Line 1-2: The word "depends" makes us think that this is one special wheelbarrow, and we almost feel like the wheelbarrow is being personified at this moment.
Line 3-4: Our speaker uses enjambment to split the word "wheel" from the word "barrow." This makes us think about wheelbarrows more carefully. We realize that, just like the word "wheelbarrow," a wheelbarrow is composed primarily of two parts: a wheel and a barrow (the part you put stuff into).
Line 3-4: That image of the red wheelbarrow is pretty darn powerful. We see it very clearly in our minds, and all our speaker has to do to paint the image for us is to tell that it is a "red wheelbarrow." If that isn't magic, we don't know what is.
Line 6: The assonance of "beside" and "white" gives this line momentum and movement.
Line 7: Our speaker uses enjambment to break apart "white chickens." By placing "chickens" on its own, we feel like these must be some important chickens.