The role of nitrogen is not explained well. Termites may have it in their gut bacteria but it had to come from somewhere. If it is not from nitrogen-fixing bacteria then there is seemingly no net advantage.

Termite nests form the base or at least the focus of many forest patches in tropical grasslands (savannas) worldwide. In places where seasonal flooding is the limit to tree growth, simple elevation may be the factor. Elsewhere, though, better "tilth" in an otherwise hard clay soil (especially in the dry season) or the bringing up of mineral nutrients from subsoils to leached surface zones may play a role. Termites are very important in plant ecology in the tropics.

It goes to show, nothing is better then nature. It looks like its the tunnels that provide roots air and access to water is the main contributer to the yield increase, not the N.

Roots need air and water, these fields where not getting those most likely due to over appliication of fertilizer or insufficient tilling, ect...

If you consider ants and termites to be part of the Soil Food Web then it makes sense. All insects are here to help digest what we consider waste material so it can be utilized by other things for nutrition.
There are many people that seem to subscribe to the school of thought that says all insect are bad and therefore must be destroyed. However, a few are realizing that all insects play some beneficial role in our universe, they have evolved for a reason and that reason has nothing to do with being a pain in our necks.

I don't know about crop yields, but I saw an interesting show on History or some channel, where they designed the air conditioning system of a large commercial building in Zimbabwe based upon the termite mounds. This system uses a fraction of the energy normally required to cool a building of that size.

Apparently the termites have a complex venting system in their mounds, and are constantly opening and closing holes to maintain a constant 87F (30C).

Cool, it is about time the Dry-land farmer catch a break.

An interesting side note here, the huge, 15-20 ft high termite mounds in Southern Africa were built by a now-extinct species of termite, and as mentioned above, form a unique ecosystem on their own.

I dunno how old some of these things are, but the natural termite 'cement' that holds them together is so tough that it will take a day to knock one of those things down with a bull dozer, and the commercial farmers use dynamite.