In-Row Spacing and Yield of Individual Corn Plants.

Most research has shown that modest non-uniformity of corn plant spacing has little effect on grain yield, but the extent to which this results from compensatory growth among adjoining plants is not known. In a series of studies we established by hand-thinning plant stands with a substantial amount of plant-to-plant spacing variability, then measured per-plant yield as a function of the space in the row occupied by that plant. In one experiment, plants in 76-cm wide rows that averaged 20.3 cm apart with a standard deviation of interplant spacing of 6.3 cm showed no correlation between plant spacing and grain weight per ear, while plants that averaged 16.2 cm apart with a standard deviation of interplant spacing of 9.2 cm showed a linear, positive correlation between plant spacing and grain weight per plant. A second experiment showed similar trends: a stand with plants 21.6 cm apart and a plant spacing standard deviation of 7.6 cm showed no relationship between per-plant spacing and grain yield, while a higher-density stand with plants 17.6 cm apart and a standard deviation of interplant spacing at 6.6 cm showed a weak but positive relationship between per-plant spacing and per-plant grain yield. Whether a plant was about midway between its two neighbors or close to one of its neighbors made little difference in per-plant grain yield or in each plant's response to the amount of space it occupied. These results indicate that random variability in per-plant grain weight is considerably larger than the variability related to the amount of space occupied by each plant.