I agree with Tracy; cytoplasmic male sterility can be used to produce hybrids
with no pollen and thus no kernels (cobs develop but have no grain), provided
of course that the hybrids are not planted near pollen fertile maize.
I also agree that such non-grain hybrids do not compete with grain-bearing
hybrids for amount of nutrient per hectare. I think that in the past, people
have tried producing very late and tall, male-sterile hybrids. Plants were
impressively large and seemed to make a lot of nutrient per hectare, but the
total still was not as much as on grain-bearing hybrids of adapted maturity.