Hello,

I do know with certainty that gypsic horizons have a bad drainage capacity. So, I would use a C or D group for Gypsic xerosols depending what you consider as C or D.

By the way, I guess that Calcic yermosols may be in C. I am not sure of this point.

Anyway, you can observe run off and drainage in field and in lab depending your project´s requirements- e.g. It might be enough just estimating the group.

I hope this information will be useful for you.

Regards,

Jesús

It looks as if you are using the FAO/UNESCO soil map of the world with the FAO legend. On the map there are texture indications (1)= sandy (2) = loamy and (3) = clayey which may give you additional info to derive the drainage class. In the absence of other information I would consider Gypsic Xerosols imperfectly drained and Calcic Yermosols moderately well drained. 

Thanks for all,these are valuable comments,plz I want more precisely info ,it is urgent for my project.

Rrgards

In my opinion you must mainly considere the depth of the soils, the textural class (with specially consideration to % clay) and the type of bedrock under the soil. Slope steepnes might be also helpful. 

Low soil depth (< 30-40 cm; A C horizons), high clay content and impervious bedrock means a D hydrologic group, moreover if slope is steep. Stoniness also can promote surface runoff. These soils have very bad drainage conditions.

If soil is deeper (> 30-40 to 60-80 cm; A (B) C or A B C horizons), moderate clay content, the bedrock is also deeper and slope steepness is moderate, with no much stoniness you can considere a C hydrologic group.

Progresive more soil depth, less clay and much sand content, slow steepness and stoniness drive to B, and A hydrologic groups.

If you can study soil infiltration rate, you would obtain a better result, but with soil data observations could be enough.

For more information:Part 630 Hydrology National Engineering Handbook. NRCS. USDA. Chapter 7: Hydrologic Group Soils. 2007.

In order to answer your question, it is important to know some data as slope, horizon's depth, and texture / granulometry. Regarding the clay content, it is important the percentage and also the type of clay to calculate the infliltration rate / water retention capacity / maximum soil mixture retention, etc...  

Furthermore, you can use the "runoff calculator page":  http://www.esf.edu/ere/endreny/GICalculator/SoilInstruction.html

Group A is sand, loamy sand or sandy loam types of soils. It has low runoff potential and high infiltration rates even when thoroughly wetted. They consist chiefly of deep, well to excessively drained sands or gravels and have a high rate of water transmission.

Group B is silt loam or loam. It has a moderate infiltration rate when thoroughly wetted and consists chiefly or moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures.

Group C soils are sandy clay loam. They have low infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water and soils with moderately fine to fine structure.

Group D soils are clay loam, silty clay loam, sandy clay, silty clay or clay. This HSG has the highest runoff potential. They have very low infiltration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface and shallow soils over nearly impervious material.

http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17757.wba