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Agronomy Journal 93:1049-1053 (2001)
© 2001 American Society of Agronomy

CORN

Row Spacing, Plant Density, and Hybrid Effects on Corn Grain Yield and Moisture

Dale E. Farnham*

Dep. of Agron., Iowa State Univ., Ames, IA 50011. Iowa Agric. and Home Econ. Exp. Stn. Journal Paper no. J-18919

* Corresponding author (dfarnham{at}iastate.edu)

Received for publication June 12, 2000.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Producing corn (Zea mays L.) in narrow row spacings has been attempted over the last several decades with varying degrees of success. The objectives of this study, are to determine: (i) if there is a different optimum plant density or (ii) if hybrids of varying relative maturity respond differently for corn grown in narrow row spacings (38 cm) compared with conventional row widths (76 cm). These studies were conducted at six locations across Iowa over 3 yr. Averaged across years, locations, and plant densities, corn grown in 76-cm row spacings produced higher yields than that grown in 38-cm rows (10.5 vs. 10.3 Mg ha-1, respectively). Harvest moisture content of corn grown in 38-cm row spacings was significantly less than that of corn grown in 76-cm row spacings (160 vs. 161 g kg-1, respectively). Averaged across years and locations, there was no statistically significant (P < 0.05) yield difference between the two row spacings for four of the six hybrids tested. Hybrid MAX23 yielded significantly more grain in 76-cm row spacings (9.4 vs. 8.9 Mg ha-1) while ‘MAX454’ yielded more grain in 38-cm row spacings (10.0 vs. 9.8 Mg ha-1). It is thus concluded that optimum plant densities for narrow-row corn production are similar to those required to produce maximum yields for conventional wide-row corn production. In addition, a strong hybrid x row spacing interaction among the six hybrids tested here suggests that certain hybrids may perform better at prescribed row spacings.

Abbreviations: GDU, growing degree unit


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
CORN PRODUCERS continually search for methods that will help them increase yields, reduce costs, or a combination of both. Plant distribution in the field, as affected by plant density and/or row spacing, has been one area that has received a great deal of attention over the last several decades. As plant densities continue to increase, an obvious course of action would be to narrow row spacing, distribute plants more equidistantly across the field, and reduce interplant competition.

Producing corn in narrow rows is not a new concept. Research in the 1960s compared wide row spacings (102 cm) with narrow row spacings (<=76 cm). In Iowa, Shibles et al. (1966) showed roughly a 1.5% yield increase for 76-cm row spacings compared with 102-cm row spacings and an additional 3.5% yield advantage for 51-cm row spacings. In Georgia (USA), Brown et al. (1970) showed a 33.7% yield increase for corn grown in 51-cm rows compared with 102-cm rows. In Virginia, Lutz et al. (1971) reported a 5% yield increase for 76-cm row spacings compared with 102-cm row spacings and an additional 2.7% yield advantage for 38-cm row spacings. In Canada, Fulton (1970) reported that under conditions of adequate soil moisture, higher plant densities (54362 plants ha-1) produced higher yields than lower densities (39536 plants ha-1), and rows spaced at 50 cm produced higher yields than rows spaced 100 cm apart. In addition, Fulton reported a significant plant density x row spacing (50 cm) interaction in only one of four experimental years, indicating that the effect of narrow row spacings was greater at high plant densities than at low plant densities. Despite rather inconsistent results, farmers slowly began transitioning towards growing corn in narrow rows (76 cm). Much of this interest was fueled by documented yield advantages for soybean [Glycine max (L.) Merr.] grown in narrow rows (<=76 cm).

More recent research on corn row spacings has produced mixed results. In a summary of research on the effects of narrow row spacing on corn conducted across the U.S. Corn Belt, average yield differences from northern to southern locations showed a 6.2% advantage for narrow row spacings in the north that diminished as the trials moved south where wide row spacings showed a 4.1% advantage over narrow row spacings (Gray, personal communication, 1999). In Minnesota, Porter et al. (1997) reported a yield advantage (7%) for narrowing row spacings from 76 cm to 51 or 38 cm. In New York, Cox et al. (1998) showed a 4.2% increase in silage yield for corn grown in 38-cm row spacings compared with 76-cm row spacings. In the New York study, row spacing x hybrid interactions were not detected, suggesting that producers can select corn hybrids for yield and quality characteristics that were evaluated at 76-cm row spacings. In many cases, although statistically significant, the economic significance of these modest yield increases must also be considered. For instance, in Indiana, Nielsen (1988) showed a 2.7% yield advantage for 38-cm row spacings compared with 76-cm row spacings. This small yield increase must be weighed against the rather high cost of switching to narrow-row corn production (Hallman and Lowenberg-DeBoer, 1999). The investment will involve more than simply purchasing a different corn planter, which in itself is a costly endeavor. In addition to the planter, harvesting equipment will need to be purchased or altered, pest management systems will need to be altered, and tractor tire tread width may require alteration.

Many producers wonder if there is a different optimum plant density for corn grown in narrow rows. Another frequently asked question is whether or not specific hybrids are better adapted to the narrow-row environment than others. In short, if shorter season hybrids that were adapted to northern locations were moved to more southern locations, would the same yield response be realized? For these reasons, the objectives of this study were to (i) determine if there is a different optimum plant density for corn grown in narrow rows (38 cm) compared with conventional wide rows (76 cm) and (ii) determine if corn hybrids varying in relative maturity respond similarly to different row spacings.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Row Spacing x Plant Density
This study was conducted over 3 yr (1997–1999) at six locations across the state of Iowa, each at an Iowa State University outlying research and demonstration farm. The six locations were Sutherland (northwest), Kanawha (north central), Nashua (northeast), Ames (central), Lewis (southwest), and Crawfordsville (southeast). Each area represents a different cropping environment in the state. Nitrogen, P, and K fertilizers were applied according to yield potentials and soil test levels (P and K) for each site. Pre- and postemergence herbicides were applied as deemed necessary at each location. Postemergence herbicides were applied by driving perpendicularly to the corn rows, thus equalizing tire damage to the corn across all row spacings. No postemergence cultivation was done on any of the plots. Hand weeding was done where necessary.

The experimental layout was a randomized complete block design in a split-plot arrangement with three replicates. Whole-plot treatments were row spacings (38 or 76 cm) and split-plot treatments were plant densities (59000, 69000, 79000, or 89000 plants ha-1). The previous crop at each site was soybean. A single hybrid [N4640Bt (Novartis Seeds, Minneapolis, MN)], resistant to European corn borer (Ostrinia nubilalis Hubner) and of 102- to 106-d relative maturity (Minnesota Relative Maturity Rating System), was evaluated. A White (AGCO) 6100 series corn planter outfitted with a 6900 series splitter attachment was used to plant all plots. Individual plots were 6 rows (76 cm) or 11 rows (38 cm) wide by 12.2 m long. Planting and harvesting dates are shown in Table 1. Plots were overplanted and hand-thinned to achieve the desired target plant densities. All plots were mechanically harvested using a combine outfitted with a 76-cm cornhead. The center two (76-cm row spacing) or four (38-cm row spacing) rows of each plot were harvested, and grain yield (adjusted to 155 g kg-1 moisture) and harvest moisture data were recorded for all plots. To ensure that all plots were harvested to the same efficiency, plots were gleaned following mechanical harvesting, and any dropped ears were added to the yield for that respective plot.


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  		Table 1. Planting and harvesting dates for row spacing x plant density and row spacing x hybrid studies at different Iowa locations from 1997 to 1999.

 
Data for each location and year were analyzed using standard analysis of variance (ANOVA) and General Linear Model (GLM) techniques, and means were separated using Fisher's protected least significant difference (LSD) comparisons (SAS Inst., 1996). Data for the six sites were combined over years because the same hybrid, row spacings, and plant densities were evaluated at each site and homogeneous variances were observed for yield and grain moisture. Regression analysis on the means of each plant density and grain yield were performed where appropriate. Linear or quadratic equations were selected according to the significance (P = 0.05) of the regression coefficients.

Row Spacing x Hybrid
This study was conducted for 3 yr (1997–1999) at the same six locations mentioned previously. As described previously, N, P, and K fertilizers and pre- and postemergence herbicides were applied as deemed necessary at each location. Postemergence herbicides were applied by driving perpendicularly to the corn rows. No postemergence cultivation was done on any of the plots. Hand weeding was done where necessary.

The experimental layout was a randomized complete block design in a split-plot arrangement with three replicates. Whole-plot treatments were row spacings (38 or 76 cm), and split-plot treatments were hybrids. The previous crop at each site was soybean. Hybrid selections were based on relative maturity using the Minnesota Relative Maturity Rating System. Hybrids used, all from Novartis Seeds, were MAX23 and N4242Bt (94- to 102-d relative maturity), MAX21 and N4640Bt (102- to 108-d relative maturity), and MAX454 and N6800Bt (110- to 114-d relative maturity). These hybrids were selected not only for their maturity rating, but also because they were considered top-yielding, elite hybrids for their maturity range. The same corn planter mentioned above was used to plant these plots. Individual plots were 6 rows (76 cm) or 11 rows (38 cm) wide by 12.2 m long. Planting and harvesting dates are shown in Table 1. All plots were overplanted and hand-thinned to achieve a final harvest plant density of approximately 69000 plants ha-1. All plots were harvested as described previously. Grain yield and moisture data were recorded for all plots. Data were analyzed using standard ANOVA and GLM techniques, and means were separated using Fisher's protected LSD comparisons (SAS Inst., 1996).


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
SUMMARY AND CONCLUSIONS
 REFERENCES
 
Growing Conditions
Growing conditions were quite variable from location to location across the state as well as from year to year. Conditions were drier than normal at all locations in 1997, with total seasonal (April through October) precipitation amounts ranging from 8 to 25% (southwest and north central, respectively) lower than normal. Normal growing-season precipitation for Iowa varies from 597 (northwest) to 687 mm (southeast). The dry conditions were fairly evenly distributed across the state with the exception of northeast Iowa, which was slightly wetter than normal in the latter half of the growing season (July through October). Western Iowa, in general, was warmer than normal, with total seasonal growing degree unit (GDU) accumulations averaging 3 to 4% greater than normal. Normal growing-season GDU (30–10°C system; Cross and Zuber, 1972) accumulations range from 1619 (northwest) to 1893 (southeast). Early season (April through June) accumulations in western Iowa tended to be cooler than normal, with the heat coming in the latter half of the growing season. Eastern Iowa, being slightly cooler than normal, had GDU accumulations averaging 3 to 8% lower than normal.

Both precipitation and GDU accumulations were above normal for the 1998 growing season for all locations. Total seasonal precipitation amounts ranged from 5 to 77% greater than normal (northwest and southwest, respectively). Excessive rainfall was common across the state during the first half of the growing season. Total season GDU accumulations ranged from 4 to 17% greater than normal (north central and southwest, respectively). Precipitation totals for the 1999 season were mixed across the state. All locations reported greater-than-normal precipitation for the first half of the season, with northwest Iowa reporting 50% and southeast Iowa reporting 28% less precipitation than normal for the latter half of the season. Total season GDU accumulations for the 1999 season were slightly less than normal for all locations except southeast Iowa, which reported a 2% higher accumulation than normal.

Row Spacing x Plant Density
Averaged across years and locations, there were significant plant density and row-spacing effects on corn grain yields and moisture contents (Table 2). Average grain yields were greater (P <= 0.05) for 76-cm row spacings (10.5 Mg ha-1) than for 38-cm row spacings (10.3 Mg ha-1). In 38-cm rows, as plant density increased from 59000 to 79000 plants ha-1, corn grain yield increased from 9.9 to 10.6 Mg ha-1 (7.1% increase), with no further increase in yield as plant density increased from 79000 to 89000 plants ha-1 (Table 2). In 76-cm row spacings, corn grain yield increased from 10.1 to 10.8 Mg ha-1 (6.9% increase) as plant density increased from 59000 to 89000 plants ha-1 (Table 2). There was no significant row spacing x plant density interaction for grain yield. Lack of significant row spacing x plant density interaction was also reported by Nielsen (1988) and Cox et al. (1998) and by Porter et al. (1997) at two of three locations.


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  		Table 2. Effect of row spacing and plant density on corn grain yield and moisture at different Iowa locations from 1997 to 1999.

 
Averaged across locations, plant densities, and years, grain moisture content of corn grown in 38-cm rows (160 g kg-1) was slightly lower (P <= 0.05) than that of corn grown in 76-cm rows (161 g kg-1) (Table 2). The grain moisture difference observed between row spacings was of no practical significance, which agrees with the findings of Porter et al. (1997), who showed no row-spacing effect on corn grain moisture content. There was a significant row spacing x plant density interaction for grain moisture, primarily because corn grain moisture was slightly greater for 76-cm row spacings at 79000 plants ha-1. Again, this difference in grain moisture was small and of no practical significance.

Regression analysis of means for years and locations showed that grain yield had a significant linear response to plant density for 12 of the 18 site-year combinations tested (Table 3). The Crawfordsville location in 1997 was the only site-year combination to show a significant quadratic response to plant density. Only two sites, Ames and Nashua, produced significant linear responses to plant density in all 3 yr of the study. These results, along with the strong plant density x year and plant density x location interactions observed in this study suggest that optimum plant density will vary from year to year and from location to location. Furthermore, based on the grain yield data from this study, optimum plant densities for corn grain production should be similar for either 38- or 76-cm row spacings.


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  		Table 3. Regression equations and coefficients of variation for yield responses to plant populations when averaged across two row spacings (38 and 76 cm) at different locations in Iowa from 1997 to 1999.

 
Row Spacing x Hybrid
Averaged across all years, locations, and hybrids, corn grain yields did not differ between row spacings; grain moisture contents were lower for 38-cm row spacings. As in the row spacing x plant density study, grain moisture contents were statistically different between row spacings but of no practical significance (Table 4). For both row spacings tested, as hybrid maturity increased, yields also increased. Similarly, as hybrid maturity increased, grain moisture content increased.


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  		Table 4. Effect of row spacing and hybrid on corn grain yield and moisture by location, 1997–1999.

 
There was a significant hybrid effect for grain yield. In addition, there was a significant hybrid x row spacing interaction for corn grain yield and significant row spacing x year, hybrid x year, and hybrid x location interactions. When averaged across locations and years, MAX23 performed better in 76-cm row spacings (7% greater) while MAX454 yielded better in 38-cm row spacings (2% greater) (Table 4). These responses contradict what commonly has been assumed about hybrid maturity, row spacing, and yield potential: Longer season hybrids generally produce larger plants (leaves and stalks) and are more sensitive to higher plant densities than are shorter season hybrids grown in 76-cm or wider row spacings. Less is known regarding hybrid adaptation to narrower row spacings. Thus, it has been speculated that shorter season hybrids would be better adapted to narrower row spacings, especially at higher plant densities. Other studies have shown no interaction between hybrids and row spacings. Nielsen (1988) compared two contrasting hybrids (one a short-statured type with nonerect leaves and the other a taller type with erect leaves) at two row spacings (38 and 76 cm) and found no significant hybrid x row spacing interaction. Similarly, Cox et al. (1998) tested eight hybrids for silage production and observed no hybrid x row spacing interaction. The data from this study suggest that certain hybrids do respond differently (grain yield) to varying row spacings.


   SUMMARY AND CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
REFERENCES
 
Responses to narrowing row spacing in corn have been varied and inconsistent. This study evaluated the impact of row spacing, plant density, and hybrids on corn grain yield and moisture. Based on the results of this study, optimum plant densities for wide (76 cm) and narrow (38 cm) row spacings are similar. There does not seem to be any advantage to adjusting plant density either higher or lower as the distance between rows narrows from 76 to 38 cm. These findings agree with those of several previous studies (e.g., Bitzer and Herbek, 2000; Porter et al., 1997). Paszkiewicz (1996), however, did show a favorable advantage for 57-cm row spacings over 76-cm spacings at all plant densities tested.

Additionally, selecting hybrids for use in specific row-spacing environments based on relative maturity rating alone may limit the yield potential of the production system. Of the six hybrids tested in this study, the later maturing hybrids tended to perform slightly better in the narrow-row environment while the earlier maturing hybrids tended to favor the conventional wide-row environment. This is contrary to popular thinking, whereby it has been assumed that the narrower architecture of early maturing hybrids would be a better fit for the narrow-row environment and the larger, leafier architecture of fuller season hybrids would result in better adaptability in wider row-spacing environments. The ideal hybrid(s) for narrow-row corn production may exist currently; or, through genetic engineering, true narrow-row hybrids may be developed. Either way, the economic significance of the potential yield advantages and the cost to switch to narrow row spacings must be evaluated as well.

There may be alternative strategies that would make use of narrow row spacings for corn more attractive. Hoff and Mederski (1960) stated that equidistant planting provides a uniform vegetative canopy early in the season and may reduce soil erosion. Teasdale (1995) reported that growing corn in 38-cm rows at high plant densities may have the potential for improving weed control in reduced-herbicide systems. Teasdale also stated that additional research is needed to understand how narrow row spacings and higher plant densities can be effectively integrated into weed management systems. Likewise with the other strategies, additional research is necessary to determine if narrowing corn row spacings may be a profitable production technique.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Project no. IOWO-3469, and supported by the Hatch Act and State of Iowa.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 




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