Just as you don't really need a machine with six foot tall tires to prepare a seedbed, you don't necessarily need a machine suspended from a gantry or with legs long enough to lift it above corn tassels to deal with small stuff at ground level. Sometimes it would be nice to have something smaller, a lot smaller, slithering along among the stalks, beneath the leaves.
Maybe it moves on little wheels, maybe like a snake, maybe like a centipede. Maybe it has low-set, horizontal snips in place of a mouth, as for shearing off crabgrass every time it grows back. Maybe it uses its tail like an ovipositor, to plant seeds. Maybe it produces a loud hiss to scare off hungry rabbits and deer.
Probably it would keep tabs on soil moisture and possess an array of chemical sensitivities for detecting various soil conditions, like whether anaerobic decomposition is happening near the surface.
Such a device might also apply dusts or mists to the underside of leaves, for example to control fungal growth with a light application of copper salts, or caterpillars with spores of a particular strain of bacteria.
Whatever the details, there's a place for smaller devices, representing considerably smaller investments, in a mix of machines that collaborate to manage productive land.