Unless it's something small, like you may run on a quad bike, up to 4 gpm approx, you'll need to run a dedicated circuit as NIW suggests. However if it is small, or someone else wants to run a small sprayer, the following may apply.
It's possible but not guaranteed, that your tractor may have wiring for a rear work lamp installed from factory sitting somewhere near your ROPS. If it has, the circuit is rated at 10 amps, so depending on your sprayer pump motor load, you may be able to utilize it. Even if a rear work lamp is installed, you still could use it if you don't use your work lamp at the same time, and possibly just unplug, and plug your pump in. However, running a new circuit would be needed if your pump current draw is ~8A or above to negate voltage drop. For small sprayers, depending on your flow and pressure requirements, even if your pump is rated at 10 amps, you may only actually draw 8 amps or less. YMMV