How to convert FAO soil class into USDA soil class?

Hi,

FAO and USDA (and other systems) are not readily interchangeable, however there are more or less equivalents. I hope these tables and the attached pdf would help.

Hi dear Koffi; 

Can you clarifiy what do you want to convert because you mention textural class for USDA system , and Soil order for the FAO classification? 

Hi,

soil names from your FAO map and textural classes are not the same. It will be possible to find some "texture windows" from the soil name but it is time consuming and need expert knowledge in the FAO soil classification system.

I.e  Vertisol are soil with high clay content, consequently the texture classe of the soil is clay on average. Often Podzols are sandy, or loamy sandy.

But, all the other soils can cover more or less all textural classes.

What are you modelling?

Cheers

Dear Mr Jerome Juilleret, Thank you for your answer. I am modelling groundwater recharge. Thank you you

Dear Yacine, I have a soil types described as Dystric Leptosols, Eutric Gleysols, Eutric Leptosols, Eutric fluvisols, Ferric Lixisols, Gleyic Lixisols, Haplic Lixisols, Haplic Luvisols, Lithic Leptosols. I want to find the corresponding texture. Thank you

Dear Koffi,

For your model (what is the model?):

Leptosol (either Dystric, Eutric or Lithic) are thin soil, so no real water storage.

Lixisols and Luvisol (either Ferric, or Haplic) are soil with an argic Bt horizon consequently the texture is finer than sandy loam and should have at least 8% of clay. But, this is a minima, depending of the texture of the overlying horizon, the texture of the argic Bt horizon can be very clayey. As already wrote before, it is not possible to obtain a texture only from the soil name.

In a hydrological point of view your Gleyic Lixisols are soil  saturated with permanent water table the majority of the year.

Regards

Dear Jerome, 

The model is WetSpass. Thank you for your help.

I agree with the responses above, but I find it strange that you only have FAO soil names without texture indication. Even the FAO Soil Map of the World had texture classes, albeit broad ones. Could you specify what soil map you are using? the Harmonized World Soil Databasev1.2 contains estimates for clay, silt and sand and has a relatively high resolution for large regions. The SOTER databases from FAO and ISRIC also may be of help.   

Thank Mr Nachtergaele, I got this data from a colleague. So I will check on this sources that you mentioned.

Hi Kouakou,

interesting, I am working also on this topic. I am modeling groundwater recharge using SWB code (USGS). My soil map data has not only the soil type but also other  information, in which texture classes are most important. I think for the name, you get only hydraulic group. You definitely have to have texture information. Otherwise, you can use it from FAO map but keep it mind the map is in 1:5.000.000 scale, I think.

Hi everyone, I'm working on a flood vulnerability index based on GIS tools, and I need to build a layer of soil composition which I can then link to a higher or lower runoff potential... For my case study, I have only found a map of the type of soils using the FAO classification, but this doesn't give me an idea of how permeable or impermeable a soil type is.

Anyone has an idea about how can I translate FAO classification to the actual content of clay, sand or silt?

Hi Luisa,

the problem is that you will use a "agro-pedological "information (FAO map) to asses the surface runoff potential, not an easy task.

In fact the FAO legend (replaced  by WRB) classify soil based on type of diagnostic horizon and depth of the diagonstic horizon, (but also other diagnostic features, but let's be simple). So , on your FAO map, the cartographic unit with the soil name does not give you (most of the time) the depth of the diagnostic horizon.

Furthermore, most of the time the diagnostic horizons are not directly link to one texture, but with experience, the FAO legend  and work you can find it.

The problem is that you can have a big difference in texture between the topsoil and the subsoil , the latter can be your diagnostic horizon. As an exemple, in a Luvisol characterized by a clayic horizon , the topsoil can be clay, silt or sand. Do you follow me.

For other soil you can find an easier relation. Like vertisol, in this case the soil is clayey, for Podzol it's sand.

What are the main soil in your catchment?

Cheers

 http://www.fao.org/soils-portal/soil-survey/soil-classification/fao-legend/key-to-the-fao-soil-units/en/

I am working on watershed management for Shivalik foothills,INDIA. My study area constituting Regosols ( Eutric Regosols (Re) ) soil with three different texture classes. How do i classify this in Arc-SWAT as soil map showing only one series (Re53-2b) FAO soil unit for whole watershed?

In NBBS-LUP three Mapping unit soil Taxonomy are: 001 Typic Ustorthents 003 Typic Ustorthents 005 Typic Ustorthents

001 is loamy skeletal soil with loamy surface on very steep slopes of shivalik hills,moderately shallow to Moderately deep moderately eroded and moderately gravelly, excessively drained 003 is calcareous, sandy soils loamy skeletal soils with loamy surface on Moderately steep slopes with severe erosion and moderate stoniness moderately shallow 005 is is loamy skeletal with coarse loamy soil with loamy surface on very steep to steep slopes of shivalik hills,moderately shallow to Moderately deep moderately eroded and severely gravelly, excessively drained

See the link:

https://www.agvise.com/educational-articles/soil-texture-classification-which-system-do-i-need/

Hi Csaba Csuzdi what paper is the first table (FAO_USDA conversion) from?

Many thanks

Dear Lucy,

It is from a classroom PPT, I do not find the paper at the moment. However here you are an other one with reference.

Have you checked

how do i convert the soil classification by FAO into different hydrological soil groups(i.e A,B,C and D ) for determining curve number?