For forages to produce in drought-like conditions, they must be carefully managed, says Dan Undersander, University of Wisconsin-Extension forage agronomist.
“Good management of moisture-stressed forages will increase maintenance of a good stand and reduce the loss of forage production,” he says. “Management of alfalfa, grass hayfields and pasture each has some special considerations.”
An alfalfa grower with a drought-stressed crop has to decide whether to cut or not. Drought-stressed alfalfa flowers at a shorter height than normal; it should generally be cut for yield and not to encourage regrowth.
“New growth won’t come from the part of the plant that has flowered, but will come from new shoots from the crown of the plant when sunlight stimulates new bud development,” Undersander says.
Because of the way alfalfa responds to drought stress, cutting only encourages regrowth if the uncut crop shades alfalfa crowns. “If plants are tall and thick enough to make for a decent harvest, then go ahead and cut,” he adds.
“Cut drought-stressed alfalfa at 50-100% flower. If you can see through to the crown of the plant, don’t cut. Sunlight is reaching the crown and new buds will develop. If the plants are 10” or less with flowers, let them regrow on their own without clipping. The regrowth will come up through the short flowering plants and produce more yield. Also, farmers should remember that alfalfa that is 8-10” tall will be very high in quality even if it ripens to have seed heads because of the large amount of leaves in relation to the amount of stem.”
Rory Lewandowski recommends harvesting alfalfa toward 100% bloom to allow the plant to build non-structural carbohydrate reserves.
The Ohio State University Extension ag and natural resources educator says growers who cut alfalfa in drought conditions should cut it at the normal height, which will allow them to gain optimum yield. But some growers might find that there isn’t enough quantity to make a machine harvest cost-effective.
“In those cases, it’s much more economical to let livestock salvage a low-tonnage yield by grazing the alfalfa.” Take precautions against bloat, however, he adds.
Don’t mow drought-stressed new seedlings until August, unless you need to control weeds. “But if a new stand is pure alfalfa, let it go,” Undersander says.
Plants respond differently to drought stress. While legumes such as alfalfa increase in quality, grass quality decreases when it gets dry. Because grasses put out more stem and heads, producers should adjust livestock rations accordingly, the Wisconsin specialist says.
Fertilize grass pastures with 40 lbs nitrogen/acre and 5-10 lbs sulfur/acre in early August; it will mean an additional 1-2 tons/acre of forage and an extra month or two of grazing, he says.
If grazing corn or sorghum-sudangrass, watch for nitrate toxicity – especially if growth was reduced to less than 50% of normal and/or high levels of nitrogen were applied. Freeze or have forage samples analyzed immediately for nitrate levels, as nitrate will decline in tissue over a three- to four-hour period. If above toxic levels, hay or other forage should be fed in mornings and corn grazed a couple hours in the afternoons.
For detailed information, check this University of Wisconsin factsheet.