1
Plant Population and Hybrid Impacts on Corn Grain and Forage Yield and
2
Nutrient Uptake
3
4
ABSTRACT
5
Corn (Zea mays L.) production recommendations must be periodically evaluated to
6
ensure that production practices remain in step with hybrid genetic improvements. Since
7
most of the recent increases in corn grain yield are due to increased optimum plant
8
density and not increased per plant yield, this study was undertaken to measure the
9
effects of plant population and hybrid on corn forage and grain yield and nutrient uptake.
10
Plant population (4.9, 6.2, 7.4, and 8.6 seeds m-2) and corn hybrid relative maturity (RM)
11
[early (108 day RM); medium (114 day RM); and late (118 day RM)] combinations were
12
evaluated in five site years under irrigated and non-irrigated conditions. The interaction
13
of hybrid with plant density was minimal. The latest RM hybrid outyielded the medium
14
and early hybrids by 550 and 1864 kg ha-1, respectively. Grain yield was highest at 8.5
15
plants m-2. Total stem yield was also greatest at the highest plant density but only 340 kg
16
ha-1 more than at 7.4 seeds m-2. Based on grain yield response over sites, the estimated
17
optimum population was 7.6 seeds m-2 which is 0.7 seeds m-2 higher than the current
18
recommendation at this average yield level (11.5 Mg ha-1). Grain nitrogen (N),
19
phosphorus (P), and potassium (K) uptake were highest for the medium hybrid and
20
resulted from greater nutrient concentrations and not yield. Nutrient uptake levels varied
21
by population with the lowest levels observed at the lowest and highest plant densities.
22
At 4.9 seeds m-2 this is explained by lower biomass yield. At the 8.6 seeds m-2 rate, N
23
and K supply may have been limiting resulting in lower overall concentrations.
1
1
INTRODUCTION
2
Plant Density
3
Recent increases in corn yields are attributed to greater stress tolerance of modern
4
hybrids, especially stress from interplant competition (Tokatlidis and Koutroubas, 2004).
5
Most of the increase in yield per unit area has been the result of increased optimum plant
6
population and not increased grain yield per plant. This is the result of more efficient
7
capture and use of resources such as water, sunlight and nutrients. Modern hybrids have
8
greater leaf longevity, more efficient root systems, and greater assimilate supply available
9
for translocation to developing grain (Tollenaar and Wu, 1999).
10
While relative corn grain yield levels have varied by environment, researchers
11
have recently reported maximum yields at or near the highest studied populations in a
12
number of locations (Nafziger, 1994; Staggenborg et al., 1999; Stanger and Lauer, 2006;
13
Thomison and Jordan, 1995; Widdicombe and Thelen, 2002) and not the parabolic
14
relationship previously reported (Alessi and Power, 1974; Karlen and Camp, 1985). On
15
sandy, coastal plain soils Karlen and Camp (1985) found that increasing plant density
16
from 7 to approximately 10 plants m-2 resulted in yield decreases unless supplemental
17
irrigation was applied. Recent research in the mid-Atlantic evaluating the effect of row
18
spacing and population found a significant interaction of these factors in only one of 28
19
instances (Kratochvil and Taylor, 2005). However under relatively high-yielding
20
environmental conditions (9.5 Mg ha-1), grain yields did not decrease in response to high
21
plant densities until the threshold of 10 plants m-2 was passed.
22
Total corn biomass, measured as silage yield, has been shown to be influenced by
23
plant density in New York, USA, where maximum economic forage yield was calculated
2
1
to occur at 9.8 plants m-2 (Cox et al., 1998). These authors found no interaction of row
2
spacing and plant population for forage yield.
3
South Carolina research reported that at a plant density of approximately 7 plants
4
m-2, leaf area index (LAI) averaged 4.3 and increased to 5.9 when population was
5
increased to 10 plants m-2 (Karlen and Camp, 1985). These authors concluded that there
6
was no net advantage to the higher LAI at the higher population since the threshold level
7
of 3.5 to 4.5 (Eik and Hanway, 1966) was reached with the lower population.
8
9
Harvest index (HI) is known to decrease with increased plant density, especially
when plant density is above that required for maximum yield (Center and Camper, 1973;
10
DeLoughery and Crookston, 1979). Recent research has found this to be the result of
11
increasing barrenness at higher densities (Tollenaar et al., 2006). Kiniry and Echarte
12
(2005) report a general response of HI to plant density. Reviewing four recently
13
published studies, HI remained constant when plant density was less than 10 plants-2, but
14
above this threshold, HI decreased at a rate of -0.012 units per plants m-2.
15
Nutrient concentration is generally held to be independent on plant density
16
whether for grain (Ottman and Welch, 1989; Overman et al., 2006) or forage (Hoff and
17
Mederski, 1960). However increasing plant density through narrower rows has decreased
18
grain N concentration (Stickler, 1964). In instances where plant populations are
19
insufficient to use all applied nitrogen, N concentration in grain and forage rises with
20
increased N rates, but at appropriate populations, higher N rates were used effectively
21
(Jordan et al., 1950)
22
Hybrids
3
1
In a corn forage study, Cox et al. (1998) studied eight hybrids with a range in RM
2
of 100 to 112 days across a range of plant populations and found that while there were
3
yield differences among hybrids, interactions with population were uncommon.
4
Deloughery and Crookston (1979) report that HI decreased with RM (75 day to 130 days
5
for ten hybrids) but only with environmental stress.
6
Nutrient concentration is known to vary widely among corn hybrids and is highly
7
dependent on environment (Ferguson et al., 1991; Heckman et al., 2003; Schenk and
8
Barber, 1980). Average reported values corn grain and 12.9, 3.8, and 4.8 g kg-1 of N, P,
9
and K, respectively (Heckman et al., 2003).
10
In row spacing by plant density studies in Indiana, hybrid RM differences had
11
little effect on grain yield, but greater stalk breakage was noted for one hybrid (Neilsen,
12
1988). Nafziger (1994) also found no hybrid by plant density interactions for two
13
hybrids. In an eastern Corn Belt study of plant population and corn hybrid prolificacy it
14
was concluded that environment, genetics, and plant population main effects were more
15
important to optimum grain yield than the hybrid by population interaction (Thomison
16
and Jordan, 1995). In eastern Nebraska, a later RM hybrid was found to produce greater
17
forage yield while the earlier hybrid had higher grain yield (Alessi and Power, 1974)).
18
Neither forage or grain yield by RM interacted significantly with plant density.
19
Conversely, recent Michigan research found significant interactions for plant density and
20
hybrid for grain yield and moisture of six hybrids (Widdicombe and Thelen, 2002). In
21
spite of the fact that the majority of published studies report no, or occasional, RM by
22
plant populations interactions, many growers and practitioners believe this to be the case.
4
1
The objectives of this research were to examine the effect of plant density and corn
2
hybrids of different RM on corn biomass and grain yields and nutrient uptake.
3
4
5
MATERIALS AND METHODS
Small plot field studies were conducted in 2005 near Blacksburg, VA (37 12’ N,
6
80 34’ W) on a Hayter loam (fine loamy, mixed, active, mesic Ultic Hapludalf) and Mt
7
Holly, VA (38 5’ N, 76 43’ W) on a State fine sandy loam (fine loamy, mixed,
8
semiactive, thermic, Typic Hapludalf) and in 2006 at Mt. Holly. The Blacksburg site was
9
non-irrigated while trials were conducted under both irrigated and non-irrigated
10
conditions at Mt. Holly. Experimental design was a randomized complete block with a
11
split plot arrangement of treatments and four replications. Main plots were plant
12
population (4.9, 6.2, 7.4, and 8.6 seeds m-2) and subplots were corn hybrid relative
13
maturity [early – Pioneer® Brand ‘34B97’ (108 day RM); medium – Pioneer® Brand
14
‘33M54’ (114 day RM); and late – Pioneer® Brand ‘31G66’ (118 day RM)]. Planting
15
dates and agronomic information for the five site years are listed in Table 1. Plots were
16
planted with a Wintersteiger 2600 vacuum plot planter (Wintersteiger Inc., Salt Lake
17
City, UT) and were four, 76-cm rows wide by 8 m long. In all cases the previous crop
18
was soybean at Mt. Holly trials and corn at the Blacksburg site. Starter fertilizer at a rate
19
of 43 kg N ha-1 and 5 kg P ha-1 was applied 5 cm below and 5 cm to the side of the seed
20
at planting. Total N rates in 2005 were 263, 190, and 170 kg N ha-1 at Mt. Holly
21
irrigated, Mt. Holly non-irrigated, and Blacksburg, respectively. Total N applied in 2006
22
was 252 kg ha-1 at the irrigated Mt. Holly site and 180 kg N ha-1 for the non-irrigated site.
23
Phosphorus and K were broadcast prior to planting at rates indicated by Virginia Tech
5
1
soil test recommendations (Donohue and Heckendorn, 1994). Planting, emergence, and
2
harvest dates as well as weather information were collected at all locations (Table 1).
3
Weather information was gathered using Watchdog™ (Spectrum Technologies Inc.
4
Plainfield, Illinois) weather stations at each site.
5
Aboveground biomass was hand harvested from each plot at the R6
6
developmental stages (Ritchie et al., 1992). A total of five consecutive plants in the outer
7
two rows were harvested at soil level. Total plant biomass as well as stem, leaf, and
8
reproductive biomass dry matter were determined by separating the components and
9
drying them to a constant weight in a forced-air oven at 60° C. Biomass yield (kg ha-1)
10
was calculated as the product of individual plant weight and measured plant population.
11
Stem and leaf tissue and grain from the R6 sampling date were ground to pass a 1-
12
mm screen. Total carbon and N concentration for each sample was determined via a
13
LECO Tru-Spec® CHN dry combustion analyzer (LECO Corporation, St. Joseph, MI).
14
Samples were digested using HNO3/HClO4 acid solution. Phosphorus (P) concentration
15
was determined colorimetrically (Kuo, 1996) and K concentration determined by atomic
16
absorption spectroscopy (Helmke and Sparks, 1996). Nitrogen, P, and K uptake for
17
grain and forage (stem and leaf ) was calculated as the product of biomass yield of the
18
respective plant component and nutrient concentration (%) within each component.
19
Grain was harvested from the center two rows from each plot using a Massey
20
Ferguson 8XP plot combine. Plot weight, grain moisture, and test weight were
21
determined using a Graingage™ system (Juniper Systems, Logan, UT). Grain yield from
22
all trials is reported at 155 g kg-1 moisture. Harvest index (HI) was calculated by
23
dividing grain yield by total plant biomass.
6
1
2
Statistical analysis was performed using the GLM procedure available from SAS
3
(SAS Inst., 2004). Due to interaction effects of treatments across years and locations,
4
data from each site year were analyzed and presented separately. Mean comparisons
5
using a protected LSD test were made to separate RM and plant population effects where
6
F-tests indicated that significant differences existed (P<0.10). Regression was applied to
7
evaluate plant density impacts on grain and forage yield and nutrient uptake across sites.
8
RESULTS AND DISCUSSION
9
Blacksburg 2005
10
Leaf yield was influenced by both plant density and corn hybrid (Table 2). As
11
population increased from 4.9 to 8.6 seeds m-2 leaf weight increased in a linear manner
12
(526 kg ha-1) but then decreased at the highest population. The medium maturity hybrid
13
had the greatest final leaf weight. Grain yield was more than 2600 kg ha-1 lower for the
14
early maturity hybrid than for the other two entries (Table 2). This is a river bottom site
15
typified by foggy, hazy mornings and relative cool nights. Because of the relatively
16
cooler night time temperatures, longer season hybrids typically offer a yield advantage.
17
Similar to the trends observed for leaf yield, increasing plant population up to 7.4 seeds
18
m-2 resulted in increased grain N and P uptake but with the further increase in plant
19
population to 8.6 seeds m-2 a decrease in uptake of 51 kg N and 12 kg P ha-1 was
20
observed (Table 2). Leaf+stem K uptake was higher at 7.4 seeds m-2 than at any other
21
population.
22
Mt. Holly Non-Irrigated 2005
23
Total stem, leaf, and grain yield was significantly lower for the early season
24
hybrid at this site (Table 3). Later maturing hybrids often accumulate more leaf and
7
1
stem biomass and thus more nutrients and carbohydrates that can be translocated to the
2
grain after anthesis. This allows more total assimilate to be available for grain production
3
in these longer season hybrids. Total grain N uptake was 31 kg ha-1 greater for the
4
medium maturity than for the early hybrid, again similar to the results observed for plant
5
growth parameters (Table 3). There was a significant interaction of population and
6
relative maturity for leaf+stem N uptake at this site, however main effects are still
7
presented for the sake of consistency. This was the only instance that an interaction
8
occurred for any of the investigated variables and in this case was due to low uptake
9
levels associated with the lowest population.
10
Mt Holly Irrigated 2005
11
Stem yield again exhibited a quadratic response to plant population with the
12
highest yield of 11,482 kg ha-1 reached at a population of 7.4 seeds m-2 (Table 4). The
13
early hybrid had approximately 700 kg ha-1 less stem dry weight than the medium or late
14
hybrids. Total leaf dry matter was higher at the two higher population treatments
15
compared to the lower populations (average of 3611 versus 2689 kg ha-1) (Table 4). Leaf
16
mass was again lowest for the early hybrid. Grain yield was lowest (13,713 kg ha-1) for
17
the lowest population and was increased by 1,400 kg ha-1 by increasing population to 6.2
18
seeds m-2. Grain P and K uptake were also lowest for the lowest population density at
19
this site (Table 4).
20
Mt Holly Non-Irrigated 2006
Stem yield was lower at 6.2 seeds m-2 (6150 kg ha-1) than at the 4.9 or 8.6 seed m-
21
22
2
rates but was not different from 7.4 seeds m-2 (Table 5). The late maturity hybrid
23
produced greater stem biomass yield than either of the others, probably due to the
8
1
expected longer vegetative growth period. A linear increase of leaf yield in response to
2
plant density was observed at this site. Leaf yield increased at a rate of nearly 300 kg ha-1
3
for each additional plant m-2 (Table 5). A similar trend was observed in response to
4
increasing relative maturity with the greatest leaf yield of 2961 kg ha-1 associated with
5
the late hybrid. This was the only site year in which HI was impacted by treatment.
6
Harvest index was significantly lower at 4.9 seeds m-2 than at other densities, probably
7
due to the high relative stem yield (8135 kg ha-1) in this treatment (Table 5). The late
8
hybrid had the lowest HI of 0.301. Significant differences are the result of greater leaf
9
yield at similar a grain yield. Grain P and K uptake were lowest at 6.2 seeds m-2 and
10
11
12
highest at the 7.4 seeds m-2 density.
Mt Holly Irrigated 2006
Stem yield was lower for the medium RM hybrid compared to the late hybrid but
13
was similar to the early hybrid (Table 6). Leaf yield was 874 kg ha-1 greater at the 8.6
14
seeds m-2 density than at 4.9 seeds m-2, but no differences were observed among the other
15
treatments. Leaf biomass yield increased by 429 kg ha-1 for the medium versus the early
16
hybrid and 480 kg ha-1 for the late versus the medium hybrid (Table 6). Grain N uptake
17
was significantly lower at 8.6 seeds m-2 which might indicate a deficiency at this high
18
plant density. The lowest observed grain N uptake (135 kg ha-1) was associated with the
19
late maturity hybrid while there were no other differences by maturity. Conversely,
20
stem+leaf N uptake was highest in the late hybrid and lowest (59 kg ha-1) for the medium
21
hybrid. Grain P uptake was least at 4.9 seeds m-2 and this corresponds to the numerically
22
lowest grain yield. The late RM hybrid also had slightly lower grain P uptake than the
23
others. Grain K uptake was lowest at 4.9 seeds m-2 (35 kg K ha-1) and again is explained
9
1
mostly by the lower numerical yield for this treatment. Similar grain K uptake was noted
2
between the early and late hybrids with significantly more (4 kg ha-1) K taken up by the
3
medium hybrid.
4
5
Plant population effects on yield and nutrient uptake
Overall, grain yield increased in a quadratic manner with increasing plant density
6
(Figure 1) and while the rate of increase was declining, the yield was greatest at the
7
highest plant density. The impact of plant density in these studies is similar to that
8
reported by Kratochvil and Taylor (2005) and Widdicombe and Thelen (2002)
9
(approximately 300 kg ha-1 increase for each seed m-2) and more than that reported by
10
others (Farnham, 2001; Karlen and Camp, 1985). This may be due to the ability of the
11
specific hybrids chosen to compensate with larger ears in response to less interplant
12
competition. The growing environment was also favorable in all years of this study and
13
so plant to plant competition for water may have been less a factor than would be seen in
14
many instances. Stem and leaf yield also generally increased with increasing plant
15
density (Figure 1). Grain N uptake increased incrementally up to 7.4 seeds m-2 but
16
decreased in the last increment (Figure 2). This same trend was evident in forage N and
17
K uptake (Figure 3) and may be the result of nutrient limitations at these high plant
18
densities since yield was still increased. Grain P and K uptake were similar across the
19
range of densities at 38 and 42 kg ha-1, respectively. Leaf+stem P uptake was also
20
essentially the same (17 kg P ha-1) across plant densities (Figure 3).
21
22
23
CONCLUSIONS
Grain yield was highest at the highest plant density with a total advantage of
1141 kg ha-1 over the 4.9 seeds m-2 treatment. The late hybrid outyielded the medium
10
1
and early hybrids by 550 and 1864 kg ha-1, respectively. Total stem yield was also
2
greatest at the highest plant density but only 340 kg ha-1 more than at 7.4 seeds m-2.
3
Overall results for leaf yields were similar to those for stem yield. Solving for the
4
optimum population based on the quadratic model for grain yield results in an estimated
5
optimum of 7.6 seeds m-2. This is slightly higher than the current recommendation of 6.9
6
seeds m-2 that would be recommended for this average yield level (11.5 Mg ha-1).
7
Harvest index was generally unaffected by treatment in these studies. This is not
8
surprising given the findings of Kiniry et al. (2005) who report a basically constant HI
9
with plant densities below 10 plants m-2, at which point HI begins to decrease at a rate of
10
11
-0.012 units per plant m-2 increase.
Grain N, P, and K uptake was highest for the medium RM hybrid. Since grain
12
yield for this hybrid was not the highest, these uptake values result from greater nutrient
13
concentrations in the grain. Leaf+stem N uptake for this medium hybrid was the lowest
14
of the three but K uptake was highest. Nutrient uptake levels varied somewhat by
15
population with the lowest levels observed at the lowest and highest plant densities. At
16
4.9 seeds m-2 this is explained by generally lower biomass yield. At the 8.6 seeds m-2
17
rate, N and K may have been limiting resulting in lower overall concentrations in tissue.
18
While numerous studies over the years have investigated the effect of plant
19
population and hybrid characteristics on yield, recent increases in corn hybrid stress
20
tolerance and standability make revisiting these basic studies worthwhile. Based on
21
results from these studies, plant density recommendations at these high yield levels may
22
need to be revised upwards. Correspondingly, recommended N and K nutrient levels
23
should be evaluated to ensure that adequate but not excessive supplies are available. To
11
1
meet the needs of plant densities this high, fertilizer rates may well need to increase
2
concomitantly.
12
Table 1. Production practices, sampling dates, and environmental conditions, 2005-2006.
Total N applied
---kg ha-1--263
R6 Biomass
Sampling Date
---date--09/01/2005
GDD
Planting to
Sampling
----°C---1688
Rainfall
Planting to
Sampling
----mm---490
30 yr-mean
growing season
rainfall
----mm---455
Grain Harvest
---date--09/20/2005
04/20/2005
190
09/01/2005
1689
493
455
09/19/2005
05/09/2005
05/14/2005
170
09/20/2005
1484
394
452
10/05/2005
MT Holly Irrigated
04/26/2006
05/03/2006
252
08/30/2006
1665
410
456
09/20/2006
MT Holly Non-irrigated
04/28/2006
05/04/2006
180
08/29/2006
1658
409
456
09/22/2006
MT Holly Irrigated
Planting Date
---date--04/19/2005
Emergence
Date
---date--04/25/2005
MT Holly Non-irrigated
04/13/2005
Blacksburg
Experiment
13
Table 2. Analysis of variance and means for stem, leaf and grain yield, harvest index, and N, P and K uptake in response to plant
population and relative maturity, Blacksburg, 2005
Source of
Variation
Block
Population
Block*Population
Relative Maturity (RM)
Population*RM
Block*Population*RM
Density
---plants m-2--4.9
6.2
7.4
8.6
LSD
RM
Early
Medium
Late
LSD
df
3
3
9
2
6
24
Stem Yield
2095962
15874801
13019592
4145858
2434027
30950870
Leaf Yield
268893
1691979 ***
383085
952804 ***
301302
1133168
Grain Yield
2970054
17742849
7037293
15378885 *
3838368
12614450
-----------------------------kg ha-1----------------------------4281
855
11129
4678
1061
11593
5845
1381
12295
4899
1126
12018
ns
191
ns
4525
5030
5222
ns
969
1300
1048
163
9776
12399
13103
1616
HI
0.011
0.009
0.008
0.019
0.005
0.013
----------N uptake---------Grain
Leaf+Stem
2297
106
4572 *
44
840
27
1084
32
462
143
4206
56
---------P uptake---------Grain
Leaf+Stem
90
5
209 *
2
38
3
34
1
31
9
324
5
----------K uptake---------Grain
Leaf+Stem
29
4
25
1942 **
133
114
147
1337
46
454
236
1059
--------------------------------------------------------kg ha-1-------------------------------------------------------0.478
170
46
36
10
36
105
0.513
177
45
37
9
37
110
0.526
181
51
41
10
41
144
0.470
130
45
29
10
47
111
ns
43
ns
11
ns
ns
20
0.535
0.469
0.486
ns
***,**,* - Significant at the 0.01, 0.05, and 0.10 level, respectively.
14
149
173
171
ns
44
48
48
ns
32
39
37
ns
10
10
9
ns
32
45
44
ns
111
132
109
ns
Table 3. Analysis of variance and means for stem, leaf and grain yield, harvest index, and N, P and K uptake in response to plant
population and relative maturity, Mt Holly Non-Irrigated, 2005
Source of
Variation
Block
Population
Block*Population
Relative Maturity (RM)
Population*RM
Block*Population*RM
Density
---plants m-2--4.9
6.2
7.4
8.6
LSD
RM
Early
Medium
Late
LSD
df
3
3
9
2
6
24
Stem Yield
27530833
30619921
40339801
35396227 **
22674926
89683643
Grain Yield
32016330
95105621 ***
11032462
54997876 **
8104451
25376120
HI
0.011
0.005
0.008
0.001
0.004
0.030
-----------------------------kg ha-1----------------------------6339
1675
11988
7903
2161
12451
8452
2637
13123
8008
2302
13909
ns
601
1868
0.469
0.439
0.490
0.466
ns
6463
8342
8222
1388
Leaf Yield
2870702
5741041 **
3817424
5085059 ***
1866044
5760509
1734
2401
2446
363
11321
13643
13639
2266
0.472
0.459
0.468
ns
***,**,* - Significant at the 0.01, 0.05, and 0.10 level, respectively.
15
----------N uptake---------Grain
Leaf+Stem
3489
6
9547
1952
3781
1105
4279 *
25
1383
893 *
2966
709
---------P uptake---------Grain
Leaf+Stem
53
61
548
27
172
72
141
30
73
71
144
56
----------K uptake---------Grain
Leaf+Stem
63
158
527
8720
179
3336
144
3486
49
1396
127
3021
--------------------------------------------------------kg ha-1-------------------------------------------------------171
57
42
20
44
126
193
99
46
24
46
210
185
88
46
21
46
203
198
75
50
23
50
182
ns
ns
ns
ns
ns
ns
173
204
183
23
79
78
82
ns
43
47
48
ns
23
23
20
ns
43
49
48
ns
163
204
174
ns
Table 4. Analysis of variance and means for stem, leaf and grain yield, harvest index, and N, P and K uptake in response to plant
population and relative maturity, Mt Holly Irrigated, 2005
Source of
Variation
Block
Population
Block*Population
Relative Maturity (RM)
Population*RM
Block*Population*RM
Density
---plants m-2--4.9
6.2
7.4
8.6
LSD
RM
Early
Medium
Late
LSD
df
3
3
9
2
6
24
Stem Yield
6805014
66458345 **
33769250
17248025 **
2522255
52843379
Grain Yield
4552003
167512818 ***
4133849
21092372 **
7028214
7725426
HI
0.005
0.013
0.005
0.006
0.002
0.010
-----------------------------kg ha-1----------------------------8842
2614
13713
8791
2763
15149
11482
3692
14887
10738
3530
15090
1789
322
1378
0.411
0.422
0.470
0.476
ns
9241
9939
10709
1142
Leaf Yield
498847
10503882 ***
1093256
5706049 ***
1031401
3772209
2699
3216
3536
329
13267
14727
16134
1733
0.464
0.446
0.424
ns
***,**,* - Significant at the 0.01, 0.05, and 0.10 level, respectively.
16
----------N uptake---------Grain
Leaf+Stem
613
857
10586
351
514
2935
2169
176
1347
929
1401
1511
---------P uptake---------Grain
Leaf+Stem
28
216
606 **
77
30
532
64
41
73
86
114
456
----------K uptake---------Grain
Leaf+Stem
27
12843
678 **
10498
62
9367
95
7239
86
5928
111
9420
--------------------------------------------------------kg ha-1-------------------------------------------------------220
130
46
28
48
215
242
137
53
29
55
235
234
149
52
31
54
281
232
137
53
27
55
242
ns
ns
8
ns
6
ns
214
277
206
ns
144
137
135
ns
47
55
51
ns
29
31
26
ns
47
58
53
ns
236
266
228
ns
Table 5. Analysis of variance and means for stem, leaf and grain yield, harvest index, and N, P and K uptake in response to plant
population and relative maturity, Mt Holly Non-Irrigated, 2006.
Source of
Variation
Block
Population
Block*Population
Relative Maturity (RM)
Population*RM
Block*Population*RM
Density
---plants m-2--4.9
6.2
7.4
8.6
LSD
RM
Early
Medium
Late
LSD
df
3
3
9
2
6
24
Stem Yield
7058667.63
26681189 *
28564724.6
31564665.7 **
17247575.8
41169416.6
Leaf Yield
498633.92
9599699.4 ***
1531544.4
5358128 ***
1143356.7
3460839.7
Grain Yield
15664242
5275737
7097692
1642716
1424773
3901866
HI
0.004
0.003 **
0.001
0.006 *
0.002
0.006
-----------------------------kg ha-1----------------------------8135
2190
7794
6150
2203
7001
7329
2579
8143
7818
3332
8025
1645
392
ns
6891
6676
8551
1044
2197
2547
2961
305
0.303
0.337
0.328
0.327
0.031
7517
7839
7867
ns
0.337
0.333
0.301
0.033
***,**,* - Significant at the 0.01, 0.05, and 0.10 level, respectively.
17
----------N uptake---------Grain
Leaf+Stem
2452
257
1687
5598
423
1256
524
1484
683
1898
1034
2909
---------P uptake---------Grain
Leaf+Stem
78
52
39 **
113
4
115
12
14
18
15
48
138
----------K uptake---------Grain
Leaf+Stem
62
5218
48 **
2941
2
4376
4
532
18
8823
50
7253
--------------------------------------------------------kg ha-1-------------------------------------------------------99
50
24
12
32
154
88
38
21
7
29
148
103
44
25
11
34
175
109
41
25
11
31
188
ns
ns
4
ns
2
ns
101
98
100
ns
44
36
52
ns
24
23
24
ns
11
9
10
ns
32
33
30
ns
160
169
164
ns
Table 6. Analysis of variance and means for stem, leaf and grain yield, harvest index, and N, P and K uptake in response to plant
population and relative maturity, Mt Holly Irrigated, 2006.
Source of
Variation
Block
Population
Block*Population
Relative Maturity (RM)
Population*RM
Block*Population*RM
Density
---plants m-2--4.9
6.2
7.4
8.6
LSD
RM
Early
Medium
Late
LSD
df
3
3
9
2
6
24
Stem Yield
14625089.1
3476418.7
13461379.4
22842546.9 **
7908444.35
41476981.2
Leaf Yield
2462992.1
4651133.7 **
3207713.8
6613854.5 ***
1261407.7
4861178.9
Grain Yield
155664242
5275737
7097692
1642716
1424773
3901866
HI
0.007
0.007
0.002
0.013
0.005
0.007
-----------------------------kg ha-1----------------------------7295
2558
9754
7377
3022
11256
7487
3091
10664
7838
3432
11041
ns
551
ns
7208
6834
8506
1301
2580
3009
3489
316
0.317
0.321
0.309
0.269
ns
10577
10422
11038
ns
0.320
0.322
0.271
ns
***,**,* - Significant at the 0.01, 0.05, and 0.10 level, respectively.
18
----------N uptake---------Grain
Leaf+Stem
23
5
415 **
449
31
97
35
826 **
230 **
374
70
240
---------P uptake---------Grain
Leaf+Stem
1
25
32 *
99
4
33
1
119 **
9*
31
4
45
----------K uptake---------Grain
Leaf+Stem
1
22
55 **
873
5
1321
23 *
150
11
3044
13
3051
--------------------------------------------------------kg ha-1-------------------------------------------------------150
95
29
17
35
197
151
52
36
14
43
162
154
87
35
14
41
196
138
55
34
12
45
180
10
ns
4
ns
4
ns
156
154
135
9
74
59
84
15
34
34
32
2
14
13
15
3
39
44
40
3
175
176
201
ns
Figure 1. Average grain, stem, and leaf yield as affected by plant density.
14000
y = -68.54x2 + 1235.3x + 6452.7
R2 = 0.9987
Yield, kg ha -1
12000
10000
y = 55.462x2 - 496.16x + 8039.1
R2 = 0.9512
8000
Stem
6000
4000
Leaf
y = -31.854x2 + 653.85x - 501.16
Grain
R2 = 0.9632
2000
0
0
1
2
3
4
5
6
Plant Density, seeds m
19
7
-2
8
9
10
Figure 2. Grain N, P, and K uptake as affected by plant density.
Grain Nutrient Uptake, kg ha-1
200
180
160
N
140
P
y = -2.9491x2 + 40.011x + 36.176
120
K
R2 = 0.9885
100
80
y = -0.781x2 + 11.36x - 1.671
60
R2 = 0.9972
40
2
y = -0.1012x + 3.102x + 26.226
R2 = 0.9883
20
0
0
1
2
3
4
5
6
7
-2
Plant Density, plants m
20
8
9
10
Leaf+stem Nutrient Uptake, kg ha-1
Figure 3. Leaf+stem N, P, and K uptake as affected by plant density.
250
y = -5.3935x2 + 80.539x - 109.72
R2 = 0.7944
200
N
P
150
K
y = -1.9127x2 + 25.608x - 5.9771
100
R2 = 0.3843
50
y = 0.002x2 - 0.2181x + 18.334
R2 = 0.3628
0
0
1
2
3
4
5
6
Plant Density, plants m
21
7
-2
8
9
10
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