Subject: How can I tell in which environment organic things will decompose fastest?

I thought I might put banana peels in different materials such as regular soil, 
sand, or pebbles. I would leave them in there for about a month and then weigh 
them to see which has decomposed the most. I know that moisture content, 
oxygen, and temperature affect decomposition rates, but how can I tell which 
material absorbs the most heat or water? And even then, would it make a 
difference? In other words, is there a way of measuring oxygen, moisure 
content, and temperature in soil?

Re: How can I tell in which environment organic things will decompose fastest?