New Zealand Journal of Agricultural Research abstracts
Influence of herbicide applications on the decomposition, microbial biomass,
and microbial activity of pasture shoot and root litter
D. A. WARDLE
K. S. NICHOLSON
A. RAHMAN
AgResearch
Ruakura Agricultural Research Centre
Private Bag 3123
Hamilton, New Zealand
Abstract Pure swards of each of four pasture species
(
Lolium perenne L.,
Trifolium repens L.,
Senecio jacobaea
L., and
Carduus nutans L.) were established in glasshouse conditions and
subjected to one of three treatments: spraying with 2,4-D/picloram mix;
spraying with glyphosate; or unsprayed. After the sprayed swards died, all
above-ground and below-ground tissue was harvested, air-dried, and placed in
nylon mesh litter-bags which were positioned in the field. Decomposition,
microbial basal respiration, and substrate-induced respiration (proportionally
related to the glucose-responsive microbial biomass) of this litter was then
monitored over 338 days. Both herbicide treatments inhibited decomposition of
T. repens and
L. perenne shoot tissue and
C. nutans root
tissue, but stimulated that of
C. nutans shoot tissue, indicating that
herbicides may influence decomposition of different species in different ways;
the possible reasons for this are discussed. However, the rapid decomposition
of most of the tissues considered in this study suggest that herbicides are
unlikely to exert substantial long-term effects on plant litter persistence.
Microbial basal respiration and substrate-induced respiration of most of the
litter types considered were initially very strongly enhanced by both herbicide
treatments; however, this effect was highly transitory for all tissue types
except one, and for some of the tissue types a strong inhibition of these
microbial variables in the herbicide treatments followed. It therefore appears
that microbial build-up on litter from herbicide-killed plants (and the
subsequent decline) occurs earlier than that from unsprayed plants, probably
because herbicide-induced plant damage increases the availability of readily
utilisable microbial substrates. The retardation of leaf litter decomposition
in herbicide treatments was often associated with reduced microbial activity
and biomass, indicating strong linkages between soil-associated microflora and
decomposition processes. This study also indicates that newly developed
approaches for simultaneously assessing decomposition and the microbial biomass
of leaf litter have considerable potential for investigating impacts of
ecological factors on plant litter-microbial interactions.
Keywords basal respiration; 2,4-D; plant litter;
decomposition; glyphosate; herbicide; microbial biomass
PDF file of entire paper: medium quality (793K); (scanned from paper original: notes about this process)
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