Weed Seed Bank Assessment in Organic Crop Rotations : Comparing the weed suppression effect from intercropping field pea and spring barley, with sole cropping and black fallow

Sammanfattning: In the urge to mitigate the negative impact of weeds, like reduced yields, both agricultural and horticultural production have heavily relied on herbicides for weed control. This has led to vast environmental problems like human health risks and negative impact on biodiversity. Consequently, other measures relying more on the ecological properties controlling weeds have been explored. One such attribute is the competitive ability of crops. Intercropping is one method of increasing the competitive ability of crops against weeds regarding acquisition of light, nutrients and space. Field pea, Pisum sativum, and spring barley, Hordeum vulgare, are a good combination for intercropping with weed suppression effect. Sole cropping of oat, Avena sativa, has also a highly competitive ability against weeds. The weed seed bank is the viable weed seeds in the soil and evaluation of its composition can give indications of soil, crop and weed management. The aim of this thesis is to examine the weed seed bank of organic crop rotations in Alnarp, Sweden. The aim is also to see if there is an impact of intercropping of pea and barely on the weed seed bank compared to sole cropping of pea and oats and the weed management technique black fallow. The most abundant species in the weed seed bank in the organic crop rotations in Alnarp were similar with two other seed banks related to organic crop rotation in Scandinavia. The Alnarp seed bank had however a higher species richness. Analysis could not detect any significant difference in impact from the treatments intercropping pea+barley, sole crop pea, sole crop oat and black fallow on the weed seed bank. In the present study it was concluded that weed seed bank assessments could be an uncertain method if the treatments have similar characteristics and the assessment is done after only one cropping season. Treatments that have similar characteristics need to go on for a longer time for the effects to be visible in analysis. However, this study constitutes a good baseline for future research on the weed seed bank and the impact from intercropping and sole cropping.