COLUMNS
Forages
Late-Summer Management of Perennial Forages

by Everett D. Thomas

Now is when you should be deciding on which alfalfa and other perennial legume fields will remain in legumes or legume-grass for another year. This decision may influence your current fertilization practices as well as late summer and fall harvesting decisions. As I’ve mentioned before, whenever you can substitute manure for commercial fertilizer you should do so. This makes both environmental and economic sense. U.S. and world demand for potassium fertilizer has been at record highs in 2010, and while prices have come down, muriate of potash is still expensive. If soil fertility is low and you’ll be rotating the field into a row crop such as corn in 2011, you might consider waiting until after you harvest the last crop before applying manure. There’s a practical limit to the amount of manure you can apply to a forage crop that will be harvested in the coming weeks, especially if the manure contains bedding such as straw. However, after that last cutting is made, application rates can be somewhat higher, with less concern about the amount of bedding in the manure. Following are two other topics to consider as summer winds down.

Should you take a fall harvest of alfalfa?

The simple answer: Harvest alfalfa in the fall only if you really need the feed. Several studies have shown that taking a fall harvest of alfalfa, at least in the northern half of the U.S., is a case of robbing Peter to pay Paul. That’s because the alfalfa plant compensates for a fall harvest by producing less growth the following spring. Add to this the low yields we often get from a fall harvest and the economics of taking that late-season cutting become pretty dicey. The most recent research was done in Wisconsin, which typically has similar winter conditions to much of the northeastern U.S. After three years of research, the alfalfa yield from a fall harvest ranged from 0.3 to 0.9 tons per acre, with an average of 0.6 tons per acre. That’s not much considering the amount of work it takes to get it. Since it’s almost impossible to get alfalfa dry enough to make hay during the fall, that means harvesting as hay crop silage, involving a lot of horsepower and fuel. The Wisconsin agronomists found that first cutting yields the following year were reduced by about as much as the fall yield, thus the Peter and Paul analogy. Finally, there’s the issue of “feedability” (if indeed that’s a word). We’ve taken a fourth (fall) cut of alfalfa for silage several times at Miner Institute, and it seemed to ferment well. On paper it looks like “forage rocket fuel,” with high crude protein and low fiber levels. However, our dairy farm manager says it doesn’t feed nearly as well as it tests, and anyone who’s ever fed cows will know what he means by that statement.

One reason given for harvesting alfalfa in the fall is to prevent a heavy crop from smothering the alfalfa during the winter. In all the time I’ve been working with farmers, as well as managing the Miner Institute crop operation, I’ve never seen this occur. What usually happens is that killing frosts dry up the alfalfa leaves, most of which then fall from the plant. What remains standing are the alfalfa stems, and even if they lodge there aren’t enough of them to smother the crop. The dead stems, even if they break off as most do, provide protection for the alfalfa crowns by catching and holding snow. During a winter with limited snow cover you can often pick out these fields from fall-harvested ones by the added amount of drifting snow they’ve caught and held. Other research has found that these old stems only add about 1 percent to the NDF level of the first harvest the following spring. So, before heading to the alfalfa field with the mower-conditioner this fall, ask yourself: Is this trip really necessary?

Should I plow or can I get another year out of this stand?

If you’re looking at a field and asking yourself this question, the answer is usually no, there aren’t enough alfalfa plants to make it worth leaving another year. However, the decision isn’t that simple, especially where alfalfa is seeded with a forage grass. The best way to answer the question is to look at yield records for the field. (You do have yield records, don’t you?) An increasing number of large farms have drive-over scales, making record keeping much easier. However, even if you don’t have scales you can approximate the relative yield by counting the number of bales, forage wagons, trucks, etc., for each harvest. If the field used to yield 40 truckloads of forage but this year only yielded 20 loads, unless there was a good explanation (such as dry weather), this field might be a good candidate for crop rotation.

You can determine the future yield potential of clear alfalfa stands by counting alfalfa stems. We used to say to count plants, but older alfalfa plants often have more stems per crown and therefore each plant yields more forage. Marvin Hall, the Pennsylvania State University forage specialist, says that an ideal established stand has at least 55 stems per square foot. As the stem count declines below this number, yields decline; if the count is less than 40 stems per square foot you should rotate the field out of alfalfa.

That’s for clear alfalfa. I think you can get by with somewhat less than 40 stems per square foot if you have a good stand of productive grass. This means a cool-season grass such as timothy, orchardgrass or tall fescue, not a weedy species such as native bluegrass or meadow foxtail. In the end, let yield be the deciding factor; that and your need to rotate out of alfalfa or alfalfa-grass to keep your crop rotation of hay crop forages and corn or other row crops in balance.

Ev Thomas has worked as an agronomist in New York for 42 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 a 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.