Agriculture is an incredibly broad word that includes both crop and animal based production. Feel free to check the dictionary of your choice (webster, oed, etc), an academic definitions paper like [1], or even the relevant wiki page. You're defining cultivation instead.
And not to belabor the point, but the Navajo and the Apache also engaged in crop cultivation. It was simply less important for them in the 19th century, so it's not what I mentioned first.
Herding is not a form of agriculture; it is pastoralism.
Agriculture means cultivating fields.