BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Medicago sativa | Alfalfa 



GENERAL BOTANICAL CHARACTERISTICS : 
Alfalfa is an introduced perennial herb. It can reach 24 to 35 inches
(60-90 cm) in height, with 5 to 25 or more erect stems per plant, which
arise from a narrow, woody crown.  It has a deep taproot, 10 to 17 feet
(3-5 m) in sandy soils, and 23 to 30 feet (7-9 m) under favorable
conditions [50,110].  Many older plants have roots up to 63 feet (19 m)
deep.  A record depth of 130 feet (39 m) was reported in the roof of a
mine tunnel in Nevada [39].  Varieties are available with different root
system types:  taproot, branching roots, rhizomatous, and creeping
(horizontal rootstocks that give rise to independent plants) [94,110].
The roots form nodules in association with Rhizobium spp. bacteria,
which fix atmospheric nitrogen.  Alfalfa also has endomycorrhizal
associates [27].

Saponic glycosides are found in alfalfa, which are suspected of
contributing to bloat in ruminants [29].


RAUNKIAER LIFE FORM : 
   Hemicryptophyte
   Geophyte


REGENERATION PROCESSES : 
Alfalfa is obligately insect pollinated.  Bees are the major insect
pollinators of alfalfa.  Leafcutter bees (Megachile rotundata) and
alkali bees (Nomia melanderi) are efficient pollinators.  Honeybees
(Apis mellifera) also visit alfalfa flowers but are not as efficient for
pollination [50].

There are approximately 200,000 seeds per pound (441,000 seeds/kg) [50].
On average, 45 to 73 percent of seeds are hard and require scarification
for efficient germination [116].  The percentage of hard seeds varies
with the area producing the seed.  In warmer climates, such as southern
California, the number of hard seeds is around 20 percent; in cooler
areas in Washington, the amount of hard seeds is around 40 to 50
percent.  Similarly, lower altitude areas have lower proportions of hard
seed than corresponding higher altitudes [43,25].  The most common
method for scarification is mechanical means [93].  Hard seeds became
permeable to water after 4 minutes at 219 degrees F (104 deg C) [90].
Radiation treatments were also effective in rendering hard seeds
permeable; radio frequencies were found to be the most efficient [113].
Busse [10] found that extreme cold also efficiently releases seed for
water uptake.

Seeds can be long-lived.  Seed stored in unheated sheds attained 81
percent germination after 19 years [54].  In soils previously unoccupied
by rhizobial nitrogen-fixers the seeds need to be inoculated with
Rhizobium bacteria for root nodule formation nitrogen fixation [40,110].

Seedlings of alfalfa are not very aggressive, but established plants are
very competitive, especially the creeping rooted varieties [50].


SITE CHARACTERISTICS : 
Alfalfa is well adapted to a wide range of climatic and edaphic
conditions, but it does best in deep, loamy soils with porous subsoils.
It is intolerant of flooding, waterlogging, or poor soil drainage.  It
requires large amounts of lime.  Alfalfa does not do well on acid or
very alkaline soils, although it will tolerate some alkalinity.  It has
fair salt tolerance [47,50,110].  It is naturalized to roadsides, old
fields, and waste places [37].

Alfalfa will tolerate drought and is known as a good producer in dry
years.  It needs about 12 inches (30 cm) of precipitation per year on
good soils, 14 inches (36 cm) on less favorable soils [111].  Irrigation
greatly enhances productivity in dry climates [50,106].

Regional elevation distributions are as follows:

	Utah		4,500 - 8,600 ft     (1,364-2,606 m)
	Colorado	4,800 - 8,500 ft     (1,455-2,576 m)
	Wyoming	        3,700 - 8,800 ft     (1,121-2,667 m)
	Montana	        3,400 - 6,600 ft     (1,030-2,000 m) [27]
	Idaho             up to 8,000 ft     (up to 2,424 m) [110]

Alfalfa does poorly at higher elevations [53,109].


SUCCESSIONAL STATUS : 
Obligate initial community species

Alfalfa is probably not shade tolerant.  In a study of alfalfa planted
on chained aspen parklands, alfalfa cover decreased steadily as
overstory canopy increased [7].


SEASONAL DEVELOPMENT : 
Alfalfa is generally considered a cool-season species, although
succulent growth can take place through the summer.  Growth begins early
in the spring [84,119].  Flowering takes place from May to October,
depending on latitude [37].

Some reported dates for anthesis are as follows [27]:

	Utah		June-August			
	Colorado  	May-October
	Wyoming   	June-September
	Montana   	June-August
	North Dakota	June-September 

Alfalfa can remain green throughout the summer, and dies back in the
fall with heavy frost.  There is a critical period in early fall for
transfer of food reserves to the roots [50].

Related categories for Species: Medicago sativa | Alfalfa