The higher proportion of corn silage in many dairy cow rations has become old news in some sense. Over the last few decades, dairy producers and nutritionists have really unlocked the potential of corn silage in producing milk economically in geographic regions where the climate supports high forage diets.
In addition to being a forage and grain in one — contributing digestible fiber and energy to the diet — as a single harvest system, corn silage is touted for its productivity per acre and feed consistency. Land is expensive and cows like consistency, making these benefits significant.
Conversely, while perennial grass and legume crops are still fairly common on many farms, the drop in overall acres as well as inclusion rates in common dairy diets speaks to its challenges. These forages require multiple cuttings per year, often for less total yield and potentially drastic differences in nutritional value between cuttings.
A version of this trend toward more corn and less perennial hay crops also includes the greater use of winter cereal grains, namely triticale and winter rye, as a double crop with corn silage in many northern climates. The logic is evident: one cutting per year with good yields and more consistent nutritional value outweighs multiple cuttings of hay. Plus, the potential of more total tonnage per acre from two crops on the same acre is attractive. Still, it needs to be considered that one cutting per year also means that if the timing does not work out, it could leave you with a year’s worth of poor-quality feed.
Soil and production impacts
It seems like a pretty straightforward story, but as with most things, we need to dig a little deeper. Agriculture continues to be under the microscope related to environmental impact, and a positive point for dairy has been crop rotations, where the sod portion of the rotation has many ecological benefits.
Using a cover crop after corn silage is a highly beneficial conservation practice that provides soil cover between corn crops and is certainly better than continuous corn silage with no cover crop. The issue is not with the corn and cover crop; it is with the lack of other crops.
Studies around soil health in cropping systems continue to point to corn silage as one of the most challenging crops to achieve improved soil health goals, largely due to the minimal residue left after harvest. Cover crops are a way to help offset this lack of residue, as is manure; however, the value of a more diverse crop rotation, particularly one including perennial hay crops, should not be overlooked. Perennials provide a rest to the soil and allow for the development of a root system that cannot be achieved with most annuals, allowing for the cycling of nutrients deeper into the soil profile.
The corn crop following perennial hay also benefits from nitrogen credits and an apparent rotation boost. The frequent mowing of a hayfield can help manage weeds that become increasingly problematic with continuous corn and can break up other pest life cycles often associated with monocultures.
Striking the correct balance with your farm’s resources comes with many tensions — it wouldn’t be dairy farming if it didn’t. We need to consider all the pros and cons, including ecological factors and their impact on the footprint of a gallon of milk, when making our rotation decisions.
