Golgari Rot Farm and land play

[Frogster]

If I have one land in play

and I play a Golgari Rot Farm

and other player responds by using rain of rust on my other land

What happens? Does the other land end up in my hand or in graveyard? Does Golgri Rot farm end up in my hand or on the battlefield? Is the rain of rust countered?

[Kenji]

Returning a land to your hand happens as a result of Golgari Rot Farm's triggered ability. If your opponent responds to the ability with [mtg]Rain of Rust[/mtg, their spell resolves first and destroys your other land, assuming that's what they selected as the target when they cast their spell.

In that case, Golgari Rot Farm will be returned to your hand, because returning a land to your hand must be done if possible, and if the Farm is your only land remaining, then that's what will be returned to your hand.

Note also that Golgari Rot Farm's triggered ability resolves even if it leaves the battlefield, since abilities exist independently from their source once they're activated or triggered. So, if the opposing player really wanted to set you back, they would destroy your Golgari Rot Farm -- this way, you still have to return the other land, and you no longer have the Farm to play later.

[Frogster]

so if the golgari rot farm gets returned to my hand, can I play a different land or did i use up my land quota for the turn?

[DatAsh]

You played a land, and cannot play another.