Seasonal Abundance and Spatial Pattern of Setaria faberi, Chenopodium
album, and Abutilon theophrasti in Reduced-Tillage Soybeans
Dawit Mulugeta and Chris
M. Boerboom
A better understanding of the influence of various crop and
weed management practices on spatiotemporal dynamics of weeds
could improve the design of integrated weed management systems.
We examined the influence of 18- and 76-cm soybean row spacings
on emergence pattern and spatial aggregation of giant foxtail,
common lambsquarters, and velvetleaf seedling cohorts. In
addition, we characterized the soil seedbank and determined the
quantitative and spatial relationship between the seedbank and
seedling populations. Viable seeds of about 10 weed species and
twice as many species of seedlings were identified in the weed
community. Giant foxtail and common lambsquarters were the
predominant species in the seedling and seedbank population,
respectively, each accounting for 60 to 70% of the total weed
species density. Emergence of giant foxtail, common
lambsquarters, and velvetleaf depleted 12 to 33%, < 2% and 12
to 49% of the seedbank in the upper 10 cm of the soil profile.
Peak time and periodicity of weed emergence was not influenced
by soybean row spacing, and peak time of emergence of giant
foxtail, common lambs-quarters, and velvetleaf occurred 3 to 4,
3 to 6, and 3 to 9 weeks after soybean planting (WAP),
respectively. Magnitude of giant foxtail emergence 5, 6, and 9
WAP was 98, 96, and 76% greater in 76- than in 18-cm row
soybeans only when the population of 76-cm row soybeans was 57%
lower than the 18- cm soybeans in 1997. Giant foxtail and common
lambsquarters seeds in the seedbank were aggregated in 1996 and
1997 according to the Taylor power law (TPL) and the negative
binomial distribution (NBD). The TPL and the NBD were similar in
describing the spatial aggregation of giant foxtail and common
lambsquarters but not some velvetleaf seedling cohorts. The
spatial aggregation of seedlings varied among cohorts for
different weed species and was likely due to species-specific
biological characteristics that influence seed dispersal,
germination, and seedling emergence. Within a 1.5-ha area,
aggregation declined with decreasing density. Within a 24-m 2
area, the level of aggregation of all weed species decreased as
seedling densities increased. These results indicated that
soybean row spacing influenced neither weed emergence pattern
nor weed spatial aggregation; thus, several management decisions
can be similar in 18- and 76-cm row soybeans.
Weed Science, 47:95-106. 1999 |
