How is the title of "How much land does a man need?" ironic?
You have asked two questions and so I have edited it down to one according to enotes regulations. The title of this biting parable is very clearly ironic. This is most clearly summed up in the last paragraph of the story. But first, let us remember two facts: first of all, what we see throughout the story is that Pahom, as he acquires more and more land, becomes dissatisfied with the amount of land he had and continually wants more. Secondly, let us also remember there is a big distinction between the two words "want" and "need". What we "need" and what we "want" are often poles apart, but many people lack the wisdom to tell the difference.
Let us now consider the end of the story:
HIs servant picked up the spade and dug a grave long enough for Pahom to lie in, and buried him in it. Six feet from his head to his heels was all he needed.
So, after all of Pahom's grumbling and complaining, it turned out that all the land he needed - and all the land any of us need - was enough for a burial plot. There is an additional note of irony in that his own spade - the one thing he refused to give up during his run - is used to dig his grave. This of course puts all of Pahom's complaints throughout the story into sharp contrast:
"Our only trouble is that we haven't land enough."
"As it is, I am still too cramped to be comfortable."
Thus Tolstoy's parable paints a depressing picture about materialism - gaining more often does not lead to happiness, but to more greed and suffering.