You can use the LOS method. I send you an attachment of the theory and equations and one report with application in several countries based on european project

And the report is in this file

Does your soil database in humic substances contents?

http://iris.lib.neu.edu/aes/vol6/iss1/1/

If you have good soil data base, and a good comprehensions of the association of such soil properties with land quality variations, you have most of the work done...It would useful to know the objective of the study? Then, you should evaluate soil properties that are affected by management or factors that you are interesting to evaluate. Using geostatistical tools maybe you can produce a map integrating the different soil variables into a GIS porgram or similar (?). The important issue to be addressed is which soil property has an strong relationship with land use and/or land degradation under the site-specific conditions of the study area (e.g. SOC, SOC light fractions, biological and/or biochemical variables, etc.).

there are good geo-spatial tools, such as SURFER by Golden Software and MapInfo by MapInfo Inc. Using these will allow to conduct trend analyses as well as overlap with land use features. Hope this help. Irina Cech.

Interesting Irina!. Good options.

Thanks, Martin. Nice thing about three approaches that one can use 2D 3D options, which is great when communicating results to the public. Very visual. After that one can use cluster statistical analyses, which we normally do, but that is a bit too involve and may be sufficient just to stay with the description of a spatial trend.

Try GIS. I recommend ArcGIS spatial and geostatistical tools (e.g. Combine…). Good luck!

I also used ArcGIS in the past for the same purpose and, once you are familiar with the software, it is very powerful and informative. But, as mentioned above, you will first need data on your soil to feed the software. If you do not have data yet, I would advice you to first choose how you will interpolate your data before sampling, this will help you in designing an efficient sampling.

The SoLIM software has a number of tools designed specifically for soil mapping. More information here: http://solim.geography.wisc.edu/software/index.htm

Select specific soil quality indicators that are relevant to your research objective (s). you can then carry out soil survey of few points to gather information on soil properties of the area. Interpolation method can be used for prediction of soil properties of unsampled area using ArcGis.

My expierience of field work, interpoliation methods based on field work data are not enough for soil analysis. You can used sattelitte image and create map using traning site like land use land cover superwise classification maps. (1) To select some criteria for example, you take rocky land training sample for thin soil, scrub land training sample for shallow soil, dense forest for high soil depth, barren land  indicate shallow to thin soil, agriculture land also indicate moderate to good soil depth (2) You can incresed the accuracy using NDWI or SWI. These index are indicate soil moiture level. Generally high soil moiture indicate high soil depth, low soil mouiture indicate low soil depth (for details Ref my paper:Use of IRS P6 LISS-IV data for Land Suitability analysis for Cashew Plantation in Hilly Zone) Plz dont forget some factores influence on soil moisture i.e texture etc. (3) after interpoliate the field work data for reference. (4) Verify accuracy assessment (5) Last combine the above three methods, you are getting best map of soil depth. Using this methods  soil depth map accurcy will be more time interpoliation map..