A Look Back at a Hot, (Mostly) Dry Summer

In the April 2016 issue, we noted that some weather models predicted hotter-than-normal conditions in the Northeastern U.S. This came to pass, but what the models didn’t predict was the moderate to severe drought conditions that affected much of the region.

Precipitation varied widely from almost normal in northeastern New York to bone dry in other areas. One farmer in northern New York reported that he didn’t have any measurable rainfall between June 5 and Aug. 13, and New York agricultural officials reported it was the most serious drought in that state in at least 20 years.

Rainfall (actually soil moisture) and air temperature affect crop yield and quality. Hot weather decreases crop quality and increases the rate of maturity. But what’s really bad for crops is the combination of heat and excess soil moisture.

Despite many days when the temperature exceeds 100 F, Arizona farmers grow excellent quality alfalfa with sufficient water, usually provided by irrigation. High temperatures in the absence of excess water can result in good yields and high quality. Summers in the southeastern U.S. are also hot, but there’s usually an abundance of humidity and rain. This is terrible for anyone trying to grow alfalfa, which is why this species isn’t nearly as common in the Southeast. High humidity increases disease incidence above the soil surface, while saturated soils also take their toll.

Lignin, part of a plant’s cell walls, is derived from the Latin word meaning “wood.” Lignin is about one-third of the dry weight of wood and is responsible for strengthening the wood in trees. Lignin is also present in crops; without lignin, alfalfa and corn plants would be lying flat on the ground Although a little lignin is essential, too much is bad because it’s indigestible by dairy cattle and other ruminants.

The combination of heat and wet soils affect forage quality, but in the case of alfalfa and other forage legumes such as clover and birdsfoot trefoil, the main impact is on the stems, which contain much of the lignin found in the plant. The leaves don’t have any structural function in the plant so they contain very little lignin. Therefore, alfalfa leaves aren’t much affected by the weather conditions that can wreak havoc on the stems. Hot weather increases the leaf-to-stem ratio of alfalfa, so while yields may be lower, the forage quality of the entire plant may be similar to alfalfa grown under more favorable conditions. As temperatures rise, the difference between the low and high lignin parts of the plant increase. Therefore, whether it’s a hot summer or a general warming of the climate, it’s important to manage alfalfa to retain as many leaves as possible. Just as the low-fiber grain in corn harvested for silage is Mother Nature’s “crop insurance,” so are the leaves on an alfalfa plant.

Managing alfalfa for high leaf retention

Farmers can take two steps to retain a high proportion of alfalfa leaves from mowing through baling or ensiling. The first is the type of mower-conditioner used, rollers or impellers (also called flails). Rollers create a crushing action, while impellers have a stripping action. Their use depends on the species of hay crop. Research in the U.S. has found when alfalfa is conditioned with an impeller conditioner, there’s a small increase in leaf loss compared with rollers.

Italian researchers found that alfalfa conditioned with an impeller resulted in alfalfa hay that was about 1 percent lower in crude protein than the same crop conditioned with rollers. The University of Wisconsin reported similar results: Impellers result in 2 percent to 3 percent higher field losses with alfalfa, and all of these losses are leaves, so quality is reduced significantly. Roller conditioners are also reported to result in a faster drying rate of alfalfa.

I’m not opposed to impeller conditioners; in fact I think they do a superior job in forage grasses. That’s why they’re so popular in Europe, where there’s a lot of intensively managed grass but not a lot of alfalfa. While the drying rate of alfalfa is slower with impeller conditioners, the drying rate of grasses is higher. Each type of conditioner has its place.

The second step in alfalfa leaf retention is windrow management, specifically the width of the mowed windrow. Wide windrows dry the alfalfa more evenly than the same crop managed in narrow windrows. There’s been plenty of research on this but we still have a long way to go since many farmers are still managing alfalfa in 3- or 4-foot wide windrows. Consider what must happen in these narrow windrows for the entire windrow to average 35 percent to 45 percent dry matter, which is the normal range in dry matter contents we usually see on farms.

The alfalfa in the middle of a narrow windrow dries very slowly – perhaps not at all for many hours after mowing. Meanwhile, the alfalfa on the top continues to dry until the leaves are bone-dry. When the alfalfa is chopped, these leaves shatter and either fall directly to the ground or are pulverized by the chopper knives and blow back onto the field instead of into the self-unloading wagon or forage truck. This can result in a loss of several points of crude protein between stem and silo.

With careful crop management, we can make the most of the weather that comes down the pike.