Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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EFFECTS OF BUCKWHEAT RESIDUE ON EMERGENCE AND EARLY GROWTH
OF EIGHT WEED SPECIES. V. Kumar, D.C. Brainard, and R.R. Bellinder, Cornell
University, Ithaca, NY.
ABSTRACT
Cover crops and their residues improve soil health and suppress weeds.
Buckwheat is a rapidly growing, summer annual cover crop that is widely grown by
organic farmers in the Northeast, but little is known about the effects of buckwheat
residue on weed suppression. The objectives of this research were (1) to evaluate the
effects of buckwheat residue on emergence and early growth of eight weeds, and (2)
to evaluate the possible role of nitrogen and allelochemicals in the suppression of
sensitive weed species by buckwheat residue. To achieve these objectives, both field
and growth chamber experiments were conducted in 2005 and 2006. For growth
chamber trials, field-grown buckwheat was mowed and incorporated 40 days after
planting. Soil was taken from plots with and without buckwheat residue 0 and 15 days
after incorporation. Seeds of four summer annuals: Powell amaranth (PA); hairy
galinsoga (HG); barnyardgrass (BYG); and common purslane (CP), and four winter
annuals: yellow rocket (YR); corn chamomile (CCM); common chickweed (CK); and
shepherd's purse (SP) were sown in pots and both emergence and growth were
monitored daily for 20 days. The possible role of nitrogen in suppression of three
sensitive species (PA. CCM, and SP) was tested by applying 0, 40, 80, and 160 kg/ha
N to both buckwheat and bare ground pots. To determine the possible role of
allelochemicals in weed suppression, a separate growth chamber study was
conducted in which activated carbon (50ml/l) was applied to weeds grown in both
buckwheat (greenhouse grown) and bare soil pots. In 2005, fresh buckwheat residues
significantly reduced the emergence (36 to 74%) and biomass (36 to 90%) of all weed
species except barnyardgrass. After 15 days, only PA suppression occurred. In 2006,
fresh buckwheat residues suppressed emergence of only three species (PA, CP, CK)
either had no effect or enhanced early growth of all eight weed species. Addition of N
overcame the suppression of emergence and growth of CCM and SP but not that of
PA. For PA, buckwheat residue suppressed emergence in the absence of activated
carbon (p=0.053), but had no effect on emergence in the presence of activated carbon
(p=0.46). In field trials conducted in 2006, PA, BYG, CK, and SP were sown in bare
soil and buckwheat plots, immediately after buckwheat incorporation. Emergence of
PA, CK, and BYG was reduced under buckwheat plots compared to bare soil by 72,
45, and 20%, respectively, but had no significant effect on SP. The preliminary results
suggest that CCM and SP are suppressed by buckwheat residue due to lack of
available nitrogen, whereas allelopathy may play an important role in suppressing PA
emergence. Ongoing research will examine (i) nitrogen dynamics following buckwheat
incorporation to further elucidate the role of nitrogen in weed suppression and (ii) the
potential role of fungal pathogens in suppression of emergence of sensitive species.
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