Silage corn should be seeded at 35,000 kernels/acre – whether it’s Bt, non-Bt, brown midrib (BMR) or a silage-specific Bt hybrid, says William Cox, Cornell University crops and soils scientist.

“You can jack it up a little higher without worrying too much about an adverse effect on quality. And I don’t think we need to worry about BMRs or silage-specifics getting penalized at these seeding rates. They seem to show as good a response as the others,” says Cox.

He studied eight hybrids at four seeding rates – 25,000, 30,000, 35,000 and 40,000 – on New York silt-loam soils in 2008 and 2009.

“Both were non-stress years,” he points out. “I would expect the results would be applicable to other silt-loam soils in northern latitudes in Michigan, Wisconsin and Minnesota.” He wouldn’t recommend such high seeding rates in warmer climes, such as southern Illinois or southeastern Pennsylvania or Kentucky.

Grain-corn studies have shown that modern hybrids require higher seeding rates to maximize yields as compared to hybrids available in the 1990s.

“We didn’t have any studies for how it was for silage yields,” Cox says. “But the major impetus for doing the research was to look at brown midrib and silage-specific hybrids. There was a general feeling that the seeding rates would not be that high.”

So he compared three Bt and one non-Bt hybrid as well as two each of BMR and silage-specific Bt hybrids.

“We were expecting to see that they (the Bt hybrids) would require higher seeding rates for maximum yield and that the brown midrib and the silage-specific required lower seeding rates.

“But what we found was that all hybrids did best at about a 35,000-kernel/acre seeding rate, which isn’t that different from what I found in the 1990s.”

What was different was that fiber digestibility and starch didn’t change as seeding rates increased. That means quality wasn’t impacted negatively as it was nearly 20 years ago, Cox says.

“The protein still went down a bit and the fiber still went up a bit, but very little.” In the past, Cox has suggested using 34,000 kernels/acre as a good compromise between higher yield and lower quality.

“But now it seems you get the higher yields and don’t lose as much on the quality, so we are recommending for all silage hybrids to drop at seeding rates of about 35,000 kernels/acre.”
The yield gap between BMR and other hybrids is also narrowing – at least with the two BMRs that Cox tested. They only took a 7-8% yield hit as compared to the 15-20% yield lags shown from early BMRs.