Entwood. A desert place where in old times a large magic forest it pushed was reduced sands some by the black magician, Pitermarkogier in order to create an army to be horrible and frightening the orcs. Your castle is the last rampart against the obscure world of the black magician. Your oil will be I think of a very great help of this invasion.
I have 2 tips for you,
First off, your text description looks as if it comes from a translator tool, if you have troubles with the english language, you can ask one of the other members here to translate it properely from your own language to english for you.
Secondly, try using small brush sizes (no larger than 3x3 in my opinion) when equalising/placing dirt and alike.