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Evaluation of plant population density on growth, grain yield and yield components of four maize hybrids.


The response of maize hybrids (zea mays L.) to plant population is different. Increased plant density results in higher grain yield per unit area [14]. It's reported that improving grain yield due to increased plant population was achieved on a narrow spectrum [19]. Grain yield results from the increased pollen-to-silking interval and the fallowing barrenness reduced at higher plant population [2]. Higher grain yield produced due to higher plant density [6,8,10]. It's reported that plant population densities from 5 to 5.6 plants [m.sup.-2] were considered optimal [8]. However other researches reported that the optimal density for acquiring higher corn grain yield was 7.5 plants [m.sup.-2] [13]. Other researches indicated that optimal plant density ranged from 5 to 8 plants [m.sup.-2] [4]. Greater plant densities result in lower yields due to of competition for water, light and nutrients between plants [16]. Response of Maize to plant density in row is more than row space. More densities lead to low rates of seed production as a result of competition for light and humidity [23].

Maize grain yield per unit area shows a curvilinear response to plant population. For each production system, there is a population that optimizes the use of available resource, allowing the expression of maximum attainable grain yield in that environment [3]. The ideal plant number per area will depend on several factors, such as water availability, soil fertility, hybrid maturity group and row spacing [9]. It's reported that the late maturity hybrids are less sensitive to plant density [21]. The higher height of plant at grain filling, the lower sensitivity to plant density [1]. It's stated that hybrids with high grain filling period of more leaf area and leaf area index were correlated with grain yield [17].

The objectives of this study were to evaluate the impact of different plant densities of maize hybrids on growth, yield and yield components.

Materials and Methods

A field excrement was conducted at Dezful Research Farm of Azad University Khouzestan, Iran (32[degrees]22' N latitude, 48[degrees]32' E) in 2008 growing season. Soil pH was 7.5 and soil texture was clay loamy. This research was arranged as split-plot design based on randomized complete block design with three replications. Main plots were assigned to hybrids of corn (Ks.c704, Ks.c700, K47 and k78) and subplots to plant population densities (7, 8. 9 and 10 plants [m.sup.-2]). Prior to seed sowing 100 kg [ha.sup.-1] phosphorus in form of super phosphate triple and 250 kg [ha.sup.-1] nitrogen in form of urea were broadcasted and incorporated into the soil. Fifty percent of urea was used at sowing time and residual was applied as top dress at 4-6 leafy stage.

Corn seeds were disinfected and sown by hand on July 15. Irrigation was performed after sowing. Plots were kept free of weeds, insects and diseases. The plots were 8 meter long and consisted of eight rows, 0.75 m apart. The space between blocks was 2 m and between each plot was 1 m was apart.

Samples consisted of a 2 [m.sup.2] area of center of row of each plot after leaving two rows in the border areas were hand harvested at physiological maturity stage. The six ears were separated in order to determine the seed yield and yield components. Random samples were taken from each plot to determine seed and straw moisture, seed yield, total dry matter and seed dry matter. These samples were Oven dried at 72[degrees]C for 48 hours [15].

In order to determine green leaf area index lamina length (L) and maximum lamina width (W) were used to calculate leaf area (A) as in Montgomery [2].

A = [alpha] LW

Where [alpha] = 0.75. The ears of different treatments were collected once every week two weeks after flowering. Three ears were harvested at each sampling, and 10 seeds from each ear were separated and each separately dried at 72[degrees]C for 48. Physiological maturity and final harvest at the end of the yield with yield components were calculated [2].

The data was analyzed using the SAS (9, 1) software. When F-test was significant at P < 0.05 level, Duncan's multiple range test was used to separate the means.

Result and discussion

Crop performance:

Figure 1 shows the changes on leaf area over the growing season. Leaf area index (LAI) in closed till pollination, then the LAI declined. this could be due to aging of leaves and retranslocation of photosynthetic materials. LAI were different among maize hybrids. The Ks.c 704 hybrid had the highest LAI compared to other hybrids. This in turn resulted in higher grain yield (Table1). The length of growing season of sk704 was grater than the other hybrids. The LAI of other hybrids were as follow ksc700 > ksc47 > ksc78.

Effects of different plant densities on LAI showed that with increasing plant density from 7 to 10 plants [m.sup.-2], the LAI increases (Fig. 2). The lowest and highest LAI were at 15 and 75 days after planting respectively. The highest density of (10 plants [m.sup.-2]) results in LAI of 6 and corresponding LAI for the lowest density of 7 plant [m.sup.-2] was 4.5. It's reported that with increasing plant density of 3 to 12 plants [m.sup.-2] LAI increased and late maturity hybrids had the highest LAI than early maturity hybrids [12]. Similar results were also reported for plant densities of 10 to 12 plants [m.sup.-2] [14, 2]. It's indicated that early maturity hybrids should be planted with high density, since these hybrids generally have a lower height, produced fewer leaves [14].

Figure 3 shows changes on seed weight of different days after flowering. Seed weight of maize is considered a critical component of yield. All hybrids had the highest seed weight after 49 days of flowering and no further changes can be seen after that. However, at the time of maximum grain weight Ksc704 hybrid with 39 mg had the highest seed weight and k78 hybrid with (35 mg) the lowest seed weight. It's indicated that since the plant photosynthetic activity is reduced to 3 weeks before the old leaves, early maturity makes the rest of the season favorable for their growth and it does not reduce the yield hybrids [11]. It's showed that late maturity hybrids had the highest seed weight due to used readily accessible environmental factors such as light, water and nutrient [1].

Effects of different plant densities on seed weight showed that with increasing plant density from 7 to 10 plants [m.sup.-2] the seed weight decreased significantly (Fig 4 and Table 1). The Ks.c 704 hybrid had the highest seed weight (28.3 mg) compared to other hybrids. The seed weights of other hybrids were as follow Ksc700, K47, K78 (22, 21 and 20 mg, respectively) (Table 2). It's reported that with increasing plant density of 18 plant [m.sup.-2] seed weight reduced [5]. Other researches indicated lower seed weight with increasing plant densities due to increased competition between plants for the environmental factors [16].

Crop yield:

The effects of hybrid, plant density and their interactive effects on total dry matter were significant (Table 1). Mean of comparison of total dry matter showed that Ks.c704 and Ks.c700 hybrids had the highest total dry weight of plants 1995.6 and 1945.3 g [m.sup.-2] respectively and the lowest total dry matter 1812.6 and 1866.1g [m.sup.-2] for k47 and k78 hybrids respectively (Table 2). Its seems that the longer growth periods was responsible for the higher total dry matter of these two hybrids. The lowest and highest of total dry mater were obtained at 7 and 10 plants [m.sup.-2] 1775.4 and 1998.2 g [m.sup.-2] respectively (Table 2). The interactive effects plant density and hybrids showed that all hybrids at plant density of 10 plants [m.sup.-2] (Table 3). It's indicated a positive correlation between yield and dry matter accumulation in different maize hybrids [3]. Other researches reported that maximum dry matter was obtained at density of 7.9 plants [m.sup.-2] [16,23]. The effect of hybrid on the number of rows per ear was not significant. This subject coordinated to the genetic characteristics and showed genetic similarity in hybrids (Table1). It's indicated that number of rows in ear was mainly genetically affected and the environment will be less affected. They also showed no significant effect on the trait number of rows per ear [9]. The effect of plant density on the number of rows per ear was not significantly but related to the maximum plant density of 8 plants [m.sup.-2] (14.16) inverse plant density of 10 plants [m.sup.-2] (14.6), respectively. Also they showed that the plant density of the number of rows per ear no significant effect on the trait and the genetic trait is more to the environment interaction effect plant density and hybrid on the number of rows per ear trait was not significant [9]. Other research reported that the number of row in ear on interaction effects plant density and hybrid was not significant [20]. It's showed that higher plant density reduced number of rows per ear in whole hybrids their experiment [2]. Similarly reported that reduced number of rows per ear with plant density to 14 plant [m.sup.-2] [5].





Our results showed that effect hybrid and the interactive effect of hybrid and plant density of number of seed in row in number of seed in row was significant (Table 1). Hybrids of Ks.c704 and Ks.c700 had the highest (26.4 and 25.4) number of seeds in the row and k78 (23.6) had the lowest number of seed per row (Table 2). The plant density effects on number of seed row showed that the plant density of 8 (24.8) and 10 plants [m.sup.-2] (22.1) were highest and lowest respectively (Table 2). Its stated that increased plant density reduced the number of seed in rows [5]. Expressed that increasing plant density up to 9.5 plants [m.sup.-2], seed number of ear and seed number per row should be lower than the number of rows per ear and 1000 grain weight. Other researches suggested that increasing plant density reduced the number of seeds in rows, and this caused a significant decrease in yield [16,23]. Our result showed that the maximum number of rows of the Ks.c704 was plant density of 8 plants [m.sup.-2] (27.9) and the lowest hybrid of the k78 was at the plant density of 10 plants [m.sup.-2] (24.09). This suggested that the plant density was greater influence than the optimal number of seeds per row (Table 3). Other researches reported the increasing density from 4 to 8 plants [m.sup.-2] reduced the number of seed rows per ear and reduce the number of rows of seed slowly [13,10].

Results showed that the effects of hybrid, density and the interactive effects were significant on the 1000 weight seed (Table1). The Ks.c704 and Ks.c700 hybrids had highest (305 and 295 g) and k78 hybrid had the lowest (254 g) 1000 weight seed (Table 2). The late maturity hybrid due to greater opportunities for growth and dry matter accumulation in the grain and the durability of the LAI of the seed weight than early maturity hybrids (Table 2). The most direct effect on grain yield had 1000 weight seed and it can be reason highest grain yield in the Ks.c 704 and Ks.c 700 hybrids be compared to other hybrids. It's showed that the Ks.c 704 hybrid had greater seed weight compared to other hybrids [13]. It's demonstrated that the hybrid with late maturity with increasing growing period, seed weight was higher than other hybrids and hence higher yield [3]. The highest and lowest 1000 seed weight were obtained of plant density of 8 and 10 plants [m.sup.-2] (285 and 256 g) respectively. This can be due to competition among plants for resources environmental that with increasing plant density, seed weight was also reduced (Table 2). The results showed that interactive effects in the plant density of 8 plants [m.sup.-2] in SC704 and Ks.c700 had the highest yield, but the hybrids k47 and k78 in the highest density of 10 plants [m.sup.-2], had the highest yield. Because height of plant of two hybrids (k47 and k78) was smaller than hybrid (Ks.c704 and Ks.c700) the greater plant density to achieve maximum yield (Table 3). It's reported that early maturity hybrids with increasing plant density compare to lately maturity had the lowest 1000 seed weight [23].

The effects of hybrid, plant density and interactive affects their on grain yield were significant. Hybrid Ks.c704 had the highest grain yield (845.1 g [m.sup.-2]) than other hybrids (Table 1 and 2). It's showed a significant positive correlation between LAI with grain yield for hybrid S.c704 compared to other hybrids [17]. Plant density 8 plants [m.sup.-2] (775.2 g [m.sup.-2]), the highest grain yield and plant density of 7 plant [.m.sup.-2] (721.3 g [m.sup.-2]) of had the lowest yield (Table 2). Increase in plant density of 8 plants [m.sup.-2] appropriate plant density and optimum use of space nutrition is without competition in plant canopy. The other Studies showed that Ks.c704 hybrid of grain yield was higher. The highest levels of grain yield in plant density were 8 plants [m.sup.-2]. Due to the plant density of grain yield components like number of rows, number of grains per ear and grain weight than other higher plant density [13,10]. Other researches experimenting on various plant densities observed corn grain yield increased with increasing plant density to 9 plants per [m.sup.-2] and higher densities of the competition for resources between plants decreased [7]. The interaction effects between hybrid and plant density on yield was significant. Mean comparisons revealed that the hybrid and plant density of 8 plants [m.sup.-2] with the Ks.c704 hybrid (812.3 g [m.sup.-2]) had the highest grain yield. The Ks.c700 hybrid is also the highest yield compared to the same density of 8 plants [m.sup.-2] (800.3 g [m.sup.-2]). While the two other hybrids means, k78 and k47 highest grain yield at the highest density of 10 plants [m.sup.-2] (Table 3). The reason for this is that the two hybrids (k78 and k47) a height of less than two hybrids (Ks.c704 and Ks.c700) and also they were early maturity, and therefore the hybrids to achieve high grain yield potential will require more plant density. Similar researches with increasing plant density 8 to 9 plant m-2 increased grain yield [16,23,18,5].

Hybrid and plant density effects on harvest index were significant (Table 1). The Ks.c704 hybrid had highest harvest index (42.1%) and other hybrids of Ks.c700, k47 and k78 were (41.8, 39.3 and 38.7, respectively). A positive correlation between economic grain yield and biological yield suggests that high index reflects the yield of each hybrid could be higher than the hybrid in the grain yield obtained from Ks.c704 hybrid. This can be due to a larger leaf area index and more leaf area durable as well as factors that increase the harvest index. The lowest harvest index (36.3%) was obtained at high plant density of 10 plants [.m.sup.-2] and harvest index was higher (41%) for plant density of 8 plants [m.sup.-2]. Reduction in plant density, higher harvest index, resulting from increased plant dry matter can be attributed to a negative relationship between biological yield and harvest index (Table 2). Interactive effects of harvest index were significant (Table 1). The Ks.c704 hybrid and the plant density of 8 plants [m.sup.-2] had the highest of harvest index. This can be due to a larger leaf area, leaf area index and yield strength compared to the optimal plant density, the same 8 plants per [m.sup.-2] can take advantage of all the environmental and economic yield benefits to be closer to its grain yield potential. The two hybrid k47 and k78 due to short plant height and more early maturity in its highest plant density is the same as 10 plants per [m.sup.-2] have been able to reach the highest harvest index and grain yield. These results confirm the notion that the more early maturity hybrids, leaf area and plant height is reduced to achieve higher yield, should be plant densities. Its reported that the increase in maize grain yield due to biological yield of most of the increase [22]. Other researches stated that lower harvest index with increased plant density for maize hybrids [2,23,16,13].


Our results reported clearly indicated that the hybrid ksc704 with plant density 8 plants [m.sup.-2] had the highest yield.


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(1) Mehdi Sadeghi, (2) Ahmad Naderi, (3) Shahram Lak, (4) Ghodrat Allah Fathi

(1) Department of Agronomy, Science and Research Branch, Islamic Azad University, Khouzestan, Iran.

(2) Department of Agronomy, Agriculture and Natural Resources Research Centre, Ahwaz, Khouzestan, Iran.

(3) Department of Agronomy, Science and Research Branch, Islamic Azad University, Khouzestan, Iran.

(4) Department of Agronomy, Ramin Agriculture and Natural Resources University, Ahwaz, Iran.

Corresponding Author

Mehdi Sadeghi, Department of Agronomy, Science and Research Branch, Islamic Azad University, Khouzestan, Iran.

E-mail: Tel: +989133368849 Fax: +9806416260890
Table 1: The effects of hybrids and different plant density on some
ergonomic trait of maize hybrid.

 S.O.V df LAI Grain Yield Total Dry Seed
 Matter Weight

Replication 2 1.8 (ns) 64.3 (ns) 483.1 * 2.7 (ns)
 Hybrid(H) 3 35.37 * 306404.1 ** 84198.9 ** 53.6 *
 Eroor1 6 1.675 395.8 658.1 2.51
Density(D) 9 16.4 * 25859.8 ** 63125.3 ** 24.6 *
 H x D 3 1.45 * 483.5 * 8741.2 ** 2.17 *
 Eroor2 24 1.05 215.7 457.5 1.57
 (%CV) -- 3.47 5.85 8.31 5.2

 S.O.V Number of Number of 1000 Seed Harvest
 Seed in Seed in Weight Index
 Row Ear

Replication 3.6 (ns) 0.25 (ns) 45.3 (ns) 2.5 (ns)
 Hybrid(H) 71.5 ** 0.871 (ns) 685.5 ** 79.1 **
 Eroor1 3.35 0.361 11.9 0.675
Density(D) 32.8 ** 3.27 (ns) 442.8 ** 7.38 **
 H x D 3.2 * 0.046 (ns) 11.5 ** 0.693 *
 Eroor2 2.11 0.321 8.5 0.441
 (%CV) 7.48 9.71 6.22 8.86

* , ** Significant at the 0.05 and 0.01 probability levels,

Table 2: Comparison of mean effect plant density on some agronomic
traits of maize hybrids.

 Treatment Leaf Area Seed Weight Grain Yield
 Hybrid Index (mg) (kg

 Ks.c704 4.7 (a) 28.3 (a) 8450.2 (a)
 Ks.c700 4.2 (b) 22.0 (b) 8141.0 (b)
 K78 3.5 (c) 20.0 (c) 7021.0 (d)
 K47 3.7 (b) (c) 21 (b) (c) 7352.0 (c)
 plant Density
(plant. [m.sup.-2])
 7 3.6 (c) 18.6 (b) 7213.0 (d)
 8 3.8 (a) (b) 20.8 (a) 7752.0 (a)
 9 3.9 (a) (b) 21.0 (a) 7426.0 (b)
 10 4.2 (a) 22.0 (a) 7328.0 (c)

 Treatment Number of Number of Total Dry
 Hybrid Row in Ear Seed in Row Matter (g

 Ks.c704 14.9 (a) 26.4 (a) 1995.6 (a)
 Ks.c700 14.8 (a) 25.7 (a) 1945.3 (a)
 K78 14.2 (a) 23.6 (c) 1812.6 (c)
 K47 14.4 (a) 24.5 (b) 1866.1 (b)
 plant Density
(plant. [m.sup.-2])
 7 14.5 (a) 28.4 (a) 1775.4 (c)
 8 14.6 (a) 28.6 (a) 1889.9 (b)
 9 14.5 (a) 22.9 (b) 1941.3 (a) (b)
 10 14.4 (a) 22.8 (b) 1985.9 (a)

 Treatment Harvest 1000 Seed
 Hybrid Index (%) Weight (g)

 Ks.c704 43.3 (a) 305.0 (a)
 Ks.c700 41.8 (a) 294.0 (b)
 K78 38.7 (c) 254.0 (c)
 K47 39.3 (b) 262.0 (c)
 plant Density
(plant. [m.sup.-2])
 7 40.6 (a) 273.0 (b)
 8 41.0 (a) 285.0 (a)
 9 37.3 (b) 270.0 (b)
 10 36.6 (b) 256.0 (c)

For given means within each column followed by the same letter are not
significantly (p < 0.05).

Table 3: Interaction effects of plant density on some agronomic traits
of hybrids corn.

Hybrid Plant Density Grain Yield Number of Number of
 (plant (kg Row in Ear Seed in Row
 [m.sup.-2]) [ha.sup.-1])

 7 7712.0 (c) 14.7 (a) 27.2 (a) (b)
 8 8123.0 (a) 14.9 (a) 27.3 (a)
Ks.c704 9 8054.0 (b) (c) 14.5 (a) 27.2 (a) (b)
 10 7994.0 (b) 14.3 (a) 27.1 (b)

 7 7353.0 (b) (c) 14.5 (a) 27.1 (b)
 8 8002.0 * 14.6 (a) 27.2 (a) (b)
Ks.c700 9 7827.0 (b) 14.3 (a) 26.8 (b) (c)
 10 7613.0 (c) 14.4 (a) 26.1 (b) (c)

 7 6001.0 (e) 14.1 (a) 24.1 (e)
 8 6353.0 (d) 14.1 (a) 24.2 (c) (d)
 K78 9 6564.0 (d) (c) 14.2 (a) 24.3 (c) (d)
 10 6852.0 (d) (c) 14.2 (a) 24.4 (c) (d)

 7 6192.0 (d) 14.1 (a) 24.2 (d)
 8 6453.0 (c) (d) 14.2 (a) 24.3 (c) (d)
 K46 8 6963.0 (c) (d) 14.2 (a) 24.3 (c) (d)
 10 7205.0 (b) (c) 14.3 (a) 24.6 (c)

Hybrid Total Dry Harvest 1000 Seed
 Matter Index Weight
 (g (%) (g)

 1875.7 (c) 41.1 * 300.0 *
 1916.2 (b) 42.3 (a) 305.0 (a)
Ks.c704 1975.3 * 40.7 (b) 295.0 (b)
 2005.6 (a) 39.8 (b) (c) 290.0 (b)

 1860.6 (c) 39.5 (b) (c) 295.0 (b)
 1903.2 (b) 42.0 (a) 303.0 *
Ks.c700 1925.3 * 40.6 (b) 287.0 (b) (c)
 1941.3 * 39.2 (b) (c) 280.0 (b) (c)

 1691.2 (e) 35.4 (d) 235.0 (e)
 1762.6 (d) 36.4 (c) 244.0 (d)
 K78 1815.1 (b) (c) 36.1 (c) 259.0 (c) (d)
 1846.1 (b) (c)37.1 (b) (c) 265.0 (c)

 1722.1 (d) 35.9 (c) 247.0 (c) (d)
 1791.7 (d) 36.0 (c) 254.0 (c) (d)
 K46 1836.2 (b) (c)37.9 (b) (c) 266.0 (c)
 1887.4 (b) (c)38.1 (b) (c) 273.0 (b) (c)

For given means within each column followed by the same letter are not
significantly (p < 0.05)
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Title Annotation:Original Article
Author:Sadeghi, Mehdi; Naderi, Ahmad; Lak, Shahram; Fathi, Ghodrat Allah
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Jan 1, 2012
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