The impact of the season in which cereals are sown on the diversity of the arable weed flora in rotational fields in Denmark
Hald A.B. (1999) The impact of changing the season in which cereals are sown on the diversity of the weed flora in rotational fields in Denmark. Journal of Applied Ecology, 36, 24-32.
Background
During the last half century agriculture intensification, especially in northern Europe, has led to a change in the weed flora of arable fields. Surveys have shown that there has been a dramatic decrease in the weed flora of fields under rotational cultivation during the last 30 years. This trend has been particularly noticeable in winter cereals, a crop of increasing importance in the landscape. The weed flora of spring and winter cereals was compared in 19 unsprayed fields during a 5-year study to test the hypothesis that cereal type exerts no effect on the flora or on the absolute and relative abundance of single species.
Action
Survey sites: Vegetation surveys were carried out between 1988 and 1992 in 6-m wide crop margins in 22 experimental fields distributed all over Denmark.
Study design: Within each experimental field were permanently unsprayed and sprayed plots laid out in four blocks; the farmer determined the crop rotation. Only results from the unsprayed plots are described here. The weed flora in each 6 × 20 m experimental plot was surveyed in 10 permanently located 0.1 m² circles in spring in all five years. The species were identified and individuals of each species counted. The number of experimental fields was reduced to 19, as each field was required to support at least one spring and one winter cereal sample during the 5-year period, resulting in a total of 72 samples. The analyses were performed using species density (floristic) and plant density (abundance of single species and higher taxa) characteristics
Consequences
A total of 114 species was found. In all, 97 were found in spring cereals and 87 species in winter cereals. The mean species density was more than 25% lower in winter than in spring cereals.
Accumulated species richness was also lower in winter than in spring cereals. The lower richness in winter cereals was also reflected in the distribution of common species e.g. the fifth most widespread species occurred in 20 spring samples, but only in 15 winter samples. Similarly, the tenth most widespread species occurred in 17 spring and 12 winter samples. In most cases, two species contributed ≥50% of the plants within a sample.
Among the weed species analysed for abundance with a known season of germination, most (94%) are able to germinate in spring cereals, but fewer (62%) are able to germinate in winter cereals. Some species occurred indifferently of season of crop sowing; all but one of these species are able to germinate both in the spring and autumn.
Among the tested plant genera and families, Chenopodiaceae (mostly fat hen Chenopodium album), Fabaceae and Polygonaceae were found to occur with higher density in spring cereals, while speedwells Veronica spp. and Caryophyllaceae (mostly common chickweed Stellaria media) occurred with highest relative abundance in the vegetation in winter cereals.
Plant species and taxa that are important food resources for arthropod herbivores occurred at greater densities in spring than in winter cereals and, in addition, occurred with the highest relative abundance in spring cereals.
Conclusions: In this Danish study, change in land use from spring to winter cereals resulted in a reduction of more than 25% in weed density and weed species. Plants that are important food resources for arthropod herbivores also occurred at greater densities in spring than in winter cereals.
Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at: http://www.blackwell-synergy.com/doi/full/10.1046/j.1365-2664.1999.00364.x