Alfalfa is a big crop in Pinal County, which goes hand in hand with another leading part of farm income, livestock.
In Arizona a typical yield of alfalfa is around eight tons per acre. It is important for the grower to know when it is time to replace an alfalfa stand in order to produce the most.
Different factors lead up to the decision to replace a stand, such as the cost of the stand, the hay price and how much the stand produces.
“Generally alfalfa can grow as much as it can,” said Ayman Mostafa, area agent in agriculture with the University of Arizona. “Different research has found that you can get the best year out of an alfalfa stand from about three to five years.”
In an article published by the University of Arizona Cooperative Extension, Fields Crops IPM Program, agronomy specialist Mike Ottoman gives an example of replacing a stand.
“Replacing an alfalfa stand with yields of 2 ton/acre less than a healthy stand will pay for itself in three years if the cost of the alfalfa establishment is $900/acre, hay price is $150/acre and harvesting costs are assigned on a per basis,” Ottoman wrote.
To determine how much a stand yields, the grower should go by the density of the stems rather than the plants because some plants have stems but do not contribute to the yield.
“The stems should be counted when about 6 to 10 inches tall,” Ottoman said. “Stands may need replacement regardless of average plant or stem density if plants are not uniformly distributed or if many bare spots exist.”
Data from the University of Wisconsin states that stem density is the best way to estimate yield potential regardless of the stand’s age. It is, however, just an estimation, and the actual yield will vary depending on fertility, water and other factors.
Weeds can pose a problem for the stand, but so can the alfalfa itself as the plant contains compounds that are toxic (medicarpins) to the seedlings. Affected seedlings can either develop improperly or it can lead to killing the whole plant.
“A newer alfalfa stand has less medicarpins than an older stand,” Ottoman said. “To avoid autotoxicity, delay seeding alfalfa into a field previously in alfalfa by at least two weeks after tillage or three weeks after herbicide-kill of the old stand.”
Ottoman does warn that a crop harvest after herbicide may result in poor quality.
The benefit to replacing an alfalfa stand is the establishment cost decrease, while the quality and quantity increases, which leads to an increase in hay price.