Some data about the productivity of wild-grass seeds from:

Harlan, Jack R. (1989). Wild-grass seed harvesting in the Sahara and
Sub-Sahara of Africa. In: Foraging and farming: the evolution of plant
exploitation (Harris, DR & Hillman GC, eds). London, Unwin Hyman:

Over 60 species of grasses have been harvested for their grains in Africa.
Most of these are famine or scarcity foods or are harvested casually and
opportunistically. Several species, however, have provided food on a
massive scale and have been staples for a number of tribes.

Natural stands of wild grass can give very respectable yields of
high-quality food. Yields of 500-800 kg/ha are not uncommon and 1 ton/ha
can occasionally be obtained. This is in the range of many subsistence
farmers growing domesticated cereals and as much or more than farmers in
England obtained from domesticated wheat in the Middle Ages. Harlan cites
Chevalier, who described an African wild-grass harvest and stated that one
adult could easily gather 10 kg in a mornings effort. In an experiment with
wild einkorn wheat in Turkey Harlan himself yielded almost 1 kg of
pure-grain equivalent per hour of work, and the grains were far more
nutritious than domesticated wheat. This wild wheat harvest returned 40-50
kcal of energy for every kcal expended. Harlan stated, that this was far
more efficient in terms of the ratio of consumable output energy to energy
expended in harvesting than any form of agriculture so far studied.


Another interesting question is the  toxicity of many tubers. In the
following article Jones hypothesizes that the first farmers may have
preferred toxic plants. Maybe less susceptibility to pests is one reason
why in many parts of the world cereals are a primary crop for agriculture?

Jones DA (1998). Why are so many food plants cyanogenic? Phytochemistry
47(2):155-162

Abstract: A disproportionately large number of the most important human
food plants is cyanogenic. The accumulated research of numerous people
working in several different disciplines now allows a tenable explanation
for this observation. Cyanogenesis by plants is not only a surprisingly
effective chemical defence against casual herbivores, but it is also easily
overcome by careful pre-ingestion food processing, this latter skill being
almost exclusive to humans. Moreover, humans have the physiological ability
to detoxify cyanide satisfactorily, given an adequate protein diet. It
appears that early in the domestication of crop plants the cyanogenic
species would have been relatively free of pests and competitive
herbivores, as well as having good nutritional qualities, and thus ideal
candidates for cultivation by the first farmers.

Ruediger Hoeflechner