Fertilizer is best applied as a granule. Herbicide (as a post-emergent) is best as a liquid.
Remember the water you are carrying weighs 75 pounds, the spreader and sprayer, about 50 pounds.
What if you have to go uphill? Worse yet, what if you are going downhill towards a pond?
The 50 pound capacity Earthway spreader weighs a comfortable 27 pounds.
A good back pack sprayer weighs about 43 pounds full.