W. Bond et al., CHANGES IN THE WEED SEEDBANK FOLLOWING DIFFERENT WEEDING TREATMENTS IN DRILLED SALAD ONION AND CARROT CROPS GROWN IN ORGANIC AND CONVENTIONAL SYSTEMS, Biological agriculture & horticulture, 16(2), 1998, pp. 203-215
Changes in the soil weed seedbank were monitored over a single growing
season in field experiments with drilled salad onion and carrot crops
following different weeding treatments. Viable weed seed numbers were
determined in soil samples taken at crop sowing and at harvest. When
the crops were left weedy until harvest, seed numbers in soil increase
d by between two- and seventy-fold due to the influx of fresh seed. Th
ere was much less change in weed seed numbers in the soil when crops w
ere kept weed-free until harvest or weeded once at 4, 5 or 6 weeks aft
er 50% crop emergence. An estimate of the seedbank at harvest in the w
eeded treatments as a proportion of that of the unweeded control was d
erived using a log-linear model that included a covariate adjustment f
or seed numbers at sowing. There was little difference in the proporti
on remaining when crops were weeded once or kept weed-free throughout.
The results were similar in carrot and salad onion crops grown in org
anic or conventional cropping systems. The findings highlight the risk
of a rapid increase in the soil seedbank if weed control is neglected
in a single crop. However. there was no indication that limiting weed
control to one carefully-timed weeding would increase the potential w
eed population in subsequent crops.