Understanding Why Rye Works as a Cover Crop
October 16, 2009
Agricultural Research Service (ARS)
scientists may soon find a way to enhance the weed-killing capabilities of a
cereal grain that enriches the soil when used as a winter cover crop.
Rye is often grown in winter and killed in the spring, so the dead stalks
can be flattened over soybean and vegetable fields to block sunlight and
prevent spring weeds from getting the light they need to germinate. The effect
makes rye a popular alternative for organic farmers who grow crops without
herbicides. Ryes roots also capture nutrients and hold the soil in place,
reducing erosion and run off.
Teasdale, research leader of the
Sustainable Agricultural Systems Laboratory in Beltsville, Md., is working
with ARS chemist
Rice to see whether organic compounds released by rye in the soil play a
role in suppressing weeds and whether those compounds can be exploited to
improve ryes weed-killing capabilities. Although compounds in rye are
known to inhibit weed growth, little is known about how they behave in the
Teasdale and Rice grew rye in winter, killed it in spring and either tilled
the stalks shallowly into the soil or left them untilled on the surface. They
then took weekly soil samples to extract chemicals from them and tested the
soils to see how lettuce and pigweed grew in them. They also measured levels of
a family of organic compounds called benzoxazinoids, released from the rye,
which are believed to play a role in weed suppression.
The researchers found that weeds began to grow better as concentrations of
the compounds diminished, within a few weeks of when the rye was killed. The
compounds reached peak levels about a week after the rye was killed and dropped
significantly within two or three weeks. The preliminary results suggest that
the benzoxazinoids do affect soil chemistry and may enhance ryes
The work is part of an effort to clarify such issues as how long rye should
be grown before being killed, the amount of biomass needed to maximize its
effects, and the impact of weather and soil conditions on its effectiveness.
more about this research in the October 2009 issue of Agricultural Research
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.