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Total precipitation, mean maximum air temperature, and accumulated growing degree days (GDD) at the Purdue University Agronomy Center for Research and Education (ACRE) for the months of April to September during 2005, 2006, 2007 and the period 1971 to 2000.

 
Total precipitation Mean maximum air temperature Accumulated GDD
Month 2005 2006 2007 30-yr mean 2005 2006 2007 30-yr mean 2005 2006 2007 30-yr mean
mm °C
April 51 88 108 91 19 20 15 16 152 152 109 108
May 46 131 95 111 23 21 27 23 214 204 301 228
June 51 61 72 108 30 27 28 27 368 335 354 339
July 117 156 59 102 30 30 28 29 398 445 358 401
August 51 136 148 94 30 28 31 28 402 380 416 370
September 122 72 46 76 28 24 28 25 317 234 306 271
6-mo total 438 644 528 582 1851 1749 1844 1717
6-mo avg. 27 25 26 25



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Analysis of variance significance levels for fixed effects in 2005, 2006, and 2007 as determined using SAS PROC MIXED (SAS Institute, 2004). Variables are maize per-unit-area grain yield (GYA); nitrogen use efficiency (NUE); per-plant grain yield (GYP); per-plant grain yield variability (GYCV); per-plant kernel number (KNP); individual kernel weight (KW); R6 (Ritchie et al., 1996) per-plant aboveground vegetative (VBP) and total (TBP) biomass; per-plant harvest index (HIP); per-plant anthesis–silking interval (ASIP); V5, V14, and R1 PHT; V14, R1, R3, and R6 (sixth-internode) stem diameter (SD); R1 green leaf area index (LAIG); and V14 (12th leaf), R1, R3, and R5 (uppermost earleaf) single-photon avalanche diode (SPAD).

 
Sources of variation GYA NUE GYP GYCV KNP KW VBP TBP HIP ASIP V5 PHT V14 PHT R1 PHT V14 SD R1 SD R3 SD R6 SD LAIG V14 SPAD R1 SPAD R3 SPAD R5 SPAD
2005
 Hybrid (H) NS‡ NS NS * NS * NS NS NS NS ** ** NS NS NS *
 Plant density (D) ** ** ** ** ** ** NS * ** ** ** ** ** ** ** **
 H × D NS ** NS NS NS NS NS NS NS NS NS NS NS NS NS *
 N rate (N) ** ** ** ** ** ** NS * ** ** ** NS ** ** ** **
 H × N NS NS NS NS NS ** NS NS NS ** NS NS NS * NS NS
 D × N ** NS NS NS NS NS NS NS NS NS NS NS ** ** ** NS
 H × D × N NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS *
2006
 H NS NS NS NS ** ** NS NS NS ** ** ** ** ** ** ** NS NS ** ** *
 D ** ** ** ** ** ** ** ** ** ** NS ** ** ** ** ** ** ** ** ** **
 H × D NS ** ** ** * NS NS * NS * NS NS NS NS NS NS NS NS NS NS *
 N ** ** ** ** ** ** ** ** ** ** NS ** ** ** ** ** ** ** ** ** **
 H × N NS NS NS ** ** ** NS NS ** ** NS NS NS NS NS NS ** NS NS NS *
 D × N ** NS NS ** NS NS NS NS * ** NS NS NS NS NS NS ** ** * NS NS
 H × D × N NS NS NS * NS ** NS NS NS NS NS NS NS NS NS NS NS NS * NS NS
2007
 H NS NS NS * ** NS ** NS NS ** NS NS ** ** ** ** ** ** ** * ** *
 D ** ** ** ** ** ** ** ** ** ** NS ** ** ** ** ** ** ** ** ** ** **
 H × D NS NS NS NS NS NS NS NS NS * NS * ** NS NS * NS NS NS NS NS NS
 N ** ** ** ** ** ** ** ** ** ** NS ** ** ** ** ** ** ** ** ** ** **
 H × N NS NS NS ** NS NS NS NS NS ** NS * NS NS ** ** * NS NS * NS NS
 D × N * NS ** NS NS NS NS NS NS ** NS NS NS NS ** ** NS ** NS NS NS NS
 H × D × N NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS
* Significant at the 0.05 probability level.
** Significant at the 0.01 probability level.
Per-plant grain yield variability is expressed using the coefficient of variation (CV).
NS, nonsignificant at the 0.05 probability level.



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Plant density and N rate effects on maize per-plant kernel number (KNP) and individual kernel weight (KW) for 2005, 2006, and 2007.

 
KNP KW
Treatment effect 2005 2006 2007 2005 2006 2007
Plant density, plants ha−1 mg kernel−1
 54,000 626a† 595a 513a 303a 335a 381a
 79,000 494b 484b 388b 269b 298b 359b
 104,000 428c 385c 341c 247c 266c 300c
N rate, kg N ha−1
 0 460a 385a 344a 233a 247a 284a
 165 537b 538b 466b 288b 318b 358b
 330 551b 541b 432b 297b 334b 397b
Within each year, means with different letters indicate statistically significant differences at the 0.05 probability level between either plant densities or N rates.



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Plant density and N rate effects on maize V5, V14, and R1 (Ritchie et al., 1996) plant height (PHT) for 2005, 2006, and 2007.

 
PHT
2005 2006 2007
Treatment effect V5 V14 R1 V5 V14 R1 V5 V14 R1
Plant density, plants ha−1 cm
54,000 37a† 184a 256a 48a 196a 258a 54a 208a 247a
79,000 38a 180ab 244b 48a 191b 254a 54a 200b 239b
104,000 38a 178b 242b 47a 185c 249b 53a 197b 234c
N rate, kg N ha−1
0 38a 177a 242a 48a 176a 238a 54a 189a 230a
165 38a 182ab 249b 48a 197b 262b 54a 209b 244b
330 38a 183b 251b 48a 198b 262b 53a 208b 245b
Within each phenological stage for a given year, means with different letters indicate statistically significant differences at the 0.05 probability level between either plant densities or N rates.



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Plant density and N rate effects on the observed (LAT), predicted (LÂT), and estimated (LÁT) total green leaf area per plant; on the area of the largest leaf of destructively (LA o ) and nondestructively sampled (LÁ o ) plants; on the total number of green leaves (NLT) per plant; on the positions of the earleaf (x e) and largest (xo ), lowest (x L), and highest (x H) green leaves (leaves numbered from the bottom to the top of the plant for all initiated leaves); and on the b coefficient of Eq. [3] for maize grown in 2006 and 2007 and measured at R1 (Ritchie et al., 1996).

 
Year Plant density N rate LAT T T NLT x L x H x e xo LA o o b
plants ha−1 kg N ha−1 cm2 plant−1 leaf no. cm2
2006 54,000 0 5410a§ 5445a 5203a 11.2a 11.4a 21.6a 14.4a 13.0a 692a 661a 0.020a
165 7255b 7349b 7114b 13.7b 9.0b 21.6a 14.4a 13.3ab 756b 733b 0.022ab
330 7417b 7456b 7229b 13.7b 8.7b 21.4a 14.4a 13.7b 764b 741b 0.023b
79,000 0 4417a 4467a 4271a 10.5a 11.5a 21.0a 14.3a 12.9a 610a 582a 0.022a
165 6132b 6187b 6360b 12.8b 9.4b 21.2a 14.3a 13.2ab 664b 684b 0.022a
330 6059b 6093b 6377b 12.8b 9.4b 21.2a 14.3a 13.7b 657b 690b 0.024a
104,000 0 3696a 3733a 3526a 10.1a 11.8a 20.9a 14.3a 12.8a 548a 517a 0.023a
165 5665b 5728b 5680b 12.4b 9.6b 21.0ab 14.2a 13.2a 635b 631b 0.022a
330 6021b 6072b 5933b 12.8b 9.4b 21.3b 14.2a 13.2a 663b 648b 0.023a
2007 54,000 0 5705a 5783a 5192a 11.2a 9.7a 19.9a 13.9a 12.1a 700a 628a 0.021a
165 7045b 7127b 6782b 13.3b 7.6b 19.9a 13.8a 12.5a 762b 726b 0.026b
330 7247b 7390b 6963b 13.4b 7.4b 19.8a 13.8a 12.4a 772b 728b 0.024ab
79,000 0 4153a 4184a 3745a 10.0a 10.5a 19.5a 13.6a 11.9a 579a 522a 0.024a
165 6765b 6913b 5893b 13.0b 7.6b 19.6a 13.7a 12.0a 752b 641b 0.026a
330 6552b 6633b 5966b 13.2b 7.5b 19.7a 13.6a 12.3a 717b 645b 0.026a
104,000 0 3698a 3724a 2906a 9.3a 11.0a 19.4a 13.5a 11.6a 578a 453a 0.024a
165 5942b 6078b 4993b 12.5b 8.1b 19.6a 13.5a 11.8a 688b 565b 0.025a
330 5654b 5795b 5135b 12.7b 8.0b 19.6a 13.5a 12.0a 667b 591b 0.029b
ANOVA
Sources of variation
2006  Hybrid (H) NS¶ NS * NS ** ** ** NS ** ** NS
 Plant density (D) ** ** ** ** ** ** ** NS ** ** NS
 H × D NS NS NS NS NS NS NS NS NS NS NS
 N rate (N) ** ** ** ** ** NS NS ** ** ** NS
 H × N NS NS NS NS NS NS NS NS NS NS NS
 D × N NS NS NS NS NS * NS NS NS * NS
 H × D × N NS NS NS NS NS NS NS NS NS NS NS
2007  H ** ** ** ** ** ** ** ** ** ** NS
 D ** ** ** ** ** ** ** ** ** ** NS
 H × D NS NS NS NS NS NS NS NS NS * NS
 N ** ** ** ** ** NS NS NS ** ** **
 H × N NS NS NS NS * NS NS NS NS NS NS
 D × N ** ** NS ** * NS NS NS NS NS NS
 H × D × N NS NS NS NS NS NS NS NS NS NS NS
* Significant at the 0.05 probability level.
** Significant at the 0.01 probability level.
Determined for destructively sampled plants.
Determined for tagged, nondestructively sampled plants.
§ For each column within year and plant density, means with different letters indicate statistically significant differences at the 0.05 probability level.
NS, nonsignificant at the 0.05 probability level.