Any idea what kind of plant this is?

[steiny]

This is coming up (sparsely) in my food plot.
I planted BioLogic Green Patch Plus and New Zealand Perennial on this plot.

This plant is not growing outside the plot anywhere that I can see - it is the first time I've seen it.

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[Dotch]

Looks like you have a yellow nutsedge plant there. Should have a triangular stem and like most sedges, prefers wetter areas generally speaking. These plants are perennials and reproduce by seeds and rhizomes. They also produce tubers or nutlets which will sprout a new plant if the plant is pulled. The tubers are edible, the flavor reminding one of a hazelnut.

[steiny]

It definitely has the triangular stem!

Would this have been in the seed I put in the plot?

[Fawkinnae]

Sedges have edges.

[Dotch]

This is coming up (sparsely) in my food plot.
I planted BioLogic Green Patch Plus and New Zealand Perennial on this plot.

This plant is not growing outside the plot anywhere that I can see - it is the first time I've seen it.

Is that like Ruffles have ridges?  Guess I'd be surprised if it came in by seed. In order to get as big as the plant in the picture, it may have been hiding there in a vegetative stage when you worked the plot. The leaves are shiny but it maintains that triangular stem characteristic in the vegetative stages. Nutsedge can hide pretty easily amongst grasses and broadleaves. It doesn't tolerate mowing very well however so that may be one method of trying to get it under control eventually if it gets to be a problem. It can be controlled with glyphosate but it is one of those that will take a pretty good dose, several quarts per acre of the 41% material, to eliminate it. Typically if the forage you've planted catches well it should help smother it out.