I would like to know if there's a way to ensure every sample has the same initial conditions when performing soil experiments. The samples are going to be enclosed in containers of 13 cm height and 18 cm width.
Is there a soil sieving and packing procedure to ensure equal moisture distribution?
This is very interesting. First, there must be some discussion about this in the literature about soil moisture probes since they basically conductivity as a function of soil moisture. Second, I think that unless you have a reason to test soil just collected from the ground, you'd need to "treat" all the samples prior to testing.
Since you don't specify any limits on the initial conditions, I suggest you might try starting by saturating the samples and then taking readings as they drain to field capacity and dry further. If you kept the samples in a temp and humidity controlled room (or container), the process would be repeatable.
The one "problem" I see with my suggestion is that the initial quantity of moisture in the soil at saturation will differ based on soil characteristics. However saturation and field capacity are soil-relevant properties, so this might actually be a benefit.
The only other way I can think of is to oven dry each of the samples, then add a measured volume or mass of water to each sample. Then you could mix the sample by shaking in a larger container for a specific amount of time. Basically - as long as you define the steps you take to make your samples, it should be repeatable.
