Impact of Variability in Plant Spacing on Corn Yield R.W. Heiniger and T.A. Smith. INTRODUCTION
R.W. Heiniger and T.A. Smith
Table 1. Sites selected for the study along with information on soil type and the management practices used.
PLANT POPULATION AND PLANT SPACING VARIABILITY
The only population difference among treatments was between Treatments A, B, C, and D and Treatment E (Fig. 2). The large variability in the stand in Treatment E often resulted in multiple plants at a single site. This created competition for light which often led to the loss of one of the plants. Even so differences in plant population among the treatments were small with little or no impact on final yield. In comparison, there were large and consistent differences among treatments in PSV (Fig. 3). The use of cone units resulted in predictable levels of PSV across locations. Furthermore, the differences ranged from an almost perfect spacing (Treatment A) to large gaps and multiple plants at given locations (Treatment E) that were present from seeding throughout the season (see inset photos). Because of the way seed dropped from the cone units the patterns in plant spacing were similar to what was observed in farm fields.
YIELD RESPONSE TO PLANT SPACING
There were significant differences in corn yield among each the treatments with the check having the highest yield and Treatment E, with severe skips and gaps, having the lowest yield (Fig. 4). The pattern of declining yield among the treatments was similar to the linear pattern in increasing PSV. Plots of yield as a function of PSV revealed linear relationships across all six sites with R2 ranging from 0.46 at Currituck in 2007 to 0.81 at Pasquotank in 2005 (Fig. 5). Comparisons of the slopes of the linear equations which represent the amount of yield lost as the variability in spacing between plants increases using full and reduced models found no significant differences in slopes at the Hyde, Pasquotank, Pamlico, Beaufort, and Perquimans sites. However, the slope at the Currituck site differed from all of the other sites except for Perquimans. This indicates that for most of these sites a single relationship can be used to measure grain loss from increasing levels of variability in plant spacing (Fig. 6).
Figure 1. Slot arrangements for the Almaco cone for treatments D and E. All 31 slots were open for treatment C.
Figure 6. Relationships between yield loss and increases in PSV for the combined sites of Hyde05, Pasquotank05, Pamlico06, and Beaufort06. The slope of the linear response differed at Currituck in 2007 possibly due to the use of a different hybrid.
Where it was possible to combine sites, a common relationship between PSV and yield (Fig. 6) indicated that, on average, corn yield was reduced by 0.126 Mg ha-1 for each cm increase in PSV (5.1 bu acre-1 for each inch). This loss is twice as high as the losses reported by Nielsen (1991; 2004) of 2.2 and 2.5 bu acre-1, and considerably higher than the losses reported by Liu et al. (2004b) of 1.5 bu acre-1 or Doerge et al. (2002) at 3.4 bu acre-1. Yield losses at the Currituck location (0.061 Mg ha-1 for each cm or 2.44 bu acre-1 per inch) were similar to previous reports. Since Currituck was the only location where a different hybrid was used differences in yield losses to PSV may be related to the hybrid grown.
Clearly, variability in plant spacing can cause significant yield losses in the southeastern US. A survey of sixteen grower fields in North Carolina found PSV values ranging from 7.04 cm (2.77 in) to 16.61 cm (6.54 in) with an average of 12.29 cm (4.84 in). This means that growers are losing 1.55 Mg ha-1 or 24.6 bu acre-1 due to non-uniform plant spacing. These losses could be reduced by careful planter calibration and, as shown by the difference between planting at 4.8 and 12.9 km h-1, reductions in planting speed particularly in rough no-till conditions. An increase in planter speed alone increased PSV by 2 cm and decreased yield by 0.4 Mg ha-1 (6.4 bu acre-1). As corn growers continue to increase plant populations it is important that they take steps to slow down planting speed and to calibrate the planter if they are to realize increases in yield potential.
The Proc Mixed procedure in SAS (SAS Institute, 2006) was used to determine if there were differences in PSV (measured as the standard deviation of the distances between plants in the row), plant population, and grain yield among the five treatments. When differences were detected Fisher’s Protected LSD was used to separate means. Regression analysis was used to examine the relationships between PSV and grain yield at each site. Full and reduced models were used to determine if the slopes of these relationships differed among site-years.
The site-year by spacing treatment interaction was not significant for any of the variables of interest indicating similar responses of grain yield, plant population, and PSV to changes in plant spacing across the environments tested in North Carolina (Table 2). The main effect of spacing treatment was significant for all three variables (Figs. 2, 3, and 4).
Table 2. Significance of the influence of site-year and spacing treatment on PSV, plant population, and grain yield.
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Figures 2 and 3. Plant population and plant Spacing Variability achieved by the five changes in either speed or seed drop mechanisms. Error bars indicate that only treatment E had differences in plant population and that consistent and large differences were found in PSV across locations.
Figures 4 and 5. Yield response to the plant spacing treatments across locations and to changes In PSV within each location.
Skips with Doubles