Alfalfa in some areas of Pennsylvania is experiencing water stress and the question of alfalfa management during this time is being raised. But before we discuss the management of water-stressed alfalfa, let's look at how alfalfa responds to drought conditions.
Alfalfa is commonly referred to as a drought-tolerant plant. During the onset of drought conditions, alfalfa will stop using carbohydrates for stem and leaf production and store those carbohydrates in the roots.
This provides high levels of root carbohydrates for long-term survival if drought conditions persist and the leaves become photosynthetically inactive.
However, alfalfa's ability to survive a drought does not mean that alfalfa will not show drought-related symptoms. Water-stressed alfalfa will experience decreased stem elongation and, in some cases, mature more rapidly. Leaf production is less affected by water stress than stem elongation. This results in higher forage quality of water-stressed plants than their unstressed counterparts.
To harvest or not to harvest?
The primary criterion influencing the decision to harvest drought-stressed alfalfa should be based on the cost of harvesting and the value of the forage. The alfalfa plants may look weak and severely stressed during a drought; however, harvesting at the stage of plant development when you would normally harvest is recommended as long as adequate alfalfa is present to justify the cost of harvesting.
The plant, even though it may be very short, will already have stored more than enough root carbohydrates to ensure survival if the drought persists or ensure regrowth if sufficient rains remove the drought conditions.
Emergency forages in dry years
Because of the drought conditions and the resulting less than anticipated forage growth, I'm sure you have been asked what alternatives farmers have for forage production once the drought breaks. Here are some suggestions and sources for more detailed information.
Farmers who graze:
These farmers may not have been able to produce sufficient hay/silage to get through the winter. For them, an option is to plant some forage crops in August (hopefully it will be raining again by then) that can provide grazing this fall and allow hay/silage to be made from their traditional pasture land. Following are some options:
• Forage Brassica (e.g. Rape or turnip)
• Small grains (e.g. wheat, barley, rye, or triticale)
Farmers who don't graze:
Most of the crops that could be planted at this late time and produce some forage are better suited for harvesting as silage rather than hay. These crops are listed below.
• Summer-annual grasses (e.g. sorghum, sudangrass, sorghum-sudan hybrids and millet).
In some areas, these crops will not mature before cool fall weather and frost stop their growth. In a situation where the drought-damaged corn has been harvested in July, then these crops may be the only option because of herbicides used on the corn and the greater potential for carryover due to the dry conditions.
• Small grains (oats and rye, use taller varieties). Small grains should be planted as soon as possible and harvested for silage in the milk to soft dough stage. Generally, the milk stage is less desirable than the early dough stage because it is less palatable and studies indicate that animal performance may be reduced.
Moisture levels between 60 and 70 percent are best for ensiling small grain silage. Small grain silage below 60 percent moisture is difficult to pack and excessive heating and nutrient loss may occur.
In addition, making sure that the theoretical length of cut is less than 3/8 inch is important with small grains because some stems are hollow and filled with air. Minimizing the length of the chopped material will help minimize silage heating and maintain forage quality.
In a Penn State study conducted at the Landisville (Lancaster Co.) Research Center, small grains yielded more than sorghum-sudan grass when both were seeded on August 5.
Yield and TDN of four crops seeded on August 5
• Corn (harvest on 10/5) – 1.5 ton per acre and 61.2 percent TDN
• Sorghum-sudan hybrid (harvest on 10/5) – 1.6 ton per acre and 61.2 percent TDN
• Oat (harvest at soft dough) – 2.1 ton per acre and 75.8 percent TDN
• Rye (harvest at soft dough) – 2.1 ton per acre and 68.4 percent TDN FG
—From Penn State Field Crop newsletter, Vol. 12 No. 19
Dr. Marvin Hall
Forage Specialist
Penn State University
