I have grown tomatoes, although not commercially. I did notice that growing tomatoes did NOT require:
- Any plowing.
- Any harrowing/raking/furrowing.
- Any use of a petroleum-based fertilizer.
- GMO seeds.
- A tractor/horse-drawn implements.
- Bundling and drying after harvest.
- Burning the stubble (or collecting it in a second harvest for feeding animals, to be used as fuel, etc).
There’s a heck of a lot more to growing plants than water, sunlight, and soil requirements. The amount of labor required (whether performed by muscle or petroleum power) to plant, tend, and harvest tomatoes is miniscule compared to that of “staple” grains like rice, wheat, and corn.
It’s easy to compare “apples to apples” and stick to quantifiable factors like soil and water requirements instead of taking into account the larger effect on the environment from using petroleum-powered machines to perform the near-Herculean amounts of labor required to grow grains. Furthermore, grains require a tremendous amount of processing even AFTER being harvested while tomatoes do not.
And that’s to say nothing of the large-scale destruction of the soil’s biosphere by all the plowing, furrowing, raking, and burning that is required for many “staple” grains.
The only thing you need to do for a tomato plant is a) make a tiny hole big enough for the seed and b) provide a small margin of non-competitive space (either sympathetic plants like marigolds, a thin layer of straw, etc) around it. The soil biosphere (including worms, fungi, and bacteria) remains intact and healthy after planting tomatoes instead of being literally ripped to pieces when grains are planted.
Only in some Platonic universe (such as aboard the ISS space station) can you look at tomatoes and say they are “costlier” to grow than wheat.