The Slades (which has, in other locations, early forms including Le Slade and Le Slade), refers to land in a marshy depression or a strip of marshy greensward[2].
The Slades was used as a commonable meadow in the 17th century[3] and known as Slades lane leading fields known as Slades Ground in the 1840s, so possibly related to a surname of the same meaning.
References:
[1] Whiles, J., 1995. Calne at War. 1st ed. Chippenham: Antony Rowe.
[2] Cavill, P., 2018. A New Dictionary of English Field-Names. 1st ed. Great Britain: English Place-Name Society.
[3] Calne: Economic history | British History Online. 2019. Calne: Economic history | British History Online. [ONLINE] Available at: https://www.british-history.ac.uk/vch/wilts/vol17/pp79-94. [Accessed 04 September 2019].
References:
[1] Whiles, J., 1995. Calne at War. 1st ed. Chippenham: Antony Rowe.
[2] Cavill, P., 2018. A New Dictionary of English Field-Names. 1st ed. Great Britain: English Place-Name Society.
[3] Calne: Economic history | British History Online. 2019. Calne: Economic history | British History Online. [ONLINE] Available at: https://www.british-history.ac.uk/vch/wilts/vol17/pp79-94. [Accessed 04 September 2019].