.
However, stem base weight of
unclipped plants increased during early June because of elongation and
enlargement of the stems of floral tillers,
Rains received the last of
June and early July stimulated tiller initiation and growth during Julyand early August.
White et al. (1972) showed that the number of
tillers taller than 5 cm increased during July.
were not counted during this period.
Tillers less than 5 cm
However, limited soil water
(Fig. 3) again stopped tiller initiation and growth from the middle of
August through early September (Fig. .2).
The 2.74 cm of rain received
September 21 again stimulated growth and the weight of stem bases
increased from the last of September through October.
-34-
Table 3»
The date undipped autumn^-initiated, (1968) floral tillers of
green needlegrasg reached successive developmental stages
during 1969 (White et al., 1972).
Developmental Stages
Date
Tillers started growth
August 15, 1968
Emergence of first leaf*
September 1968
Over-wint ering
Winter 1968-69
Start of spring growth
April 5i 1969
Emergence of second leaf
April 22, 1969
Emergence of third leaf
May 12, 1969
Head, inoboot
May 26., 1969
First head appearance
May 29, 1969
Emergence of fourth leaf
June 2, 1969
First anthesis
June 9, 1969
Full anthesis
June 12, 1969
Milk stage
June I?, 1969
Soft dough stage
June 24, 1969
Hard dough stage
July 7, 1969
First seed ripe
July 7, 1969
Start of seed dissemination
July 7, 1969
Completion of seed dissemination
July 2$,11909
*Leaf collar appears.
O
O
U n dipped
Clipped
I
VJ
Y
M
CO N
CO CO
i
O <T> 0) (T) O O
CM —
April
May
June
July
Aug.
Sept,
Oct.
Fig. 2. Weight of stem bases (averaged over N levels) from ten green
needlegrass plants during 1969 when clipped five times from Maythrough July 1969 or left unclipped.
3 0 - 6 0 cm
Witting
R 0IPL _
VC
°
3 0 -6 0 cm
Wilting point
0 - 3 0 cm
5 - d a y Mean Air Temperature (C)
Temperature =^7
0 - 3 0 cm
ro ro ro ro ^r
in io
June
Fig. 3- Five-day mean air temperatures and mean soil water content in the
0- to 30- and 30- to 60-cm depths during 1969.
/
-37-
Analysis of TNC Data
The anlysis of variance of the TNC data for the first period of
1969, April 8 to May 8, was made separately from that of the second
period of 1969, May 20 to November 8.
During the first period, the
clipping treatments had not yet been applied, therefore only plants on
the unclipped plots were sampled for TNG.
The N by date interaction
for TNC data during the first period was highly significant (Table 4)
■and the N by clipping by date interaction during the second period was
highly significant (Table 5)•
Therefore, neither the. N' by date means
nor the clipping by date means were
used to interpret TNC
effects of N rate and clipping frequency on
TNC data were
data.
The
analysed
using only the averages of the data over replications.
Seasonaj Variation of TNC
The concentration of TNC in the stem bases of unclipped green
needlegrass varied considerably during the growing season and was
related to growth.stage, Fig. 4.
The percentage of TNC in non-
fertilized, unclipped plants decreased from lS>% after the start of
spring growth on April 5 to lb°/o on April 28 after the emergence of the
second leaf.
The TNC accumulated rapidly after emergence of the
second leaf and reached about IS% on May „20 just before the boot
stage, then decreased slightly with
heading (May 29)then increased
to lS>% at first anthesis (June 9)•
The TNC declined after anthesisto
-38-
Table 4.
Analysis of variance of percentage of TNC in stem bases of
green needlegrass from April 8 through May 8, 1969.
Source of Variance
df
SS
MS
Nitrogen
2
68.28
34.14
Error (A)
9
11.57
1.28
.3
86.06
28.69
6■
29.76
4.96
Error (B)
27
39.90
1.48
Total
4?
235.57
Dates
Nitrogen :
x Dates
C. V. (A) = 7 .5%
C. V. (B) = 8.0#
F Value
26.56**
19.41**
-
3.35**
/
-39-
Table 5-
Analysis of variance of percentage of TNG in stem bases of
green needlegrass from May 20 through November 8, 1969.
Source of Variance
df
SS
MS
F Value
Nitrogen
2
71.94
33.97
Error (A)
9
48.37
3.37
Clipping
I
739.36
739.30
Nitrogen x Clipping
2
13.65
7.82
Error (B)
9
10.22
1,14
Dates
11
1415.58
128.69
64.4l**
Nitrogen x Dates
22
.231.74
■ 10.53
5.27**
Clipping x Dates
11
131.14
11.92
3.97**
N x C x D
22
125.30
3.70
2.85**
Error (C)
198
393.39'
' 2.00
Total
287
■3205.04
'
C. V. (A) = 15.5#, C. V. (B) = 7.1#, C. V, (C) = 9 . 3 *
6.69*
668.59**
6.88*
.
ill Ii
I
I I
CO N
Il Ii
Ifl
CO CO
O 0) 0) 0) O O
CU CU
CU —
June
Fig. 4.
Percentage of TNC in stem bases of unclipped green needlegrass
during 1969 with and without N fertilization during 1968.
-40-
□ -- □ O N
O------O 70 N
A ------ A 140 N
-4l-
a low of 9% on July 22 just prior to completion of seed, dissemination*
Following seed dissemination,
TNC increased to 19% in late September
and then decreased to lG% in November.
Effects of Clipping
Clipping five times in 19$9 reduced the TNC level an average of
3 to ^ units lower at all sampling dates than that of unclipped plants
(Fig. 5); however, the seasonal variation of TNC was similar for both
treatments.
The TNC of clipped plants decreased to a low of 9% on
July 10, which was 12 days earlier than the lowest TNC level in
unclipped plants.
The TNC of clipped plants increased similarly to
unclipped plants after July 22.
The terminal TNC value (November) of
clipped plants was 13% in contrast to 17% for unclipped plants.
The effect of clipping was hard to distinguish following the third
clipping because the TNC level 13 days after clipping increased at
about the same rate in both unclipped and clipped plants.
However,
clipping significantly reduced the TNC level on all dates except on
May 29 and July 22=
The lack of a significant reduction of TNC by
clipping of May 29 and July 22 was associated with increased herbage
production during these periods (White et al., 1972).
Greater herbage
production would be associated with more leaf area and in turn should
increase the photosynthetic capacity of the plants.
Clipping in 1969 reduced the weight of stem bases during 1969 by
an average of 30% for the season (Fig. 2). White et al. (1972).
_V)Ch CVj
^
16
-P-
D ------D
O------O
CO N
CO CO
O
cvj
0)
cvj
0)
0)
O O
Undipped
Clipped
CVJ —
June
Fig. 5.
Mean percentage of TNC (averaged over N levels) in stem bases of
green needlegrass during 1969 when clipped five times from Maythrough July 1969 or left unclipped.
-43-
report ed that clipping in 1969 decreased dry matter yield during 1969
by 2h%.
The effect of clipping appeared to persist in 1970 and 3.971.
Clipping significantly decreased dry matter yield by 2h% in 1970 (Table
6) and also reduced the inflorescence height by 20% in 1970 (White et
al., 1972).
Clipping appeared to decrease dry matter yield by 12# in
1971 (not significant).
Effects of N Fertilization
Undipped plants.
When growth began April 3, the percentage of
TNC in the stem bases of N-fertilized, unclipped plants was less than
in stem bases of non-fertilized, unclipped plants (Fig. 4).
The TNC in
N-fertilized plants decreased to its lowest spring level earlier than
in non-fertilized plants.
From April 28 to May 20, TNC accumulated
rapidly in plants on all N treatments.
Nitrogen fertilization increased
the percentage of TNC at inflorescence emergence (May 29) and at first
anthesis (June 9).
Because soil water (Fig. 3) was apparently limiting
plant growth, Nfertilization did not affect TNC on June 19.
However,
the l40 kg of N decreased TNC on June 30 compared to that of the 0 and
70 kg of N rates.
Application of 140 kg of N/ha initiated tiller growth
(increased stem-base weight) earlier after the late June rains than
either the 0 or 70 kg of N rate (Fig, 6), and this may have been
associated with the TNC decrease on June 30,
-44-
Table 6 .
Residual effects of N fertilization in November 1968 and
clipping in 1969 on dry matter yield of green needlegrass
during 1970 and 1971.
Clipping
Frequency
N rat e,. kg/ha
70 '
0
140
Avg.
---- kg/ha ---1970
Undipped
640
1130
1525.
1100 a*
Clipped
400
920
II85
835 b
Avg.
520
C
1025 b
1355 a
1971
'" '' ..
Undipped
190
320
'470
325 a
Clipped
1$5
263
405
285 a
Avg.
190 a
290 ab
440 b
*Average values for clipping treatments or for nitrogen treatments
followed by the same letter are not significantly different -at the 5%
level of probability.
6»
15
-£+r
12
O N
O ----- O 70 N
A ------ A 140 N
□ ----- □
CO 0) CO CO
o
CD 0) 0) O O
CU —
CVJ CVJ
June
Fig. 6.
Weight of stem bases from ten unclipped green needlegrass plants
during 1969 with and without N fertilization during 1968.
The magnitude of TNC decrease after anthesis was inversely
proportional to N-fertilization rate and was apparently related to new
tiller formation.
Nitrogen fertilization increased the number of new
tillers formed following rains in late June and early July,
From July
2 to 29, tiller numbers increased 0, 2,5: and 37 -0% on plots fertilized
with 0, 70, and 140 kg of N/ha, respectively' (White et al,, 1972),
The
l40 kg of N increased the weight of stem bases earlier than did the 70
kg of N following the late June and early July rains (Fig. 6),
The 70
kg of N increased the TNC on August 12 over that of the 0 kg of N
while the 140'kg of N did not.
The 70 kg of N may have increased the
TNC because it initiated tiller growth later than did the 140 kg of N.
The TNC concentrations remained equal among N-fertilizer treatments
from mid-August through mid-September when soil water tension at 0 to
30 cm exceeded the wilting point (Fig. 3 )•
When growth resumed after a
September 21 rain, TNC decreased in the stem bases of non-fertilized
plants and in plants fertilized with 70 kg of N.
However, the TNC in
stem bases of plants fertilized with l40 kg of N did not decrease.
Clipped plants.
From May 20 to July 10, TNC of non-fertilized
plants declined in a linear manner from 17 to 7*5% (Fig. 7)•
In
contrast, the decline of TNC in fertilized plants was more variable.
Nitrogen fertilization did not affect TNC of clipped plants when
sampled two days after clipping.
However, approximately 13 days after
clipping, N appeared to increase (not significant) the TNC on May 20
12
□ ------- □
O ------- O
A ------- A
co h- co co o (D m cn o o
CM CO
ON
70 N
140 N
<n —
June
Fig. ?•
Percentage of TNC in stem bases of frequently clipped green needlegrass during 19&9 with and without N fertilization during 1968.
-47-
O
-48-
and June 9, and significantly increased TNG on June 30, July 22, and
August 12.
The l40 kg of N increased TiNC of clipped plants on July 22 and the
70 kg of N increased TNG on August 12.
The l40 kg of N probably
increased TNG earlier because it increased tiller initiation (stem
base weight) earlier than the 70 kg of N following the late June and
early July rains (Fig. 8).
The TNG level of clipped plants on all N treatments decreased
follbwing autumn growth which began after the September 21 rain.
The
decrease in TNG was greater in plants not fertilized <?r fertilized with
70 kg of N than in plants fertilized with 140 kg of N.
Residual effects of the November 1968 application of N were present
in both 1970 and 1971»
In 1970, residual N from the 70 kg and 140 kg
of N applications increased dry matter yield 100 and 123%, respectively
(White et al., 1972).
Also residual N from, the l40 kg of N treatment
increased the inflorescence height in 1970 by 15% more than did either
the 0 or 70 kg of N (White, 1971)•
In 1971, th§ residual from the
140 kg of N application increased'the dry matter yield by 130% (Table
6)0
Residual N from 70 kg of N appeared to increase the dry matter
yield by 50% (not significant). .
70 N
140 N
-49-
5
9
I
I
CO N
Fj
T
CO CO
F nTI
O 0) 0) 0) O O
CU CU
CU —
June
Fig. 8.
Weight of stem bases from ten frequently clipped green needlegrass
plants during 1969 with and without N fertilization during 1968.
-50-
Total Nitrogen
In the stem bases of unclipped green needlegrass, the percentage
of total N (Figo, 9) varied inversely with the percentage of TNC (Fig. 4)
during the spring and early summer.
During the remainder of the season,
total N concentrations remained near 1.5% while-TNC concentrations
fluctuated greatly.
Frequent clipping of green needlegrass increased the percentage of
total N (Fig. -10) during July and at the same time decreased the TNC
level (Fig. 5) in the stem bases.
The increase in percentage of total
N (Fig. 10) during June and July by clipping was accentuated by a
decrease in dry weight of the stem bases (Fig. 2),
Also, the increased
N during July may have resulted because clipping extended the period of
plant growth (White et al., 1972), and resulted in N uptake for a longer
period.
Clipping had no effect on the percentage of total N in the
stem bases during the autumn of 1969.
Thus, clipped plants at the end
of the growing season of 1969 had the same percentage of total N as
unclipped plants but less TNC for winter survival and spring growth
initiation.
a on
■O 70 N
/4 0 N
I
CO N
CO CO
O 0) m
(D O O
<NJ —
June
Fig 9-
Percentage of N in stem bases of unclipped green needlegrass during
1969 with and without N fertilization during 1968.
4
U n dipped
Clipped
'
'I
'
a) N co CO o (D m m o O cH CU CU
June
Fig. 10.
Mean percentage of N (averaged over N levels) in stem bases of
green needlegrass during 1969 when clipped five times from May
through July 1969 or left unclipped.
DISCUSSION
Seasonal Variation of TNC
The TNC concentrations always decrease with early growth until
photosynthesis in exposed leaves can supply the energy required for
respiration and growth.
The rate, duration, and amount of this TNC
decrease vary among species and environmental conditions.
needlegrass had produced
When green
of its maximum annual upstretched-leaf
height, it had attained sufficient leaf area and photosynthetic
capacity to stop carbohydrate reserves from decreasing further.
Blue-
bunch wheatgrass (Agropyron spicatum) had produced by/0 (McCarty and
Price, 194-2), and mountain bromegrass (Bromus marginatus), only 10#
of its maximum annual upstretched-height before carbohydrate reserves
ceased decreasing (McIlvanie,, 194-2).
Green needlegrass is somewhat
like crested wheatgrass, since it started increasing its TNC level
earlier than bluebunch wheatgrass because of earlier leaf development,
smaller percentage of floral tillers,, and later initiation of stem
elongation (Hyder and Sneva, 1959).
The TNC decrease in late May coincided with higher air
temperatures (Fig; 3) and rapid elongation of floral tillers during the
booting stage.
The carbohydrate reserves of perennial ryegrass,
orchardgrass, meadow fescue (Festuca pratensis), and timothy also
decreased during the period of rapid elongation of floral tillers
-54-
(Waite and Boyd, 1953)•
Hyder .and Sneva (1959) found that removing the
inflorescence from crested wheatgrass at emergence did not stop
carbohydrate reserves from decreasing in a manner similar to that in
plants allowed to develop seed.
The TNG level (Fig, 4) during the last of May and early June
appeared to fluctuate inversely with air temperature (Fig. 3)•
The
TNG decreased during periods with higher temperatures and increased
during periods with lower temperatures.
Among others, Brown (1939)
working with Canada blpegrass (Poa compressa), Kentucky bluegrass, and
orchardgrass, and also Sullivan and Sprague (1949) working with
perennial ryegrass, found that temperatures above optimum for plant
growth decreased the carbohydrate reserves.
Loss of TNG in unclipped plants was greatest from anthesis to
completion of seed dissemination.
trends reported in the literature.
This was not anticipated from TNG
Typically the lowest level would
occur after initiation of spring growth, 'during the second or third
leaf stage.
A marked decrease in TNG during seed dissemination also .
has been reported for orchardgrass (Colby et al«, 1966), needle-andthread (Stipa comata),! and squirreltail (Sitanion hystrix) (Coyne and
Cook, 1970)•
In our studies, the process of seed ripening can not
entirely account for the TNG decrease, because the TNG of clipped
plants decreased similarly to those of unclipped plants.
Although the
TNG loss in clipped plants may be entirely due to utilization of
-55-
reserves following clipping, the similarity of TNC trends of clipped
and unclipped plants is striking.
The TNC decrease in July is probably
not related to temperature because TNC increased during August when the
temperature was much higher than during July (Fig, 3)•
The decrease in TNC during July was probably related to tiller
initiation and growth following the late June and early July rains.
White et al. (1972) showed that the percentage of phosphorus and crude
protein in the herbage increased during early July indicating renewed
growth activity.
The weight of stem bases (Fig. 2) increased during
the last of July and early August.
White et al. (1972) also reported
that tiller numbers increased during July, thus indicating that late
June and early July rains had caused new tiller initiation.
Coyne and
Cook (1970) also reported that new tiller growth following seed ripening
caused the TNC level to decrease in needle-and-thread, squirreltail,
and Indian ricegrass (Oryzopsis hymenoides) in Utah.
Loss' of photosynthetic area of green needlegrass could have
contributed to the TNC decrease during seed ripening.
All leaves of
floral tillers senesced within one .week following seed ripening (White
et al., 1972). -The first leaf of vegetative tillers initiated during
the autumn of 1968 senesced during May 1969.
The second, third, and
fourth leaves of vegetative tillers initiated in the autumn were 75; 55,
and 35 days old, respectively, from the date that their collar appeared.
The maximum photosynthetic capacity of the leaves of tall fescue (Jewiss
-56-
and Woledge, I967) and orchardgrass (Treharne et al. , 1968) occurred
when the leaf blades first emerged from the sheath, and then decreased
with age.
The life span of an orchardgrass leaf, after it reached full
extension, was about 28 days.
The TNC increased during August and early September in both clipped
and unclipped plants, even, though new leaf length on clipped plants did
not exceed 10 cm.
During this period the mean air temperature reached
26 C, which is 6,9 C above normal, and the soil water content was
below the wilting point in the O- to 50-cm depth (Fig. 3)•
Wardlaw
(1968) reported that TNC increases if drought restricts elongation
growth but does not severely limit photosynthesis.
This would seem to
be true for both clipped and unclipped green needlegrass plants in late
summer.
The resumption of growth after a September 21 rain (Fig. 2) caused
the TNC level to decrease during the autumn.
McCarty (1938) also found
that autumn growth of mountain bromegrass in Utah decreased the
carbohydrate reserves.
The seasonal variation of TNC shown in Fig. 4 would not necessarily
be characteristic of seasonal variation of TNC in green needlegrass
grown at other locations or even for the same location in another year.
Colby et al. (1966) showed that the seasonal variation of total fructose
in the stem bases of orchardgrass was different when the plants were
-57-
grown in Massachusetts than when they were grown in Hokkaido, Japan
(Fig. I).
Effects of Clipping
Clipping five times in 1969 reduced yield in 1970 and 1971.
While
this yield reduction was partially due to the lower TNC level of clipped
plants in the autumn of 1969, other factors may be involved.
Clipping
apparently reduced rooting depth, since we found that less water was
extracted from the 90- to.l20-cm depth under clipped plants (White and
Brown, 1972).
Others have found that,frequent clipping of orchardgrass
essentially stopped root extension (Crider, 1955; Davidson and
Milthorpe, 1966b).
In other studies, clipping was found to decrease
labeled phosphorus uptake for 8 days following clipping (Davidson and ■
Milthorpe, 1966b) or until new roots grew into the labeled phosphorus
zone (Oswalt et al., 1959).
In our study, frequent clipping represented an intensity of
herbage removal similar to severe grazing.
While this treatment
reduced yields .in subsequent years, it did not kill the plants.
Our
TNC data show that for unclipped plants, the' most critical period for
herbage removal,was during seed dissemination.
Although we did not
measure the effects of sequential single clipping on subsequent yield,
data from Idaho (Pearson, 1964; Wright, 1967) showed that clippingneedle-and-thread grass, a closely related species, during seed ripening
-58was most detrimental to the following year's herbage production.
Clipping five times in 1969 reduced the TNC level 3 to 5 units at
all sampling dates below that of unclipped plants and presisted even
after clipping had ceased.
Troughton (1957) noted that clipping
decreased the-TNC level at the end of the growing season proportional
to the number of clippings taken during the growing season and inversely
proportional to the time interval between clippings.
Cook (1966) in a
review article noted also that clipping reduced TNC level at the end of
the growing season and tfiat,the reduction of TNC was inversely
proportional to the length of time between the date of the last clipping
and the end of the growing season.
Often severe herbage removal by cutting or grazing will decrease
herbage production in subsequent years (Weinmann, 1948).
Clipping
crested wheatgrass grown in arid conditions reduced dry matter yield
the following year only when the growing season precipitation was much
below normal and it did not decrease yields when the growing season
precipitation was much above normal (Hyder and Sneva, 1963).
The
reduction in, dry matter yield was related to reduced carbohydrate
reserves present during September.
However, clipping perennial ryegrass
the previous year had no effect on dry matter production when grown
under humid conditions (Baker, 19575 Baker, i960).
reserves had been restored by early autumn.
The carbohydrate
-59-
Effects of N Fertilization
Environmental conditions play an important role in carbohydrate
utilization and storage.
Any conditions or treatments, such as higher
temperature or N fertilization, that increase meristemactic activity
with early spring growth should increase the rate and amount of TNG
decrease.
The greater TNG decrease associated with N fertilization has
been documented many times.
Rapid depletion of TNG can increase the
plant's susceptibility to damage from herbage removal; however, if
reserves are used to increase leaf area, this partially offsets the
loss of reserves by increasing photosynthetic capacity.
The early
spring mobilization of energy increases leaf area, herbage productivity,
and eventually, TNG concentration.
attain "these benefits.
Herbage removal can be delayed to
Following N fertilization, a short delay in
herbage removal will allow N to increase the plant's productivity
because green needlegrass restores TNG quickly and N fertilization helps
restore it even faster.
After the third-leaf stage, N fertilization increased TNG under
favorable plant growth conditions and had no effect under unfavorable
conditions. . Nitrogen increased TNG level during May and June probably
because it increased the leaf area.
In order to increase the leaf
area, N had to increase the leaf width (not measured) because it did
not increase the upstretched-leaf height of floral tillers nor the
number of leaves per tiller (White et al., 1972).
Nitrogen fertilization
-G o -
increased, TNC during seed dissemination because it increased tiller
initiation and growth,•
During the period of clipping, TNC was sampled at approximately
2 and 13 days after each clipping.
The TNC tended to increase between
the 2nd and 13th day following clipping ip plants on N-fertilized plots.
Had TNC been sampled later in the clipping interval (21 days), TNC
probably would have been greater in N-fertilized plants.
Assuming that
these levels at 21 days were equal to or above those at 13 days, TNC
must have dropped precipitously during the 2-day period following
clipping.
The large loss of TNC immediately after clipping has been
reported by other investigators (Alberda, 1966; Davidson and Milthorpe,
1966b; Sullivan and Sprague, 1943).
Total. Nitrogen
Recent reports have suggested that stored protein may be an
important source of energy reserves (Davidson and Milthorpe, 1966b;
Dilz, 1966; Sheard, 1968).
Smith and Silva (1969), however, reported
that very little, protein was translocated from roots to tops of alfalfa
after cutting.
Alberda (1966) reported that all dry matter loss in
perennial ryegrass plants following a pretreatment —
placing the plants
in a nutrient solution in the dark at 30 C for a short period —
be accounted for by the loss of TNG.
could
In our study, N (crude protein)
was not stored and utilized in a manner similar to that of TNG, thus
-6lN is not a major reserve energy source in green needlegrass, which
supports Smith and Silva's (1969) conclusion.
SUMMARY AND CONCLUSIONS
The effects of nitrogen (N) fertilization and clipping on seasonal
variation of total nonstructural carbohydrate.'(TNC) concentration in
the stem bases of dryland green needlegrass were measured in 1968 and
1969. Residual effects of these treatments were measured in 1970 a,nd
I97L*
A factorial combination of three levels of N and two levels of
clipping, were assigned to plots ih a completely randomized split-plot
design with four replications.
Ammonium nitrate was broadcast on main
plots in November 1968 at 0, 70, and l40 kg of N/ha,
The two clipping
treatments applied on the subplots were (A) plants undisturbed until
sampled (unclipped) and (B) plants clipped to a 5-cm height at about
2f-day intervals on May 7 and
28, June 17, July 8 and 29.
A preliminary study was conducted during October 1968 to determine
where greeh needlegrass stored the major proportion of TNC and number
of samples required to adequately measure the percentage of TNG.
The
preliminary study showed that live stem bases of green needlegrass
(October 1968) contained twice’the percentage of TNC as live roots.
The coefficient of variation of TNC in live stem bases from individual
plants was 20% and in live roots, 37%°
The coefficient of variation of
TNC was 16 .3% in live stem bases and 21.7%.in live roots when 10 plants
V "
were composited per sample and the main plots were arranged in a
completely randomized design with four replications.
-63-
During I969, plants were sampled at about 10-day intervals from
April 8 through August 12, on September 2 and 27, and on November
8,
Stem bases were dried weighed, then analyzed for TNG and total N
content.
',
Residual effects of N fertilization and clipping treatments
on dry matter yield in 1970 and 1971 were determined from samples
harvested when seed was ripe.
The concentration of TNC in the stem bases of unclipped green
needlegrass.varied considerably during the growing season and was
related to growth stage.
The percentage of TNC in hon-fertilized,
unclipped plants decreased from l8 to l4% from growth initiation after
winter--dormancy (April 5) until after second leaf formation (April 28).
The TNC increased after second leaf formation to 19% just before boot
stage (May'26),' decreased slightly at heading (May 29) and increased
back to 18% at first anthesis (June 9)*
Following first anthesis, the
initiation and growth of new tillers decreased TNC to 9% by completion
of seed dissemination (July 26).
The TNC increased to 19% in late
September during a period in which drought had stopped plant growth.
Plant growth resumed after a late September rain and the TNC decreased
to 16% by November.
Seasonal variation of TNC in clipped plants was similar to that in
unclipped plants but 3 to 5 units lower at all sampling dates.
The
TNC of clipped plants decreased to a low of 9% on July 10, which was
12 days earlier than the lowest TNC level attained by unclipped plants.
-64The TWC qf- clipped plants increased similarly to unclipped plants after
July 22.
The TNC concentration in clipped plants during November was
13% in contrast to 17% in unclipped plants.
appeared to persist in 1970 and 1971,
The effect of clipping
Clipping significantly decreased
dry matter yield in 1970 and appeared to decrease dry matter yield in
1971 (not significant).
Nitrogen fertilization decreased TNC only.from growth initiation
until the second leaf formation.
Thereafter, N fertilization of
unclipped plants increased TNC under favorable plant growth conditions
and had no effect under unfavorable conditions.
Nitrogen fertilization
increased the percentage of TNC at heading (May 29) and at first
anthesis (June 9)•
The magnitude of TNC decrease after anthesis was
inversely proportional to N fertilization rate and was apparently
related to new tiller development and increased photosynthesis following
the late June and early July rains.
The TNC level of clipped plants on
all N treatments decreased in the stem bases of green need'legrass
following autumn growth which began after the September 21 rain.
The
decrease in TNC was greater in plants not fertilized or fertilized with
70 kg of N than in plants fertilized with l40 kg of N.
Nitrogen
fertilization of clipped plants did not affect TNC within two days after
clipping, but increased it within 13 days after clipping.
Residual N
from the November 1968 application increased dry matter yield of
clipped and unclipped green needlegrass in 1970 and 1971-
-65-
In the stem bases of unclipped green heedlegrass, the percentage
of total N varied inversely with the percentage of TNC during the
spring and eariy summer,
Duripg the remainder of the season, total
N concentrations remained near 1.5% while TNG concentrations
fluctuated greatly.
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M O N T A N A STATE UNIVERSITY LIfiRlRTFS
3 17 6 2 1001 1 6 6 0 5
cop. 2
CO UK E PUCE
BINDERY
COLLEGE PUCE, W a
White, Larry M
Carbohydrate reserve:
of green needlegrass