How much carbon and humus are in the soil?

Turfgrass creates a lot of soil organic matter (SOM), also called humus, and the quantities of carbon (C) in that organic matter might surprise you.

I made this chart to summarize the amount of C in the top 10 cm (4 inches) of a turfgrass rootzone. Specifically, in the sand-based rootzones used for intensively-trafficked sporting surfaces around the world.

I was wondering how much change in soil C to expect for a change of 0.1% (1 g/kg) in SOM. When the SOM changes by 0.1%, there’s a difference of about 70 g C/m2 in the top 10 cm of the rootzone, which is also 700 kg/ha, 14 lbs/1000 ft2, and 610 lbs/acre.

This calculation shows the scale of humus creation and C addition by turfgrass to the soil.