Plant spacing

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If you’ve been to farm shows in the past few years you’ve probably noticed that efforts to improve planting accuracy of corn has become a full-blown obsession.  However, most published studies show that at the accuracy normally achieved in commercial settings there is little to no benefit to be gained from decreasing the standard deviation in plant spacing.  Furthermore, many of the stresses that cause plant-to-plant variation occur during the growing season and are best handled by sufficient fertilizer and crop protection.

Why the obsession?  My theory is that it’s because plant spacing is something that can be seen easily, whereas fertilizer placement and herbicide uniformity are abstract to all but the most diligent of farmers.

This year we tracked the growing characteristics and yield of over 1200 individual plants.  We also measured the position of each plant so that we could analyze the spatial relationships.

The figure above (click on figures to enlarge) shows the plant spacing signature– the x and y coordinates are the distances from each neighbor and the z coordinate is the frequency.

The figure below is a yield map of sorts, an idea for mapping yield by plant spacing that came from Tom Doerge, currently the Corporate Life Scientist for John Deere.  It’s the best way of visualizing the effect of plant spacing variations on yield.  The map was created by a geostatistics program that averages the yield for duplicate x-y coordinates and then interpolates (Krig) between the points to create a smooth map.  The colors represent yield levels.

Along each axis we have the distance from each neighboring plant.  Points closer to the origin are a higher local population and points further from the origin are lower population.  The diagonal lines connecting the same number on each axis are isolines for population.  The midpoint between the axis is perfect spacing and the “unevenness” increases with proximity to one axis or the other.  The map shows that there was a big cost to skips, but not too much effect from unevenness unless it was really extreme– a double or close to it.  Also, the effect of being really uneven was only meaningful at very high populations.

While an emphasis on plant spacing might not be statically optimal, it might be dynamically optimal.  In other words, most of us are doing a good enough job right now that we should work on improving fertilizer placement, drainage, and other factors that have a huge effect on yield.  But in the future when plant populations are much higher, spacing will be more important.  So working on getting it right now might have a payoff under future conditions.


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