Abstract
The paper presents the analysis of changes in weed infestation in spring barley cultivated in the years 1990-2004 in crop rotation with a 25% proportion of this cereal (potato - spring barley - sowing peas - winter triticale), when it was grown after potato, and in crop rotation with its 75% proportion (potato - spring barley - spring barley - spring barley), when it was grown once or twice after spring barley. In the experiment, no weed control was applied. Every year in the spring (at full emergence of the cereal) and before the harvest, the composition of weed species and weed density of particular weed species were determined, and before the harvest also their biomass. Weed density increased linearly on all plots during the 15-year period. The average values confirm the increase in weed biomass in the case when spring barley was grown once or twice after this crop; however, those differences were influenced by the previous situation only during some seasons. Weed density and biomass showed high year-to-year variability and a positive correlation with the amount of precipitation and a negative correlation with temperature during the period of the study. A negative correlation between the yield of barley and weed biomass was shown.
Highlights
Among agricultural technical factors, high doses of nitrogen fertilizers, simplified structure of crop rotations and application of herbicides have had the strongest influence on the weed community structure development (Hyvönen, 2004)
Minor differences between the positions are the resultant of varying effects during individual years (Fig. 1) when potato, as a weed-controlling previous crop, fulfilled its role in the spring only on 4 occasions, while on 3 occasions the density of weeds after potato was higher during that period compared to both fields in which barley was cultivated once or twice after spring barley
The linear year–to–year trends determined for weed density in individual positions were increasing
Summary
High doses of nitrogen fertilizers, simplified structure of crop rotations and application of herbicides have had the strongest influence on the weed community structure development (Hyvönen , 2004). Simplifications in crop rotations, both in Poland and worldwide, tend towards increasing the share of cereals in them (Buczyński and Marks , 2003; Hyvönen , 2004; Smith et al 2008). Among the cereals, spring barley is considered to be a weak competitor for weeds because of its delicate structure and relatively low height of the plants (Buczyński and Marks , 2003). Long–term studies and observations seem to be valuable They show whether and when an agricultural ecosystem, and with it the weed community, “get used” to the repeated external factor and relative stabilisation occurs at a level different from the baseline (M a h n , 1984). Studies conducted over whole decades allow identification of the species withdrawing from fields and endangered and show those representing increasing expansiveness (Latowski , 2002; Andreasen and Stryhn , 2008; K a a r and Freyer , 2008)
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