Seasonal emergence of weeds in cultivated soil in New Zealand



Patterns of seedling emergence of ten weed species from soil cultivated at intervals of approximately one month are described. All species examined showed clearly defined emergence patterns. Polygonum persicaria L. seedlings emerged in spring and early summer. Seedlings of Chenopodium album agg., Portulaca oleracea L. and Solanum nigrum L. emerged in late spring, summer and early autumn.Plantago major L., Rumex spp. (mostly R. obtusifolius L.) and Trifolium spp. (mostly T. repens L.) emerged mostly in spring and early summer. Coronopus didymus (L.) Sm. and Juncus bufonius L. tended to emerge in both autumn and spring.Veronica persica Poir. emerged in spring, summer and autumn. Close similarity between emergence patterns in New Zealand and northern Europe, despite differences in rainfall and temperature, suggests that annual dormancy:nondormancy cycles of seeds buried in the soil are largely responsible for seedling emergence patterns. In New Zealand, seedling emergence tended to be more spread out than in Europe, although seasonal patterns were still distinct. Further work on dormancy cycles in these species would be useful, as would a comparison of the factors inducing and breaking dormancy of comparable seed populations in northern and southern Europe and New Zealand. When seeds were left buried for several years before being encouraged to germinate, seedling emergence patterns tended to be of smaller amplitude, although the overall patterns were still very similar.