Leave them in the ground. They are a good source of organic matter.

Ditto.

Well, depends. Roots left to rot in the soil create an increase in the microbes that consume roots. Which is fine except if you are repeat planting the same crop. Tomatoes planted again in the same spot--any damage or weakness in the new crop's root system--there is a large microbe population ready to attack them, see?

So that is one reason why crop rotation is a good idea.

Some plants have more vulnerable root systems than others, so there is variation in that regard. Tomatoes in particular have all kinds of microbes that like to feed on their root systems. Corn, maybe not.

Thanks hoovb. So like for instance, if I planted a bunch of leafy vegetables-different types of onions, parsly, lettuce- they'd be fine in the same soil? do microbes damage the soil in any way?

thanks, irisgal

there are beneficial microbes in the soil, and there are "bad" microbes that attack specific things, such as tomato roots. Healthy soil is like a jungle of microbes, good and bad, predator and preyed upon.

Crop rotation means planting something completely different, and since onions, parsley, lettuce are not closely related to tomatoes, they should be okay.

Tomatoes, potatoes, peppers, and eggplant are all more closely related to each other, so (for example) you should not plant potatoes in the spot where you just had tomatoes.

got it thanks!

all good advice
i would add (IMHO) that older dead roots are better than recent dead roots.
the older they are, the more they have broken down.
if you have a lot of them, and they are recent, they could consume some of the Nitrogen in the soil, to make them break down.
it would be like tilling in a bunch of green leaves into the soil.
More than likely, its not enough to worry about
and you could add a bit of N fert if its a concern.

on the positive side, they also provide small pockets for air and water to hold and travel.
some people plant beet, alfalfa and other crops (especially legumes) , cut the tops off and leave the roots on purpose.
some people wait a few months or more before using the land, some use it right away.

Love your answer. Thanks for the variation. I guess I'd better add some nitrogen because I also tilled some finished banana pepper plants in there. You said green leaves use up nitrogen to break down, right? Well, I better get to work!