The cost of harvesting and value of the forage should be the primary determining factors when it comes to deciding whether or not to harvest drought-stressed alfalfa, according to Marvin Hall, Penn State University forage specialist. He says if adequate alfalfa is present to justify the cost of harvesting, producers should consider cutting the crop at the normal time.
Hall points out that alfalfa is commonly referred to as a drought-tolerant crop. During the onset of drought conditions, alfalfa stops using carbohydrates for stem and leaf production and stores those carbohydrates in the roots. This provides high levels of root carbohydrates for long-term survival if drought persists and the leaves stop performing photosynthesis. However, alfalfa's ability to survive a drought does not mean that it won't show drought-related symptoms. Stem elongation declines and in some cases the plants mature faster. Leaf production is affected less than stem elongation, so forage quality may be higher than normal.
Alfalfa plants may look weak and severely stressed during a drought, but producers need to make the final harvesting decision based on economics. Hall indicates that, even though the plants may be very short, they will already have stored more than enough root carbohydrates to ensure survival if the drought persists, or to support regrowth if sufficient rains remove the dry conditions.
Source: Penn State University.