Farming Magazine - November, 2009

COLUMNS

Forages: Fall Crop Topics

PHOTO COURTESY OF ERAN CHESNUTT/SXC.HU.

By now almost all forage crops have been ensiled or mowed away. Some farmers test forages as they’re harvested, since the analysis will provide some idea of their quality. This is fine for dry hay, but rations shouldn’t be balanced using pre-ensiling analyses, since significant changes occur in silage during and after fermentation. Dry hay changes much less after baling unless the hay went in too wet. (It’s no coincidence that there are more barn fires following wet haying weather.) Following are a few suggestions as we head into the winter feeding season.

Corn silage is a dynamic feedstuff

I discussed dairy farm crop dynamics as it related to fertilizer in my August crops column, but will touch on the concept again this month. One of the definitions of the term “dynamic” is something that’s not in equilibrium, and that almost perfectly describes corn silage. Some farmers think that corn silage is stable once fermentation has ended, which is normally one to two weeks post-ensiling. However, changes are still occurring, especially in the starchy kernels, and recent research suggests that these changes continue for much longer than we previously thought. A European study using 15 bunker silos on commercial dairy farms found that starch (and, to a lesser extent, crude protein) continued to increase in digestibility for many months after ensiling. In fact, the highest starch digestibility occurred in the last time period studied: 10 months after ensiling.

No one is suggesting that you wait 10 months before feeding “new crop” corn silage, but the point is that the corn silage you feed next spring will probably be more digestible than it is now. You won’t know, however, unless you have the silage tested. The availability and reliability of in vitro digestibility analysis has increased in recent years, but farmers still aren’t using this test nearly as much as they should.

How often should you test ensiled forages?

To some extent this depends on the types of silos you have. One advantage of bunker and stack silos is that they’re filled horizontally—layer after layer, hopefully no more than 6 inches at a time—but during feedout they’re unloaded vertically. This greatly limits rapid changes in silage quality.

For example, assume you filled a bunker silo with the corn from three large fields, two that were well-eared and one that had a serious weed control problem and as a result wasn’t nearly as high in quality. The lower-quality crop would be would be layered in with the good corn, and as the silage was fed out, much of the corn from the three fields would be blended.

PHOTO BY KIMBERLY STOCKWELL-MORRISON.

The extent of blending of forage from the three fields would depend on how the silo was filled: The normally recommended way to fill a bunker silo is by using the “progressive wedge”, whereby a fairly steep ramp (about a one-on-three pitch) is maintained as the silo is filled from back to front. Using this system, if three fields were used to fill the silo, the back of the silo may contain corn from only one field. However, with today’s big self-propelled choppers and multiple hauling trucks, many small and medium-size bunker silos can be filled so quickly that I don’t think the progressive wedge system is ideal. So much forage is coming into the silo that it’s hard to spread a thin enough layer across the ramp and the part of the silo that’s being filled. If you can, fill the whole bunker silo in three days or less, spread even layers across the whole length and width of the silo, and fill it “bottom to top” instead of using the progressive wedge. It’s much easier to spread a thin layer this way, and thin layers are critical to achieving high silage density. Also, if several fields are used to fill the silo, there will be less variability in silage quality during feedout. For most bunker and stack silos, testing silage once a month is probably adequate, though you should work with your dairy nutrition consultant on this topic.

Silage bags are a different situation entirely: If two or more fields are used to fill a silage bag, changes in silage quality can occur from one feeding to the next. If you’re using silage bags, here are two recommendations: First, avoid putting forages of widely different quality or composition into the same bag. Even if you think the forage is similar, mark on the bag where the change from one field to the other occurred. That way, when changing from one silage to the other, you can be on the lookout for herd performance problems.

One thing you should not do is sample silage bags through the plastic! We’ve tried to do this several ways at Miner Institute, with generally terrible results. Last year at a large dairy conference, a dairy nutritionist asked me to please tell people not to sample silage bags in this manner. He said he’d seen disaster after disaster when people—both farmers and well-meaning dairy consultants—started poking holes in silage bags. By sampling the forage going into storage, you should have a general idea of quality. If there’s enough silage (all from one field or of very similar composition) in the bag, and you’ll be feeding it out for weeks rather than days, sample from the face and try to get the analysis back ASAP.

Sampling silage from tower silos is like buying a pig in a poke unless you know what went in when and marked the layers during ensiling. When we had tower silos at Miner Institute, we would mark the forage from separate fields by sending a few broken-up Styrofoam egg cartons up the chute. When we saw Styrofoam pieces of a certain color appearing in the silage, we knew we were about to change silages. While we only did this when we expected that there would be a significant difference in quality, it really works and is cheap—an unbeatable combination.

Ev Thomas has worked as an agronomist in New York for over 40 years, first with Cornell University Cooperative Extension, then with the William H. Miner Agricultural Research Institute in Chazy, N.Y., including managing its 680-acre crop operation. He continues to work part-time for Miner Institute and is now an agronomist at Oak Point Agronomics. He has written our Forage column for over 10 years and has been an expert contributor on a number of other topics. Comment or question? Visit www.farmingforumsite.com and join in the discussions.