The chernozem contains a very high percentage of humus, anywhere up to
about fifteen percent, and also important organic minerals such as
phosphorus and ammonia. The depth of the chernozem has been measured at
anywhere from forty to two hundred and fifty inches, but is usually about a
foot deep. Because it very fertile and does not require any fertilizer, it
is considered some of the best soil in the world for growing grains. The
"black earth" region of Ukraine extends throughout about two-thirds of the
country.
[permaculture] Black Earth Region of Russia, Ukraine and Siberia,
Lawrence London, 11/27/2012