Crops yield

Average yield of ancient wheat crops (from a field experiment in Britain):
Emmer: 202.43 g/m^2 = 2024.3 kg/ha
Spelt: 331.90
Club Wheat: 204.53
source: Environmental Factors and the Yield Potential of Ancient Wheat Crops

Wheat yield by country (2003-2004):
Highest (#1 UK) 7.78 -> Low (#26 Kazakhstan) 0.97
Average = 3.1 metric ton/ha = 3100 kg/ha
Average rice yield = 5 mt/ha = 5000 kg/ha
source: NationMaster

Typical yield of foxtail millet grain 小米:
800-900 kg/ha = 80-90 g/m^2
source: wiki