The New Zealand Defence Forces adopted the new khaki uniform in 1891. Considering the piping on the cuffs and the national badge on the collar it would have to be after 13 Nov. 1900, when those were added to the uniform for Boer War service. It's possible he's in one of the mounted rifles units-http://www.nzmr.org/colonial.htm
Have you tried the New Zealand Army museum? They might be able to identify it further.
Here's a New Zealand mounted infantryman in the field