Effects of tillage and mulch on weed seed production and seed banks in sweet corn.
The effects of tillage (till, no-till), mulch (none, dead Secale cereale [rye]), and crop competition (none, sweetcorn) on weed seed production and seed banks are reported. Data are presented for Amaranthus retroflexus, Chenopodium album, Portulaca oleracea and Digitaria sanguinalis. These constituted the majority of the weeds present during the cropping season. Seed bank data for a suite of winter annuals active during the fallow season are also presented. Weed seed production was estimated by dimension analysis. Most seeds were produced by the first cohort of plants to emerge. Amaranthus and Digitaria showed significantly greater seed production in no-till than in till treatments. Seed production by Amaranthus, Chenopodium and Portulaca was significantly greater in the absence of a sweetcorn crop. The only effect of Secale cereale mulch was to decrease seed production by Portulaca in 1 year. Differences among treatments in the number of seeds produced per unit area were primarily due to effects on individual plant size and seed production. Effects on seedling density and rate of survival to maturity were of secondary importance. Seed banks of Digitaria were greater in no-till than in till treatments, whereas the seed banks of winter annual forbs were greater in till treatments. Presence of a sweetcorn crop did not affect seed banks until the final year of the study, at which time seed banks of Amaranthus, Chenopodium and Portulaca were greater in the absence of a crop. An uncropped treatment which did not receive herbicides had exceptionally high seed production and seed banks of Amaranthus and Chenopodium, but not Portulaca and Digitaria, which apparently suffered from competition with the 2 larger species.