The first type of withdrawal—germination leading to emergence—is, of course, how weeds begin to compete with and harm crops each season. It is also the foremost mechanism for debiting the seed bank, an effective strategy if emerged seedlings are easily killed by subsequent cultivation or flaming (the stale seedbed technique, for example). Even in species with relatively long-lived seeds such as pigweeds, velvetleaf, and morning glory, the vast majority of weed emergence from a given season’s seed rain takes place within two years after the seeds are shed (Egley and Williams, 1990). Thus, timely germination (when emerging weeds can be readily killed) can go far toward minimizing net deposits into the seed bank from recent weed seed shed. Knowing when to promote or deter weed seed germination, and how to do so for the major weeds present, are important skills in seed bank management.
One way to estimate a field’s weed seed bank is to wait and see what weeds emerge during the first season. However, knowing something about seed bank content before the season starts can help the farmer prevent severe weed problems before they develop. Davis (2004) recommended the following simple procedure for scouting the weed seed bank:
Inputs (“Deposits”) and Losses (“Withdrawals)
While it is sometimes advantageous to cause weed seeds to germinate, it is important at other times to keep them quiescent long enough for the crop to get well established. Several practices can help reduce the number of weeds emerging in the crop.
Published August 20, 2013
The number of viable seeds remaining from a given year’s weed seed return declines over time as a result of germination (successful or fatal), predation, and decay. The percentage remaining declines in an approximately exponential manner, similar to the decay curve for a radioactive chemical element—the time for the number to decline by 50% is roughly the same, regardless of the initial num. The half-life of weed seeds varies widely among weed species; for example, hairy galinsoga and some annual grass weeds, such as foxtail species, last only one to a few years, whereas some curly dock and common lambsquarters seed can last over 50 years.
14%. Multiple cohorts were produced between February and October. No-till systems produced higher emergence rates than conventional tillage systems. Seedlings of B. tournefortii did not emerge from 5 cm soil depth; therefore, diligent tillage practices without seedbank replenishment could rapidly reduce the presence of this weed. A soil-moisture study revealed that at 25% of water-holding capacity, B. tournefortii tended to produce sufficient seeds for reinfestation in the field. Brassica tournefortii is a cross-pollinated species, and its wider emergence time and capacity to produce enough seeds in a dry environment enable it to become widespread in Australia. Early cohorts (March) tended to have vigorous growth and high reproduction potential. This study found B. tournefortii to be a poor competitor of wheat (Triticum aestivum L.), having greater capacity to compete with the slow-growing crop chickpea. Therefore, control of early-season cohorts and use of rotations with a more vigorous crop such as wheat may reduce the seedbank. The information gained in this study will be important in developing better understanding of seed ecology of B. tournefortii for the purpose of developing integrated management strategies.
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Date and time: Sun, 25 Jul 2021 15:54:39 GMT