Thirteen species of sweet clover have been tested by the Office of
Forage-Crop Investigations to determine their economic value. With
the exception of white sweet clover, yellow biennial sweet clover, and
yellow annual sweet clover, but four species in the somewhat limited
tests have given sufficiently good results to merit special attention,
and none have so far proved superior to white sweet clover, which is
now extensively grown in many States.
A species of Trigonella[4] is often referred to as blue-flowered
melilotus or blue-flowered sweet clover. While this plant is closely
related to the plants belonging to the genus Melilotus, it does not
belong to this genus and therefore should not be called sweet clover.
It is an erect, quite leafy, very fragrant annual, which produces a
fair growth. It may prove of value as a green-manure crop or as a catch
crop under certain conditions, but at the present time it is not to be
recommended where sweet clover can be grown successfully. In most tests
Trigonella has produced less forage than the better species of sweet
clover.
[4] _Trigonella caerulea_.