The way the answer is put no, not at all.

There are lots of metrics above so i won't repeat anything. But i will state the obvious:

The pasture land will sequester carbon **regardless of the operation of the farm**. It is not a mandatory part of the farm cycle from this perspective.

So the farm itself has a carbon emission cost and carbon sequester from the pasture cannot be subtracted.

However it is not possible to determinate the potential for carbon sequestration compared used an unused pasture. In overall more research is needed as various sources indicate:
https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1526-100x.2000.80054.x
https://dl.sciencesocieties.org/publications/sssaj/abstracts/58/1/SS0580010175
https://link.springer.com/article/10.1007/s10457-012-9573-x
https://www.sciencedirect.com/science/article/abs/pii/S1871141311001016