In the post-Marian Roman army, of course. I know that Caracalla also increased soldiers' salaries and pensions, so I wonder if that increase was also in land grants.
Absolutely yes, land grants were the reason most of the freed slaves were enrolling into the army in the years before A.D.
The quantity of land granted depended to the military career and to the discretion of the commander, however the system was very accurate in the distinction of such grants. In fact, Romans applied a method of land division to all conquered lands: such system was called Centuriatio, which means division in Centurias. Each Centuria would then be composed of 100 Heredia, and each Heredium is composed of 2 Jugera.
The Jugerum is the basic measure for land plots, and it's the amount of land plowed in a day by a couple of oxen. It measured 71x35,52 m. Although the amount for soldiers varied, we know that in 173 B.C. after the conquest of the Emilian plains and Liguria, ten Jugera were assigned to Roman Colons and three Jugera to Latin colons.
Edit: grammar