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چکیده
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An experiment was conducted to study the effect of different rotations on weed seed bank of farming ecosystems in autumn 2011 at arable fields, orchards and pastures of Kurdistan province in Iran. Crop rotations were continuous dryland wheat (Wd), continuous irrigated wheat (Wi), wheat-sugarbeet (WS) and wheat-chickpea (WCh), samples of nearby pasture (P) and orchards (Or) were also taken for comparison purposes. Sampling sites were arranged in a W pattern across the fields by auger and samples were taken at 0-5 cm, 5-15cm and 15-25 cm soil depths. Results revealed that certain weed species often are adapted to specific crops and others are compatible in all circumstances. The maximum weed seeds density was recorded in the P and Or systems and they were accumulated in the upper soil layer 0-5 cm (87 % and 54%, respectively), while in Wd and Wi due to moldboard plowing weed seeds were concentrated at soil depth of 15-25 cm (87 % and 54 %, respectively). In other rotation the seeds were evenly distributed throughout the tillage depth. The results of PCA showed that weed communities in Wd and Wi systems were nearly identical, but showed significant differences compared to other rotations. The maximum Shannon’s diversity index was detected in Wi and Wd rotations with higher density in the upper soil layer 0-5 cm (2.1 and 2.4, respectively) and its values decreased with increasing depth. Result of the present study showed that weeds have evolved in response to agricultural activities. This evolution will continue and therefore this fact should be taken in the development of weeds management practices.
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