The New Agriculture Network's on-line newsletter with seasonal advice for field crop and vegetable growers interested in organic agriculture.

Vol. 4, No. 3 - May 23, 2007

Managing the soil seed bank in organic crops John Masiunas Dept. Natural Resources and Environmental Sciences University of Illinois     Figure 1. The life cycle of an annual weed. Note the importance of seed in the life cycle of an annual weed.

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Figure 2. The processes affecting the size of a weed seed bank. Seed rain from weed plants within a field represent the largest input. Long range dispersal of uncommon species can be a source of new weed problems. Seed predation can eliminate seed predispersal or when it is on the soil surface. Failed germination is considered the greatest loss from the soil seed bank. (From Figure 1 of Anil Shrestha. Weed seed banks and their role in future weed management.)

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Figure 3. The annual dormancy cycle in buried weed seeds for winter annuals (WA) and spring-germinating summer annuals (SA). Hatched areas are where germination is possible. The size of this hatch area would vary depending on the length of the emergence time for a weed. Note the WA axis runs from January to January while the SA curve runs from July to July. The figure shows three levels of dormancy: D = dormant; CD = conditionally dormant; and ND = non-dormant. The solid line represents the dormancy level of the seed and the dotted line represents the temperature favorability for germination. (From: Figure 1 of Baskin, J. M. and C. C. Baskin. 1985. The annual dormancy cycle in buried weed seeds: A continuum. BioScience 35:492-498.)

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Figure 4. The process an immature mustard seed undergoes until emergence. A dormant seed is released from the mother plant. Once in the soil, the seed goes through processes releasing dormancy. These include after ripening which allow the immature seed to mature. The mature seed also has to be stratified (exposed to cool, moist conditions) to reduce inhibitor levels in the seed. A stratified mature seed absorbs water (imbibes) and when exposed to light will start germination by expanding its radicle (seed root) and mobilizing stored food for seedling growth. (From http://www.mpiz-koeln.mpg.de/english/research/koornneefGroup/soppe/work/index.html)

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