Forage Focus 2019: Alfalfa Grass Management for Silage
Joe Lawrence of the Department of Animal Science at Cornell University in New York State gave two talks at the Ontario Forage Council’s Forage Focus 2019 Conference. This article will address his second presentation, entitled “Alfalfa Grass Management for Silage.”
Lawrence started his presentation by identifying a couple of reasons why farmers started mixing alfalfa and grass together. The first reason was because of variable soil drainage and soil quality. Some fields have all sorts of different types of soil and lots of range in terms of drainage. Even if the farmer wanted to grow a pure alfalfa stand in that field, often the alfalfa simply wouldn’t grow in some spots, and then they might as well mix in grass just to take advantage of the empty areas. The second reason Lawrence identified was yield and quality. Even in perfect ‘alfalfa ground’ there are good arguments to be made that mixing grasses with the alfalfa will result in a higher yielding and higher quality forage.
A 30% grass and alfalfa mix, when compared to a pure alfalfa stand, can result in a total harvest increase of between one and two thirds of a ton more dry matter per acre. Additionally, the grass mix has a 6-7% higher NDFd measurement than the pure alfalfa, which means there was more digestible matter in the grass/alfalfa mix. Finally, in terms of protein the grass/alfalfa and the pure alfalfa mix are roughly equivalent. Overall, there’s not really a downside to growing a grass and alfalfa mix if the soil will allow it.
An important consideration for a mixed stand is the type of grass to be used. This can be tricky, as the grass and the alfalfa must mature at roughly the same time. Another consideration is how aggressive the grass is. If you pick a grass variety that’s too aggressive, it’ll outcompete the alfalfa quickly and in a matter of a couple of years the percentage of grass to alfalfa will be skewed. For example, Reed Canary grass behaves well for the first couple of years because it is slow to establish, but once it is established it can rapidly take over a field. A type of grass must also be considered for its tolerance to wet soils, especially if its being seeded where the alfalfa won’t grow because of poor drainage. Lawrence says that Reed Canary grass was the go-to for grass/alfalfa mixes in New York state until a few years ago, when Tall Fescue became more favoured due to its lower seed price and good yield and quality statistics. Currently, Lawrence says that Meadow Fescue is rising in popularity for similar reasons.
Some thought must be put to the variety of alfalfa selected for a mixed stand as well. There are all sorts of varieties of alfalfa with different attributes that can be considered. A reduced-lignin variety of alfalfa, for example, often gives a 5-10% increase in digestible fibre compared to more conventional varieties. There are also varieties that are resistant to pests like the Potato Leafhopper insect.
The current recommendation that Lawrence gave was a mix of Meadow Fescue at 1 or 2 pounds per acre and high quality alfalfa between 12 and 14 pounds per acre.
Lawrence closes this section of his presentation with a pros and cons list of growing mixed stands of grass and alfalfa.
These are the reasons why a farmer could grow mixed stands in fields that could grow pure alfalfa. But what about fields where mixed stands are a necessity because of drainage or variable soil quality? Lawrence addresses those concerns next.
An important aspect of a situation where alfalfa fields have empty spots that are filed in with grass is the variable forage. As the field is harvested, there will be patches of grass and patches of alfalfa, which have different nutrient, protein and fibre contents. Is that harvest going into a bunk silo or an upright silo or into silage bales? In mixed fields, the alfalfa and grass are already mixed together so the ratio of grass to alfalfa is relatively consistent in feed. In fields where grass is used to fill in gaps, it can be hard to ensure that the grass and alfalfa are fed in consistent rations. In silos, especially upright silos, forages are often mixed together fairly well, meaning that the alfalfa and grass have more of an opportunity to mix together. In silage bales, however, there can be a lot of variation in content between them. Compensating for this difference in content and quality involves additional time and labour. One way to keep track of bales with different quality is to individually mark ones that are mostly grass or mostly alfalfa so that later on in the year the farmer can compensate during feeding.
It can be difficult to tell exactly what the percentage of grass to alfalfa is in a field. In general, farmers need to get out into their fields to do estimates. Farmers often overestimate the percentage of grass in a mixed field because it’s taller and more noticeable. Lawrence mentioned that one of his colleagues is working on a cell phone application where a farmer would take a picture of a field and the app would tell them what the percentage of grass and alfalfa is, but the app isn’t widely released yet. Another option Lawrence noted was to send a forage sample to a lab to be precisely analyzed. This can take a while and isn’t always practical, but a farmer can estimate the grass percentage, send the sample in to the lab, see what the actual percentage is, and then use that information to inform their future estimations.
Above is an example of two fields, one with a 10% grass to alfalfa mix, the other with a 25% grass to alfalfa mix. These photos illustrate how difficult it can be to gauge the grass content in a field.
Lawrence closed his presentation with a summary. He said that a 20-30% grass to alfalfa mix is ideal because it’s the point at which the benefits of the grass and alfalfa reach the best balance. For grass variety, Meadow Fescue looks like a good choice across much of Ontario. Finally, late maturing grass should be chosen to match up with the maturity of alfalfa.