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Many weeds produce seed with extended longevity (See Table 1).
| Table 1. Germination percentage
(viability) of seed buried for different periods of time (Duvel
1902) |
| Species |
Germination
(%)
|
Burial
time (years) |
| Shepherds purse (Capsella bursa-pastoris) |
47 |
16 |
| Greater plantain (Plantago major) |
84 |
21 |
| Blackberry nightshade (Solanum nigrum) |
83 |
39 |
| Rye (Secale cereale) (crop) |
0 |
1 |
The population of viable weed seeds in the soil seed bank is controlled by the rate of input from mature plants and the rate of mortality.
Seeds in the soil die due to external factors such as;
 | disease, |
| decaying organisms, and |
| predation by animals; |
and to internal factors such as;
| Respiration of food supplies stored in the seed, |
| Enzyme action leading to breakdown of stored food, |
| Coagulation of proteins, |
| Accumulation of toxic products (eg. ethylene, ethanol), and |
| Degeneration of DNA. |
The number of weed seeds in the soil is also influenced by farming practices
(See Table 2).
| Table 2. Number of weed seeds found in soil under different cropping systems |
| Cropping regime |
Seed/m2 |
| Continuous wheat |
34 000 |
| Mixed crops |
28 000 |
| Derelict arable land |
46 000 |
| Old arable land |
250 |
| Commercial vegetable crops |
>86 000 |
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Steve Adkins
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