Marginal product of capital net of depreciation I am trying to understand how marginal product of capital net of depreciation is the following:



Given that the production function is quite standard



I understand the first term of the marginal product, but I am asking about the depreciation part.
This is a misuse of terms.

The marginal product of capital net of depreciation is indeed $MP_k - \delta$, there is no doubt about it.  

What the authors mean  is that 

$$R = 1 + (MP_k - \delta)  $$

is the "gross return on capital" factor. In fact a few lines below the equation they call it exactly that, which is the correct term. Here "gross" reflects the inclusion of $1$.