Crop photosynthesis and the flux of carbon dioxide below the canopy.
Bare soil evolved a maximum of 7 g CO2/m2/day in summer and a minimum of 1 g/m2/day in winter; the Q10 was 3. Root respiration, i.e. the difference in CO2-flux between fallow and cropped soil, was usually about 1-3 g/m2/day. The amount of soil C assimilated by crops was about 6% of net carbon uptake for rapidly growing grass in spring and about 20% for other crops (kale, barley) in summer. Release of C from the soil was 0.4 kg/rn2/yr and the half-life of soil organic matter was 22 years. In most weather, photosynthesis was independent of soil CO2 flux. F. s.-R.B.