SYUDIES 0N "FILLERENG OF SUD‘ANGRASS
(SORGHUM SUDANENSE, STAFF)
WITH $PECEAL ATTEN'HON TO
ME EFFECTS OF RiDGING

The“: for the Degree of DH. D.
MICKEGAN STATE UNIVERSITY

Teh- chien Shem
1964

THESIS

This is to certify that the

thesis entitled

 

' . ' ‘ "P lwﬁw‘v "‘77

Studies on Tillerlng of Sudnngrass \SUL h 1

Sudanense, Stapf) with Sgecial att‘
to the Lffects of Ridging

presented by

Teh—chien Shem

has been accepted towards fulfillment
of the requirements for

’1
an

 

D degree in

5.

 

Major professor

Date 414/; [7/]: / 7&4!

0-169

 
   
 

    

LIBRARY

Michigan State i
University ;
r.

ABSTRACT

Studies on Tillering of Sudangrass (Sorghum.sudanense, Stapf)

'with Special.Attention to the Effects of Ridging
By Teh-Chien Shen

Experiments were conducted in the field and under controlled
conditions to study the tillering process of Sudangrass, its
reaction to light intensity, nutrition and more especially to ridging
treatments. (Ridging - the heaping of soil over the plant crowns.)

Sudangrass plants produced more than enough tiller buds for
normal tillering under favorable conditions before the tillering
stage. Seedlings at the nth leaf stage differentiated n+2 primary
tiller buds or their primordia on the main stem and even secondary
tiller buds on the first four primary ones.

Ridging had a marked effect in reducing the number of tillers
per plant in all experiments conducted in growth chambers and green,
house. under field conditions, early ridging reduced the number of
stalks per unit length of row and yield when seeded at 10 pounds
per acre. These effects disappeared when ridging treatments were
applied at a later time or on plots with a.higher seeding rate of
20 pounds per acre.

The effects of ridging in suppressing tillering were mainly due
to the medhanical hindrance of soil on the emergence of tillers and
the reduction of the oxygen supply for developing tiller buds. Young
tillers were etiolated.and often became crooked when they were arrested

in the ridged soil.2 Peroxide addition in the ridged soil increased

the number of emerged tillers per plant.

Low light intensity delayed the tillering process , suppressed
further grmth of young tillers , and enhanced the effect of ridging.
Low light intensity of 300 f .c. almost completely suppressed tillering.

Nutrient deficiency reduced the number of tillers per plant but
had no interaction with ridging. Higher fertilities advanced tillering
and increased the number of tillers of ridged plants later in the
growing season.

Ridging treatments generally increased the plant height, dry
weight and yield of a single plant. These effects were attributed
to the well developed cram parts and root system.

Ridging was considered to be a possible practice for increasing
yields of crops of Gramineae when time of ridging and spacing were

well arranged.

STUDIES ON TILLERING OF SUDANGRASS (SORGHUM SUDANENSE, STAFF)

WITH SPECIAL ATTENTION TO THE EFFECTS OF RIDGING

By

Teh-chien Shen

A.THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirement
for the degree of

DOCTOR OF PHILOSOPHY

Department of Crop Science

196%

Approved: [122%

/
I
' ”1

ACKNOWLEDGEMENT

The author expresses his sincere appreciation to Dr. Carter M.
Harrison for his guidance in this research and for his helpful advice
in the preparation of the manuscript.

Gratitude is expressed to Dr. Wayne M. Adams, Dr. Robert S.
Bandurski, Dr. Ray L. Cook and Dr. Stephen T. Dexter for their critical
review of the thesis and helpful suggestions and to Professor Hubert

M. Bram and Dr. Milo B. Tesar for their assistance with the research.

ii

TABLE OF CONTENTS

mowcrION O O O O O O O O O O O O O O O O O O O O
REVIEl/J OF LI'IERA'I'IJRE O O O O O O O O O Q 0 O O O O 0

Experiment I. Effects of Ridging on Tillering and
Growth of Sudangrass. . . . . . . . .

mm MID MODS. O O O C O O O O O O O O O 0

Greenhouse Experiment
Field Experiment

EXIJERIWAL RESLJIJIS O O O O O O O O O O O O O O 0

Greenhouse Experiment
Field Experiment

Experiment II. Anatomical Study of Tiller Formation
MERIAIJS AND PmODS O O O O O 0 O O O O O O O O O
EMRIPENTAIJ RBSIj-[J'IS O O O O O O O O C O O O O O 0

Experiment III. Effects of Shading on Tillering and
Its Interaction with Ridging. . . .

MWAI‘mm-Iomooooooooooooooo
EMRIWALRESULT'S000009000000000

Experiment IV. Effects of Fertility on Tillering of

PmTERIMS AFID mmODS. O O O O O O O O O O O O O O O O O O O ‘0

Growth Chamber Experiment
Greenhouse Experiment

EWERI FMAIJ RES ULTS O O O O O O O O O O O O O O O O O O O O 0

Growth Chamber Experiment
Greenhouse Experiment

iii

Ridged and
Nonsridged Sudangrass Plants . . . . . . . . . .

Page

10

10

12

16
16

19

27
27

28

32

32

3Q

Experiment V. Effects of Peroxide
on Sudangrass . . .

MATERIALS AND METHODS. .

EXPERIMENTAL RESUETS . .

DISCUSSION . . . . . . . .
SW. 0 O O O O. O O O O

IJIERATURE CITED . . . . .

iv

and

Page

INTRODUCT I ON

The extent of tillering is one of the factors which affect the
yield of crops belonging to the grass family, Gramineae. The yield
of a sugarcane crop may be simply expressed by the product of the
average weight of millable stalks and the total number per unit area
of land. Tillering becomes more important When profuse tillering,
thinestemmed cane varieties are used in commercial production as
in Taiwan during recent years.

In the cane production area of Taiwan, ridging or "earthing up"
has been practiced by the farmers for a good many years. The most
narked effect of this practice is suppressed tillering. However,
yield data have Shown that ridging to a suitable height at the right
time is of value in sustaining a higher yield. This increased yield
is attributed to the effects of ridging in suppressing late tillers,
preventing lodging and improving drainage of the field, though the
effects of ridging on the tillering process and the subsequent growth
and development of sugarcane plants are still not clearly understood.

Sudangrass has growth and tillering habits similar to sugarcane
and was used as the experimental plant in this study of tillering and
its possible control. various segments of the environment were
controlled to see what effect suCh measures would have on the tillering

process.

REVIEW OF LITERATURE

Tillers are lateral shoots coming from axillary buds at the nodes
of grass plants. They are connected by vascular tissues (2) with
the main stem. Therefore, tiller formation and grwth are closely
related with the development and the physiological condition of the
main stems.

The differentiation of tiller buds seems not to be affected by
environmental factors . Studying rice seedlings grown under three
seed spacings, Nishikma and Hanada (10) found a definite relation-
ship bemeen the development of main stems and the differentiation
of tiller buds. When the nth leaf had emerged, i.e. at nth stage,
the (n+“0th leaf of the main stem had differentiated, and simultane-
ously the primordia of the (n+2)th and (n+l)th tillers were found
as merely swellings in the axils of the (n+2)th and (n+1) th. leaf
respectively. The nth tiller, which was a primordium at (n-2)th
and (n—l)th leaf stages, began to develop and grow as a tillering
bud differentiating one or two leaf primordia at nth stage , and
thereafter continued to grow if the environmental factors were
suitable.

The development of young tillers and their further growth, on
the other hand, are found to be related to the status of the main
stems and are affected by environmental factors . Direct evidence of
translocation of organic food material from the main stem to the

tillers and vice versa under normal conditions have not been reported .

However, experiments have shown that translocation of materials between
main stems and tillers took place under certain conditions. Dungan (2)
reported that tillers might nourish the main stem under some conditions.
Removing tillers from corn plants in the early milk stage caused a
slight reduction in yield and test weight of grain. Rosenquist (ll)
covered the tillers of common Nebraska dent field corn with a layer of
burlap to exclude light and prevent photosynthesis. Both main stem
and tillers developed poorly. Labanauskas and Dungan (7) reported

that foliated main stems of cats increased the yield of tillers from

21 to 58% compared to that of tillers attadhed to defoliated main
stems. Fbliated tillers increased the yield of the main stem.from 33
to 58% compared to that of main stems to which defoliated tillers were
attadhed. Therefore, tillers and main stems of growing plants inter-
dhange materials sudh as water, foods and nutrients under certain con-
ditions.

Takahashi, Okajima, Takagi and.Honda (18) found that during the
life time of rice plants, the concentration of nitrogen in leaf blades
and leaf sheaths decreased gradually while that in stems increased at
the tillering stage. In phosphorus deficient plants, the concentration
of nitrogen in the SIBHIWES low during the tillering stage. These plants
had only a small number of tillers. Potassium deficiency did not cause
a decrease in the number of tillers; translocation of nitrogen from
leaves to stems was also high during the time of tillering. They suggested
that nitrogen content in the main stem.may play a significant role in

the development of tillers.

Rikaki (3) studied the effects of light intensity on the growth
of nain-culms and tillers of rice. He found that tillering and the
growth of tillers were more sensitive to light intensity than the
growth of mainstems. Under higi light intensity, the grwth of
tillers was greater than that of main-culms . On the contrary, under
low light intensities, the growth of tillers was shorter than that
of main-culms. The repression of growth by low light intensity on
lately emerged tillers was stronger than that on old tillers. The
order of repression was (1) the tiller that will emerge in future,
(2) the tillers that are emerging now, and ( 3) the main stem. The
effects of shading on the deve10ping plants were thus (1) decrease
in number of tillers and (2) decrease in the ratio of tillers/ main
stem in respect of their dry weights.

Sato and Shimizu (12) investigated competition in composition
of tillers under 15 different planting densities adjusted by the
number of seedlings (1-5) per hill and that of hills per unit area
(36-72 hills per tsubo). On the number of tillers analysed according
to their order, third tillers decreased on any plot under intense
effect of competition, second tillers began to decrease at the point
of 3-'+ seedlings per hill in spite of an increase in number of hills
per unit area. First tillers increased with the increase in number

of seedlings per hill so far as this experiment was concerned.

Working on dry land crops, Sieglinger and Martin (14), and
Wiggans and Frey (20, 21) found that a decrease in spacing or increase
in planting rates decreased the number of stalks or head-bearing culms
per plants in sorghum and oats respectively.

Kaukis and Reitz (5) planted u oat varieties at the spacings of
2.5 and 5.0 inches apart in 7 inch rows. At the 2.5 inch spacing,
regression of yield on number of tillers expressed in grams per
tiller was within the range of 0.8251 to 1.155. At the wider spacing,
the corresponding values were 1.117 and 1.580. Based on the varieties
grown over the 2-year period, 7 5% more grain was produced under the
5 inch spacing than under a spacing of 2.5 inches. The data indica-
ted that 77% of the total yield increase in the widely spaced plants
resulted from increased tillering, 16% from increased yield per
tiller, and 796 from the interaction of both factors .

Burger and Campbell (1) reported the average number of tillers
per 3 square feet of Sudangrass at 3 drill spacings (it, 8 and 16 inch
row width) and 3 rates of seeding (12, 18 and 2a pounds per acre). In
the first harvest, number of tillers per 3 square feet increased with
increasing seeding rate and decreased with increasing row width in the
drilled plots. However, any differences in tiller counts which might
have been attributed to either rate or method of seeding in the first
harvest were largely lost by the end of second harvest.

The effects of ridging or "earthing up" on sugarcane have been

reported in several papers published in Taiwan. Lee (8) reported that

ridging sugarcane plants to a height of #0 cm above the seed piece
decreased the number of tillers from 11.16 per stool in nonpridged
plot to 9.81 in the ridged plot. The total number of millable stalks
of non-ridged plots was 20% more than that in the ridged plots.
However, average stalk length, diameter and weight per stalk of
ridged plants were higher than those of the control. No significant
difference in cane tonnage and sugar yield were obtained. It was
found that early tillers formed between September and December made
up 50% of the total yield of ridged plots while 66.9% of the total
yield of nonpridged plots was contributed by tillers formed between
November and February. MOre plants lodged in the noneridged plots.

LOh and Tseng (9) reported that #0 to 60 lateral sprouts were
produced by a single stool under the ground surface whiCh could become
tillers should the environmental conditions be favorable. In fact,
with the exception of the thinpstalked varieties whiCh usually pro-
duced 20 to 50 tillers, the two-eyed stool of the existing varieties
commercially planted in Taiwan produced only 10 to 20 tillers during
the tillering period. The remainder usually died before they emerged.
These authors suggested that high mortality of emerged tillers was
caused by sugarcane borers and the lack of rooting of tillers. Ridging
was proposed for suppressing late tillers and to promote early tillers
into millable stalks.

Experiments conducted by Sun and Liu (16) on a fine sandy loam

soil in the Tainan area of Taiwan showed that ridging to 30 cm decreased

the number of tillers over non-ridging. However, the mortality of
emerged tillers was also significantly reduced by ridging. No signi-
ficant difference was found between the number of millable stalks per
plot at the time of harvest. Increased length of stalk and 12% more
millable cane yield was obtained by ridging. The authors suggested
that the ridging practice might increase cane yield through minimizing
lodging, inhibiting the development of late tillers and accelerating
the rate of elongation of stalks .

Sun, Liu, Tang, Chow, Sze, Chang and Ho (17) reported the regional
tests of the ridging practice conducted on 123 farms of Taiwan Sugar
Company in two successive crop years . Three ridging practices in sugar-
cane culture namely (1) the customary system consisting of three soil
applications beginning from 2-3 months after planting and ending with
a total thickness of 30-36 cm above seed sets; (2) the simplified system,
in which only one soil application, 20-25 on above the seed sets was
made right after the rows close in, planting furrows being first filled
up through intertillage; and (3) non-ridging except with the leveling
of furrows through intertillage . It was concluded that ridging before
the start of the rainy season was of value in sustaining a higher yield
under the environmental conditions of all cane-growing districts of
Taiwan (with the possible but improbable exception of the East Coast
Plains which were not included in this study). All varieties reacted

similarly to the custmary and the simplified system of ridging except

N:Co 310, the thinpstalked variety, whiCh reacted favorably to the
more elaborate high ridging system.

Halwagy (u) mentioned the effect of producing a robust shoot by
periodical burial by sand on AgrOpyron junceum L., E1ymg§_arenarius L.
and Ammophila arenaria Link and reported his trial on the responses of
wheat to different depths of transplanting. This author transplanted
wheat culms of the length of 50 cm into clay loam.soil at depths of
10, 15, 20, 25 and 28 cnh It was shown that the 15 cm depth gave the
maximum.tota1 number of shoots, number of flowering shoots, dry weight
of Shoots, dry weight of Spikes and dry weight of whole plants.
Further increase in depth of transplanting decreased the number of
Shoots and the other items. Field trials in this respect were pro-
posed by the author. Ridging;may be a substitute for deep trans-
planting in agricultural practice.

KriShnaswamy and Thangavelu (6) observed that under deep water
conditions, tillers of rice were produced from upper nodes. This
suggests that a high oxygen supply may be needed for the development
of tiller buds. It is possible that under the conditions of ridging,
limitation of oxygen supply may also be one of the factors whiCh suppress
the development or growth of tiller buds.

Working on the relationship of the growth of sugar beet roots and
oxygen diffusion rate of soils, Wiersma and MOrtland (19) applied calcium.
peroxide as an oxygen supplier in clay, silty clay loam.and loamy sand

with free water table 12 inches from the surface of the soil. Peroxide

treatment increased the beet yield on the loamy sand which had the
lowest oxygen diffusion rate.

Scott (13) applied calcium peroxide in a compacted soil layer
of a bulk density of 1.95 and found that more fibrous roots of
alfalfa were present in the compacted layer receiving peroxide
treatments as compared to compaction without peroxide . He concluded
that impedance is not the physical soil factor which restricts the
growth of roots in unconsolidated layers with a bulk density as
high as 1.95 but that oxygen is the factor restricting or retarding

the normal growth of roots.

Experiment I. Effects of Ridging on Tillering
and Growth of Sudangrass

MATERIALS AND METHODS

Greenhouse Experiment

Piper Sudangrass seeds were sown on Sims clay and Grandby sand
in 10 inch clay pots on February 1, 1963 . One plant was kept in each
pot after thinning. Simulative ridging was made by adding 1 1/ 2 inches
more soil to the pots to cover the basal parts of plants at different
stages of development. The first ridging treatment (R1) was applied
on February 22 when plants had an average height of 15 .9 cm on clay
soil and 13.5 cm on sandy soil. The second ridging treatment (R2) was
applied on March 11 when the primary tillers of plants on clay soil
had an average height of 17.0 cm and on sandy soil 114.2 cm. The third
ridging (R3) was applied on plants grown on clay soil on April 1 when
the longest secondary tillers were about 15 cm in length. It was
applied to the plants on sandy soil on April 10 when they attainded
the same stage of development. Non—ridged plants were used as a
control (R0) . Four plants were used for each treatment. Mode of tiller-
ing was observed during the course of the experiment. Plants were har-
vested on April 27 .

Field Experiment

This experiment was conducted on the Crop Science Farm of Michigan

10

11

State University at East Lansing, Michigan. The soil was Conover loam
with moderate natural fertility. The land was fertilized with l+00
pounds of 5—20-20 fertilizer per acre and disked on May 8; soil was
harrcmed on May 11%, 1963. Piper Sudangrass was seeded on May 15.
Ammonium nitrate was broadcast on the surface at a rate of 300 pounds
per acre on May 20, about 8 days before emergence.

Piper Sudangrass was seeded at 10 and 20 pounds per acre. Ridging
treatments were applied at different times by earthing the rows with
soil to cover the basal 2 inches of the stem.

R0 treatment -- non-ridged control .

R1 treatment - ridging on June 13 when plants had 6 leaves .

R2 treatment - ridging on June 21 when plants had 7-8 leaves.

R3 treatment -- ridging on June 29 when plants had 8-9 leaves.
A complete randomized block design was used. Each block consisted of
8 treatments; each plot 5, 10-foot rows 10 inches apart. Treatments
were replicated 6 times.

There was adequate moisture for germination and early growth.
The field was dry during late June and early July. Plots were sprinkler
irrigated with 2—3 inches of water on July 6 and it rained on July 2“.
Two cuttings were made on July 20 and August 31. Number of stalks per

yard of the central three rows was counted one day before each harvesting.

EXPERIMENTAL RESULTS
Greenhouse Experiment

The number of tillers was counted as they emerged from the leaf
sheaths or the ridged soil during the course of the experiment.
Sudangrass plants grew more vigorously on Sims clay and developed
more tillers than those on Grandby sand. During the late part of
this experiment, e.g. in April, plants on the sandy soil showed signs
of nitrogen deficiency although 2.5 gm. of 15-15-15 fertilizer had
been applied to the soil of each pot at planting time. R1 and R2
treatIents reduced the number of tillers of plants on both soils.
Average date of the appearance of the first tiller in the R1 treatment
was about 10 days later than in the non-ridged plants in the clay soil
culture while the appearance of the first tiller of the R1 treatment
in sand culture was about 19 days later than where not ridged
(Figure 1, 2 and Table I).

The mode of tillering was very uniform on both soils. The first
two tillers from the axils of the first and second foliage leaves
emerged on the same day or successively within 2 or it days. The tiller
from the axil of the third leaf appeared about 10-20 days later
depending on the vigor of growth. These primary tillers were in the
same plane as the foliage leaves. The secondary tillers arose immediately

after or a few days later than the development of the third primary tiller.

l2

13

Figure 1. Plants grown on clay soil. A, non-ridged control,
B, C, and D are plants of R1, R2 and R3 treatments,
respectively.

Figure 2. Plants grown on sandy soil. A, non-ridged control,
B, C, and D are plants of R1, R2 and R3 treatments,
respectively.

ll}

 

 

 

 

 

15

In this experiment, most of the secondary tillers of the plants grown
on clay soil started to grow between H2-53 days after planting while
those of plants on sandy soil started to grow between 53-60 days after
planting. The secondary tillers grew on planes perpendicular to that
of the primary tillers. The fourth primary tiller and the axillary
buds in a higher position grew occasionally and irregularly at later
periods of growth.

Field Experiment

In the first cutting, the first ridging treatment (R1) reduced
both fresh grass yield and number of tillers per yard at the 1% level
of significance at a seeding rate of 10 pounds per acre. However,
ridging'had no effect when.the seeding rate was increased to 20 pounds
per acre. The high rate of seeding increased both fresh grass yield
and the number of stalks per yard significantly at the 1% level (Table II).
A significant coefficient of correlation of 0.uuu0 between freSh grass
yield and the number of stalks per yard was Obtained. r values of 0.8327,
1.0000 and 0.7915 were obtained by analysis of covariance of ridging,
seeding rate and their interaction respectively, but none of them was
significant at the 5% level due to low degrees of freedom. No significant
effect of ridging was fcund in the second cutting. The seeding rates,
however, still had effects on both freSh grass yield and the number of

_ stalks per yard. The coefficient of correlation between number of

16

stalks per yard and yields decreased to 0.3698 in the second crop.

It was significant at the 5% level.

Experiment II . Anatomical Study of Tiller Formation
MATERIALS AND METHODS

Piper Sudangrass seeds were sown 1 cm below the surface of
builder's sand in wooden trays on April 11+, 1963. They germinated
uniformly on April 18 . Complete nutrient solution was applied twice
a week.

Samples of the basal part of stems were taken at different

stages of development .

 

Date of sampling Stage of growth

 

April 18 First foliage leaves were 1.5-2.0 cm out of
the coleoptile; first leaf stage

April 20 Second leaves were 1.5-2.0 cm out of the first
leaves; second leaf stage

April 25 Third leaf stage

April 30 Fourth leaf stage

May 5 Fifth leaf stage

May 9 Sixth leaf stage

 

Tillers became apparent at the sixth leaf stage.

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Samples were fixed in a mixture of ethyl alcOhol, water and
formaldehyde (60:u0:u by volume). Paraffin sections were made and
stained with safranin, orange G and gentian violet by the Fleming

triple stain method.
EXPERIMENTAL RESULTS

Differentiation of primary tiller buds was studied in longitud-
inal section cut in the same plane as that of the foliage leaves.
Pﬁcroscopic observations revealed the differentiation of axillary
buds and their development.

At the first leaf stage, 5 nOdes had been formed on the main
stem (including the node of the coleoptile). Three bud primordia
were found in the axils Of the first three foliage leaves on 5 out
of 10 plants observed. These primordia were just small groups of
cells at the axils. Four plants were found to have 2 bud primordia
in the axils either of the first and second leaves or of the second
and third leaves. One plant had not formed any bud primordia.
Figures 3, 4 and 5 show the bud primordia at thisstage. NO bud had
been formed at the node of the coleoptile and no bud appeared in the
following stages of growth. Macroscopic observations also showed
that it was not a tiller bearing node.

At the second leaf stage, 6 nodes had been formed on the main
stem. Mbst plants Observed had u bud primordia. Differentiation in
size occurred. Basal bud primordia grew faster than those located
at higher nodes. The first bud had already differentiated one node on M

out of 8 plants Observed.

20

.At the third leaf stage all plants had 7 nodes on the main axis
‘with 5 buds and their primordia at the axils of foliage leaves. The
first axillary bud had differentiated 2-3 leaves and the second
axillary buds had l-2 leaves.

This pattern of differentiation held true until the fifth leaf
stage. At the nth leaf stage, n+u nodes had been formed on the main
stem. n+2 axillary buds had been differentiated (Table III). At
the sixth leaf stage, eleven nodes had formed on the main stems and
most plants had a total of 9 axillary buds, some as yet still in
the primordial stage. The five basal buds had differentiated leaves
(Figure 6).

Table III. Differentiation of primary tillers*

 

 

 

Stage of No. of nodes No. of axillary No. of nodes differentiated
development on the main buds differenp on axillary_buds
stem** tiated

lst 2nd 3rd nth 5th 6th
lst leaf stage 5.0 2.3 0.0 0.0 0.0 0.0 0.0 0.0
2nd leaf stage 6.0 3.9 0.5 0.0 0.0 0.0 0.0 0.0
3rd leaf stage 7.0 5.0 2.1 1.1 0.0 0.0 0.0 0.0
nth leaf stage 8.0 6.0 3.5 3.0 1.7 0.0 0.0 0.0
5th leaf stage 9.” 7.2 5.0 9.8 3.7 0.0 1.7 0.0
6th leaf stage 11.0 8.9 6.8 6.7 5.5 2.0 mm 0.0

 

*Data from 7—10 plants for each stage.
**Including coleoptile node.

21

Figure 3. Longitudinal section of Sudangrass seedling at the first
leaf stage Showing the primordium.of tiller bud at the
axil of the first foliage leaf. #3

 

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1..

Figure 4. Longitudinal section of Sudangrass seedling at the first
leaf stage showing the primordium of tiller bud at the
axil of the second foliage leaf.

22

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23

Figure 5. Longitudinal section of Sudangrass seedling at the first
leaf stage showing the primordium of tiller bud at the
axil of the third.fOliage leaf.

Figure 6. Longitudinal section of Sudangrass seedling at the sixth
leaf stage showing young tillers, tiller buds and tiller
bud primordia at the axils of first through ninth foliage
leaves with bud primordium.at the axil of seventh leaf
missing in this section.

 

 

 
  
 
  

 

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25

The development of secondary tillers was studied with longitudinal
sections cut at planes perpendicular to that of the foliage leaves .

It was found that secondary tillers started to differentiate at the
fourth leaf stage. A maximum number of 2 secondary tiller bud primordia
had been found on the first primary tiller and one on the second pri-
mary tiller. The leaf on the first node of the primary tiller was

a protective sheath. NO bud was found at this node.

The differentiation of secondary tiller buds followed the same
pattern of that of the primary tiller buds. At the sixth leaf stage
secondary tiller buds had been formed on the first four primary
tillers (Table IV). The first and second tiller buds already had

2 and 1 leaves differentiated respectively (Figure 7).

Table IV. Differentiation of secondary tillers*

 

No. of secondary tillers“
Primary tillers I(th leaf stage 5th leaf stage 6th leaf stage

——_7

lst tiller 2 3 5
2nd tiller 1 3 1+
3rd tiller 0 2 3
LLth tiller 0 l 2
5th tiller 0 0 0

 

—————

* Data from 5 plants for each stage.

*9‘ Maximum mlmber found on single plant.

26

          

   

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tiller of a
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a of secondary tiller buds at the axils of

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.1.

Longitudinal section of the first pr'

Figure 7.

Experiment III. Effects of Shading on Tillering

and Its Interaction with Ridging

MATERIALS AND METHODS

This experiment was conducted under controlled conditions in a
growth Chamber. Piper Sudangrass seeds were sown in 16 ounce cottage
cheese cartons on February 19, 196“. .A loamy soil was used. .After
germination, seedlings were thinned gradually to 3 plants per culture.

Temperature in the growth Chamber'was adjusted at 25°C. Plants
were illuminated with fluorescent light. Light intensity at the
level at the tOp of the pots was 2,000 f.c. The growth Chamber was
separated into U. compartments with white paper boards on March 3
when plants were at the fourth leaf stage. Light intensity in each
compartment was adjusted by Shading with layers of cheesecloth. Four
light treatments were applied as follows.

Full light - 1,800 f.c.

Reduced light 1 - 1,120 f.c.

Reduced light 2 690 f.c.

Reduced light 3 - 300 f.c.

The paper board septa were baffled to increase air circulation
Ibetween compartments when air was blown across the Chamber by the
circulating system. Temperature in the chamber measured after light
treatments had been applied varied with time between 22-29°C, however,

no appreciable difference was found between compartments. During

27

28

the light period, soil temperature at the surface was usually l-2°C
lower than the air temperature due to evaporation in the full light
compartment. It was about 2.5°C lower in the 300 f.c. compartment
than in the 1,800 f.c. compartment.

There were ten pots in each compartment, each with 3 plants.
On MarCh H, plants in 5 pots were ridged by adding on another cottage
Cheese carton, with bottom removed, as a collar and filling in soil
to 2 inChes.

All treatments were harvested on MarCh 27, 1964.
EXPERIMENTAL RESULTS

Nonpridged plants.started tillering on MarCh 9, 19 days after
planting, under all light treatments except 300 f.c. For ridged
plants, however, the appearance of the first tiller*was delayed from
1 to 5 days by shading. Figure 8 shows the tillering process of
ridged and nonpridged plants under different light intensities.
Reduced light treatments only prolonged the process of tillering of
non-ridged plants for a few days without decreasing the number of
tillers per plant. The number of tillers on ridged plants at the
end of the experiment were reduced at 1,120 and 690 f.c. at 5% and
1% levels of significance respectively (Table V). Significant
differences in total length of tillers and total dry weight of
tillers per plant were only fOund between ridged and noneridged plants
under 690 f.c. fluorescent light. The percentage of plants tillering

also was reduced.greatly by shading on ridged plants. Under 300 f.c.

29

light, neither noneridged nor ridged plants tilleredt Ridging increased
the height and dry weight of plants slightly under alllight treatments.
The effect of shading on the dry weight of plants was significant at

the 1% level.

The number of tillers shorter than 2 inChes on non-ridged plants
and those that had not emerged from soil on ridged plants were com,
pared. A large proportion of differentiated tiller buds grew longer
than 1/2 inch.but failed to emerge when plants were ridged. This
proportion increased with increased.shading.

Roots were found in the ridged soil at the three higher light

treatments.

numb" of ﬁller: per plant

 

30

 

 

2-0 '-
|~5r
I-O "
0.5-
0-0 1 J
IS 20 25 30 35 40
days on" planting
Figure 8. Effect of shading on tillering of Sudangrass under

different light intensities. 0 1,800 f.c., 0 1,120 f.c.,
‘ 690 f.C., —' m-ridgﬂ’ ”- ridged.

31

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Experiment IV. Effects of Fertility on Tillering of Ridged

and Non-ridged Sudangrass Plants

MATERIALS AND METHODS

Growth Chamber Experiment

Piper Sudangrass seeds were sown in.builder's sand in 16 ounce '5
cottage Cheese cartons on April 3, 1964. Two 6 inCh glass tubes
(1 inCh in diameter) were one-third buried in the sand. More sand

was added to the tubes to a level one inCh above the outside sand

 

surface. Two seeds were sown in eaCh tube. After germination,
seedlings were thinned to one per tube. Plants were illuminated 12
hours daily with fluorescent light of the intensity of 2,000 f.c. at
pot level. Temperature in the Chamber was controlled at 20-25°C.
Plants were watered with modified Hoagland nutrient solution.

On April 17, 36 cultures were selected and separated into 3
groups. The 12 0f the first group were used for full nutrient
treatment and‘watered.with nutrient solution A (full strength
Hoagland nutrient solution) every two days. Each of the 12 cultures
of the second group was leached discontinuously with a total amount
of 500 ml tap water at the start of the treatment and was watered
afterward with nutrient solution A every six days and with nutrient
solution B (1/10 strength in macronutrients and full strength in
micronutrients of modified Hoagland nutrient solution) on the days

when nutrient solution.A.was applied on group 1 but not on group 2.

32

33

Each culture of the third group was leached with a total amount of
1,000 ml tap water at the start of treatrent and was watered after-
ward with nutrient solution B every two days . Three days after the
nutrients were applied, all plants of group 2 and 3 showed signs of
insufficient nutrient supply .

On April 18, a simulated ridging treatIent was applied on one
of the two plants in each pot by adding 2 inches of greenhouse loamy
soil into the glass tube as shown in Figure 9. The ridged soil was
usually wet due to the capillary water arising from the sand.

All plants were harvested on May 11, 1961+.
Greenhouse Experiment

Greenhouse loamy soil was screened through a 1/2 inch screen
and was ‘thormg‘rdy mixed before planting. Ten to twelve seeds were
sown in each of 611 10 inch clay pots on February 2, 19611. 15-15-15
fertilizer was applied at the rates of 0, 250, 500 and 1,000 pounds
per acre and was mixed with the soil one inch below the seeds .

Each fertility treatment consisted of 16 pots . After germination,
seedlings were thinned gradually to 3 plants per pot. Simulative
ridging was made on 8 pots of each fertility treatment by adding 2
more inches of soil to each culture on February 18 , when plants had
attained 7-8 inches in height . At this time , plants were in the
‘tl'lird leaf stage . Plant development was apparently retarded under

the greenhouse conditions. The first cutting was made on April 16.

30

After the first cutting, the ridged soil was removed from.u
out of the 8 ridged cultures of eaCh fertility treatment. Regrowth
of the second crop and its yields were recorded. A second cutting

was made on May 26.

EXPERIMENTAL RESULTS

Growth Chamber Experiment

Figure 9 and the height and the dry weight yields of plants in
Table VI Show that nutrient supplies were successfully controlled
by the method used in this experiment. Analysis of variance showed
that the effect of nutrient treatment on the total dry weight of
plants was significant at the 1% level.
The development of tillers of non-ridged and ridged plants
at different fertility levels is shown in Figure 10. Ridging delayed
tillering and significantly reduced the number of tillers per plant
of the full nutrient treatment at the time of harvest. However,
no significant difference in the total length and total dry weight
of tillers per plant was obtained (Table VI) . Ridging treatment
Trad less effect on plants of low nutrient treatment. Average number
of tillers per plant‘was reduced from 2.08 of control plants to 1.75

of the ridged plants but the difference was not significant statistically.

35

 

 

Figure 9. Picture taken one week before harvest. From left
to right, full nutrient, 10w nutrient and very
low nutrient treatment. In each pot, left,
ridged plant; right, non-ridged plant.

numb" of llllara par plant

3-5

2-5

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36

20 25 30 35 40
days aHar planllng

Effects of nutrients on the tillering of ridged and
non-ridged Sudangrass. 0 full nutrient, a low
nutrient, A very low nutrient, —— non-ridged,
--- ridged.

37

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38

Ridged plants with full nutrient had an average of 0.u2 non-
emerged tillers per plant. This was much higher than the average
number of tillers whiCh were shorter than 2 inches on the non-ridged
plants. At the low fertility level, ridged plants had an average
of 0.67 nonpemerged tillers per plant in comparison with 0.50
Short tillers on eaCh nonpridged plant. Percentage of plants till-
ered were the same between ridged and nonrridged plants at both high
and low nutrient levels.

Only one plant of the very low nutrient treatment formed one
tiller one week.after the start of nutrient treatment. This tiller
remained the same size for the duration of this experiment. At
the end of the experiment another tiller on the same plant had
attained a height of 2 inChes. AAll other plants had either tillers

under 2 inChes in length or had nonsemerged tillers only.

Greenhouse Experiment

I. First cutting

During early springtime, light intensity and temperature were
very variable in the greenhouse. Temperature could be maintained
at 75-80°F only on cloudy days when natural light intensity was low.
On sunny days, light intensity increased to above 2-3,000 f.c. but
it was usually accompanied by an increase in temperature to above
90-95°F. Sudangrass grown under these conditions elongated exten-
sively, had tender leaves in an early stage of development and was

retarded in tillering.

39

Tillering of ridged and non-ridged plants of 4 different
fertility levels are shown in Figure 11. All ridged treatments
tillered.nuch later than the noneridged ones. Higher fertility
hastened tillering in.both ridged and non-ridged plants.

Yield data are shown in Table VII. The soil used in this
experiment contained enough nutrients that plants did not show signs
of nutrient deficiency. Higher fertilities seemed to increase the
dry weight of plants, however, statistical analysis showed that
the effect was not significant. Number of tillers per plant was
not affected by added fertility, however, the total dry weight of
tillers per plant was affected at the 5% level. Ridging significantly
reduced the number of tillers per plant in 0, 250 and 500 pound per acre
treatments, but no significant difference among the total dry weights
of tillers per plant could be attributed to the effects of ridging.

After the tillering stage only main stems grew to maturity
While all tillers remained in their juvenile stage. This is Shown
by comparing the dry weight of the main stem.and the total dry weight
of tillers per plant in Table VII.

Ridged plants outyielded non-ridged plants in all cases.
Significant differences were Obtained in 0, 500 and 1,000 pound per
acre treatments.

II. Second cutting
Tiller development of the second cutting is shown in Figure 12.

Nonpridged plants sent out tillers faster than the ridged plants.

 

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Removing ridged soil also hastened tillering.

Yield data are shown in Table VIII. Ridged plants had the highest
yield; plants with ridges removed in the second crop also outyielded
the noneridged plants though the latter had more tillers (Figure 13).
Nbst of the differences in yields are significant at l or 5% levels.

The advantages in growth vigor and yields of ridged plants in
either the first or second cutting may be attributed to the well
developed crown parts of the plants. Non-ridged plants developed
tillers and roots only from.nodes near the soil surface. Ridged plants
developed more roots from 2 or 3 nodes higher up when they were
covered by soil (Figure 10). In the second cutting, noneridged
plants did not show any responses to fertilizer. Plants with ridges
removed during the second crop were also paler in color than the
ridged plants.

Table VIII. Dry weight (gm) of nonpridged and ridged plants grown
at different fertility levels

 

Fertilizer (lbs/acre)

 

 

Treatment 0 250 500 1,000 Average
Non-ridged 2.50 a* 2.05 ab 2.1M ab 2.85 ab 2.50 ab
Ridge removed in

second crop 6.26 6.63 a c 7.08 a c 9.80 a 7.uu a c
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* Means in the same column with the same letter are different at
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per acre; G—I, 500 lbs per acre; J-L, 1,000 lbs per acre.
In each fertility group: left, non-ridged; middle, ridged
with ridge removed in second crop; right, ridged plants.

I+5

 

 

 

Figure 11+. Crown and root system of non-ridged (left),
ridged with ridge removed in the second crop
(middle) and ridged (rigit) plants of 500
lbs per acre treatment. Note difference in
crown and type of root gowth.

Experiment V. Effects of Peroxide Treatment and Ridging

on Sudangrass
MATERIALS AND METHODS

Calcium peroxidel was used as an oxygen supplier. Information

from the manufacturer2

indicates that it decomposes slowly at a rela-
tive humidity of 80 percent and loses 11.7 percent of its active
oxygen per week. Scott (13) reported that when being mixed in soil
this chemical released oxygen at rather a constant rate over a period
of 7 weeks.

One 6 inch glass tube (1 inch in diameter) was one third buried
in the soil in a 1+ inch clay pot. Soil was added in the tube and
Sudangrass seeds were sown in the tube at 3 inches from the upper
end. 'Iwo Sudangrass seeds were sown in each tube on May 23, 1961+.
After germination seedlings were thinned to 1. Plants were grown in
the grwth chamber at 25°C and withlZ hOLm illumination. Light intensity
was 2,000 f.c. at the level of the top of the pot. On June 5,‘ 60
uniform plants were selected and were divided into 3 groups . Plants of
the fir$t group were ridged by adding 2 inches of greenhouse loamy soil
into the glass tube. Plants of the second group were ridged with the
same kind of soil with 1% calcium peroxide mixed into it. A small glass
tube (l/H inCh in diameter, 5/8 inch in length) filled with 0.13-0.15 gm
calcium peroxide was put beside the basal part of the stem of each plant

of the third group, then, these plants were ridged as group one.

 

1Courtesy of Dr. E. A. Erickson, Department of Soil Science, Michigan
State University.

2Buffalo Electro Chemical Company, Inc. Buffalo

1&6

l+7

Soil in the glass tube was kept wet by daily watering.
Light intensity was reduced to and was kept afterward at
1,000 f.c. after the ridging treatment was applied.

All plants were harvested on June 21.

EXPERIMENTAL RESULTS

The tillering of Sudangrass is shown in Figure 15 and Table
IX. Plants of all treatments tillered at about the same time. 1%
calcium.peroxide mixed in the ridged soil seemed to increase the
total length of tillers and the total dry weight of tillers per
plant, but the differences were not significant statistically.
Calciunlperoxide applied in the small tubes which were buried in
the ridged soil increased the number of tillers during the latter
period of this experiment. It also increased the total length and
dry weight of tillers per plant. However, only the difference of
number of tillers between this treatment and the ordinary ridged
plants was significant at the 5% level. A.difference of 0.05 gm
was Obtained in the average dry weight of tillers per plant between
this treatment and the ordinary ridged treatment. The number of non-
emerged tillers was reduced by the peroxide treatments. Calcium
peroxide applied in glass tUbes had more effect than that mixed
with the soil. Percentage of plants tillered was not affected by

peroxide treatment.

 

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DISCUSSION

Anatmiical studies showed that Sudangrass seedlings differen-
tiated more than enough tiller buds for the nornal tillering pro—
cess under favorable conditions. The effects of light intensity,
nutrition and ridging on tillering are thus a.natter of influencing
further development of these buds. The order of tiller bud forma-
tion is identical with that of rice plants reported by Nishikawa
and.Hanada (10). Buds of secondary tillers had been formed before
the appearance of prinary tillers. The formation of secondary tiller
buds follows the same pattern as the formation of primary tiller
buds .

Light intensity, probably combining with temperature, is the
primary factor controlling tillering of young Sudangrass plants.
Under suitable conditions, Sudangrass attained the tillering stage
20-27 days after planting as shown in the growth chamber experiments.
Plants grown in the greenhouse under relatively low light and high
temperature during early springtime attained the tillering stage
30-50 days after planting. Decreasing light intensity to 690 f.c.
only prolonged the tillering process but did not reduce the number
of total tillers per plant during the period of experimentation,
though the dry weights of plants markedly decreased with decreased
light intensities. At 300 f.c. light, tillering was almost come
pletely suppressed. It seemed that a threShold existed between

300-700 f.c. for tillering under experimental conditions.

50

51

Low light intensity and relatively high temperature was also
found to suppress further development of young tillers. Tillers
stayed at their juvenile stage.while only the main stems attained
maturity. Sullivan (15) mentioned that 80°F‘was the temperature
for highest yield of dry matter of Sudangrass under controlled
conditions. FUkaki (3) reported that under high light intensity,
the growth of tillers was greater than that of the main stem.
Otherwise, under low light intensity, the growth of tillers was
less than that of the main culm. This was also true in Sudangrass.
{A similar phenomenon.was observed in the experiments conducted in
growth Chambers when shading developed because of the density of
experimental plants. Under the experimental conditions, light
intensity was sufficient for plant growth and tillering. However,
during the late period of these experiments self-shading on tillers
by the leaves of the main stem.occurred. Tillers usually stOpped
growth.under this condition. This may account for the fact that in
Experiments III, IV and V significant differences between treatments
were usually obtained in the number of tillers per plant but not in
the total length or dry weight.

Experiment IV, conducted in the growth chamber, showed that at
the tillering stage, low fertilities markedly reduced the number of
tillers at time of harvest. This relationship was also clearly shown

at the beginning of the tillering stage of the greenhouse fertilization

52

experiment which lasted for a muCh longer time and was harvested at
the flowering stage. In the later period of this experiment, not muCh
difference was found in the total number of tillers of plants at

the different fertility levels. Therefore, a low nutrient supply
might only delay tillering or prolong the tillering process similar
to the effect of low light intensities. It is interesting to compare
the plants of the 300 f.c. light intensity treatment of Experiment

III and those of the very low nutrient treatment of Experiment IV.
Plants of these two treatments were of similar height at harvest time
but were quite different in dry weight. Plants grown under low light
intensity had very poor dry matter accumulation; on the other hand
plants grown under very low nutrient supply had mudh more dry matter
per plant. The latter had an average of 1.02 tillers per plant

though they did not attain the 2 inch criterion for counting in these
experiments. Plants under very low light intensity had only 0.20

suCh tillers per plant. This suggests that the effect of light intensity
on tillering is more profound than that of nutrient supply.

Greenhouse and field experiments (Experiment I) Showed that the
ridging treatment reduced the number of tillers per plant and significantly
reduced the number of stalks per unit length of row and the yield of
Sudangrass at 10 pounds per acre seeding rate. These reductions in
number of stalks in the row and yields were not found when the rate of

seeding was increased to 20 pounds per acre. Ridgings applied after the

53

appearance of primary tillers and before the appearance of secondary
tillers also reduced the number of tillers per plant under green-
house conditions when a single plant occupied enough space for
development. Ridging treatment applied at a similar stage in the
field did not have the same effect. This shows the possible use
of a ridging practice in commercial crop production when spacing
and time of ridging are controlled.

The primary effects of ridging on tillering may be considered

to be the meChanical hindrance of soil on the emergence of tillers

 

few;

and the reduction of oxygen supply for the growth of tiller buds.
Tillers of Sudangrass generally come out through the leaf sheaths

and at the same time press it apart from the main stem. Young tillers
usually form an angle from the main stem.as Shown in Figure 16.

Tiller buds of ridged plants emerge from.soi1 usually with diffi-
culty. The first primary tiller usually cannot emerge from the ridged
soil because the leaf sheath of the first leaf is shorter than 2
inChes. Without its protection the first tiller bud generally be-
comes crooked in the soil as Shown in Figure 17. Tiller buds at

the axils of the second and third leaves have better protection from
the leaf sheaths. However, difficulties in emergence may be caused
by the close contact of the leaf sheath.with the main stem. These
young tillers were etiolated and also became crooked and were very

often arrested in the ridged soil.

5’4

Low light intensities greatly enhanced the effects of ridging.
Ridged plants had more non-emerged tillers than emerged ones under
low liglt intensities (Figure 18). It shows that under higher light
intensity, plants could overcome the unfavorable conditions caused
by ridging and send out more tillers.

The interaction of nutrient deficiency with ridging is different
from that of light and ridging. Figure 18 shows that ridging had a
similar effect in suppressing tillering at these three quite different
nutrient levels . Increase in the number of non-emerged tillers of
ridged plants and tillers under 2 inches on non-ridged plants caused
by nutrient deficiency are also nearly parallel to each other. These
plants were grown under relatively strong (2,000 f .c.) light which
was enough for normal tillering. The lack of interaction between
the effects of low nutrient supply and ridging also suggested that
light is the primary factor which affects tillering under both ridged
and non-ridged conditions while the effect of nutrient on tillering
may affect the general amount of growth and vigor of the plants.

Fertilizer addition under greenhouse conditions , however, showed
interaction of fertility and ridging effects at the late period of
the growing season. At harvest, not much difference in the total
nunber of tillers per plant was found between different fertility

treatments of non—ridged plants. However, higher fertilities increased

55

the number of tillers per plant of the ridged plants. During the
Whole growing season, the effect of fertility on the total performance
of plants apparently may be shown in part in overcoming the unfavorable
conditions caused by ridging.

The Observation of Krishnaswamy and Thangavelu (6) on the tiller-
ing of deep water’rice led to a speculation that a low oxygen supply in
the ridged soil may be a limiting factor for the develOpment and
emergence of tillers. In this research, 2 inCh ridges were applied in
most cases. Tiller buds were therefore buried at a depth of 2 inChes
iitnlthe soil surface. At this depth, the condition is usually suit-
able for the growth of roots. If oxygen supply is a factor Which
suppresses tillering of ridged plants, the oxygen.requirement of
developing tiller buds must be much higher than that of roots. Pre-
liminary tests showed that calcium.peroxide applied at a dosage as
high as 1% in ridged soil did not have any harmful effect on the growth
of Sudangrass plants and increased tillering under low (1,000 f.c.)
light intensity whiCh was known to be effective in enhancing the effect
of ridging on tillering. However, the maximum effect in increasing
tillers was Obtained When calcium.peroxide was applied in a.snall glass
tube Which concentrated the chemical in the vicinity of the basal part
of the stem.and prevented direct contact of this chemical with plants
and soil. No calcium.oxide was used as a check to balance the effect
of calcium.peroxide on the acidity of soil in this experiment because
the rate of decomposition of calcium.peroxide in soil and its solubility
are not well known.

 

 

Figure 16 .

56

 

Ridged and non-ridged Sudangrass plants. From left
to rigrt: ridged plant having two tillers from the
second and third foliage leaves; ridged plant with-
out tiller; non-ridged plant with tillers from the
axils of first three foliage leaves; and non-ridged
plants having three tillers, the third one emerging
from the leaf sheath.

 

Figure 17.

57

 

Four ridged plants on left and a non-ridged plant on
right. First three ridged plants showing different
degrees of growth of etiolated tillers of the first
and second nodes, none of them emerged from soil.
The fourth ridged plant has one non-emerged first
primary tiller, an emerged second tiller and a third
tiller which is emerging through the leaf sheath

of the third leaf. The non-ridged check has three
well developed tillers.

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59

During the course of Experiment V, efforts were made to control
the light intensity to give a critical condition for tillering for
the ridged plants. However, it was not very successful. High light
intensity applied before the ridging treatment apparently had its
residual effect on tillering in the early tillering stage. Plants
tillered much faster than expeCted. Calcium peroxide showed its
effect only at the latter period of this experiment when the vigor
of tillering was slowed down. Plants could not be maintained in the
growth Chamber any longer due to the limitation of space.

Sugarcane agronomists attributed the effect of ridging on
increasing cane yield to preventing lodging, inhibiting the develOp-
ment of late tillers and accelerating the rate of elongation of
stems. The author Observed that roots come from the lower nodes of
the main stem distributed in the ridged soil of Experiment III.

The plant height and dry weight of ridged plants were generally higher
than those of nonpridged plants. Efforts were made to prevent this
effect in the nutrient experiment by minimizing the amount of ridged
soil in the glass tubes. However, a significant difference in dry
weight of plants between ridged and non-ridged plants was still Obtained.
The fertilizer experiment conducted in the greenhouse Showed that plants
reacted more to ridging than to the fertilizer treatments. .A very
marked effect of ridging was found in the second cutting. Better crown
and root system development of ridged plants was observed in these cases

and it may have accounted for the increased growth and yield of the

60

shoot in Sudangrass. The additional root system developed within
the ridge may have a possible significance in increasing yields of

other crops of the Gramineae.

SUMMARY

Investigations were conducted to study the tillering process
of Sudangrass, its reactions to light intensity, nutrition and

more especially to ridging treatment.

1. An anatomical study showed that Sudangrass seedlings had
differentiated more than enough tiller buds for the normal
tillering process under favorable conditions before actual
tillering began. Thus the effects of environmental factors
and ridging on tillering are influencing fUrther development
of these buds.

2. Ridging treatments reduced the number of tillers per plant in
all experiments conducted in the growth chambers and greenp
house. Early ridging applied before the tillering stage
showed.maximum.effects. Uhder field conditions, the effect
of ridging in reducing yield may be prevented by late appli-
cation or increasing the rate of seeding.

3. The primary effects of ridging on tillering are attributed
to the mechanical hindrance of soil on the emergence of
tillers, subsequent etiolation and the reduction of the
oxygen supply required by growing tiller buds.

H. Light intensity markedly affected tillering. Low light
intensities delayed and prolonged the tillering period.
Under 300 f.c. light intensity, tillering was almost come

pletely suppressed.

61

5.

62

Marked interaction between light and ridging treatment was
observed. Low light intensities enhanced the effect of ridging.
Under low light intensity, the main stem.grew fast while tillers
remained in the juvenile stage.

Nutrient deficiency reduced the number of tillers but did not
have an.interaction with ridging treatments in the Short tenn
experiment. Under greenhouse conditions, higher rates of
fertilizer application increased the number of tillers per plant
of ridged treatments at the late period of the growing season.
Ridging generally increased the plant height, dry weight and
yield of a single plant. These effects were attributed to the

better developed crown parts and root systems of ridged plants.

10.

12.

LITERATURE CITED

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of seeding on the original stand, tillering, stem diameter,
leaf-stemrratio and yield of Sudangrass. Agron. Jour. 53:
289-291.

Dungan, G. H. 1931. An indication that corn tillers may nourish the
main stalk under some conditions. Jour. Amer. Soc. Agron.
23: 662-670.

FURaki, S. 1957. The investigation on the tillering of rice plant
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Halwagy, R. 1961. The effect of depth of transplanting on
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Kaukis, K., and L. P. Reitz. 1955. Tillering and yield of oat
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Krishnaswamy, V., and S. Thangavelu. 1960. Preliminary Observation
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Labanauskas, C. K., and G. H. Dungan. 1956. Interwrelationship
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Lee, T. T. 1953. Influence of hilling operation on yield composition
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LOh, C. S., and P. M. Tseng. 1953. Studies on tillering of sugarcane
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