Why should you bump corn seeding rate in 2021?

By Dave Nanda, Ph.D., Seed Genetics Direct, Director of Genetics

What plant population do you want to get for your corn?  Suppose you just upgraded your planter with electric drives and all the bells and whistles. You want to wind up with 32,000 plants per acre at harvest, so you figure if you seed just over 32,000 seeds per acre, you will have all the plants you need for your desired yield.

However, no matter how much technology you have on your planter, some slippage will occur between the seeding rate and final population. If you plant 32,000 seeds per acre, you won’t always get 32,000 plants per acre at harvest. In fact, most of the time, you would more likely get closer to 30,000 plants per acre. Seed germination is not 100%, no matter whose seed you plant, so you can’t assume every seed will germinate. If you want 32,000 plants at harvest, you should consider seeding rates closer to 33,000 to 34,000. 

Some agronomists suggest using a 5% figure as a guideline. If you want 32,000 plants per acre, then plant at least 33,600 seeds per acre. That allows for the 5% of seeds that likely will not germinate or will not turn into a productive plant for whatever reason. Some agronomists suggest adding even a larger cushion to your seeding rate.

While scouting this summer I picked a spot in a row where there was a 12-inch gap between the plants within a row. Did the planter not drop a seed or did the seed fail to germinate? The time to find out is earlier in the season before the seed would deteriorate, if it was there. When we dug a couple inches deeper in this instance, we found the seed. It just didn’t germinate. We don’t always know why.

Besides seeds that just don’t germinate, you will also get seeds that attempted to germinate but encountered problems. Perhaps it was too cool and wet or the soils were compacted. Perhaps the seed was under a small rock. The seedling may leaf-out underground and not emerge. If it does emerge, it may emerge late and may not catch up to its neighbors and develop a productive plant. We did the same check in 2019 in a different field and with a different hybrid. In that case, we checked five locations within rows where there was a skip. Four out of five times, the seed was there but didn’t germinate. In only one case was it likely a true planter skip.

This year’s crop has not even been harvested yet, so why talk about 2021? Farmers always have to plan ahead and order supplies in advance — especially seeds — in order to get needed hybrids and traits for the upcoming season. Remember to account for slippage when ordering. Many farmers have increased their inputs of fertilizers, herbicides and fungicide applications, but plant populations have not kept pace with the other inputs.

When I was inspecting a field in central Indiana, it was obvious a lot of sunlight was being wasted, even in taller corn at the time. We can’t keep increasing the ear size any more. To increase yields in the future, we will need to plant thicker and increase the number of plants per acre. I believe that corn plants with a different architecture and tolerance to higher plant density will be part of the secret to higher yields in the future. Higher planting populations will be needed to get there.

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