Published online April 11, 2006

Corn Response to Nitrogen Rate, Row Spacing, and Plant Density in Eastern Nebraska Charles A. Shapiro and Charles S. Wortmann* a range of low densities, a gradually decreasing rate of yield increase relative to density increase, and finally a yield plateau at some relatively high plant density (Duncan, 1984; Ottman and Welch, 1989; Thomison and Jordan, 1995). Nitrogen demand also increases as plant density increases (Penning de Vries et al., 1993). Higher plant density combined with narrower row spacing results in a more equidistant planting pattern that is expected to delay initiation of intraspecific competition (Duncan, 1984) while early crop growth is increased (Bullock et al., 1988). Soil NO3–N, soil organic matter content, and historic yields might be considered in estimation of fertilizer N requirements for corn (Oberle and Keeney, 1990; Vanotti and Bundy, 1994a, 1994b), as well as legume credits, manure application, and irrigation water N (Peterson and Varvel, 1989; Hergert et al., 1995). Nitrogen response models might be further improved by considering the effects of row spacing and plant density. This study was conducted to test three hypotheses for irrigated corn production in eastern Nebraska: (i) increased plant density and reduced row spacing result in increased harvested N and corn grain yield under adequate soil water conditions; (ii) yield increases with applied N are greater with plant densities beyond 61800 plants ha21 and row spacing ,0.76 m; and (iii) optimum N rate can be more accurately estimated using a model that considers row spacing and plant density.

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

ABSTRACT Efficient use of N by corn (Zea mays L.) is financially and environmentally important, and may be improved with higher plant density and reduced row spacing. Hypotheses were tested that irrigated corn yield in northeast Nebraska is increased by reducing row spacing from 0.76 m and increasing plant density above 61 800 plants ha21, and that grain yield response to applied N is greater with reduced row spacing and increased plant density. Field experiments were conducted for 3 yr comparing the effects 0.76- vs. 0.51-m row spacing, three plant densities, and four N rates on crop performance. The soil was a silty clay loam (mesic Cumulic Haplustoll). Nitrogen rates ranged from 0 to 252 kg N ha21. Plant N concentration and biomass and grain yield were not affected by plant density. Decreasing row spacing from 0.76 to 0.51 m resulted in 4% more grain yield. Grain yield response to applied N and N rates for optimum yield were not affected by row spacing. Nitrogen application resulted in mean increases of 22% more biomass production and 24% more grain yield. The N response function was linear in 1996, quadratic in 1997, and quadratic with decreased yields at the high N rate (252 kg N ha21) in 1998. Grain yield was not affected by increasing plant density above 61 800 plants ha21 but was greater with narrow row spacing. Yield response to applied N was similar for all planting arrangements. Optimal N rate cannot be better predicted by considering plant density and row spacing.

N

ITROGEN fertilizer is a major input for corn production in the Midwest. Ideal N management optimizes grain yield, farm profit, and N use efficiency while it minimizes the potential for leaching of N beyond the crop rooting zone. Efficiency of use of applied N is variable, with a mean of only 33% of applied N recovered by cereal crops (Raun and Johnson, 1999). Demand for N increases with biomass yield, which may be enhanced by reduced row spacing and greater plant density (Jordan et al., 1950). The effect of decreasing corn row spacing from a mean of 1.07 to 0.90 m was estimated to result in an overall mean yield increase of 175 kg ha21 (Cardwell, 1982), while most farmers have reduced corn row spacing to 0.76 m or less. Corn yields may be further increased by reducing row spacing from 0.76 to 0.38 m (Nielsen, 1988; Widdicombe and Thelen, 2002), but there may be little advantage to further reduction (Porter et al., 1997). Corn grain yield typically exhibits a quadratic response to plant density, with a near-linear increase across

MATERIALS AND METHODS Site Characteristics, Experimental Design, and Treatments The study was conducted at the University of Nebraska Northeast Research and Extension Center–Haskell Agricultural Laboratory near Concord, NE (428239 N, 968579 W) during 1996, 1997, and 1998. The soil is classified as an Alcester silty clay loam (mesic Cumulic Haplustoll) with 30 g kg21 soil organic matter and 6.1 pH in the surface soil. Soil Bray-P1 was 32, 26, and 22 g kg21 and exchangeable NH4OAc K was 330, 229, and 301 g kg21 in the 0- to 0.30-m depth for 1996, 1997, and 1998, respectively. In the spring, before N fertilizer application, mean soil NO3–N concentration to a depth of 0 to 0.76 m was 11.4, 2.9, and 7.2 mg kg21 for the respective years. The experimental design was a randomized complete block in a split-split-plot treatment arrangement with three replications. The main plot factor was plant density with targeted densities of 61 800 (low), 74 160 (medium), and 86 520 (high) plants ha21. Intended populations were not achieved in every year; hence the terms low, medium, and high will be used in the discussion. The low planting rate is typical of populations grown under irrigation in the area in which this research was conducted. The main plot size was 12.2 by 24.4 m. Row spacing treatments (0.51 and 0.76m) comprised the split plots, which measured 6.1 by 24.4 m. These treatments aimed for withinrow distances between plants of 0.22, 0.18, and 0.15 m and 0.32, 0.26, and 0.23 m for the 0.76- and 0.51-m row spacing at the

C.A. Shapiro, Northeast Research and Extension Center–Haskell Agricultural Lab., Univ. of Nebraska, 57905 866 Rd., Concord, NE 68728; C.S. Wortmann, 279 Plant Science, Univ. of Nebraska, Lincoln, NE 68583-0915. Contribution of the Univ. of Nebraska Agric. Res. Div., Lincoln, NE, as Journal Series no. 14529. Received 10 May 2005. *Corresponding author ([email protected]). Published in Agron. J. 98:529–535 (2006). Corn doi:10.2134/agronj2005.0137 ª American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA

529

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

530

AGRONOMY JOURNAL, VOL. 98, MAY–JUNE 2006

low, medium, and high plant densities, respectively. The splitsplit factor was N fertilizer rate (0, 84, 168, and 252 kg N ha21); N was surface applied (unincorporated) using dry NH4NO3 (34–0–0) with a 3-m-wide Barber spreader (Barber Engineering Co., Spokane, WA) on 11 June 1996, 10 June 1997, and 19 May 1998. Experimental units in the split-split plot measured 3.0 by 12.2 m. The trial was conducted on a different part of the same field each year, with the whole field planted in corn during the 3 yr. Corn was always the preceding crop. The site was irrigated with 25.4 mm of water using a lateral irrigation system when soil water was ,50% of field capacity. There were four, five, and three applications in 1996, 1997, and 1998, respectively. Irrigation water contained 20 mg L21 NO3–N and 5 kg ha21 N as NO3 was applied with each irrigation event. Daily weather data were collected at the laboratory (Fig. 1).

Crop Management The land was prepared for planting by disk followed by cultivator tillage. Corn hybrid Pioneer 3394 (matures at 1290 growing degree days) was planted on 29 May 1996, 8 May 1997, and 5 May 1998. The 0.51-m rows were planted with a 12-row John Deere 7300 custom-built planter and the 0.76-m rows were planted with an eight-row John Deere 7100 planter (Deere, Inc., Moline, IL). Weeds were controlled using preplant herbicides.

Field and Plant Measurements Yield data were collected on 4 Nov. 1996, 22 Oct. 1997, and 24 Sept. 1998. Plants were cut at the surface from the central 6.1 m of the two middle rows in the wide-row plots and the three middle rows in the narrow-row plots. Ears were separated, shelled, weighed, and the moisture content was measured. Grain yields were adjusted to 155 g kg21 water content. Biomass yield was calculated from stover and grain weights, which were adjusted to oven-dry weights after subsamples of grain and stover were dried at 608C. Grain and stover subsamples were analyzed for N content using the Dumas dry oxidation procedure (Bremner, 1996). Total plant N content was determined by combining stover N and grain N estimated on the basis of 0 g kg21 water. Harvest index and N harvest index were calculated by dividing grain dry weight by biomass dry weight, and harvested grain N uptake by total plant N uptake, respectively. Agronomic efficiency of applied N (AEN,

kg grain yield increase kg21 N applied) and apparent recovery efficiency of applied N (REN, kg total N uptake kg21 N applied) were determined as: AEN 5 (GY1N 2 GY0N)/N and REN 5 (UN1N 2 UN0N)/N, where GY is the grain yield (kg ha21), UN is the aboveground plant N accumulated (kg ha21), N is the amount of applied N (kg ha21), and 1N and 0N refer to treatments with and without N applied, respectively. The number of seeds planted at each row spacing to achieve each target plant density differed due to planter differences (Table 1) but the data were analyzed and results interpreted under the assumption that row spacing and plant density treatments were independent of each other (Teasdale, 1998).

Data Analysis Crop performance data were analyzed using the SAS PROC GLM procedure to develop the ANOVA for a splitsplit-plot design. The PROC MIXED procedure was used to make tests of simple effects (Little et al., 1996). Row spacing was treated as a qualitative variable, and plant density and N rate as quantitative variables. For PROC MIXED, plant density, row spacing, and N rates were treated as fixed effects, and year and replication were treated as random effects.

RESULTS AND DISCUSSION Plant Nitrogen Grain N concentration and uptake were affected by the N 3 year interaction (Table 2). There was a positive linear relationship between N rate and grain N concentration in 1997 and 1998, but with no effect of N rate on grain N concentration in 1996 (Fig. 2a). Grain N uptake increased with N rate in 1997 and 1998 with significant linear and quadratic responses, but uptake reached a plateau at the 84 kg ha21 N rate in 1998 while uptake increased with higher N rates in 1996 and 1997 (Fig. 3). Grain N uptake was also affected by the row spacing 3 year interaction, as N uptake was less with 0.76- than with 0.51-m row spacing in 1996 and 1997, but unaffected by row spacing in 1998 (Table 3). At the highest plant density, the simple effect for the row spacing 3 N rate 3 year interaction was significant for grain N content for the 168 and 252 kg ha21 N rates (Table 4). Grain N uptake was further increased at the highest plant density by increasing the N rate to 252 kg ha21 with 0.51-m row spacing but decreased with 0.76-m spacing in 1996 and 1997, while grain N uptake Table 1. Seed drop to achieve intended plant densities for two row spacings. Row spacing Density

Intended plant density 22

plants m 1996 Low Medium High 1997 and 1998 Low Medium High

Fig. 1. Precipitation, and accumulation of growing degree days (GDD) following crop emergence, for the growing seasons of 1996, 1997, and 1998.

0.51 m† seeds m

0.76 m 22

6.18 7.41 8.65

6.84 7.90 9.37

6.42 7.78 9.39

6.18 7.41 8.65

7.39 8.79 10.13

7.41 9.39 10.18

† Narrow rows were planted with a 12-row John Deere 7300 (Deere & Co., Moline, IL) planter and wide rows were planted with an eight-row John Deere 7100 custom-built planter. Seed drop was different due to the limitations of each planter.

531

SHAPIRO & WORTMANN: CORN RESPONSE TO NITROGEN RATE

Table 2. Analysis of variance of the effect of plant density (PD), row spacing (RS), and N fertilizer rate (N) across 3 yr (YR). df

YR PD YR 3 PD RS YR 3 RS PD 3 RS YR 3 PD 3 RS N YR 3 N PD 3 N YR 3 PD 3 N RS 3 N YR 3 RS 3 N PD 3 RS 3 N YR 3 PD 3 RS 3 N

2 2 4 1 2 2 4 3 6 6 12 3 6 6 12

0.001 0.001 0.001 0.150 0.024 0.284 0.004 0.998 0.002 0.483 0.086 0.972 0.276 0.013 0.775

N conc., mg kg21 Grain 0.001 0.176 0.909 0.601 0.605 0.769 0.172 0.001 0.001 0.557 0.191 0.762 0.778 0.772 0.987

Stover 0.001 0.184 0.501 0.801 0.603 0.622 0.562 0.001 0.161 0.887 0.402 0.484 0.226 0.842 0.141

N uptake, kg ha21 Grain 0.001 0.342 0.235 0.035 0.012 0.145 0.250 0.001 0.001 0.926 0.117 0.801 0.756 0.157 0.462

increased at all N rates for both row spacings in 1998 (Table 4). Grain N concentration and uptake were not affected by plant density (Table 2). Stover N was not affected by interaction effects or by the main effects of plant 16

N Concentration, mg kg-1

a 14 12 10 8 Grain, 1996 Grain, 1997 Grain, 1998

6 4 0

50

100

150

Stover, 1996 Stover, 1997 Stover, 1998 200

250

N Rate, kg ha-1

Stover 0.001 0.473 0.597 0.103 0.973 0.865 0.633 0.001 0.144 0.571 0.302 0.066 0.696 0.804 0.227

Yield, Mg ha21

Plant

Grain

Prob. . F value 0.001 0.001 0.393 0.435 0.454 0.146 0.045 0.029 0.359 0.012 0.790 0.258 0.941 0.473 0.001 0.001 0.001 0.003 0.657 0.978 0.282 0.269 0.454 0.820 0.686 0.693 0.554 0.155 0.398 0.669

Biomass

Harvest index

N harvest index

0.002 0.274 0.127 0.018 0.144 0.457 0.517 0.001 0.001 0.927 0.287 0.357 0.464 0.656 0.990

0.662 0.008 0.108 0.797 0.267 0.782 0.074 0.227 0.291 0.572 0.059 0.085 0.147 0.698 0.997

0.018 0.282 0.028 0.981 0.210 0.292 0.187 0.001 0.003 0.632 0.034 0.047 0.624 0.809 0.414

density and row spacing. Stover N concentration increased with N application with linear and quadratic responses (Fig. 3).

Harvest Index and Nitrogen Recovery Nitrogen rate and row spacing did not affect harvest index (HI; Table 2). There was a plant density effect on HI in 1997. Harvest index at the low population was 55% and decreased to 50% at the medium and 51% at the high populations; however, populations were reduced in 1997 and the low population was below the target population by 7233 plants ha21. In other years, when the low population was closer to the target population, HI was similar at all populations (Table 5). Nitrogen HI decreased as linear and quadratic functions of N rate in 1996 and 1998, but was not affected by N rate in 1997 (Fig. 3). Harvested grain N increased less with increased N rates relative to accumulated stover N, resulting in the decreased N HI values at higher N rates. Row spacing had no effect on N HI (Table 3). The N HI was highest at the lowest plant density in 1997, but was not affected by plant density in the other years (Table 4).

20

b 160

80.0% Grain N Stover N N HI

140

N uptake (kg ha-1)

16 14 12 1996 1997 1998

10

120

75.0% 70.0%

100 80

65.0%

60

60.0%

40 55.0%

20

8 0

50

100

150

200

250

N Rate, kg ha-1 Fig. 2. The effect of N rate during three growing seasons on (a) N concentration in grain and stover and (b) biomass yield. All linear functions are significant except for grain N concentration in 1996 and biomass yield in 1998. All quadratic functions were significant except for grain N concentration in 1996 and biomass yield in 1998.

N HI

18

Biomass Yield, Mg ha-1

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

Source of variation

Harvest population

0

50.0% 0 84 168 252

0 84 168 252

0 84 168 252

1996

1997 N rate (kg ha-1)

1998

Fig. 3. The effect of N rate on N uptake and N harvest index (HI) during three growing seasons. All linear and quadratic functions were significant except for N HI in 1997.

532

AGRONOMY JOURNAL, VOL. 98, MAY–JUNE 2006

Table 3. Row spacing effect on corn, averaged across three plant densities and four N rates.†

Table 5. Plant density effects on corn, averaged across two row spacings and four N rates.† Plant density, plants ha21‡

Row spacing

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

Variable

0.51 m

Harvest population 1996 1997 1998‡ Grain N 1996 1997 1998 Biomass dry wt. 1996 1997 1998 Grain yield 1996 1997 1998

P.F

0.76 m

14.58 12.75 16.74

plants ha21 70 800 58 786 74 688 kg ha21 95.4 76.8 129.7 Mg ha21 13.97 11.84 16.80

8.96 7.81 10.26

8.40 7.25 10.53

71 818 58 287 71 309 101.8 82.6 126.6

0.373 0.663 0.004 0.011 0.022 0.222 0.087 0.011 0.876 0.013 0.014 0.231

† Row spacing effects on grain and stover N concentration, stover N content, and N harvest index were not significant in all years. ‡ Counts for 1998 were for ear number rather then plants at harvest.

The apparent recovery efficiency of applied N in the aboveground crop ranged from 0.23 to 0.58, 0.21 to 0.37, and 0.16 and 0.30 kg accumulated N kg21 applied N at the first, second, and third increment of applied N, respectively. Agronomic efficiency of applied N ranged from 5.8 to 22.1, 4.8 to 14.6, and 3.8 to 9.6 kg grain yield increase kg21 N applied at the first, second, and third increment of applied N, respectively. Differences in N use efficiency were related to grain and biomass yield response to applied N. Apparent recovery efficiency and agronomic efficiency, as well as yield increase, were greater in 1997 than in the other years. The values for these efficiency traits were generally less and declined more with increased N rate than observed by Binder Table 4. Row spacing 3 N rate 3 year interactions induced by high N rate at the 86 520 plants ha21 density.† Grain N N rate

0.51 m

Grain yield 0.76 m

0.51 m

kg ha21

0.76 m Mg ha21

1996 0 84 168 252 P.F

84.4 95.3 97.9 103.9

88.0 87.8 101.6 89.7

7.49 8.52 8.75 9.40

0.281‡

8.37 7.69 8.73 8.02 0.382

1997 0 84 168 252 P.F

57.9 74.4 92.3 100.1

46.0 57.9 89.3 83.7

6.24 7.66 8.54 8.51

0.102

5.02 6.18 8.16 7.12 0.004

1998 0 84 168 252 P.F

105.0 140.1 137.9 145.7

106.5 134.9 131.2 141.2 0.850

8.93 11.57 11.00 11.14

8.88 11.57 10.55 11.04 0.694

† The row spacing 3 N rate 3 year interactions were not significant in the ANOVA for grain N (P . F, 0.756) and grain yield (P . F, 0.693); however, the simple effect of these interactions at high plant density was significant (P , 0.001). ‡ Significance of row spacing averaged across N rate at 86 520 plants ha21 density.

Variable

61 800, low 74 160, medium 86 520, high

Harvest population 1996 1997 1998§ N harvest index 1996 1997 1998 Harvest index 1996 1997 1998 Biomass dry wt. 1996 1997 1998 Grain yield 1996 1997 1998

62 316 54 567 63 032 66.6 65.8 62.7 52.1 55.0 53.3 14.3 12.4 16.0 8.80 8.00 10.07

plants ha21 70 160 58 191 70 966 % 67.5 61.0 62.7 % 52.0 50.4 52.4 Mg ha21 14.5 12.5 17.1 Mg ha21 8.87 7.43 10.54

81 456 62 852 85 000

P.F 0.001 ,0.001 ,0.001

67.8 61.6 63.5

0.735 0.002 0.830

50.4 51.0 52.1

0.376 0.001 0.657

14.0 11.9 17.2

0.658 0.356 0.038

8.37 7.18 10.58

0.352 0.111 0.320

† Plant density effects for N concentration and content of grain and stover were not significant. ‡ Quadratic effects due to plant density were not significant for all traits. § Counts for 1998 were for ear number rather than plants at harvest.

et al. (2002) elsewhere in eastern Nebraska; this increased efficiency was due to high yield response to applied N at three of four trials.

Biomass and Grain Yield Corn biomass increased with applied N in a quadratic manner in 1996 and 1997, but the linear and quadratic functions of N rate were not significant in 1998 (Fig. 2b). In all years, the main effect of increasing N rate from 168 to 252 kg ha21 did not result in an increase in biomass. Corn biomass production was less in 1997 with the 0.76than the 0.51-m row spacing (Tables 2 and 3), but unaffected in 1996 and 1998. Biomass yield was not affected by plant density, except in 1998 when biomass was decreased at low plant density (Table 5). Mean grain yields were 8.67, 7.51, and 10.40 Mg ha21 in 1996, 1997, and 1998, respectively. The year 3 N rate interaction effect for grain yield was due to differing responses to applied N for rates above 84 kg N ha21 (Table 2). In 1998, grain yield was increased with 84 kg N ha21 applied but did not respond to additional N, with the effect that neither the linear nor the quadratic functions of N rate were significant (Fig. 4). The response of grain yield to increased N application rate was linear and quadratic in 1996 and 1997, agreeing with the results of others (Blackmer and Sanchez, 1988; Jokela, 1992; Liang et al., 1996). The reason for the N rate 3 year interaction effect is not clear but possibly more N was released from mineralization of soil organic matter in 1998 due to more precipitation in March and April than in other years. Interaction effects of row spacing with plant density and N rate were not significant for grain yield. The simple effect (Little et al., 1996), however, for the row spacing 3 N rate interaction, at high plant density, was

SHAPIRO & WORTMANN: CORN RESPONSE TO NITROGEN RATE

12

1996

Grain yield (Mg ha-1)

Y = 8.5 + 0.004 x R 2 = 0.945

10 9 8

Y = 7.9 + 0.0036 x

7

R 2 = 0.907

0.51 m 0.76 m

6 5 -50

0

50

100

150

200

250

300

Nitrogen rate (kg ha-1) 12

1997

Grain yield (Mg ha-1)

11 10

Y = 6.2 + 0.025 x – 0.000063 x 2 R 2 = 0.999

9 8

Y = 5.6 + 0.022 x – 0.000046 x 2

7

R 2 = 0.975

6 5 -50

0

50

100

150

Nitrogen rate (kg

200

0.51 m 0.76 m

250

300

ha-1)

12

1998 11

Grain yield (Mg ha-1)

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

11

10

Y = 9.4 + 0.0184 x – 0.00006 x 2 R 2 = 0.967

9 8

Y = 9.1 + 0.032 x – 0.00011x 2 R 2 = 0.688

7 6 5 -50

0.51 m 0.76 m

0

50

100

150

200

250

300

533

others who have reported yield increases of up to 10% with reduced row spacing (Hodges and Evans, 1990; Polito and Voss, 1991; Porter et al., 1997; Ulger et al., 1997; Widdicombe and Thelen, 2002). High yields can be achieved with 0.76-m row spacing, however, as was the case in 1998 when grain yields were higher than in previous years and the main effect of row spacing was not significant. The advantage of 0.51- over 0.76-m row spacing may therefore be related to management and specific growing conditions. A notable difference in the 1998 season, compared with the other seasons, is the greater rate of growing degree day accumulation following planting in May and subsequent earlier physiological maturity, but this does not offer an explanation for the lack of response to reduced row spacing. The absence of a row-spacing effect on yield in 1998 may be due to the great plant growth, resulting in canopy interception of a very large proportion of the incident incoming photosynthetically active radiation at both row spacings (Ottman and Welch, 1989). Andrade et al. (2002) found that yield response to decreased row spacing was negatively correlated to radiation interception at pollination time with the wider spacing. Radiation interception was not measured in this study, but it is likely that the proportion of incoming radiation intercepted was very high with both row spacings in 1998 due to the great amount of plant growth. The main effect of plant density was not significant for grain yield (Tables 2 and 5). These results differ with findings in Maryland where grain yield increased as plant density was increased from 56000 to 128 000 plants ha21 (Teasdale, 1998), but crop competition with weeds was a factor in that study. Porter et al. (1997) reported maximum corn grain yield at 82000 to 89000 plants ha21. Cox and Cherney (2001) reported increased corn silage yield by changing plant density from 80 000 to 116 000 plants ha21. There was no plant density 3 row spacing interaction, although theory based on plant crowding alone suggests that such an interaction should occur with a greater advantage with narrower row spacing at high plant density than at lower plant density (Duncan, 1984). Porter et al. (1997) also found that the row spacing 3 plant density interaction did not significantly affect yield. Grain yield response to row spacing and plant density might have been different for other hybrids. Porter et al. (1997), however, found in a study with six adapted, highyielding hybrids, that corn hybrids were similarly affected by plant density and row spacing.

Nitrtogen rate (kg ha-1) Fig. 4. Corn grain yield (Y ) as a linear function of N fertilizer rate in 1996 and a quadratic function of N fertilizer rate in 1997 and 1998.

significant. At the high plant density, grain yield was less at the 252 kg N ha21 rate than with the 168 kg N ha21 rate for the 0.76-m row spacing in 1996 and 1997 (Table 4) while yield was increased or unchanged for the 0.51-m row spacing. Grain yield was higher with 0.51- vs. 0.76-m row spacing in 1996 and 1997, but not in 1998. The increased yield with 0.51-m spacing is supported by the findings of

Grain Yield Response Models In 1996, a linear model, with row spacing as a factor (Bullock and Bullock, 1994), accounted for .90% of the grain yield response to applied N (Fig. 4a). The quadratic model was also significant, but the linear model is presented due to the small quadratic coefficient. The model predicted more grain production at 252 kg N ha21 for both row spacings (9.40 and 8.84 Mg ha21 for 0.51- and 0.76-m row spacing, respectively) than for lower N levels. It also predicted 6.9% more grain yield across N rates for 0.51- vs. 0.76-m spacing, with a yield

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

534

AGRONOMY JOURNAL, VOL. 98, MAY–JUNE 2006

gain of 2.2 kg ha21 mm21 for reduction in row spacing. The linear model did not allow prediction of potential maximum yield. In 1997, yield data were fitted to a quadratic yield model that predicted optimum grain yields of 8.23 and 8.60 Mg ha21 at 240 and 200 kg N ha21 for the 0.76- and 0.51-m row spacings, respectively (Fig. 4b). The rowspacing effect on grain yield was similar to that in the 1996 model. The 1997 model predicted an average yield advantage of 7.8% with 0.51- vs. 0.76-m row spacing across all N rates, with a yield gain of 2.2 kg ha21 mm21 for reduction in row spacing. In 1998, the yield response to N rate was quadratic and the maximum predicted yield was 11.12 Mg ha21 at 150 kg ha21 of N (Fig. 4c). Row spacing effects did not account for significant variation in yield response to N rates. Plant density did not affect response to applied N, but N use efficiency was increased with narrower row spacing when plant density was at the highest level. The results, therefore, suggest that it is not necessary to consider plant density (.62 000 plants ha21) in determination of N rate. Optimal N rate was affected by row spacing in 1 yr only and row spacing (,0.76 m) is not a major determinate of N fertilizer requirements. Treatment 3 corn hybrid interactions were not addressed in this study. Corn hybrid 3 N rate interactions can be important (O’Niell et al., 2004), but the effects of row spacing and plant density on this two-way interaction are not known. The lack of hybrid interactions with row spacing (Ottman and Welch, 1989) and plant density (Porter et al., 1997) suggests that the threeway interactions may not be very important and that our information on N-rate interactions with row spacing and plant density are applicable to other adapted, highyielding hybrids. The optimal N rate for grain year differed across years. The N rates to achieve 98 and 99% of maximum yield, averaged across years and row spacing, were 123 and 143 kg ha21. Nitrogen uptake with no fertilizer N applied, however, was 124, 86, and 165 kg ha21 with 132, 53, and 101 kg ha21 of N available to the crop in 1996, 1997, and 1998, respectively, from soil and irrigation water NO3–N.

CONCLUSIONS This research tested three hypotheses. The results are: (i) reduced row spacing, but not increased plant density, resulted in more crop N uptake and more grain yield; (ii) yield response to applied N was not greater with increased plant density and reduced row spacing; and (iii) optimum N rate cannot be better predicted by considering plant density and row spacing. Maximum grain yield and yield response to applied N can be achieved with 62 000 plants ha21 when weeds are well controlled. High grain yield can be achieved with 0.76-m row spacing but yield was 6 to 8% higher with 0.51- than with 0.76-m row spacing in 2 of 3 yr. Grain yield was regularly increased with application of 84 kg N ha21 but response to higher rates was inconsistent. Grain yield

response to applied N and the optimum N application rates were generally similar for 0.51- and 0.76-m row spacing and for the range of plant densities tested, but response to applied N was greater with 0.51-m rows when plant density was high. Row spacing and plant density need not be considered in a model for estimation of optimum N rate. ACKNOWLEDGMENTS We are grateful to Dr. Robert Caldwell, Dr. David Holshouser, and Dr. John Lindquist for their insights and advice at various stages of this research, and to Mark Langrud, whose Master’s thesis includes part of this research. Lisa Lunz and Ray Brentlinger provided valuable assistance to implement the fieldwork. We acknowledge the contribution of Logan Valley Implement (now Northeast Implement), who provided the narrow-row planter and combine used in this research.

REFERENCES Andrade, F.H., P. Calvino, A. Cirilo, and P. Barbieri. 2002. Yield responses to narrow rows depend on increased radiation interception. Agron. J. 94:975–980. Binder, D.L., A. Dobermann, D.H. Sander, and K.G. Cassman. 2002. Biosolids as nitrogen source for irrigated maize and rainfed sorghum. Soil Sci. Soc. Am. J. 66:531–543. Blackmer, T., and C. Sanchez. 1988. Response of corn to nitrogen-15labeled anhydrous ammonia with and without nitrapyrin in Iowa. Agron. J. 80:95–102. Bremner, J.M. 1996. Nitrogen—total. p. 1085–1089. In D.L. Sparks et al. (ed.) Methods of soil analysis. Part 3: Chemical methods. SSSA Book Ser. 5. SSSA and ASA, Madison, WI. Bullock, D., and D. Bullock. 1994. Quadratic and quadratic-plusplateau models for predicting optimum nitrogen rate of corn: A comparison. Agron. J. 86:191–195. Bullock, D., R. Nielsen, and J.W. Nyquist. 1988. A growth analysis comparison of corn grown in conventional and equidistant plant spacing. Crop Sci. 28:254–259. Cardwell, V. 1982. Fifty years of Minnesota corn production: Sources of yield increase. Agron. J. 74:984–990. Cox, W.J., and D.J.R. Cherney. 2001. Row spacing, plant density, and nitrogen effects on corn silage. Agron. J. 93:597–602. Duncan, W. 1984. A theory to explain the relationship between corn population and grain yield. Crop Sci. 24:1141–1145. Hergert, G., R. Ferguson, and C. Shapiro. 1995. Fertilizer suggestions for corn. NebGuide G74-174-A. Coop. Ext., Inst. of Agric. and Nat. Resour., Univ. of Nebraska, Lincoln. Hodges, T., and D. Evans. 1990. Light interception model for estimating the effects of row spacing on plant competition in maize. J. Prod. Agric. 3:190–195. Jokela, W. 1992. Nitrogen fertilizer and dairy manure effects on corn yield and soil nitrate. Soil Sci. 56:148–154. Jordan, H., K. Laird, and D. Ferguson. 1950. Growth rates and nutrient uptake by corn in a fertilizer-spacing experiment. Agron. J. 42: 261–268. Liang, B., A. MacKenzie, and T. Zhang. 1996. Grain yields and grain nitrogen concentration of corn as influenced by fertilizer nitrogen rate. J. Agron. Crop Sci. 177:217–223. Little, R.C., G.A. Milliken, W.W. Stroup, and R.D. Wolfinger. 1996. SAS system for mixed models. SAS Inst., Cary, NC. Nielsen, R. 1988. Influence of hybrids and plant density on grain yield and stalk breakage in corn grown in 15-inch row spacing. J. Prod. Agric. 1:190–195. Oberle, S., and D. Keeney. 1990. Factors influencing corn fertilizer nitrogen requirements in the northern United States Corn Belt. J. Prod. Agric. 3:527–534. O’Niell, P.M., J.F. Shanahan, J.S. Schepers, and B. Caldwell. 2004. Agronomic response of corn hybrids from different eras to deficit and adequate levels of water and nitrogen. Agron. J. 96: 1660–1667.

Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved.

SHAPIRO & WORTMANN: CORN RESPONSE TO NITROGEN RATE

Ottman, M., and L. Welch. 1989. Planting patterns and radiation interception, plant nutrient concentration, and yield in corn. Agron. J. 81:167–174. Penning de Vries, F., P. Teng, and K. Metselaar. 1993. Systems approaches for agricultural development. Kluwer Acad. Publ., Dordrecht, the Netherlands. Peterson, T., and G. Varvel. 1989. Crop yield as affected by rotation and nitrogen rate: III. Corn. Agron. J. 81:735–738. Polito, T., and R. Voss. 1991. Corn yield response to varied producer controlled factors and weather in high yield environments. J. Prod. Agric. 4:51–57. Porter, P., D. Hicks, W. Lueschen, J. Ford, D. Warnes, and T. Hoverstad. 1997. Corn response to row width and plant population in the northern Corn Belt. J. Prod. Agric. 10:293–300. Raun, W.R., and G.V. Johnson. 1999. Improving nitrogen use efficiency for cereal production. Agron. J. 91:357–363.

535

Teasdale, J. 1998. Influence of corn (Zea mays) population and row spacing on corn and velvetleaf (Abutilon theophrasti) yield. Weed Sci. 46:447–453. Thomison, P., and D. Jordan. 1995. Plant population effects on corn hybrids differing in ear growth habit and prolificacy. J. Prod. Agric. 8:394–400. Ulger, A., H. Ibrikci, B. Cakir, and N. Guzel. 1997. Influence of nitrogen rates and row spacing on corn yield, protein content, and other plant parameters. J. Plant Nutr. 12:1697–1709. Vanotti, M., and L. Bundy. 1994a. Corn nitrogen recommendations based on yield response data. J. Prod. Agric. 7:243–249. Vanotti, M., and L. Bundy. 1994b. An alternate rationale for corn nitrogen fertilizer recommendations. J. Prod. Agric. 7:249–256. Widdicombe, W.D., and K.D. Thelen. 2002. Row width and plant density effects on corn grain production in the northern Corn Belt. Agron. J. 94:1020–1023.