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What Population is Best for Silage Corn?

Daniel Olson

March 31, 2021

Planting populations on corn have increased by nearly 50% over the last 30 years. This has been driven by research which shows that higher population increases yields. Seed companies have embraced this as they are able to sell more seed per acre and have developed hybrids that respond to these higher populations.

This trend may be changing for livestock producers who grow corn silage. When the push for higher populations began in the 1980’s there was little understanding of the digestibility of fiber. As that understanding has increased, farmers and their livestock nutritionists have begun to value digestible fiber as an important part of ruminant nutrition. This understanding has precipitated the move toward BMR silage corn. But, while BMR corn has superior fiber quality, its agronomic challenges, lower starch and increased cost to grow has limited its acceptance in the industry. Lowering planting populations on unique corn hybrids may be a another option for farmers wanting to increase the quality of their silage.

Digestibility of corn silage can be impacted by many factors including genetics, fertility, growing conditions and spacing. Generally, in a healthy corn plant, the outside rind of a corn stalk has about half the digestibility as the inner portion. If the stalk diameter is greater- the ratio of digestible [inner] material increases in relation to the outer less digestible portion. Numerous university studies have shown a consistent quality increase in lower population corn. They also have shown decreased yields and most farmers have decided that the quality increase doesn’t offset the yield drag. While those results are the industry “average” I have been intrigued by “outlier” genetics that respond more consistently to increased spacing. Over the past 7 years I have looked at 100’s of hybrids in dozens of plots from different companies and have found hybrids in a number of programs that consistently have “stalk expansion” capabilities. The reason most studies have shown yield drag and smaller quality increases are the same reason… the stalks didn’t expand enough to offset the lower number of plants.

Besides having quality increases, lower population corn is more drought tolerant, has less disease pressure, increased insect tolerance and has better standability. Of course, it also lowers your seed bill.

How low should you go?

That is a difficult question that has an answer unique for your farm. What is considered optimal corn population for top-end yield on grain corn at your farm? Your soil types, soil fertility and water availability are all factors. Another factor is your hybrid selection.

All the hybrids I have found to work in this system are considered “flex” hybrids but not all hybrids have consistent stalk expansion. Nearly every corn company should have hybrids that will respond to lower populations. Of course, they may not encourage you to do that for obvious reasons, but I have found the by looking at your optimal grain yield population and reducing populations by 8-10K on unique hybrids, we are able to get substantial increases in fiber digestibility without the expected decrease in yield. That combination will positively impact a farm’s ration cost and profitability.

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