Neither twin rows nor high plant populations did much to improve corn silage profitability in a study on three northeastern Wisconsin farms last year. But Kevin Jarek, Outagamie County Extension agent, thinks 2011’s wet growing season may have skewed his twin-row findings.

“The results are what they are, and we always report the findings,” he says. “But I would like to try another year, and hopefully not have the challenges we did with the obscene amounts of rain both at planting and during the growing season.”

Jarek found a small yield and quality advantage for twin rows vs. single 30” spacings. But the lowest plant population – 30,000 plants/acre – was better than 35,000 or 40,000 at both row configurations when averaged across the three locations in this study.

Twin rows – in this case 8” apart on 30” spacings – delivered yield increases at each population. Yet they didn’t approach the 3-5% gains that have been reported in neighboring states.

Jarek is more confident in his plant density results because they match what Joe Lauer, University of Wisconsin Extension corn agronomist, and others have reported. Corn grown at 30,000 vs. 35,000 or 40,000 plants/acre is typically higher in starch, producing more milk per ton of silage.

“That’s consistent,” says Jarek. “So whether we have a wet year or not, that seems to be something that farmers can generally expect to happen when they plant.”

He did the study, funded in part by the Midwest Forage Association, because farmers were asking how much yield gain they could expect by switching to twin rows or jacking up populations to 40,000 plants/acre.

At each farm, full-season (95-day) hybrids were planted in twin and single 30” rows at the three planting rates. The treatments, all planted with the same twin-row planter, were replicated four times at each location.

Yields were carefully calculated for each plot, and silage samples were sent to a lab for quality testing. Neutral detergent fiber digestibility (NDFd) values were used to calculate milk per ton.

Multiplying dry matter yield by milk per ton results in milk per acre, which is the most important figure. However, Jarek discovered that small silage quality gains impact that number more than minor yield improvements.

“If you’re able to change your milk per ton by 200 lbs, and you multiply that by even a slightly smaller dry matter yield, you’re still going to end up with more milk per acre. You’ll have less feed in front of that cow, but it’ll be higher quality; hence, you’re going to get more milk in the long term.”

Averaged over the three locations and population densities, dry matter yields were one-tenth ton higher for twin rows vs. singles (6.3 vs. 6.2 tons/acre), and milk per ton was also slightly higher. Milk per acre favored twin rows by about 500 lbs, but it wasn’t statistically significant.

In the plant population comparison, 30,000 plants/acre produced slightly less silage dry matter than 35,000 or 40,000 plants/acre. But because of its higher quality, that corn produced the most milk per ton and per acre. The milk-per-acre difference between 30,000 and 35,000 plants/acre (17,944 vs. 17,436 lbs) wasn’t statistically significant, but the figure for 40,000 plants/acre was very close to being significantly lower statistically, at 16,738 lbs.

“The big story is that with 40,000 you give up a lot of quality,” he says. “You have higher seed costs, and in the end you get less milk per ton, which ultimately results in less milk per acre.”

Ear size had a lot to do with the highest plant population’s lower quality. “I took pictures of the cobs with the 40,000, and across all three sites the ears were very, very small,” says Jarek.

When Lauer became Extension agronomist in 1994, a lot of farmers were pushing corn populations to 40,000 plants/acre for silage, and he thinks that’s too high.

“Whatever you do for grain, I’d look at 2,000 or 3,000 more plants per acre for silage,” he says. “One of the risks you take on (with high populations) is more lodging potential. Even though it is silage, you can have winds come through in September.”

Twin rows can be expected to deliver smaller gains than single narrow rows, says Lauer. Going from 30” to 15” rows without changing plant population increases grain yield by 2-4% and silage yield by 6-8%, with no change in quality. The yield gain is due to more even plant spacings, but it doesn’t happen every year in every environment.

“With twin rows, the plants are still kind of close together, so it’s going to be something intermediate,” says Lauer. “Over the long haul, you could probably pay for a planter like that, but the gains are relatively small.”