Agronomy Journal 94:326-330 (2002)
© 2002 American Society of Agronomy
CORN
Row Width and Plant Density Effect on Corn Forage Hybrids
William D. Widdicombe and
Kurt D. Thelen*
Dep. of Crop and Soil Sci., Michigan State Univ., Plant and Soil Sci. Bldg., East Lansing, MI 48824
* Corresponding author (thelenk3{at}msu.edu)
Received for publication June 19, 2001.
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ABSTRACT
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Information is needed on the agronomic factors that maximize yield and quality of recently developed corn (Zea mays L.) forage hybrids. This study was conducted to determine the effect of row width (76, 56, and 38 cm) and plant density (64200, 79000, and 88900 plants ha-1) on forage yield and quality of forage specialty corn hybrids and a dual-purpose hybrid. Two of the forage hybrids evaluated were leafy hybrids, and the other one was characterized as a nutridense hybrid. The increase in forage dry matter (DM) yield when row width was narrowed from 76 to 38 cm was similar for the forage hybrids and the dual-purpose hybrid (1.1 and 0.9 Mg ha-1, respectively). However, there were significant differences in response to decreased row width between the two leafy hybrids evaluated. The narrow row production system did not impact corn forage quality nor was there a hybrid x row width interaction. As plant density increased from the lowest level to the highest, forage DM yield increased by 1.6 Mg ha-1, DM digestibility decreased from 652 to 641 g kg-1, crude protein decreased from 76 to 72 g kg-1, acid detergent fiber increased from 259 to 270 g kg-1, and neutral detergent fiber increased from 441 to 456 g kg-1. In addition, there was no hybrid x plant density interaction for these parameters. It was concluded that these forage hybrids will react to changes in row width and plant density similar to dual-purpose hybrids.
Abbreviations: ADF, acid detergent fiber • CP, crude protein • DM, dry matter • DMD, dry matter digestibility • GDU, growing degree units • HI, harvest index • NDF, neutral detergent fiber
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INTRODUCTION
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AGRONOMIC STUDIES of corn forage production systems have primarily focused on dual-purpose hybrids. Growers who plant dual-purpose hybrids have the flexibility of using them for either forage or grain production, depending on the need. In the early to mid-1990s, the seed corn industry released single-purpose commercial forage hybrids, which were developed to exhibit more favorable forage qualities. These newer hybrids have higher digestibility traits than the previous dual-purpose hybrids (Dwyer et al., 1998).
Corn forage production in row widths <76 cm has been gaining interest in recent years. To date, most contemporary research on narrow-row corn has focused on grain yield. Narrow-row studies that have involved corn forage have predominately focused on dual-purpose hybrids. A study utilizing dual-purpose hybrids by Cox et al. (1998) in New York found that corn forage yield increased by 4.2% as row width narrowed. Row width did not affect forage quality analysis for the 3 yr of the study.
Current corn hybrids can withstand higher plant densities than older hybrids (Tollenaar, 1989). Cox (1996) found that corn forage dry matter (DM) increased as plant density levels were increased. Further work by Cox (1997) established a recommendation that forage corn be planted at plant density levels 7.5% higher, on average, than corn grain. Earlier work involving forage quality and plant densities by Graybill et al. (1991) showed that some forage quality traits, including acid detergent fiber (ADF) and neutral detergent fiber (NDF) content, were not affected by increases in plant density levels.
Harvest index (HI) is defined as the ratio between ear DM and fodder DM. A high HI indicates a higher grain content in the forage. A high grain content increases corn forage palatability, energy level, and digestibility (Woody et al., 1983). The HI of older hybrids is generally reduced with increases in plant density because interplant competition reduces the grain portion of the forage (Duncan, 1984). The HI of modern hybrids generally does not decrease as plant density increases (Tollenaar, 1989).
Hybrid selection is key to improving forage quality for optimum animal output. Historically, there has been significant genetic variability for forage quality among corn hybrids. Many forage quality components, including ADF, NDF, crude protein (CP), and cell wall digestibility, depend on the plant genotype (Roth et al., 1970).
The objective of this study was to determine the effects of row width and plant density on forage yield and quality for several forage specialty hybrids.
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MATERIALS AND METHODS
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Field trials were conducted in 1998 and 1999 on a Capac loam soil at the Michigan State University Research Farm in East Lansing, MI. The soil is well drained with a pH of 6.8. Before planting, 336 kg ha-1 urea [(NH2)2CO] (46–0–0) and 224 kg ha-1 of starter fertilizer (6–24–24) were broadcast. In both years of the study, soybean [Glycine max (L.) Merr.] preceded corn.
The forage hybrids evaluated consisted of two hybrids characterized as leafy (Lfy L.L.C., Monterey, CA) and one characterized as a nutridense hybrid (ExSeed Genetics L.L.C., Owensboro, KY). A dual-purpose hybrid was also evaluated for comparison. The respective relative maturity ratings were 106, 108, 108, and 100 d. All hybrids were planted in early May in 76-, 56-, and 38-cm row widths. Each row width and hybrid type was planted at three target plant density levels of 64200, 79000, and 88900 plants ha-1. Plots were arranged in a randomized complete block design as a split-split plot with four replications. The main plots were represented by hybrid (20 by 9 m), row width was the first split (20 by 3 m), and plant density represented the split-split plot (7 by 3 m).
Plant population was determined in all plots after corn emerged. Plots were thinned by hand to establish a uniform plant population for each of the three plant density levels. Average harvested plant populations for the three established plant density levels were 60416, 74223, and 88078 plants ha-1. The corn forage was harvested with a mechanical, single row, side-mount forage harvester. The center two rows for the 76-cm row width plots, the center three rows for the 56-cm row width plots, and the center five rows for the 38-cm row width plots were harvested in late August in 1998 and early September in 1999 when the grain was approximately at 65% milk line (Wiersma et al., 1993). The forage samples from each plot, containing both fodder and grain, were weighed and oven-dried to determine forage DM yield and quality. Plants from one row of each plot were harvested by hand, and the ears were removed. The plant fodder and ears were weighed separately to determine the HI. Harvest index was defined as the ratio between ear DM and fodder DM.
Forage samples for quality analysis were ground sequentially through a Wiley mill (Christy and Morris, Chelmsford, UK) and Cyclone mill (UDY Corp., Fort Collins, CO). Dry matter digestibility (DMD) was obtained by wet chemical analysis from a 0.57-g forage sample. In 1998, a wet chemical analyses procedure, using an enzymatic technique outlined by DeBoever et al. (1986), was used to obtain DMD. A cellulase solution technique was used to obtain DMD in 1999 (Bughrara et al., 1992). Other forage quality components, including ADF, NDF, and CP, were determined with near-infrared reflectance spectrometry using a global calibration equation (Forage NIRS Network, Pioneer Hybrid Int.). Calibration and validation statistics (R2 and standard error of validation) were 0.98 and 8.9 g kg-1 (ADF), 0.98 and 10.6 g kg-1 (NDF), and 0.96 and 2.9 g kg-1 (CP), respectively.
All data were analyzed with the analysis of variance (ANOVA) and the Mixed Linear Model in SAS Statistical Software Package version 6.12 (SAS Inst., 1990). The Mixed Linear Model is able to calculate the appropriate error terms for statistical tests associated with the split-split plot design. Mean separations were obtained using Tukey's Least Significant Difference Test. Regression analysis was used to evaluate forage yield and quality data across plant density and row width. Linear regression was used for data analysis based on the evaluation of correlation coefficients. Effects were considered significant in all statistical calculations if P-values < 0.05.
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RESULTS AND DISCUSSION
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Weather patterns differed significantly in 1998 and 1999. The 1998 growing season had near-normal precipitation from May through August (Table 1). In 1998, base 10°C growing degree unit (GDU) accumulation was 95 GDU above normal but with near-normal GDU accumulation in July and August. Precipitation was 6.0 cm below the 30-yr average for the 1999 growing season. Timely precipitation (17.4 cm) in July and August increased kernel set at pollination and facilitated kernel fill. This precipitation helped boost forage yield for the season. The GDU accumulation for the 1999 growing season was slightly above normal.
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Table 1. Monthly precipitation (cm) and growing degree unit (GDU) accumulation for the 1998 and 1999 growing seasons at the experimental location. Thirty-year means have been included for comparison (1961–1990).
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The summary of the ANOVA table shows the significance of the main effects of hybrid, row width, and plant density on forage DM, DM yield, HI, DMD, ADF, NDF, and CP (Table 2). Row width affected percent DM and DM yield of corn forage (Fig. 1)
. Forage DM yield increased 1.0 Mg ha-1 as row width was narrowed from 76 to 38 cm. This increase in DM yield of 5.0% with the narrow-row system is consistent with that reported by Cox et al. (1998). There was a significant hybrid x row width interaction on forage yield (Table 2). However, the average increase in yield for the dual-purpose hybrid (4.8%) when row width was narrowed from 76 to 38 cm compared favorably with the average increase for the three forage hybrids (5.4%). The data indicate that the interaction is due primarily to differences between the nutridense hybrid, which did not respond to narrow-row widths, and the full-season leafy hybrid, which responded with a significant increase of 13.6% more DM forage yield when row width was narrowed to 38 cm. The variability in corn forage yield response to changes in row width by the forage hybrids was consistent with the variability between hybrids reported by Cox et al. (1998). In addition, these authors reported no change in corn forage quality parameters as row width narrowed. Similarly, this study showed no difference in corn forage quality for the forage and dual-purpose hybrids when row width was narrowed. As row width narrowed from 76 to 38 cm, the percent DM of the forage increased by 1.0%. In evaluating corn grain moisture, Porter et al. (1997) found increases in grain DM content at some locations in some years when row width was narrowed to 38 cm, but the results were inconsistent. These data suggest that growers can expect the yield and quality of corn forage hybrids to respond to row width reductions similar to dual-purpose hybrids.
Plant density significantly affected forage DM yield and all measured forage quality parameters, with the exception of HI (Table 2). The response of forage DM yield to plant density was linear, with the maximum DM yield observed at the highest plant density level of 88900 plants ha-1 (Fig. 2a
and Table 3). Cusicanqui and Lauer (1999) reported a quadratic yield response to plant density, with a maximum DM yield at plant density levels between 97300 and 102200 plants ha-1. The observed linear yield response to plant density suggests that the maximum plant density level of 88900 plants ha-1 utilized in this study may have been too low to establish the maximum obtainable DM yield.
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Fig. 2. Effect of harvest plant density on corn forage (a) dry matter (DM) yield, (b) percent DM, (c) acid detergent fiber (ADF) concentration, (d) neutral detergent fiber (NDF) concentration, (e) DM digestibility concentration, and (f) crude protein (CP) concentration. Data are averaged across hybrid, row width, year, and replication. For regression equations, see Table 3.
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Table 3. Regression equations for corn forage quality. Data were regressed as specified against row width and plant density. Data for row width regression analysis were pooled across year, location, hybrid, plant density, and replication. Data for plant density regression analysis were pooled across year, location, hybrid, row width, and replication.
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Plant density affected forage DMD. As plant density increased, forage DMD showed a linear decrease (Fig. 2e and Table 3). Forage DMD dropped 11.0 g kg-1 as plant density increased from lowest to highest. The percent ADF increased linearly by 10.7 g kg-1 as plant density increased from lowest to highest (Fig. 2c). Similarly, forage NDF increased by 15.0 g kg-1 as plant density increased from lowest to highest (Fig. 2d). Plant density also affected forage CP levels. As plant density increased, forage CP decreased by 3.5 g kg-1 (Fig. 2f). A hybrid x plant density interaction was not observed for all forage quality parameters measured. This is consistent with findings reported by Cusicanqui and Lauer (1999) and Cummins and Dobson (1973), suggesting that hybrid differences in forage quality vary in a similar manner across a range of plant densities. These results suggest that plant density impact on feed quality can be expected to be similar between corn forage hybrids and conventional dual-purpose hybrids.
Hybrids exhibited different harvest indices. The earlier-maturing leafy hybrid produced a significantly lower HI (Table 4) than the full-season leafy hybrid and the nutridense hybrid. The HI was affected by the two-way interaction of hybrid x plant density (Table 2). The full-season leafy hybrid and the nutridense hybrid showed a consistent HI as plant density increased. The HI increased for the dual-purpose hybrid as plant density increased from lowest to highest. The HI dropped significantly, from a value of 58 to 48, for the earlier-maturing leafy hybrid as plant density was increased from lowest to highest. This suggests that the optimum plant density for the earlier-maturing leafy variety was less than that of the other hybrids evaluated.
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Table 4. Corn forage yield and quality as affected by hybrid type. Data are averaged across row width, plant density, year, and replication.
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There were differences in DM yield among the hybrids evaluated (Table 4). The full-season leafy hybrid had the highest DM yield (22.0 Mg ha-1) followed by the nutridense hybrid (20.6 Mg ha-1). The dual-purpose and early maturing leafy hybrid had lower DM yields of 19.1 and 18.8 Mg ha-1 over the 2 yr of the study. The nutridense, dual-purpose, and full-season leafy hybrids had higher DMD levels than the earlier-maturing leafy hybrid. The earlier-maturing leafy hybrid had higher ADF and NDF levels compared with the other hybrids evaluated. Forage CP levels varied by hybrid type. The full-season leafy hybrid had a lower CP level than the nutridense and dual-purpose hybrids.
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CONCLUSION
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The average increase in forage DM yield when row width was narrowed was similar for the forage hybrids and the dual-purpose hybrid. However, there were significant differences in response to decreased row width between the two leafy hybrids evaluated. The full-season leafy hybrid had a DM yield increase of 1.4 and 2.8 Mg ha-1 when row width was narrowed to 56 and 38 cm, respectively. Conversely, the shorter-season leafy hybrid did not respond to changes in row width. As with dual-purpose hybrids (Cox et al., 1998), forage hybrids will differ individually in response to changes in row width. Therefore, growers should use discretion in selecting among specific forage hybrids to maximize DM yield. The narrow-row production system did not impact corn forage quality nor was there a hybrid x row width interaction for all forage quality parameters analyzed. This suggests that dual-purpose and forage specialty hybrids respond similarly to changes in row width.
Plant density affected corn forage DM yield and quality of the hybrids tested. As plant density increased, forage DM yield increased and DMD, ADF, NDF, and CP were adversely affected. The adverse effect of increased plant density on forage quality was similar to that reported by Cusicanqui and Lauer (1999). The lack of a hybrid x plant density interaction for these parameters indicates that dual-purpose and forage specialty hybrids respond similarly to increased plant density.
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REFERENCES
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TOP
ABSTRACT
INTRODUCTION
= nutridense hybrid, 
= dual-purpose hybrid, and 
= early maturing leafy hybrid. Data are averaged across plant density levels and replication. Regression equations are full-season leafy, y = -0.0736x + 26.17, R2 = 1.0 and dual purpose, y = -0.0233x + 20.46, R2 = 0.8. The early maturing leafy hybrid and the nutridense hybrid did not have significant regression coefficients. Data are averaged across plant density level, year, and replication.