Seed Spacing, Depth, and Planter Speed

John Woener, Consulting Agronomist

Location, location, location may be the number one priority when purchasing real estate, but location, location, location could also be a farmers number one priority when the planter rolls.  Seed location or depth is at the top of the list in planter performance.

With high population it is imperative to maintain and adjust machinery so seed spacing is even and depth control is consistent.  Planter performance is the most fundamental factor in determining what awaits the combine.  You have one chance to get it right.

What's the goal?  You want a plant spacing variability of less than 25% and all plants emerged within 48 hours of each other.  The uniformity of emergence impacts yield in good years and bad, in dry years and wet years.  Plant spacing is also important in good and bad years, but tends to play a larger role for farmers who are planting at their optimum population or in stressful growing conditions.

Late emerging plants arrive only in time to sabotage yield.  Seeds need to germinate within 48 hours of each other and emerge together.  Factors that affect emergence: uniform plant depth, seed to soil contact, uniform moisture around the seed, and soil temperatures.  The single biggest factor is uniform planting depth.  If you are scouting a field that has uneven emergence, dig several plants that have emerged and several plants that have not or just beginning to.  Measure and compare the length of the mesocotyl.  The difference in length correlates directly to the difference in planting depth.  If the mesocotyls are the same length, then the difference in emergence is likely cold soil temperatures.

When the farmer plants shallow, the nodal roots form close to the soil surface where the environment can be fairly hostile.  Dry soil, compacted soil, and soil-applied herbicides can all stress the young developing roots and the corn plant they support.  Planters should be set to place seed at 1 3/4 to 2 inches deep.

Several emergence test results were published over the winter, and in each test corn that was planted at least two inches deep emerged more uniformly and yielded more than the shallower planted corn.  I have planted corn over 3.5 inches deep and have seen corn planted that deep emerge fine.  That's not my goal though.  The point is that today's hybrids have the ability and the vigor to emerge from deeper planting depths.  If you find yourself going to the field contemplating the depth to plant at, choose deeper. 

All planters are designed to operate at a certain speed, usually between 5 and 6 mph.  Well, that is, up until this year.  Until proven otherwise, 5.5 to 5.8 mph is the ideal planting speed.  At that speed, when the seed leaves the seed tube, the seed will not have forward momentum.  If the seed has forward momentum, it will have the tendency to tumble in the seed trench causing poor spacing and /or uneven depth.  In my experience, slowing the planter down has been the number on factor in improving his stand of corn.

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