[photochemsyn]

I think the example to look at is biological nitrogen fixation, vs. the Haber-Bosch process, which operates at high pressures and temperatures and therefore has a small area footprint. You can do biological nitrogen fixation with legume (pea, bean) crops in symbiosis with nitrogen-fixing bacteria nodules, and then compost the crop to generate a nitrogen-rich fertilizer, but this means devoting large fields to the process. The Haber-Bosch process in contrast can produce much greater amounts of pure ammonia in a single location.

Haber-Bosch traditionally has relied on large fossil fuel inputs, but it's possible to get the hydrogen from the process via hydrolysis of water, powered by renewable energy (or nuclear), and use electricity instead of fossil fuels to run the high-temperature, high-pressure catalytic reaction (H2 + N2 -> NH3).

The same arguments apply to carbon capture and fixation: you can do it in an industrial setting, for example the North African desert (which doesn't support much plant growth), you could use seawater as the hydrogen source and plentiful sunlight and PV/concentrated thermal for electricity to drive the carbon capture (fans etc.) and the analogous version of Haber-Bosch (Fischer-Tropsch) for CO2 - CO + H2 -> hydrocarbons.