Fig. 1.

Total weekly precipitation, daily maximum air temperature, and accumulated growing degree days (GDD) for (A) 2005, (B) 2006, and (C) 2007 at the Purdue University Agronomy Center for Research and Education (ACRE). Timing of planting and the phenological stages V5, R1, and R6 (Ritchie et al., 1996) are indicated for each year.

 


Fig. 2.

Plant density and N rate effects on maize per-unit-area grain yield (GYA) (15.5% moisture content) and N use efficiency (NUE) for (A) 2005, (B) 2006, and (C) 2007. For each sub-subplot, GYA was calculated using the sum of that sub-subplot's machine harvest grain weight and per-plant sampling area cumulative grain weight. Arrows approximately adjacent to each vertical bar indicate the per-unit-area grain yield (15.5% moisture content) of each treatment's per-plant sampling area (GYSA). Values for NUE are expressed as the incremental agronomic efficiency from applied N (AEi), which is defined as kilograms of additional grain (15.5% moisture content) per kilogram of additional side-dress N (ΔGYA/ΔNR, see Eq. [2]). For both GYA and NUE, means with different letters (GYA: no parentheses, NUE: parentheses) indicate statistically significant differences at the 0.05 probability level within each plant density.

 


Fig. 3.

Plant density and N rate effects on maize per-plant grain yield (GYP) (15.5% moisture content) and per-plant grain yield variability (GYCV) for (A) 2005, (B) 2006, and (C) 2007. Means with different letters (GYP: no parentheses, GYCV: parentheses) indicate statistically significant differences at the 0.05 probability level within each plant density. The parameter GYCV is expressed using the coefficient of variation (CV).

 


Fig. 4.

Plant density and N rate effects on maize R6 (Ritchie et al., 1996) per-plant aboveground vegetative (VBP) and total (TBP) biomass and per-plant harvest index (HIP) for (A) 2006 and (B) 2007. For VBP, TBP, and HIP, means with different letters (VBP: lowercase, no parentheses; TBP: uppercase; HIP: lowercase, parentheses) indicate statistically significant differences at the 0.05 probability level within each plant density. Horizontal dashed lines indicate the commonly presumed HIP of 0.5 for modern North American maize hybrids.

 


Fig. 5.

Plant density and N rate effects on the anthesis–silking interval of individual maize plants (ASIP) in (A) 2006 and (B) 2007. Means with different letters indicate statistically significant differences at the 0.05 probability level within each plant density.

 


Fig. 6.

Plant density (A–C) and N rate (D–F) effects on maize V14, R1, R3, and R6 (Ritchie et al., 1996) maximum stem diameter (SD) for (A,D) 2005, (B,E) 2006, and (C,F) 2007. At each phenological stage, maximum SD was measured at the midpoint of the sixth internode. Means with different letters indicate statistically significant differences at the 0.05 probability level within each phenological stage.

 


Fig. 7.

Plant density [(A,D) 54,000; (B,E) 79,000; (C,F) 104,000] and N rate effects on the R1 (Ritchie et al., 1996) green leaf area distribution (LAD) of destructively sampled maize plants for (A–C) 2006 and (D–F) 2007. Each curve indicates the mean predicted green LAD for a given plant density-N rate treatment combination. The left and right limits/bounds of each curve are respectively defined by the mean positions of the lowest (x L) and highest (x H) green leaves of that treatment combination's destructively sampled plants (Table 5). The amplitude and point of inflection of each curve are respectively defined by the mean area (LA o ) and position (xo ) of the largest green leaf of each treatment combination's destructively sampled plants (Table 5). Lastly, each data point indicates the mean area (LA n ) and position (xn ) of each green leaf for a given treatment combination's destructively sampled plants.

 


Fig. 8.

Plant density and N rate effects on maize R1 (Ritchie et al., 1996) green leaf area index (LAIG) for (A) 2006 and (B) 2007. Means with different letters indicate statistically significant differences at the 0.05 probability level within each plant density.

 


Fig. 9.

(A–C) Plant density and (D–F) N rate effects on V14, R1, R3, and R5 (Ritchie et al., 1996) leaf greenness (SPAD) for (A,D) 2005, (B,E) 2006, and (C,F) 2007. In each year, SPAD measurements were taken on the 12th leaf at V14 and on the uppermost earleaf at R1, R3, and R5. Means with different letters indicate statistically significant differences at the 0.05 probability level within each phenological stage.

 


Fig. A1.

Regression of (A) predicted individual leaf area (LÂ n ) on observed individual leaf area (LA n ) and (B) estimated total green leaf area (LÁT) on observed total green leaf area (LAT). Each data point represents either the area of an individual green maize leaf (A) or the total green leaf area of an individual maize plant (B). Measurements were taken at R1 (Ritchie et al., 1996) at either the Purdue University Agronomy Center for Research and Education (ACRE) or Pinney-Purdue Agricultural Center (PPAC). Solid lines and accompanying statistics for both (A) and (B) describe regression relationships across locations. Dashed lines for both (A) and (B) indicate theoretical 1:1 relationships between the respective variables. N, number of observations; R 2, coefficient of determination; ** Significant at the 0.01 probability level.