Sweet corn (Zea mays L.) growth and yield are influenced by establishment methods

Abstract

Six experiments were performed in the term of three years in order to explore and
compare the effects of transplanting and direct sowing (DS) on sweet corn (Zea mays L.)
growth, earliness and yield. Different genotypes, tray cell sizes (volume) and seedling
ages were assayed. In all experiments, direct sowing was performed with a final
separation of 0.25 m between plants in each row. Growth parameters (height, leaf area
and ear size) were reduced with the increase of age and/or decrease of the tray cell size,
mainly in cultivars with early flowering i.e., low cumulative corn heat unit (CHU)
requirements. Earlier harvests were obtained in transplanting compared to direct sowing,
although with lower yields. When the thermal time accumulated by plants in the trays
was higher than 100 CHU, the yield decreased by 3.91% (R2 = 0.79) for each unit of
CHU. The results indicate that the transplanted sweet corn yield was generally lower than
of direct seeded plants, and differences grew bigger as the tray cell volume was smaller
and the seedlings age increased.

Full text

Vol 44, No. 6;Jun 2014
2 Pretoria, South Africa
Sweet corn (Zea mays L.) growth and yield are influenced
by establishment methods
Gabriel Céccoli1,2, Leandro Ismael Ortega3, Norberto Francisco Gariglio1, Juan
Carlos Favaro1, Carlos Alberto Bouzo1.
ABSTRACT
Six experiments were performed in the term of three years in order to explore and
compare the effects of transplanting and direct sowing (DS) on sweet corn (Zea mays L.)
growth, earliness and yield. Different genotypes, tray cell sizes (volume) and seedling
ages were assayed. In all experiments, direct sowing was performed with a final
separation of 0.25 m between plants in each row. Growth parameters (height, leaf area
and ear size) were reduced with the increase of age and/or decrease of the tray cell size,
mainly in cultivars with early flowering i.e., low cumulative corn heat unit (CHU)
requirements. Earlier harvests were obtained in transplanting compared to direct sowing,
although with lower yields. When the thermal time accumulated by plants in the trays
was higher than 100 CHU, the yield decreased by 3.91% (R2 = 0.79) for each unit of
CHU. The results indicate that the transplanted sweet corn yield was generally lower than
of direct seeded plants, and differences grew bigger as the tray cell volume was smaller
and the seedlings age increased.
Keywords: tray cell volume; seedling transplant; transplant age; yield; direct sowing.
1. Facultad de Ciencias Agrarias, Departamento de Producción Vegetal, Kreder 2805,
C.P. S3080HOF. Esperanza, Santa Fe, Argentina.
2. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Avenida
Rivadavia 1917. C1033AAJ. Ciudad Autónoma de Buenos Aires, Argentina.
3. Instituto de Fisiología y Recursos Genéticos Vegetales (IFRGV) Centro de
Investigaciones Agropecuarias (CIAP)-INTA. Camino 60 Cuadras km 5.5 X5020ICA-
Córdoba-ARGENTINA
Corresponding author: Gabriel Céccoli (gabrielcnbj@yahoo.com.ar)

Vol 44, No. 6;Jun 2014
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INTRODUCTION
The yield potential of a crop depends on its capacity to obtain resources from the
environment and use them to fix carbon dioxide (CO2) into biomass (Grzebisz et al.,
2013). For grain crops, it also depends on the proportion of its biomass that is partitioned
to grains (Binkley et al., 2004; Long et al., 2006). Sweet corn (Zea mays L. var.
saccharata Bailey), especially super sweet (sh2) and sugar-enhanced (se) sweet corn, is a
preferred and widely grown variety (Zhao et al., 2007). It is a warm-season crop adapted
to temperate climates though usually affected by weak seed vigor and common poor
emergence rates (Zhao et al., 2007).
In Argentina, sweet corn production has been steadily growing in recent years,
and is currently a horticultural crop of great importance for both fresh consumption and
the food industry (Bertolaccini et al., 2010). Sweet corn transplanting has been
undertaken in an attempt to increase this plant population and improve earliness. Early
spring sweet corn is usually grown in cold soils at sub-optimal temperatures for seed
germination (Hassell et al., 2003). Soil and air low temperatures hamper sweet corn seed
germination and early growth, especially in the shrunken-2 (sh-2) hybrid. Transplanting
could improve field crop establishment (Aguyoh et al., 1999), but several factors
influence transplant production and performance, such as tray cell size (volume) and age
at the time of transplanting (NeSmith and Duval, 1998). Aguyoh et al. (1999) also
mention a big shoot-to-root ratio, a lower rate of root regeneration after transplanting, and
a lower older roots intake of nutrients as constraints for transplanting in this species. The
scarce information about overcoming low seed vigor and disadvantageous environmental
conditions during early spring for this cultivar, points out the importance in obtaining
data for the management of this crop.
The aim of this work was to evaluate the effects of tray cell sizes (volume) and
seedling ages of transplanting on growth parameters, earliness and fruit yield of sweet
corn compared to direct sowing.

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4 Pretoria, South Africa
MATERIALS AND METHODS
Six experiments were conducted during three years to compare direct sowing to
sweet corn transplants from different combinations of tray cell sizes, plant ages and
genotypes. The seedlings were grown in plug trays filled with a dry commercial peat
moss and vermiculite medium (Grow Mix S1, Terrafertil®) with pH 5.3-5.8 and EC 0.3-
0.4 dS m-1. Sweet corn seeds were sown with a compressed-air operated vacuum seeder
(Sathya®); adjustments on the seeder were used to achieve high percentages of cells with
a single seed per cell. After sowing, the trays were subirrigated to saturation, misted, and
then transferred to a germination chamber. At the end of the germination period, half-
strength Hoagland solution (Hoagland and Arnon, 1950) was added to the water reservoir
and trays were placed in a heated nursery. The cumulative corn heat unit (CHU, base
temperature = 10ºC) was calculated according to Jame et al. (1999). Temperatures in
nursery and field were measured with an automatic weather station (Davis
WeatherLink®). Plant leaf area was measured non-destructively with a Licor field meter
(LI-3000®).
In the first year, three experiments were carried out: 1) transplants of 20- and 33-
day-old seedlings and 20, 40, and 120 cm3 tray cells with a normal sugary (su) cultivar of
760 CHU; 2) transplants of 19- and 27-day-old seedlings in the same cell type, but of the
sugary enhanced (se) genotype variety (905 CHU); 3) transplants of 27-, 32-, and 39-day-
old seedlings with 30 cm3 cell type alone and shrunken-2 (sh-2) hybrid (955 CHU). In the
second year: 4) transplants from 20- and 35- day-old plants using the same cell type and
genotype as experiment 1; 5) transplants of 20- and 35- day-old plants and same cell type
as the experiment 2 but using sh-2 hybrid (870 CHU); 6) transplants of17-, 25-, and 33-
day-old plants using the same cell types and genotype as the experiment 3. Measurements
were made both in the nursery and field. The substrate for transplanting was a silt loam
Molisoll (Aquic Argiudoll).
At transplanting, plant leaf area (LA), shoot dry weight (S), root dry weight (R) were
measured in replicated seedlings; root/shot ratio (R/S) and specific leaf area (SLA) were
subsequently calculated. Total yield and cob weight were determined when cobs maturity
were considered suited to fresh market consumption. This phenological phase coincided
with husk leaves remaining tight and green. In all experiments, direct sowing was
performed with a final separation of 0.25 m between plants in the row. Seedlings were
transplanted in a randomized, complete block design with four replications for each
treatment. The statistical analysis was performed through ANOVA; the means between
treatments were compared by Duncan's test, with a significance level of 5% and 1% in
certain cases. The Statgraphics Plus 5.0® computer statistical program was used to
perform the statistical analyses and graphs. ANOVA assumptions were met in all
analyses.
RESULTS AND DISCUSSION
The general appearance of sweet corn seedlings allowed recognizing differences
arising from the tray cell size used. At 20 days, seedlings grown in the 120 cm3 cells were
taller than those of 20 and 40 cm3 cells (Fig. 1 a, c). Furthermore, in 35 days-old plants, a
slight etiolation (Fig. 1 b, d) became noticeable. For experiment 6, a few days before the
harvest onset, the plant roots differed in size depending on the age of transplant, with
plant roots from direct sowing being the largest and most vigorous (Fig.2). The roots of
the plants that remained in the trays the longest (33 days) were of the lowest
development. This was also observed by Leskovar & Cantliffe (1993) in a similar work

Vol 44, No. 6;Jun 2014
5 Pretoria, South Africa
on pepper. Other research demonstrate the importance of transplanting in comparison
with direct sowing, where the first reduce the occurrence of fungi attack in the nursery
stage (Oswald et al., 2001)
Nursery stage
Tray cell size affected LA, S and R significantly increasing their values in
proportion to cell size (Tables 1 to 4, figure 1). The SLA also was proportionally
increased to cell volume in experiments 1, 2 and 5 (Tables 1, 2 and 4, respectively),
except for experiment 4 (Table 3). When R/S was analyzed, a smaller variation between
treatments was observed, detecting a significant effect (P < 0.01) in experiment 1 only
(Table 1). As expected, LA and S values raised significantly (P< 0.01) as the age of the
seedlings increased (Tables 1 to 4). There was no interaction between volume and
transplant age on seedlings LA.
Table 1. Effect of tray cell size and transplant age on leaf area (LA), shoot dry weight
(S), root dry weight (R), root to shoot ratio (R/S) and specific leaf area (SLA) of
sweet corn cv. ´Sundance´ (Experiment 1).
Volume
(cm3)
LA
(cm2)
(S) (g)
(R) (g)
R/S
SLA (cm2 g-1)
20
50
0.23
0.16
0.82
227.3
40
60
0.18
0.18
1.11
323.8
120
110
0.33
0.54
1.45
323.2
F test
**
**
**
**
**
Age (days)
20
49
0.17
0.17
1.08
283.9
33
97.6
0.32
0.41
1.17
298.9
Significance
**
**
**
n.s.
n.s.
Volume x Age
n.s.
n.s
*
*
*
n.s.: not significant; *. P < 0.05; **. P < 0.01.

Vol 44, No. 6;Jun 2014
6 Pretoria, South Africa
Table 2. Effect of tray cell size and transplant age on leaf area (LA), shoot dry weight (S),
root dry weight (R), root to shoot ratio (R/S) and specific leaf area (SLA) of sweet
corn cv. ´Sundial (Experiment 2). Results from every cell volume are means of 19
and 27 days after transplant. Values for age are averages of all cell volume
treatments.
Volume
(cm3)
LA
(cm2)
(S) (g)
(R) (g)
R/S
SLA (cm2 g-1)
20
34.8
0.16
0.16
1.15
229.3
40
50
0.21
0.22
1.15
248.1
120
59.2
0.23
0.25
1.2
267.2
F test
**
*
*
n.s.
**
Age (days)
19
36.1
0.13
0.19
1.45
275
27
60
0.27
0.23
0.88
221.4
Significance
**
**
*
*
**
Volume x
Age
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.: not significant; *. P < 0.05; **. P < 0.01.
Table 3. Effect of tray cell size (volume) and transplant age on leaf area (LA), shoot dry
weight (S), root dry weight (R), root to shoot ratio (R/S) and specific leaf area (SLA)
of sweet corn cv. ´Sundance´ (Experiment 4).
Volume
(cm3)
LA
(cm2)
(S) (g)
(R) (g)
R/S
SLA (cm2 g-1)
20
83.8
0.22
0.14
1.1
365.3
40
97.7
0.27
0.25
1.11
347.5
120
115.3
0.31
0.27
0.93
387.2
F test
**
**
**
n.s.
n.s.
Age (days)
20
34.3
0.10
0.12
1.37
351.8
35
163.6
0.43
0.32
0.73
381.6
Significance
**
**
**
**
n.s.
Volume x
Age
n.s.
n.s.
*
*
n.s.
n.s.: not significant; *. P < 0.05; **. P < 0.01.

Vol 44, No. 6;Jun 2014
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c
Table 4. Effect of tray cell size (Volume) and transplant age on leaf area (LA) shoot dry
weight (S), root dry weight (R), root to shoot ratio (R/S) and specific leaf area (SLA)
of sweet corn cv. ´Cacique´ (Experiment 5).
Volume
(cm3)
LA
(cm2)
S (g)
R (g)
R/S
SLA
(cm2 g-1)
20
67.4
0.21
0.15
0.92
304.2
40
91
0.29
0.21
0.88
286.1
120
125
0.37
0.25
0.88
317.3
F test
**
**
**
n.s.
n.s.
Age (days)
20
38.7
0.15
0.19
1.26
253.2
35
150.3
0.43
0.22
0.52
351.9
Significance
**
**
n.s.
**
**
Volume x
Age
n.s.
*
n.s.
n.s.
n.s.
n.s.: not significant; *. P < 0.05; **. P < 0.01.
20 days
35 days
Fig. 1: General appearance of sweet corn seedlings at two transplant ages grown in (left
to right at each panel) 20, 40 and 120 cm3 tray cell sizes. (a) and (b): Experiment
4; (c) and (d): Experiment 5.
a
b
d
b
c

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Field stage
When combinations of tray cell size and time at transplanting were compared, it
was observed that the largest volume tray cells (120 cm3) and shortest nursery staying (20
days) had the greatest yields, similar to those recorded in direct sowing (Table 5).
Although in experiments 3 and 6, only 40 cm3 tray cells were used, the yields of
27 and 17 old-days transplants, were greater than of direct seeded plants (P <0.05). This
was not observed in the other experiments (Table 4). This could be attributed to the fact
that a higher thermal time sweet corn genotype was used in the former experiments.
Likewise, it may have influenced the seedling recovery from root confinement stress at
the field stage. A strong decrease in yield was seen in all experiments when plants had
exceeded 30 days in the trays (P <0.05); the biggest yield loss observed at the smallest
cell size (Table 5 and 6). These same trends were observed when cob sizes were analyzed
(Table 7 and 8).
Table 5. Effect of direct sowing (DS) and tray cell volume (120, 40 or 20 cm3)-transplant
age (20 or 33 days) combinations on final yield (t ha-1) in experiments 1, 2, 4 and 5.
Treatment
(Exp. 1)
Yield
(t ha-1)
Treatment
(Exp. 2)
Yield
(t ha-1)
Treatment
(Exp. 4)
Yield
(t ha-1)
Treatment
(Exp. 5)
Yield
(t ha-1)
DS
9.02a 1
DS
13.09a
DS
10.45a
DS
12.70a
120-20
8.39a
120-19
13.03a
120-20
10.03ab
120-20
13.55a
40-20
6.78b
40-19
13.35a
40-20
9.15b
40-20
11.68ab
20-20
6.54b
20-19
12.82a
20-20
7.28c
20-20
9.71b
120-33
4.27c
120-27
7.68b
120-35
4.38d
120-35
6.22c
40-33
2.73d
40-27
6.95b
40-35
3.26de
40-35
5.35cd
20-33
2.19d
20-27
4.86c
20-35
2.62e
20-35
4.17d
1 Mean separation within columns by Tukey’s test at p = 0.05.
Table 6. Effect of direct sowing (DS) and 40 cm3 tray cell volume - transplant age
combination on final yield (t ha-1) in experiments 3 and 6 at 955 CHU after sowing.
Treatment
(Exp. 3)
Yield
(t ha-1)
Treatment
(Exp. 6)
Yield
(t ha-1)
DS
13.68ª
DS
12.86b
40-27
14.20ª
40-17
15.17ª
40-32
11.31b
40-25
11.91b
40-39
9.67c
40-33
6.94c
1 Mean separation within columns by Tukey’s test at p = 0.05.

Vol 44, No. 6;Jun 2014
9 Pretoria, South Africa
Other yield components as cob number per plant and cob size (length and
diameter), were reduced as the container volume decreased and transplant age increased
(data not shown). When the thermal time accumulated by plants in the trays was higher
than 100 CHU, the yield decreased by 3.91 % (R2 = 0.79). However, this decrease was
greater in the 20 cm3 treatment and smaller in the 120 cm3 treatment (Fig. 3). This
indicates that the older transplant (higher thermal accumulation in nursery) had the lower
final yield, although this yield loss is greater when a small cell volume is used. This was
evidenced in the 20 cm3 cell size treatment; the yield decreased almost 5% for each
increase of CHU, whereas in the 120 cm3 one, it was only of 3.19% (Fig. 3). Previous
works have reported a slower growth rate and a lower yield of sweet corn transplants that
were more than 3 weeks old at the time of transplanting (Waters et al., 1990). These
effects were attributed to more severe root damage on the older seedlings with a
subsequent increase in plant stress (Waters et al., 1990). Using cell trays of 30 cm3,
Aguyoh et al. (1999) determined that transplants must not exceed 2 weeks of age if the
aim is to obtain a marketable yield similar to direct sowing.
Table 7. Effect of direct sowing (DS) and tray cell volume-transplant age combinations,
on mean weight cob in experiments 1, 2, 4 and 5.
Treatment
(Exp. 1)
Weight
(g)
Treatment
(Exp. 2)
Weight
(g)
Treatment
(Exp.4)
Weight
(g)
Treatment
(Exp. 5)
Weight
(g)
DS
153.3ª 1
DS
245.0b
DS
183.3ª
DS
190.6bc
120-20
126.7ab
120-19
280.0ab
120-20
175.7ab
120-20
222.0a
40-20
107.9b
40-19
290.4a
40-20
160.2b
40-20
203.8ab
20-20
104.2b
20-19
261.6ab
20-20
127.3c
20-20
170.0c
120-33
68.0c
120-27
131.4c
120-35
76.0d
120-35
124.9d
40-33
43.5cd
40-27
135.3c
40-35
52.0e
40-35
107.4de
20-33
34.8d
20-27
85.2d
20-35
61.6de
20-35
91.2e
1 Mean separation within columns by Tukey’s test at p = 0.05.
Table 8. Effect direct sowing (DS) and 40 cm3 tray cell volume - transplant age
combinations on weight cob (g) in experiments 3 and 6.
Treatment
(Exp. 3)
Weight
(g)
Treatment
(Exp. 6)
Weight
(g)
DS
209.5b1
DS
250.7ª
40-27
217.3ab
40-17
234.3b
40-32
220.0a
40-25
184.5c
40-39
188.4c
40-33
135.0d
1 Mean separation within columns by Tukey’s test at p = 0.05.

Vol 44, No. 6;Jun 2014
10 Pretoria, South Africa
DS
17
25
33
As our data suggest, genotype ontogeny could be related to this yield decrease. In
long cycles conditions (Table 6), the effect of radical restriction caused by cell size- plant
age combination on final yield was smaller than in the other experiments (Table 5)
(Welbaum et al., 2001). However, is worth noticing that under stressful field conditions
the sh-2 hybrid requires higher seeding rates to ensure stand establishment. The cultivars
containing the sh-2 gene have a superior kernel quality but often germinate poorly and
display low seedling vigor (Hartz and Caprile, 1995). The transplanting of sh-2 sweet
corn with specific conditions could be a method to improve stand establishment. In this
work, 20 days-old transplants grown in 120cm3 cells (Exp. 5, Table 7), allowed obtaining
larger cobs while 27 days old transplant grown in 40 cm3 cells (Exp. 6, Table 6)
produced a higher final yield compared with direct seeded plants.
These results lead to a general recommendation for growers considering
switching to smaller cell sizes or older seedlings: they should do so with caution.
Compared to direct sowing, sweet corn transplants grown in a smaller container or aged
seedlings may produce lower and later yields.
Fig. 2. General appearance of the root systems in sweet corn plants in experiment 6, cv.
'Butter Sweet' at harvest time for direct sowing and of 17, 25 and 33 days-old
transplants (from left to right, respectively).

Vol 44, No. 6;Jun 2014
11 Pretoria, South Africa
R2 = 0,95
R2 = 0,91
R2 = 0,78
0
2
4
6
8
10
12
14
16
50 100 150 200 250 300
CHU (ºCd)
Yield (t ha-1)
120 40 20
Figure 3. Relationship between thermal time (CHU. ºCd) accumulated during the nursery
phase and final yield (Y) for all experiments considering cell size of 20 cm3 (Y =
-0.0504 CHU + 17.905); 40 cm3 (Y = -0.0439 CHU + 17.634) and 120 cm3 (Y =
-0.0319 CHU + 16.611).
CONCLUSIONS
This research has confirmed that the use of different tray cell volumes and
transplant age influence dry-matter partitioning throughout growth and development of
sweet corn seedlings. The increase in radical restriction (small tray cell) caused a sharp
decrease in seedling LA and S, being the most affected variables by the treatments. When
the thermal time accumulated by plants in the trays was higher than100 CHU, the yield
decreased by 3.91% (R2 = 0.79) for each unit of CHU. Greatest yields were obtained with
greatest volume cell size and shortest transplant age (table 6, experiment 3 and table 8,
experiment 3).
Transplanting technology is suitable if proper cell size (greater than 40 cm3) and a
suitable transplant age (less than 27 days) are chosen. This technology lead to avoid the
difficulties of germination that hybrids of sweet corn presents in medium latitudes where
soils have suboptimal soil germination temperatures.
ACKNOWLEDGEMENTS
We acknowledge the support of Universidad Nacional del Litoral for supplying the
infrastructure and equipments needed to carry out this work. We would like to thank Dr.
Abelardo Vegetti for support and useful advices to this work.

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