Can you float mana from a land before sacrificing it to pay an additional cost?

When you cast a spell with an additional cost that requires sacrificing a land (such as a spell with 'sacrifice a land' as an additional cost), you pay all costs simultaneously in a single payment window defined by CR 601.2h. Within that window, you may activate mana abilities at any time before completing payment.

Mana abilities (like tapping a basic land for mana) can be activated at any point during this cost-payment step per CR 605.3a, which states that mana abilities may be activated whenever you need mana. This means you can tap the very land you intend to sacrifice, float the mana into your mana pool, and then sacrifice that same land as part of the cost — all within the same payment step.

This works because tapping a land for mana and sacrificing it are two separate actions. The land produces mana when tapped; it is only removed from the battlefield when sacrificed. Both happen during the cost-payment window, so there is no timing conflict.

Example: You cast Crack the Earth, which requires sacrificing a land. You target your Forest, tap it first to add one green mana to your pool, then sacrifice that same Forest to pay Crack the Earth's additional cost. The green mana remains in your pool and can be used to cast another spell.

Note: This only works if the land is not already tapped. If the land is tapped, you cannot tap it again for mana before sacrificing it (CR 302.6 — a tapped permanent cannot be tapped again).