which type of ANOVA?

N mineralisation is dependent variable.
Management type (4 types) and position in valley (3 positions; nested in valley (with valley nested in management type [is this possible?])) are my independent variables. I want to test the affect of management type, position and interaction of both, on my dependent variable.

First thoughts: to do a factorial-ANOVA. But now I wonder: is a Nested-ANOVA needed?

If I had two sampling times, how could I see if there is a significant difference in the above affects? Would a repeated measures-ANOVA be suitable for this?

Is it possible to do a factorial-nested-repeated measures-ANOVA in one?
Would really appreciate any tips as I feel really helpless at the moment as nothing seems to be working (I am (trying to) using R but dont know if I keep getting errors as I dont type commands properly or because I am using the wrong tests...