Could some help me figure out some nitrogen "fixers" for a planned rocky/sandy area I'm preparing for wildflower/grass bed? My whole lot is 1/4 acre and the bed runs from east to west down the center of my yard, and water pipes run north to south from the street under the bed to the house. I heard that Purple Prairie Clover's tap-roots can go 10 feet deep in search of water! I actually thought of using this before I read more info about it today. I'm afraid those roots could tap into the pipes for a drink! While on the subject are there any other deep rooting plants I should be avoiding?
Thanks,
Vera

There is a VERY long list of legumes that are native to North American prairies, but you will have to do a little research to find out what is native to your area. Some widespread prairie legumes are:

Wild indigos (Baptisia)
Leadplant and false indigos (Amorpha)
Bush clovers (Lespedeza)
Prairie clovers (Petalostemum/Dalea)
Sensitive pea, partridge pea (Cassia/Chaemacrista)
Sennas (Senna)
Lupines (Lupinus)

I have most of these species in my prairie garden -- not because they fix nitrogen, but because the are beautiful and diverse members of prairie communities!

froggy

Mycorrhizae are fungi that help ALL vascular plants (not just legumes) take up minerals, especially phosphate, from the soil.

The somewhat similar-sounding Rhizobium bacteria are found in nodules in the roots of legume-family plants, where they capture atmospheric Nitrogen dissolved in soil moisture, then convert it to usable form for the plant.

In addition to the nice list of legumes mentioned above that would work in your setting, several other plant families have species which can fix nitrogen, including the alders (not a good plant for your sandy area) and New Jersey tea (Ceanothus americanus) which is a highly desirable prairie plant.

i knew that NJ tea fixed N but i guess never thought that its not a legume. also maybe some ref. on this topic would be nice.

froggy

NJ tea isn't in the legume family. It's in Rhamnaceae...isn't that the buckthorn family?

But the fact is that neither produces enough fixed-N to account for all the nitrogen in the proteins and nucleic acids (and other chemicals) in the plants of prairies (and other ecosystems). The missing nitrogen-fixers are blue-green algae growing in soils and dead stems and leaves (duff). Blue-green algae are major sources, and they are promoted by simply having a prairie grow well. The dead roots, leaves, and stems (biomass) provides substrate and nutrients for the blue-greens. Sunlight provides the energy.

The textbooks are incomplete.

Froggy: The non-legume nitrogen-fixing plants have bacteria other than Rhizobium. I don't remember details -- a good account would require a careful review of botanical literature.