Ian is quite right in his comments, but supposing the soil model consists of two simple layers, then the problem becomes one of interpolation method.
The interpolation method then needs to be suitable for the intended use of the final product. What resolution /scale are management activities going to be carried out on?
What scale was the data gathered on?
What is known scale of variation of the features of interest?
Soil depth is seemingly benign term. But it can the depth of a layer which is only defined by pH or soil colour. These features may have variation on a very fine resolution, always moreso than the scale of sampling. But the management action might be only applied on a whole patch, encompassing a great number of sampling points.
So explore these issues a little and the apporpriate methodology and tools will reveal themselves.