Growing high-yielding, high-quality corn is half the challenge of successful silage production. The other half is timing harvest so that forage ferments, ensiles and is preserved for later feedout.
Too wet (greater than 70 percent moisture), and the silage can sour and seep, causing low intake by dairy cows. Too dry (less than 60 percent moisture), and the silage can mold and have lower digestibility, protein and vitamins A and E. Either way, yield is reduced.
The decision to begin harvest depends upon the storage structure, the number of acres to chop for the equipment available and the environment. The decision is further complicated when custom choppers are involved because when they show up, there is pressure to harvest immediately or they may leave and not return.
There is little discussion about the consequences of mistiming corn silage harvest. The objective of this article is to describe what happens to corn silage when harvest timing is off using data derived from individual hybrids grown at various locations in the University of Wisconsin silage evaluation program.
The entire dataset consists of 27,681 observations collected from 1990-2013. Observations were categorized according to harvest moisture where forage was classified as too wet (greater than 70 percent moisture), ideal (60 to 70 percent moisture) and too dry (less than 60 percent moisture).
From the entire dataset, 8,532 observations had individual hybrids that had been harvested across these moisture categories in various environments. A minimum number of observations was set at 36 (representing more than 12 environments), leaving for the analysis a total of 5,399 observations for 109 hybrids. The results of the data analysis are shown in Table 1.
On average during the harvest season, forage moisture is lost at the rate of 0.5 percent per day, leaving a 20-day time period as forage moisture moves from 70 percent to 60 percent. Some harvest structures, like a bunker or concrete stave silo, only have half this time (10 days) to fill, pack and seal while the crop is drying down.
In this dataset, forage yield increased 1.4 tons per acre, from 7.3 to 8.7 tons per acre, as the crop matured and forage moisture decreased from 71 percent to 57 percent. The target harvest moisture for the UW trials is 65 percent. Within this relatively tight range of moisture, yield increased; however, with further drydown, leaves would be lost as well as other plant parts, and forage yield would likely decrease.
Crude protein decreased from 7.3 percent to 6.9 percent. Neutral detergent fiber decreased from 50 percent to 44 percent, while in vitro neutral detergent fiber digestibility was little changed over these moisture ranges. The most dramatic change comes with starch content, which changed from 26 percent to 34 percent as the crop matured (moisture decreased).
So when we bring all of these values together and calculate the performance indices of milk per ton and milk per acre, we find optimum quality (milk per ton) in the ideal moisture range, and when forage is too wet or too dry, milk per ton is lower. Because yield and starch content in this dataset continues to increase, milk per acre increased as the crop matured.
Although we do not have the extremes in this dataset as would likely be found in the real world, trends can be seen regarding the consequences of mistiming harvest. Little change is measured on stover quality (in vitro neutral detergent fiber digestibility).
All of the changes are occurring in the grain portion of corn silage. So if you are going to err, it is probably better to err on the more mature side of crop development. However, keep in mind there are trade-offs, including a significant increase in the risk of potential mold development. PD
Presented at the 2015 Midwest Forage Association annual meeting.
Joe Lauer is a professor with the Department of Agronomy, University of Wisconsin. He can be contacted by email.