Farming Magazine - September, 2012
Forages: Goldilocks and Your Corn Crop
If you remember your fairy tales you'll recall that Goldilocks found one bowl of the three bears' porridge to be too hot, one too cold, and one that was just right. Even though it's an old topic, we're still learning about the proper harvest maturity for corn ensiled as whole-plant silage: too wet, too dry, or just right? The increased price of grain corn has resulted in some farmers deciding to delay corn silage harvest until the plant is more mature, increasing the amount of grain in a ton of corn silage. Is this a good idea? Will the increased amount of grain more than offset any changes in the rest of the plant? To help answer this question, Luiz Ferraretto and Randy Shaver at the University of Wisconsin-Madison conducted a meta-analysis of corn silage trials.
Meta-analysis - what's that?
A meta-analysis is simply a statistical analysis of a large number of individual research trials. This is especially useful with field and forage crop evaluations, which can be greatly influenced by plant population, soil type, fertility management, weather, pest damage, etc. Looking at just one trial, even one that was carefully conducted and analyzed, including the appropriate number of replications (repetitions of each treatment), is not sufficient, as unusual weather or management factors can greatly affect the results. Meta-analysis smooths out the statistical "bumps in the road," so to speak. The University of Wisconsin meta-analysis involved 27 dairy cow studies conducted over a 12-year period, from 2000 through 2011.
The numbers, please
The researchers grouped the various trials into five categories according to whole-plant dry matter (DM): less than 28 percent, 28 to 32 percent, 32 to 36 percent, 36 to 40 percent, and over 40 percent dry matter, with the rations balanced so the variable was the dry matter content of the corn silage. While the rate of corn silage feeding varied from trial to trial, it was one of the major components of each of the rations.
First, what wasn't different between cow performance on the five dry matter categories? There was no significant difference in dry matter intake - which may surprise some - and the milk components fat and protein. Milk production was significantly lower with the most mature corn silage (over 40 percent DM), about 5 pounds of fat-corrected milk per day less compared to 32 to 36 percent DM corn silage, which is what we normally consider as the ideal corn silage dry matter. Milk production with immature corn silage (less than 28 percent DM) wasn't significantly different than with the 32 to 36 percent DM corn silage - more on this in a bit. The bottom line - and this should be encouraging to dairy farmers - is that there's about a 10-percentage-point range in dry matter (approximately 30 percent to 40 percent) where corn silage quality doesn't differ greatly. What about the old tongue-in-cheek saying, "Close only matters in horseshoes and hand grenades?" Should we add corn silage maturity to this? Read on ...
Looking past the numbers
Since corn silage quality doesn't differ much within a fairly wide range of dry matters, why do most agronomists - this one included - continue to recommend harvesting corn for silage when it's about 35 percent dry matter? I often tell farmers to aim for 35 percent DM since that allows a couple of percentage points higher or lower, in other words, 33 to 37 percent DM, and still be OK. That's for corn harvested with a silage processor. For unprocessed corn silage, aim a couple of percentage points lower (33 percent) to avoid kernels becoming too hard. Here's why, like Goldilocks' porridge, we want corn silage to be "just right."
1. Yield. As the corn plant matures from milk stage (under 28 percent DM) to 35 percent DM, what's being added each day is grain. During this time leaf loss is negligible, the two or three leaves on the bottom of each plant long since having dried up, and as long as insect control is good there shouldn't be problems with yield loss due to root lodging or stalk breakage. The meta-analysis didn't include yield; it was a nutritional study, not intended to measure any per-acre production differences. However, countless other studies have concluded that dry matter yield increases considerably as the corn plant matures from the milk or dough stage to fully dented.
2. Silage effluent. Immature corn silage can produce a large amount of effluent, and silage processors can make the situation even worse. One study found that unprocessed dough-stage corn silage produced 2.3 gallons of effluent per ton, compared to 5.6 gallons from processed silage harvested at the same maturity. Apply those numbers to a bunker silo containing 2,000 tons of corn silage and you get 4,600 gallons for unprocessed corn silage compared to a whopping 11,200 gallons if that silage is processed. For comparison, the largest semi-trailer tank has a capacity of about 9,000 gallons. Think of it: A tanker truck full of high-nutrient effluent that the farm would have to deal with, either through its silage effluent collection and treatment system or, far worse, working in and around an ocean of smelly, highly polluting "silage juice."
3. Starch availability. Over 40 percent DM corn silage poses an entirely different set of problems than does immature corn silage. Grain content is close to the max, which occurs at black layer formation. However, by now much of this grain is hard starch and can go through the cow without being adequately digested. Silage processing won't completely solve the problem. In the Wisconsin study, starch digestibility of processed corn silage that was over 40 percent DM was lower than that of unprocessed corn in the 36 to 40 percent DM category.
4. Packing effectiveness. Silage fermentation is an anaerobic process; that means you have to squeeze the air out of the forage mass, either by gravity (tower silos), hydraulic compression (silage bags), or by packing with wheeled tractors or similar equipment (bunker and stack silos). The drier silage gets, the harder it is to get adequate packing. Corn plants ensiled at over 40 percent DM may be especially hard to pack; not impossible, but certainly more of a challenge than corn ensiled at 35 percent DM. Frost dries up leaves and can make matters even worse.
The bottom line
Whole-plant corn can be ensiled at a fairly wide range of dry matter contents, ranging from less than 30 percent DM to over 40 percent DM. At the extremes, though, there are serious challenges relating to silage effluent, kernel texture and the ability to pack well enough to prevent mold and yeast formation. For top-quality corn silage, harvest the crop as close to 35 percent dry matter as possible - 33 percent if the crop will not be processed.
Ev Thomas has worked as an agronomist in New York for 45 years. He has written
our Forages column for over 13 years and has been an expert contributor on a
number of other topics.