Invasion of weeds into a weed-free field under different tillage systems
The invasion of weeds into relatively weed-free agricultural fields has not been studied extensively. Understanding the relative invasiveness of weeds into different tillage systems should enhance our understanding of weed community dynamics. Research was conducted at the Indian Head Experimental Farm in Saskatchewan from 1987 - 1998. The field was used for breeder seed production for approximately 20 years before experiment initiation and was relatively weed-free. Three rotations, differing in cropping intensity and crop competitiveness, were present in each of zero, minimum, and conventional tillage. Weed sampling occurred in all 132 cropped plots each year in mid-July and weeds were counted by species in 20 quadrats per plot. Mean weed density and percentage of quadrats containing weeds were calculated, plotted and related to climate data. In general, zero tillage was weedier in wet springs regardless of fall conditions while conventional tillage was weedier when a dry spring was preceded by dry fall conditions. Minimum tillage was weedier when a dry spring was preceded by wet fall conditions i.e. conditions between those favouring zero and conventional tillage. In general, weediness increased considerably in wet years following dry periods. Differences in moisture availability for seedling recruitment may explain these results. Weediness increased considerably in wet years following dry periods, possibly as a result of increased moisture availability and seedbank expansion during dry years.
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