Impact of Variability in Plant Spacing On Corn Yield.

Uniformity in plant spacing in corn is an intuitively important component for achieving the maximum yield potential in a given field.  Several factors can cause lack of uniformity in plant spacing.  High planter speed, lack of proper adjustment, rough field surface conditions resulting in planter bounce, and seedling pests and diseases are all common causes of non-uniformity in plant spacing.   Uneven stands may be characterized by plant spacing variability (PSV) within the row and/or by time of seedling emergence. Plant spacing variability is commonly measured by the standard deviation of consecutive plant-to-plant spacing within rows.   Previous research by Nielson (1991) and Doerge et al. (2002) found that PSV resulted in a yield loss of 167.98 kg ha^-1 for each 2.5 cm increase in standard deviation in plant spacing.  However, recent publications from Lauer and Rankin (2004) and Liu et al. (2004) report little or no yield loss due to uneven plant spacing.  All of these research trails have been done in the upper midwest or in Canada.  Five different planting treatments were used to achieve differences in PSV at six locations in the southeastern US.  These included a uniform spacing treatment using a carefully adjusted corn planter, high speed planting, use of a cone seeder, and two treatments with a cone seeder with one or more slots covered.  Field measurements confirmed uniform differences among the treatments within each of four replications.  There were strong relationships between corn yield and PSV (R² > 0.80) at all six locations with an average yield loss of 335.95 kg ha^-1 for each 2.5 cm increase in the standard deviation in plant spacing.