Two critical cropping decisions for farmers to make in September are: when to harvest corn for silage and if and when to harvest the last cutting of alfalfa or alfalfa-grass. The first decision will determine yield and quality of the corn silage available for the coming year, whereas the second can impact how well alfalfa will overwinter – as well as yield prospects for next spring.

Timing corn silage harvest

Some people may be tired of the old refrain: Don’t harvest corn for silage until it’s over 30 percent dry matter (DM), preferably 33 percent to 35 percent DM. However, since I still see recently-filled “corn silos” weeping silage effluent (a sure sign that the corn was harvested at less than 30 percent DM), and since I continue to see corn silage forage analyses under 30 percent DM, I’ll keep reminding farmers of the importance of proper harvest timing.

The excuses of today’s farmers sound uncannily similar to those of farmers from years past: “I need to chop the crop now or rain might come in and prevent harvest.” And, “If I wait too long the corn kernels will get hard and go through the cow.” Wet fall weather can certainly be an issue, but if corn is planted on good land – either naturally well-drained or fields improved by subsurface (tile) drainage – it should be able to handle most fall rain events. There may be some weather risk, but corn chopped before the correct stage of maturity will definitely be less than ideal in yield and quality. Given a choice of “maybe” vs. “definitely” when it comes to the chances of bad stuff happening, I’ll choose “maybe.”

The second excuse, of corn getting overly mature so the kernels aren’t properly digested, has to a great extent been overcome by modern harvest equipment. On-board kernel processors – more commonly called “silage processors” – when properly adjusted should crack almost every kernel, exposing the starch in the kernel to digestive bacteria and resulting in very high nutrient availability. Most corn harvested at less than 35 percent DM should have decent kernel digestibility even with the use of conventional choppers as long as the equipment is properly maintained including recommend length of cut and keeping the knives sharp.

Research has found that compared to conventionally chopped corn silage, processed corn silage results in one to two more pounds of milk per cow. However, harvesting corn silage at less than 30 percent DM can result in a bigger financial hit than that represented by a pound or two of milk production. That’s because immature corn silage has lower dry matter yield and less starch, and silage fermentation may be less than ideal. Feeding low-starch corn silage means that more corn meal or other form of starch must be provided in the ration, usually in the form of purchased grain. Silage effluent is another serious issue, especially with the increased attention by regulatory officials including state environmental inspectors conducting reviews of farms designated as concentrated animal feeding operations (CAFOs).

Fall alfalfa management

A generation ago fall alfalfa management was a fairly simple decision. In much of the northeastern U.S. alfalfa and alfalfa-grass was harvested no more than three times per season, usually resulting in the final cut coming off in late August or early September. Therefore, that last harvest wasn’t really a “fall harvest” since the Autumnal Equinox doesn’t occur until later in September (September 22 this year). After the third cut of alfalfa farmers forgot about their hay crop and got ready for corn harvest. But today’s alfalfa management is much more aggressive, with progressive farmers harvesting four cuts per season, and (even in northern areas) sometimes five cuts. This usually means that one of the harvests will be made well into September before corn silage harvest, or in October after the last of the corn has been ensiled.

When asked whether a farmer should take a fall harvest, my first question is “How much do you need the forage?” Research has shown most fall harvests to have a negative impact on first-cut yield the following year. How much impact depends on when the fall harvest was made, perhaps the fall dormancy/winter-hardiness of the alfalfa variety, and the severity of the winter, with temperature extremes and snow cover both important factors.

Some farmers are concerned that leaving what appears to be a good crop of alfalfa in the field will smother the plants. Not to worry; fall frosts will “freeze dry” the alfalfa leaves, which then fall to the ground. The plants – now mostly devoid of leaves – are no longer top-heavy and many will remain upright through the winter. Long-ago research from Purdue University found that leaving a 1-ton crop of alfalfa in the field over winter resulted in only a 1 percent increase in neutral detergent fiber (NDF) in the next year’s first cut. More recent research in the Midwest, this time with a huge 2 ton/acre crop left to overwinter, found much the same result – very modest impact on first cut forage quality the following spring.

The Midwest results gave me a good chuckle since I’ve never seen a 2-ton yield of fourth or fifth cut alfalfa, maybe not even third cut. Even the most impressive-looking field of fall-harvested alfalfa seldom yields more than a ton of dry matter per acre. This is the case even with a 7- or 8-week harvest interval (a minimum of a 45-day harvest interval is recommended prior to a fall harvest). I know from personal experience – via years of weighing yields of fall-harvested alfalfa at Miner Institute – that what looks like a really nice crop when it’s standing in the field makes a discouragingly small windrow and then a disappointing yield.

Each year Cornell University publishes the results of its alfalfa variety trials. In reviewing recent data – mid-September 2015 harvests of alfalfa established in 2013 and 2014 – in no case did any alfalfa variety yield as much as one ton of dry matter per acre. The averages were 0.64 and 0.71 tons DM/acre, similar to our yields when I managed the Miner Institute crop program. Therefore, don’t expect big yields from fall-harvested alfalfa, and before you head for the field with the mower, ask yourself: How much do I need this forage?