Question
I want to plant a cover crop to improve my clay soil on 1.5 acre home in NE Nevada before I plant a lawn.  I have read articles on Alfalfa but am concerned about alfalfa coming up in my new lawn.  1st, Is that a concern? and 2nd if I do use Alfalfa will is grow in my NE NV clay soil.

Answer
Alfalfa is a Cool season perennial legume that goes dormant in the Winter.  If you sow it in Spring (or Fall) it will grow for several seasons if you let it.

Initial growth is fairly weak and vulnerable.  Once it gets hold, it's a tough customer; few neighboring Weeds stand a fighting chance.  Alfalfa is tough enough to stand up to them.

The first best thing about Alfalfa, however, is the way it reaches deeeeeep down into the Soil to bring up nutrients from way down under.  Alfalfa roots typically grow 12 to 15 feet long.

The second best thing about Alfalfa is its Nitrogen-fixing work.  You don't need Nitrogen if you've got Alfalfa growing in your Soil.

Univ of Colorado Coop Ext devotes a full page to growing Alfalfa:

www.ext.colostate.edu/pubs/crops/00537.html

They point out that 'Phosphorus is the most limiting nutrient for Alfalfa production'.  Alfalfa also has a 'high sulfur (S) requirement, which results in occasional deficiencies when it is grown on soils low in organic matter.'  Remember that!

If there's anything that might make it hard to grow Alfalfa in Nevada, I would guess it's going to be ways to water 1 1/2 acres of Alfalfa in the hot, dry Sun.  I recall hearing some farmer discussions about 'sub-Soil irrigation' but I don't see this is going to be an option for you.  Hopefully you have a plan for not only your Alfalfa, but your Grass at some point, because watering Grass is not going to be cheap in years to come.  But that wasn't your question, was it?

So back to you.

Colorado's Agriculture Dept wrote the book on growing Alfalfa.  Mainly because Alfalfa happens to be their most valuable forage crop; annual sales hit around $233 million.

Pesticides may not directly target Legumes.  But they will destroy them.  So don't use them.

Fungicides are toxic to Rhizobia bacteria -- the secret to Nitrogen production in Legumes like Alfalfa.  So don't use them either.

One critical micronutrient for this Nitrogen fixation is Molybdenum.  Sandy Soil, acidic Soil with a pH reading below 6.0, or a Soil with high readings of Manganese and Iron generally test low for Molybdenum.  Your Clay Soil WON'T have that problem.

Clover, Alfalfa, Wheatgrass can be a Green Manure --  specialized Cover Crops that put nutrients and organic matter into your soil and make space for Oxygen-loving microbes.  Alfalfa fixes up to 150 lb of Nitrogen for each acre of land annually; Clover and other Legumes, 50 to 125 lbs.

Sow your Green Manure this Spring, and then all Summer long, mowing to keep it from flowering and going to seed.  In the FALL, September 2008, mow the Green Manure down and lightly till it in.  Waiting for the Cool Autumn weather ensures a mature Alfalfa stand with a good, solid Carbon:Nitrogen ratio and a nice dose of Humic Acid. Add Lime as determined by your Soil test, and promptly sow your Grass to retain all that delicious Nitrogen.

That's what I would do.