Land is never traded, for any currency. There is nothing illegal about it, just as someone in our world may freely trade their grandmother's grave with her not a year buried - yet one is unlikely to find either buyer or seller, or think well of them should they be found.
Land may certainly be given in return for service. The devious reader may wonder whether this distinction is simply a pretty form of words. Fie on your suspicions! Giving land is a weighty gesture of support, that almost amounts to adoption. One who gives land will be judged by the actions of the recipient, and the two will be assumed to be close allies. In any case, the vast majority of people have no land. In some areas all land is held by the nobility. In others it is held in common.
It should be noted that 'land' is considered by everyone to mean agricultural land only. The land on which a house sits is freely traded like any other commodity. The merchant nobility of the city, aping the nobility of the sword as ever, may feign reluctance to trade their 'land', but this is mere show.