How to measure plant to plant spacing in corn

• Choose plots in several "random" areas of the field; avoid selecting the best or worst area of the field. Samples should characterize the field as well as you can. Select areas that are at least 300 feet or so from field ends. If possible, determine where you intend to measure spacings before you enter the field.
• Use at least three plots (i.e. areas) in the field for each comparison (whether it is different row units on the planter, different tillage systems, different hybrids, etc.). Count at least 1/1000 of an acre for each comparison (Table 1). The goal is to measure spacings of at least 250 plants per treatment comparison.

Table 1. Length of row necessary for 1/1000th of an acre based on row spacing. From Table 4 in the Iowa State University publication "Corn Planting Guide".

• At each sampling site within a treatment:
  • Mark off (flag) your row length in each plot. It is best to record data from the same planter unit (unless you intend to check variability in planter unit performance). Using one or both of the two center rows of the planter makes that relatively easy to insure.
  • Lay a measuring tape beside the plants with the zero point of the tape placed next to the first plant.
  • Record the location of each plant relative to the tape (feet and inches). Round the measurements to the nearest inch.
  • Your first plant should have a value of 0 inches. Record every plant in the designated row length, as well as the plant beyond your second flag.
  • Once you have all the values recorded, enter these into a spreadsheet and calculate the difference between each plant. This will give you the plant to plant spacings needed to figure how accurate the spacing is in that particular field. Go to 'Accurate tools for measuring plant uniformity' to understand how to use these plant to plant spacing values.

This text, written by Roger Elmore, is taken from a Crop Watch article (University of Nebraska extension newsletter) written May 17, 2002.