Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: soil survey

Read About Your Soil

Here is a really good introduction to the use of the on-line Soil Survey from USDA.  Maybe it is easier to follow than blogs I have posted in the past.

WASHINGTON — “Soil don't get no respect,” Rodney Dangerfield might have said (but didn't). Perhaps you know your state bird or flower, but do you know your state soil?

Well, in recent years soil has begun to get more respect. Since the celebration of the Soil Survey Centennial back in 1999, each state has been given its own official state soil. It was in 1899 that the U. S. Department of Agriculture started its survey of all the soils in the country.


You might wonder what a “soil survey” really is. Isn't it all just dirt — some perhaps stickier, or redder or deeper — that lies beneath forest, meadow, farm, home and garden?

There you go again. Not enough respect.

In fact, soils are distinctive, as different from each other as robins are from blue jays. These differences are hard to appreciate, of course, because soil is mostly underground, hidden from view. But if you were to dig some holes a few feet deep and then look carefully at their inside surfaces, you would find that soils are made up of layers of varying thickness, called horizons. One soil might differ from the next not only in the thickness of its horizons, but also in their appearance and feel.

Horizons might be as white as chalk, as red as rust, or as dark brown as chocolate. A horizon might be cement-hard, gritty with sand, or stuff for sculpture. And if you were to tease the dirt along one edge of the hole so it falls away naturally — wow! — each horizon would reveal its particles clumped together in arrangements like plates, blocks or prisms. Such information, and more, has allowed soils to be classified, much as birds, flowers and other living things are.


Modern soil classification goes back only a few decades, when all the world's soils were grouped taxonomically into a dozen “orders.” Differences among orders reflect the formative influence of a particular combination of climate, plants and animals, topography, time and original rock material.

Just as all vertebrate animals are huddled together by biologists into smaller groupings (mammals, say) and those groupings into still smaller ones, so each soil order is divided and subdivided to include more distinctly different soils. At the end of the dividing and subdividing, you end up with a “soil series” identified with a proper name — like the Haven series in my vegetable garden, for example.


A particular soil becomes an official state soil by being widespread within the state; being distinctive chemically or physically; having some degree of name recognition; and, of course, getting a legislative stamp of approval. Examples include soils like West Virginia's Monongahela soil, Texas' Houston Black soil, California's San Joaquin soil and New York's Honeoye soil.

The job, now, of these “ambassadors” of the benevolent underworld is to rekindle awareness of soil's value as a natural resource that can only be renewed very slowly. Soil provides food, shelter, clothing and more, yet it is being lost at alarming rates to everything from blacktop to erosion.

Out in the garden this spring, dig a hole deep and wide enough that you can see and appreciate at least some of the various and distinctive horizons.

Then, if you want the name and a detailed description of that soil — or any soil — look at the maps and descriptions in the Soil Survey Reports issued by the U. S. Department of Agriculture, Natural Resource Conservation Service (NRCS). Search online for “soil survey nrcs” and you'll find links to soil maps for counties throughout the U.S. Or go to the link to “web soil survey.” At this site, you can type in a street address around which you “draw” your area of interest (AOI). The site will delineate the names and descriptions of soils within that AOI.

And of course this is available as an app at:


soil weathered from rock
soil weathered from rock

Posted on Monday, January 22, 2018 at 6:19 AM
Tags: mapping (1), NRCS (1), soil (25), soil survey (3), Soilweb (1), survey (3), USDA (4), web (2)

Where is Avocado Root Rot Lurking?

So where is the highest potential for avocado root rot in California?  It turns out that the Natural Resource Conservation Service has taken the soils maps that have been generated for use by growers, engineers, planners and others over the years and used the data to rate soils for their sensitivity to root rot conditions.  In many cases the county-based maps have been updated with new information, as well.  It is now much easier to see where root rot would be more likely.  The two major soil characteristics of soil texture and depth and how they affect drainage are the major parameters used to assess the root rot hazard.  The soil surveys for years were only available in printed form, and then became available online about 2005.  Just recently the added feature of identifying “root rot” soils was created. Now at the touch of a button, maps of where these soils are found are available.  It looks like all California counties can be viewed from an avocado root rot hazard, even though avocados may not be grown in that climate, like Humboldt, but who really knows what can grow there.  Soils that are conducive to Phytophthora root rot for avocados, would also be conducive for root rot in other plants species, as well.  So, this information is helpful for identifying where rhododendrons or other susceptible species might have problems, as well.

Of course, this is just the first step in assessing the potential for root rot.  Irrigation management is critical for creating root rot conditions that can occur even in soils that are not conducive to the disease.  So, a soil identified as having a higher potential for root rot does not mean you cannot plant an avocado in it.  The key is water management and how the tree is planted and how that soil is managed.

So, go to the Web Soil Survey:


Click on an Area of Interest (type in California and your county or even your address)

Once you have a map of your general area, use the tool at the top of the map to delineate the area you want to know more about 

Then click on “Soil Map” tab and you will see the map polygons or soil units for that area

Then click on “Soil Data Explorer” tab to get “Suitabilities and Limitations Ratings” on the left side

Click on “Land Management” and there is “Avocado Root Rot Hazard”

Click on “View Rating” and the map will appear with colored units showing root rot hazard along with a chart showing the root rot hazard of the different soils in the map.

Wow.  Watch out for those dark areas.


Posted on Monday, July 24, 2017 at 5:59 AM
Tags: avocado (287), cinamomi (1), citrus (335), Phytophthora (23), root rot (21), soil survey (3), soil types (1)

Soil Information

Historically if you wanted to know what soil type and the description for it, it was necessary to go to the library, NRCS office or Coop Extension office to find the soil survey.  It is a book out of print now, but it has maps with outlines of the soils of that county and the descriptions that characterize those soils.  The USDA put the Soil Survey online about 10 years ago

and it is great unless the internet goes down. 

Toby O'Geen at UC Davis has taken the same information and repackaged it so that it is easier to use

Try it.


Posted on Wednesday, November 20, 2013 at 6:49 AM
Tags: information (4), map (2), online (1), soil (25), soil survey (3), survey (3), web (2)
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