Interpreting Mojave Desert Soil though Native Plant Growth

Q. If anything, what can the different species of weeds tell someone about the soil conditions they’re found in. For example, do dandelions only grow in certain pH ranges or does puncturevine thrive only in certain sodic concentrations etc. etc.? I want to understand the most about my land via the plants that grow on it unassisted.

I apologize for the lousy picture. I took it from a slide I had made a long time ago. This is Lake Mead and showing the change in native plants (weeds) that occur with a change in soil moisture. Plants are very different closer to the Lake than further away due to less available soil moisture. As soil moisture changes, the plant communities change as well as their numbers (density) and sometimes even their height depending on the plants.

A. Which weeds are growing on native soil or disturb soils can tell you a lot. It can give hints about the chemistry of the soil and it will tell you a lot about its structure, if the soil has been disturbed or not, suitability for different plants and availability of water. 

I look at the type of weeds growing, the number of weeds and how tall they are. Wherever there is subsurface water there are a lot more plants per square meter and they are usually taller. Native soils high in phosphorus tend to favor those plants that flower more and produce seed. Crappy local native soils don’t grow much of anything. 

Dandelions for instance like disturbed soils, high phosphorus soils and they are very good at competition that’s one reason they can survive in lawns while common Bermudagrass does not. How the local plant community and the soil is managed influences which weeds grow. There are plants such as salt cedar which does favor growing in soils high in salinity but I’ve not seen a reference to sodic soils. That could be a question you could pose to Dr. Devitt. 

Some research questions I wanted to ask include different amounts of irrigation applied to a soil and how it influences native plant management and the value of soil amendments such as compost in influencing the management of native and exotic plants. To my knowledge none of those questions have been answered. Our soils typically are not classified as sodic soils but there are pockets (areas) of them in the valley. There are also pockets of high boron (a soil salt).