Agronomy Journal 93:597-602 (2001)
© 2001 American Society of Agronomy
CORN
Row Spacing, Plant Density, and Nitrogen Effects on Corn Silage
William J. Coxa and
Debbie J.R. Cherneyb
a Dep. of Crop and Soil Sci., Cornell Univ., Ithaca, NY 14853
b Dep. of Animal Sci., Cornell Univ., Ithaca, NY 14853
Corresponding author (wjc3{at}cornell.edu)
Received for publication May 19, 2000.
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ABSTRACT
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Dairy producers in the northeastern USA who grow corn (Zea mays L.) forage in narrow rows plant at 125000 plants ha-1 and fertilize at 225 kg N ha-1 because they believe narrow-row corn yields best at high plant densities and N rates. We evaluated corn in 1996 and 1997 at two row spacings (0.38 and 0.76 m), two harvest densities (80000 and 116000 plants ha-1), and six N rates (0, 50, 100, 150, 200, and 250 kg ha-1) to determine if row spacing x plant density x N rate interactions existed for dry matter (DM) and calculated milk yields. No interactions existed for DM yield, forage quality characteristics, and milk yields. Corn had greater DM and milk yields at 0.38- (20.3 and 16.1 Mg ha-1, respectively) vs. 0.76-m spacing (18.9 and 15.2 Mg ha-1, respectively). Dry matter and milk yields had quadratic-plus-plateau responses to N rates with maximum yields (20.6 and 17.1 Mg ha-1, respectively) at an N rate of 150 kg ha-1. Nitrogen accumulation at harvest, which had a row spacing x N rate interaction, had a linear response to N rates at 0.38-m spacing and a quadratic response at 0.76-m spacing. Dairy farmers in the northeastern USA can produce corn silage at similar plant densities and N fertility, regardless of row spacing. Dairy producers who have excess animal waste could apply slightly more N to narrow-row corn silage because it accumulates more N at harvest.
Abbreviations: CP, crude protein • DM, dry matter • HI, harvest index • IVTD, in vitro true digestibility • LAI, leaf area index • NDF, neutral-detergent fiber
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INTRODUCTION
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SOME LARGE DAIRY PRODUCERS in the northeastern USA produce corn silage under narrow rows (Cox et al., 1998). These producers, who have reported 3 to 4 Mg ha-1 yield responses to narrow rows, plant corn at about 125000 plants ha-1 and apply about 225 kg N ha-1 because they believe that corn silage responds best to narrow rows under high plant densities and high N rates (Deibel, 1997). Consequently, these producers apply more animal waste, which is often in excess on their farms, to narrow-row corn. Barbieri et al. (2000), however, reported a greater grain yield response to narrow rows under N deficient conditions rather than high N conditions. Cox et al. (1998) also reported that corn silage yields do not have a row spacing x plant density interaction and that optimum plant densities for silage yields are the same at 0.38- and 0.76-m row spacing. Research is needed on the response of narrow-row corn silage under high plant densities to N rates.
Rutger and Crowder (1967) evaluated three hybrids in New York at 0.46- and 0.92-m spacing and 86500 plants ha-1 and reported that row spacing did not affect corn silage yields. Bryant and Blaser (1968), however, reported that one hybrid yielded best at 0.36-m row spacing and 99000 plants ha-1 and another hybrid yielded best at 0.76-m row spacing and 74000 plants ha-1 in Virginia. More recently, Roth (1996) reported a 9% increase in corn silage yield at 0.38- vs. 0.76-m row spacing in Pennsylvania. Cox et al. (1998), however, reported only a 4% advantage for corn silage yield at 0.38- vs. 0.76-m row spacing in New York with no row spacing x plant density interaction. Cox et al. (1998) also reported that corn silage quality decreased as plant densities increased, so corn in narrow rows had optimum plant densities at about 86500 plants ha-1 for milk yield compared with 97500 plants ha-1 for dry matter (DM) yields.
Nitrogen fertilization affects corn DM production by influencing leaf area development, leaf area maintenance, and photosynthetic efficiency of the leaf area (Muchow, 1988a). O'Leary and Rehm (1990) reported that corn DM yields increased linearly at three sites and curvilinearly at five sites with inconsistent corn silage quality responses to N rates. Cox et al. (1993) reported that, in New York, maximum economic DM yields for corn occurred at an N rate of about 150 kg ha-1. Corn silage quality, however, increased as N rates increased from 0 to 200 kg N ha-1 (Cox et al., 1993). Unfortunately, higher N rates resulted in increased residual soil NO3–N concentrations (Cox et al., 1993). Cox et al. (1993) concluded that corn silage producers must balance potential benefits of higher DM yields and improved corn silage quality with the potential risk of increased residual soil NO3–N concentrations when considering N management.
Dairy producers require information on the response of corn silage under narrow rows to plant densities and N rates. We evaluated corn under two row spacings (0.38 and 0.76 m), two harvest plant densities (80000 and 116500 plants ha-1), and six N rates (0, 50, 100, 150, 200, and 250 kg ha-1). The objectives of the study were to evaluate: (i) growth, N uptake, and DM yields; and (ii) in vitro true digestibility (IVTD), neutral-detergent fiber (NDF), crude protein (CP), and calculated milk yields of corn under the different row spacings, plant densities, and N rates. We were particularly interested in determining if corn had row spacing x plant density x N rate interactions for N uptake, DM yields, and milk yields, which would necessitate different plant density and N management recommendations for production of narrow-row corn silage.
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MATERIALS AND METHODS
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Field experiments were conducted in 1996 and 1997 on a Honeoye silt loam soil (fine-loamy, mixed, mesic Glossoboric Hapludalf) at a Cornell University research farm near Aurora, NY (46°26'N, 76°26'W). The experimental site is tile-drained, and soil test values indicated a pH of 7.8 and high concentrations of P and K. The experimental site had been planted to oat (Avena sativa L.) in 1995.
The experimental site was plowed in late April in both years. The field was then staked on the next day, and urea [(NH2)2CO] (46–0–0) was hand-applied to achieve N rates of 0, 50, 100, 150, 200, and 250 kg ha-1 in the sub-subplots. The field was immediately harrow-cultipacked after N fertilization to incorporate the urea and prepare the seedbed. Pioneer Brand ‘3525’ was then planted on the same day with an air seeder (White, Coldwater, OH) in 0.38- and 0.76-m rows (alternate rows were shut off) at 86500 and 123500 plants ha-1. Starter fertilizer was applied in a band through the planter at a rate of 25, 50, and 50 kg ha-1 of N, P, and K, respectively. Immediately after planting, 2.0 kg a.i. ha-1 of cyanazine {2-[[4-chloro-6-(ethylamino)-S-triazin-2yl]amino]-2-2 methylpropionitrile} and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were applied for weed control. The experimental design was a randomized block in a split-split block arrangement with three replications. Row spacings represented main plots (36 by 6 m), plant densities represented subplots (36 by 3 m), and N rates represented sub-subplots (6 by 3 m). Subplots were thinned to final plant densities of 80000 and 116000 plants ha-1 at about the five-leaf stage of corn development.
Five random plants were selected at the silking stage from each sub-subplot to estimate leaf area index (LAI) and DM accumulation. Green leaves were measured with an LI-3100 leaf area meter (LI-COR, Lincoln, NE). The leaves and remaining plant fractions were then dried at 60°C in a forced-air drier to constant moisture. Total DM accumulation and LAI were calculated based on land area occupied by the plants after the hand-thinning process. The five-plant samples were also ground through a Wiley mill (Christy and Morris, Chelmsford, UK) to determine N concentrations by Kjeldahl procedures.
The center two rows under 0.76-m row spacing and center three rows under 0.38-m row spacing were harvested by hand in both years at the one-third to one-half milk line stage, which corresponded to about 350 g kg-1 DM in all sub-subplots, to determine DM yields. Five plants were randomly selected at harvest from each sub-subplot to estimate DM concentration, grain concentration, and forage quality characteristics. The five-plant subsample was divided into stover and ear fractions and dried at 60°C in a forced-air dryer to constant moisture. The ears were shelled after drying to determine grain concentration, which allowed for an estimate of the harvest index (HI), expressed as kg grain kg DM-1. Stover, cob, and grain were then reassembled into a whole-plant sample and ground sequentially through a hammer mill and a Wiley mill. Samples were then passed through a splitter, reduced to 50 g in weight, and further ground through a cyclone mill (Udy Corp., Ft. Collins, CO) fitted with a 1-mm screen. Samples (0.5 g) were analyzed by wet chemistry for whole-plant NDF according to procedures by Van Soest et al. (1991) and Kjeldahl N (x 6.25 = CP). Samples were also analyzed for IVTD according to Stage 1 of the procedure described by Marten and Barnes (1980). Samples (0.25 g) were incubated for 48 h at 39C in a buffered rumen fluid containing the Kansas State buffer supplemented with urea at 0.5 g L-1. Following fermentation, residues were analyzed for NDF to determine NDF digestibility. The NDF digestibility was calculated as
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Milk 95, a spreadsheet that combines DM yield and silage quality characteristics into a single term, was used to calculate milk yield produced per hectare of corn silage (Undersander et al., 1993). Total N accumulation at silking and harvest was calculated as the product of whole-plant N concentration and DM accumulation.
Years were considered random in the analysis of variance, and a mixed model was used to analyze the data with General Linear Model (GLM) procedures using the SAS Statistical Software Package (SAS Inst., 1990). Mean separation between row spacings and between plant densities were obtained for all measurements by the t-test (P = 0.05). Linear-plus-plateau and quadratic-plus-plateau models were then fit to individual data points, averaged across years, using the NLIN procedure in SAS to determine the response of each variable to N rates applied before planting. If convergence criterion were not met in NLIN, linear and quadratic models were then fit to each data point, averaged across years, using the REGRESS procedure in SAS. For the linear-plus-plateau and quadratic-plus-plateau models, plateau values were considered to be maximum for each variable (Cerrato and Blackmer, 1990). For the quadratic model, predicted maximum values were obtained by equating the first derivative of the regression equation to 0, solving for x, substituting the value of x into the response equation, and then solving for y. Predicted maximum N rates were calculated by equating the first derivative of the regression equation to 0 and solving for x. We also used predicted maximum N rates rather than optimum N rates, based on a fertilizer-to-corn price ratio, because dairy producers use mostly animal waste for N fertilizer and feed corn silage rather than sell it.
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RESULTS AND DISCUSSION
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Precipitation totaled about 400 mm from May through August in 1996, about 50 mm above normal. Growing degree days totaled about 1105°C during the same period, close to normal. Corn did not show any visible stress in 1996. In 1997, precipitation totaled about 250 mm from May through July, close to normal, so corn did not show any visible stress from emergence through the silking period. Consequently, year had a small mean square for LAI (0.31) and a small mean square for N accumulation at silking (13353) in the ANOVA model relative to the other sources (Table 1). However, precipitation totaled only 41 mm in August, which coincided with kernel set and grain fill stages. Corn prematurely senesced in 1997 because of the dry August conditions. Consequently, year had a large mean square for HI (0.145) and DM yields (253) in the ANOVA model. Nevertheless, only three interactions with years (row spacing x plant density x year for DM yield; row spacing x year for CP; and row spacing x N rate x year for NDF digestibility) existed of a possible 70.
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Table 1. Analyses of variances for leaf area index (LAI), nitrogen accumulation at silking (Ns), nitrogen accumulation at harvest (NH), harvest index (HI), dry matter yield (DMY), neutral-detergent fiber (NDF), in vitro true digestibility (IVTD), crude protein (CP), NDF digestibility (NDFd), and calculated milk yield (MY) of corn at two row spacings, two plant densities, and six N rates at Aurora, NY in 1996 and 1997
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Plant density and N rate affected LAI, but a plant density x N rate interaction existed (Table 1). The LAI of corn at 80000 plants ha-1 had a quadratic-plus-plateau response to N rates, reaching a maximum of 4.74 at the plateau N rate of 166 kg ha-1 (Table 2). The LAI of corn at 116000 plants ha-1 also had a quadratic-plus-plateau response to N rates, reaching a maximum of 6.22 at an N rate of 190 kg ha-1. Both plateau N rates exceeded the 60 kg ha-1 rate that Muchow (1988a) reported for sufficient specific leaf N (1.0 g m-2) to maximize leaf expansion rates in corn under irrigated conditions in Australia. Dry matter yield had a linear response to LAI at silking (y = 11.3 + 1.65x; r2 = 0.30, n = 72). The use of high plant densities in corn, regardless of row spacing, maximizes LAI at silking, and this may contribute to greater DM yields at harvest.
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Table 2. Leaf area index (LAI) of corn at silking at two plant densities and six N rates, averaged across years and row spacings, and regression equations (n = 36) for each plant density in response to N rates at Aurora, NY in 1996 and 1997
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Nitrogen rate affected N accumulation at silking, and no interactions existed among row spacing, plant density, and N rates (Table 1). Nitrogen accumulation at silking had a quadratic-plus-plateau response to N rates, reaching a maximum of 171 kg ha-1 at an N rate of 161 kg ha-1, regardless of row spacing (Table 3). Nitrogen accumulation at harvest, however, had a row spacing x N rate interaction (Table 1). Nitrogen accumulation at harvest had a linear response to N rates at 0.38-m row spacing but a quadratic response at 0.76-m row spacing (Table 3). Apparently, corn can accumulate more N at harvest in narrow vs. conventional row spacing. Nevertheless, N accumulation at harvest did not differ greatly at both row spacings, as indicated by similar slopes when linear regression models were fit to data sets for each row spacing (data not shown). Consequently, the use of narrow-row corn does not greatly alleviate a problem of excess animal waste on a dairy farm. Furthermore, DM yield at harvest had a quadratic response to N accumulation at harvest (y = 8.4 + 0.097x - 0.0002x2; R2 = 0.73, n = 72), which indicates maximum DM yields at about 22.0 Mg ha-1 with about 240 kg ha-1 of N accumulation. Muchow and Davis (1988) reported maximum biomass accumulation of 21.5 Mg ha-1 with 220 kg ha-1 of N accumulation.
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Table 3. Nitrogen accumulation of corn at silking at six N rates averaged across years, row spacings, and plant densities; N accumulation at harvest at two row spacings and six N rates, averaged across years and plant densities; and regression equations for N accumulation at silking (n = 72) and for N accumulation at harvest for each row spacing (n = 36) in response to N rates at Aurora, NY in 1996 and 1997
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Plant density and N rate affected the HI of corn, and a row spacing x plant density interaction existed (Table 1). When averaged across years and N rates, corn at 0.38-m row spacing had an HI of 0.41 at 80000 and 116000 plants ha-1 (Table 4). In contrast, corn at 0.76-m row spacing had an HI of 0.42 at 80000 plants ha-1 but only 0.39 at 116000 plants ha-1. Corn in narrow vs. conventional row spacing thus maintained its HI value at high plant densities, which suggests that narrow-row corn has the potential for greater grain yields at high plant densities. Dry matter yield also had a linear response to HI values (y = -3.0 + 55.3x; r2 = 0.53, n = 72), which indicates a potential for greater DM yields for corn at narrow rows and high plant densities. The HI had a quadratic-plus-plateau response to N rates, reaching a maximum of 0.43 at an N rate of 167 kg ha-1 (Table 4). Muchow (1988b) and Cox et al. (1993) reported maximum HI values at N rates of 120 to 140 kg ha-1.
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Table 4. Harvest index (HI) of corn at two row spacings, two plant densities, and six N rates, averaged across years, and the regression equation (n = 72) for the response of harvest index to N rates at Aurora, NY in 1996 and 1997
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Row spacing, plant density, and N rates affected DM yields, and no interactions existed (Table 1). When averaged across years, plant densities, and N rates, corn yielded 1.4 Mg ha-1, or 7.5% more, at 0.38- vs. 0.76-m row spacing (Table 5). Surprisingly, corn yielded 0.7 Mg ha-1, or 3.7% more, at 116000 vs. 80000 plants ha-1. In previous studies at the experimental site (Cox, 1997; Cox et al., 1998), corn had maximum DM yields at plant densities from about 85000 to 95000 plants ha-1. Dry matter yield had a quadratic-plus-plateau response to N rates, reaching a maximum 20.6 Mg ha-1 at an N rate of 151 kg ha-1 (Table 4). Dairy producers in the northeastern USA can thus derive all of the DM yield benefit associated with narrow rows with similar N management as that of conventional row spacing.
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Table 5. Dry matter (DM) yield of corn at two row spacings at six N rates, averaged across years and plant densities; at two plant densities and six N rates, averaged across years and row spacings; and the regression equation (n = 72) for the response of DM yield to N rates at Aurora, NY in 1996 and 1997
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Dairy producers, however, do not plant corn to maximize DM yields; they plant it to maximize milk yields, which are a function of DM yield and corn forage quality (Undersander et al., 1993). Plant density and N rate affected IVTD, NDF, and CP concentrations, and interactions did not exist (Table 1). When averaged across years, row spacings, and N rates, IVTD concentration averaged 7 g kg-1 less, NDF concentration averaged 13 g kg-1 more, and CP concentration averaged 3 g kg-1 less at 116000 vs. 80000 plants ha-1 (Table 6). This decrease in corn forage quality at higher plant densities contributes to a lower optimum plant density for milk yields compared with DM yields (Cox et al., 1998; Cusicanqui and Lauer, 1999). The IVTD concentration had a linear response, whereas NDF concentration had a negative quadratic-plus-plateau response to N rates, falling to 460 g kg-1 at an N rate of 112 kg ha-1 (Table 6). Also, CP had a quadratic-plus-plateau response to N rates, reaching a maximum of 65 g kg-1 at an N rate of 178 kg ha-1. The small value of the slope for the IVTD response offsets the minimum NDF concentration at an N rate of only 112 kg ha-1, so the calculated milk yield will have a similar response as DM yield to N rate.
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Table 6. In vitro true digestibility (IVTD), neutral detergent fiber (NDF), and crude protein (CP) concentrations of corn at two plant densities and six N rates, averaged across years and row spacings, and regression equations (n = 72) for the responses of IVTD, NDF, and CP to N rates at Aurora, NY in 1996 and 1997
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Row spacing and N rate affected the calculated milk yield, and no interactions existed (Table 1). Plant density did not affect milk yield because the decreased forage quality at 116000 vs. 80000 plants ha-1 offset the 3.7% DM yield advantage. When averaged across years, plant densities, and N rates, milk yield averaged 0.9 Mg ha-1, or 6% more, at 0.38- vs. 0.76-m row spacing (Table 7). The actual milk yield advantage of 0.38-m row spacing may be slightly less because of 8 g kg-1 less NDF digestibility at 0.38-m spacing (Table 7), which is not included in the milk yield calculation (Undersander et al., 1993). Nevertheless, dairy producers can clearly produce more milk by adopting narrow-row corn silage production. Milk yield showed a quadratic-plus-plateau response to N rates, reaching a maximum of 17.1 Mg ha-1 at an N rate of 150 kg ha-1 (Table 7). Dairy producers can thus plant corn silage in narrow rows at similar plant densities and N fertility as in conventional row spacing and derive all of the milk yield advantage associated with narrow rows.
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Table 7. Neutral detergent fiber (NDF) digestibility and calculated milk yields of corn at two row spacings and six N rates, averaged across years and plant densities, and regression equations (n = 72) for the responses of NDF digestibility and calculated milk yields to N rates at Aurora, NY in 1996 and 1997
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CONCLUSION
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Some dairy producers in the northeastern USA who have adopted narrow-row corn silage production plant at 125000 plants ha-1 and apply 225 kg N ha-1 because they believe that narrow-row corn requires high plant densities and N rates for maximum DM yields. In this study, however, row spacing x plant density x N rate and row spacing x N rate interactions did not exist for DM yield, forage quality characteristics, and calculated milk yield. We conclude that, despite 7.5% greater DM yield and 6% greater milk yield at 0.38- vs. 0.76-m row spacing, dairy farmers should produce corn silage at the same plant densities and N fertility, regardless of row spacing. A row spacing x N rate interaction existed for N accumulation at harvest, however, because corn in narrow rows had a linear response and corn in conventional rows had a quadratic response to N rates. Dairy producers incur no additional costs with the application of more animal waste on a particular field because the animal waste must be applied somewhere. Consequently, dairy producers who have excess animal waste on the farm could apply slightly more N to corn silage in narrow row spacing vs. conventional row spacing. These dairy producers, however, should closely monitor residual soil NO3–N and P concentrations to ensure that high concentrations of these nutrients do not accumulate after harvest.
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TOP
ABSTRACT
INTRODUCTION
