Christien, you need to standeradise  the percent WHC at different intervals of time under ambient conditions. While doing so, you analyse your soil at different time intervals, analyse the soil for WHC and simultaneously microbes. This will give an idea to what an extent soil microbes will not be affected with change in WHC, without changing any of the soil properties, so that you get a clear behavior of soil .  

Thanks parameshwar. What technique should I use to analyze the WHC? Drying the soil after taking gravietrics?

Hi Christien

You need to determine the current moisture content and the  WHC on a separate sample of the same soil (you don't need very much) and then adjust your soil with the microbes in it to the 50% mark. Take a subsample to do gravimetric moisture content on drying at 105oC. On another subsample do the WHC determination.  This method is used by soil ecologists to standardise incubation conditions when looking at soil processes. example is at

http://wrightlab.weebly.com/methods.html

scroll down and look for soil carbon mineralisation and this method has WHC in it (I would just modify this by leaving wetted up soil l in filter for longer - maybe overnight but protected from evaporation).

You then find the difference in moisture between the soil you want to test and the 50% of WHC and either add water to you sample or allow to carefully air dry by the required amount

Hope this helps

Andrew

Dr.Shirgure and Dr.Butler suggestions are interesting and probably pertinent  to question asked.

Thank you so much Andrew. So Its taking 2 small aliquots where one is saturated (to find WHC) and the other to fund current moisture. This makes perfect sense. Much obliged!

My pleasure - yes with the two aliquots of your bulk sample one can be used to measure WHC and the other current moisture content. there will be some maths involved but nothing too scary.