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Weed learning module
Self test answers
- The weed seed bank consists of the seeds in the soil. It is of interest to researchers because it indicates the average effects of weed control practices over several years time. It is of interest to farmers because it indicates the potential weed pressure in the field.
- Soil with high tilth may improve effectiveness of cultivation in several ways. First, the cultivator may be able to break weed roots free from soil better in a loose, well structured soil. Second, shallow working implements like tine weeders, rotary hoes and many specialty tools will be unable to reach the roots of seedlings that establish in the gaps between clods that form when a poorly structured soil is tilled. Finally, when "hilling up" in the crop row to bury weed seedlings, a granular soil should bury small weeds more uniformly than a cloddy soil since a line of clods will have partial gaps between them. Also, clods tend to knock over crop plants, which leaves gaps where weeds can grow.
- Timing is the essence of the matter. Incorporating green manure creates a healthy soil in the long run by providing food for earthworms, beneficial fungi and other desirable soil organisms. For the first couple of weeks after incorporation, however, the green manure appears to promote pathogenic fungi. Since many weed seeds germinate in response to changes in the soil that accompany tillage, the tiny weed seedlings that form after incorporating a cover crop should be highly vulnerable to attack. Crops that are planted later, after the organic matter has partially decomposed and the pathogens have died off, are likely less vulnerable and may benefit from the desirable organisms promoted by the green manure.
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- Crop yield response to nutrients generally levels off at moderate rates of application. Based on the biology of weeds, we hypothesize that weeds continue to increase in size and seed production up to very high rates of nutrients. Thus, we expect that high rates of compost application will benefit weeds without additional benefit to the crop, and thus tip the balance in competition for light and water in favor of the weeds.
- Although results were inconsistent between years and compost type, several species of weeds increased in size with even the highest rate of compost, whereas corn yield leveled off at a moderate compost rate, and soybean yield showed no significant response to compost rate. These facts support the hypothesis. For reasons we do not understand, the size of all species did not respond to compost rate in most combinations of year and compost type. This does not support the hypothesis. Note, however, that even if only a few species are difficult to control, the grower may still have a weed management problem.
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