CROPPING SYSTEMS INFLUENCE BIOLOGICAL WEED CONTROL
Boosting organic matter in soil creates a healthy
environment for
soil-dwelling bacteria that suppress weeds. That's
according to
Agricultural Research Service scientists who for the
first time have
determined which cropping systems provide the best home
for these
beneficial bacteria.
ARS scientists report that to create ideal soil
conditions, farmers should
rotate their crops, reduce tillage and keep herbicide
applications to a
minimum.
The beneficial microbes, called deleterious
rhizobacteria (DRB), live on or
within millimeters of--weed roots, and they feed on
substances that ooze
from those roots. As the name DRB implies, these
bacteria are bad for
weeds. Although they suppress weed growth, DRB normally
don't interfere
with crop plant growth.
Robert J. Kremer, a microbiologist with the ARS
Cropping Systems and Water
Quality Research Unit in Columbia, Missouri, says many
DRB keep weed seeds
from germinating and produce toxins and excessive
concentrations of plant
growth hormones that put the life processes of weed
seedlings in
"overdrive." Consequently, root cells may rupture and
leak, replenishing
the DRB diet. Once weakened by DRB, weeds are less able
to compete with
other plants, and they become more vulnerable to other
control measures.
Kremer and graduate student Jianmei Li researched
cultures of DRB
associated with the most dominant species of weeds in
six different
cropping systems. In general, the highest numbers of
weed-suppressing DRB
came from fields where crops were rotated, chemicals
and tillage were
minimal, and organic materials like composts were
added. DRB fared best in
a corn-soybean-wheat-cover crop rotation. An organic
strawberry system with
compost was a close second.
The researchers believe the research information can be
used to modify
current cropping practices or design novel ones to
promote development of
DRB and take advantage of their natural
weed-suppressive effects.
___________________________________________
Scientific contact: Robert J. Kremer, ARS Cropping
Systems and Water Quality
Research Unit, University of Missouri, Columbia, MO.,
phone (573) 882-6408,
fax (573) 884-5070, KremerR@missouri.edu.
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