I had a rotten tomato, and was wondering what will happen if you bury the whole fruit? I'm not expecting anything to happen this year, but maybe next year?
If you bury the fruit, you'll probably nourish the soil with the organic matter and tomato nutrients, and that's about it. Odds are, the seeds won't dry out enough, and they'll rot; they may be too deep to germinate, too.
If you rather squish the tomato flat on top of the soil and leave it there, the odds are better that you'll get a patch of volunteers next year, if it gets enough moisture when it's time to sprout.
The options range from absolutely nothing to a bunch of seedlings pushing up on the spot.
What exactly is going to happen depends on various parameters, starting from whether the seeds in the fruit were viable (“ripe” at the time of harvesting, not destroyed by the mold) to what temperature and humidity they were exposed to.
A lot of novice gardeners during lockdown have experimented with planting tomato slices and seeing the seeds sprout (happy to share their progress on Instagram). And especially after mild winters I found the offspring from fallen and overlooked fruit popping up where last year’s tomato plants stood, or the seedlings from a tomato that took a detour to the compost pile and hit the jackpot of not-quite-decomposing-plus-cozy-warmth.
Rarely you may even find tomatoes that seem perfectly fine for consumption, but some of the seeds have decided to germinate within:
Caveat: Bt just dumping the fruit you will be recreating a scenario like in the wild (overcrowding, danger from cold spring nights, the works). There’s a reason why gardeners go through the trouble of sowing and transplanting their tomato seedlings especially in climates where tomatoes are not native or hardy.
I second @Stephie 's statement "zero, one or more sprouts". Keep in mind that the new plants are most probably not genetically identical to the parent plant. I currently care for 6 tomato plants on my tiny balcony despite having never planted a single seed.
Buried decomposing matter attracts things that eat organic matter. I've managed to attract an ant colony, which for an appartement is suboptimal. On the other hand, exposed compost attracts aerial insects.
The decomposing tomato will surely contribute some nutrients to the surrounding soil.